IMPLEMENTATION AND EVALUATION OF AUTOMOTIVE CHILD RESTRAINT SYSTEMS IN MASS TRANSIT BUSES. A Thesis by. Nishant Kuber Balwan

Transcription

1 IMPLEMENTATION AND EVALUATION OF AUTOMOTIVE CHILD RESTRAINT SYSTEMS IN MASS TRANSIT BUSES A Thesis by Nishant Kuber Balwan Bachelors of Engineering, Shivaji University, 2005 Submitted to the College of Engineering and the faculty of the Graduate School of Wichita State University in partial fulfillment of the requirements for the degree of Masters of Science December 2008

2 Copyright 2008 by Nishant Kuber Balwan All Rights Reserved

3 IMPLEMENTATION AND EVALUATION OF AUTOMOTIVE CHILD RESTRAINT SYSTEMS IN MASS TRANSIT BUSES I have examined the final copy of this thesis for the form and content, and recommend that it be accepted in partial fulfillment of the requirement for the degree of Master of Science with a major in Mechanical Engineering Hamid Lankarani, Committee Chair We have read this Thesis and Recommend its acceptance: Olivares Gerardo, Committee Member Ramazan Asmatulu, Committee Member iii

4 DEDICATION To my parents Chandarani and Kuber Balwan, my sister Aarti and my fate Vidhi for their continuous motivation, support, and love iv

5 ACKNOWLEDGMENTS I would like to thank Dr. Hamid Lankarani Professor of Mechanical Engineering, for his support valuable timely guidance and encouragement throughout my graduation studies at Wichita State University. I also would like to thank Dr. Gerardo Olivares, Research Scientist from the National Institute of Aviation Research (NIAR) for giving me the opportunity and platform to work on this research project, and for his invaluable advice, continuous guidance and support while working in the Computational Mechanics Laboratory at NIAR. I also would like to thank Vikas Yadav for his support, motivation and help throughout my graduation and National Institute for Aviation Research for providing facilities required for conducting this research. I am also thankful to my colleagues and friends in the Computational Mechanics Laboratory at NIAR who helped me throughout my research work. I express my gratitude to another member of my committee, Dr. Ramazan Asmatulu, for his valuable comments and suggestions on my thesis. Lastly, I am very thankful to my parents for their continuous and unconditional support throughout my studies, and my sister for her timely encouragement. v

6 ABSTRACT Mass transportation systems and specifically bus systems are a key element of the national transportation network. Buses are one of the safest forms of transportation. Nonetheless, bus crashes resulting in occupant injuries and fatalities do occur. Each year, more than 5,800 children die, nearly 120,000 are permanently disabled, and more than 14 million are hurt seriously enough to require emergency medical care due to unintentional injury. Therefore, effort is needed to improve the performance of bus interior and structure. Child Safety is a continuing effort to improve the safety of children in mass transit buses. This project provides an overview of the implementation of two types of attachment systems Child Restraint Systems (CRS) in a mass transit buses. A series of sled tests were conducted in order to evaluate the performance of the Child Restraint Systems for typical frontal, side and rear crash scenarios. The results of the test indicate that the implementation of ISOFIX or LATCH attachments in transit bus seats mitigates the risk of severe injuries to the 12 monthold, and 3 year-old occupants; while not increasing the risk of severe injuries due to CRS interactions to other unrestraint adult passengers. In the next phase of this research, results from these sled tests were validated using the multibody analysis tool MADYMO to evaluate the performance of child safety in mass transit buses using the Federal Motor Vehicle Safety Standards (FMVSS 208) injury criteria. The Kinematics of sled tests are closely matching with that of simulations. Injury values for sled tests and simulations are well below injury criteria. The results form this study shows the 20 % variation in injury signals. This study concludes that interior for mass transit bus with child seats and restraint can be utilized in mass transit buses to improve the safety performance of childern. vi

7 TABLE OF CONTENTS Chapter Page 1. INTRODUCTION Motivation Objective Project Outline BACKGROUND AND LITERATURE REVIEW Background Statistical Data Literature Review Child Seat Classification Infant Seat Convertible Seats Booster Seats Child Seat Dimensions Infant Seat Generic Dimensions Convertible Seat Generic Dimensions Standard Bus Procurement Guidelines Attachment Methods LATCH ISOFIX General Injury Mechanisms in Crash Scenarios Head Injury Injury Criterion Head Injury Criterion (HIC) Neck Injury Criterion Thoracic Trauma Index FMVSS 208 Injury Criteria TESTING PROCEDURE AND STANDARDS FMVSS 213 Standards Terms and Definitions Test Conditions and Procedure Test Device Dynamic Test Condition Dynamic Test Procedure FMVSS 225 Standards Terms and Definitions Lower Anchorage Specifications vii

8 TABLE OF CONTENTS (Continued) Chapter Page Lower Anchorage Location Strength of the Lower Anchorage Test Requirements for Lower Anchorages BASELINE SLED TEST Overview of Sled Program Approach to Sled Test Program Methodology Sled Test Device Test Anthropomorphic Test Devices Instrumentation Data Processing Frontal Impact Test Side Impact Test Rear Impact Test Comparison of LATCH and ISOFIX Occupant Interaction Analysis Frontal Impact Test and Test and Test and Side Impact Test Test Rear Impact Test Test MADYMO MODEL DEVELOPMENT OF SLED STRUCTURE Overview of Simulation MADYMO Version Test ATDs Specifications Hybrid III3-Year-Old Child Dummy Hybrid III CRABI 12 Month Old Dummy Hybrid III 50th Percentile Dummy Hybrid III 95th Percentile Dummy Description of Occupant Environment Dummy Selection Modeling of Facet Child Restraint System Model viii

9 TABLE OF CONTENTS (Continued) Chapter Page Joint and Property Selection Modeling of Child Attachment System ATD Inertial Load MADYMO Bus Interior Model VALIDATION OF NUMERICAL MODELS Introduction Validation Approach Validation of Dummy Kinematics Injury Parameters Profile Matching RESULT AND DISCUSSION Comparison of Dummy Kinematics Frontal Impact (Configuration I) Frontal Impact (Configuration - II) Side Impact Rear Impact Comparison of Injury Parameters Head Chest Neck Femur Comparison of Profile CONCLUSIONS AND RECOMMENDATION Conclusions Recommendations REFERENCES APPENDICES A Comparison of Profile (Sprague and Gears) A.1 Frontal Sled Test A.1.1 CRABI 12-Month Old Dummy at Position A.1.2 Hybrid III 50 th Percentile Dummy at Position ix

10 TABLE OF CONTENTS (Continued) Chapter Page A.1.3 Hybrid III 95 th Percentile Dummy at Position A.1.4 Hybrid III 3-Year Old Dummy at Position A.2 Side Impact Test A.2.1 Hybrid II 50 th Percentile Dummy at Position A.2.2 Hybrid III CRABI 12-Month Old Dummy at Position A.2.3 Hybrid II 50 th Percentile Dummy at Position A.2.4 Hybrid III 3-Year Old Dummy at Position A.2.5 Hybrid III 50 th Percentile Dummy at Position A.2.6 Hybrid III 95 th Percentile Dummy at Position A.3 Rear Impact Test A.3.1 Hybrid III CRABI 12-Month Old Dummy at Position A.3.2 Hybrid III 95 th Percentile Dummy at Position A.3.3 Hybrid III 50 th Percentile Dummy at Position A.3.4 Hybrid III 3-Year Old Dummy at Position A.4 Frontal Impact Test A.4.1 Hybrid III 3-Year Old Dummy at Position A.4.2 Hybrid III CRABI 12-Month Old Dummy at Position A.4.2 Hybrid III 50 th Percentile Dummy at Position A.4.3 Hybrid III 50 th Percentile Dummy at Position B Bar Charts B.1 Side Impact Test B.2 Rear Impact Test B.3 Frontal Impact Test x

11 LIST OF TABLES Table Page 2.1 Child Seat Dimensions FMVSS 208 Injury Criteria for Various ATDS [6] Data for Hybrid III Family Used in the Present Study ATD Data Processing Filters Test Summary Frontal Sled Tests Test Summary Side Sled Tests Test Summary Rear Sled Tests Contact Definitions xi

12 LIST OF FIGURES Figure Page 1.1 Transit bus crashworthiness methodology Crash data analysis FARS [10] Crash data analysis child passenger safety 1999 FARS [10] Causes of accidental injury-related death for children 14 and under 2004 [11] Infant seat [22] Convertible seats [22] Booster seats [22] Rear facing infant seat (I) and (II) [29] Forward facing convertible seat [29] Seating dimensions and standard configuration [6] LATCH attachment [22] Lower attachments for ISOFIX CRF [29] Acceleration function for test configuration I [29] Acceleration function for test configuration I (Upper and Lower Bound)[29] Acceleration function for test configuration II [29] Child restraint fixtures [26] Lower anchorage specifications [26] Lower anchorage locations [26] ISO static force application device 2 (SFAD 2) [26] Final design of sled test BIW (Configuration I and II) Child seat anchor attachment method (FMVSS 225) Sled test facility at NIAR Locations of data channels in ATD General sled test configuration I for frontal impact tests General sled test configuration II for frontal impact tests Frontal impact sled test sled pulse General sled test configuration I for side impact tests Side impact sled test sled pulse General sled test configuration I for rear impact tests Rear impact sled test sled pulse Comparisons of LATCH and ISOFIX attachment system Ellipsoid model of hybrid III 3-year-old dummy [27] Ellipsoid model of CRABI 12 month old dummy [27] Ellipsoid model of hybrid III 50th percentile [27] Ellipsoid model of hybrid III 95th percentile [27] Mesh Geometry of infant and convertible seats Rear facing infant seat Forward facing convertible seat Joints Stiffness Functions Contact property characteristics Translational characteristics xii

13 LIST OF FIGURES (Continued) Figure Page 5.11 ATD inertial loads MADYMO setup for frontal impact test configuration - I MADYMO setup for frontal impact test configuration II MADYMO setup for side impact test configuration I MADYMO setup for rear impact configuration I Kinematics of frontal impact test (Configuration - I) Kinematics of frontal impact test (Configuration - II) Kinematics of side impact test Kinematics of rear impact test Normalized Injury Values for Test (Frontal Impact) A.1 CRABI 12-month old dummy acceleration A.2 CARBI 12-month old dummy neck forces and moments A.3 Hybrid III 50th percentile dummy accelerations A.4 Hybrid III 50th percentile dummy neck forces and moments A.5 Hybrid III 50th percentile dummy femur forces A.6 Hybrid III 95th percentile dummy accelerations A.7 Hybrid III 95th percentile dummy neck forces and moments A.8 Hybrid III 95th percentile dummy femur forces A.9 Hybrid III 3-year old dummy accelerations A.10 Hybrid III 3-year old dummy neck forces A.11 Hybrid III 50th percentile dummy accelerations A.12 Hybrid III CRABI 12-month old dummy accelerations A.13 Hybrid III CRABI 12-month old dummy neck forces and moments A.14 Hybrid II 50th percentile dummy accelerations A.15 Hybrid III 3-year old dummy accelerations A.16 Hybrid III 3-year old dummy neck forces and moments A.17 Hybrid III 50th percentile dummy accelerations A.18 Hybrid III 50th percentile dummy neck forces and moments A.19 Hybrid III 50th percentile dummy femur forces A.20 Hybrid III 95th percentile dummy accelerations A.21 Hybrid III 95th percentile dummy neck forces and moment A.22 Hybrid III 95th percentile dummy femur forces A.23 Hybrid III CRABI 12-month year old dummy accelerations A.24 Hybrid III CRABI 12-month year old dummy neck forces and moments A.25 Hybrid III 95th percentile dummy accelerations A.26 Hybrid III 95th percentile dummy neck forces and moments A.27 Hybrid III 95th percentile dummy femur force A.28 Hybrid III 50th percentile dummy accelerations A.29 Hybrid III 50th percentile dummy neck forces and moments A.30 Hybrid III 50th percentile dummy femur forces A.31 Hybrid III 3-year old dummy accelerations xiii

14 LIST OF FIGURES (Continued) Figure Page A.31 Hybrid III 3-year old dummy neck forces and moments A.32 Hybrid III 3-year old dummy accelerations A.33 Hybrid III 3-year old dummy neck forces and moments A.34 Hybrid III CRABI 12-month old dummy accelerations A.35 Hybrid III CRABI 12-month old dummy neck forces and moments A.36 Hybrid III 50th percentile dummy accelerations A.28 Hybrid III 50th percentile dummy neck forces and moments A.37 Hybrid III 50th percentile dummy femur forces A.38 Hybrid III 50th percentile dummy accelerations A.39 Hybrid III 50th percentile dummy neck forces and moments A.40 Hybrid III 50th percentile dummy femur forces B.1 Normalized injury values for Test B.2 Normalized injury values for Test B.3 Normalized injury values for Test xiv

15 LIST OF ABBREVIATIONS ATD BIW CAD CAE CAM CG CLEPA Anthropomorphic Test Device Body in White Computer Aided Design Computer Aided Engineering Computer Aided Manufacturing Center of Gravity Comité de liaison européen des fabricants d equipements et de pièces automobiles CMM CRABI CRS DOE DOT FARS FE FEA FEM FHWA FMCSR FMVSS GDV GES Coordinate Measuring Machine Child Restraint AirBag Interaction Child Restraint System Design of Experiments Department of Transportation Fatality Analysis Report System Finite Element Finite Element Analysis Finite Element Method Federal Highway Administration Federal Motor Carrier Safety Regulations Federal Motor Vehicle Safety Standard Gesamtverband der Deutschen Versicherungswirtschaft ev General Estimates System xv

16 LIST OF ABBREVIATIONS (Continued) GVWR HIC IGES ISO ISOFIX LATCH LTV MADYMO MB NASS NCSA NHTSA NIAR NTSB SBPG SI Gross Vehicle Weight Rating Head Injury Criterion Initial Graphics Exchange Specification International Organization for Standardization International Standards Organization FIX Lower Anchors and Tethers for Children Light Transport Vehicles MAthematical DYnamic MOdel Multibody National Automotive Sampling System National Center for Statistics and Accidents National Highway Traffic Safety Administration National Institute for Aviation Research National Transportation Safety Board Standard Bus Procurement Guidelines Standard International xvi

17 CHAPTER 1 INTORDUCTION The safety aspect is currently most important and utmost priority in road traffic. Protection of passengers from interior of vehicle is improving constantly now days. The interior of vehicles contain number of sophisticated passenger protection systems on the basis of standard anthropometric test dummies (5 percentile female to 95 percentile male). But as children differ from standardized adults in size and weight, they are not properly protected in such an environment without any additional systems. This can be achieved only with one system known as Child Restraint System (CRS). It acts as adapters [1]. As the name implies, CRS is intended to serve to protect the children in motor vehicle. This means during the vehicle crash biomechanical load is to be minimized as far as possible by holding the child body structure tightly. This system provides the coupling between vehicle and the child body. CRS types can vary with the weight and age of child seating, type of internal restrained system, and the direction the child faces. The general method of securing child with CRS is to hold the child with harness and/or other restraining surface (shield). The CRS with child is then attached to the vehicle seat with regular seat belt [17]. Child restraints are based on Federal Motor Vehicle Safety Standards (FMVSS) and typically involve the use of child safety seats restrained by seat lap belts. Newer automotive restraint standards (FMVSS 225) use the structure of the vehicle to restrain the child safety seat. These standards differ between North America ( Lower Anchors and Tethers for CHildren - LATCH) and Rest of the World (International Standards Organization FIX - ISOFIX). In this research child safety is conducted to improve the safety of children in mass transit buses. This project provides an overview of the implementation of ISOFIX and LATCH 1

18 equipped Child Restraint Systems in a Mass Transit Bus. A series of sled tests were conducted in order to evaluate the performance of the Child Restraint Systems for typical frontal crash scenarios also for rear and side crash scenarios. From the results from the test, the behavior of adult occupant with CRS was studied and mutlibody model validation using MADYMO has been done. 1.1 Motivation When CRS is implemented in regular traffic environment, it reduced the risk of fatal injury and chance of deaths in a motor vehicle crash by 71 percent [2], a total of 7895 lives have been saved because of the usage of child restraint systems from 1975 to 2005 [3]. By comparison, estimates of fatality reduction to adults in lap/shoulder belts for the same time period averaged about 50% [2]. These statistics show the importance of effective restraint systems and their proper usage. The CRS is used only in vehicles not in the buses and coaches. But in USA among the all Transportation modes, couches and buses are the major mode of transportation as buses are safest mode of transportation [4]. And till date the CRS haven t implemented in buses and coaches. Therefore, crashworthiness research is a continuing effort. The focus of this work was mainly on CRS and then interaction of child occupant with seating occupant in mass transit buses. As a part of child restraint system, two types of child seat attachment methods LATCH and ISOFIX were studied for their effects on injury levels. Development and testing to determine the optimum means of child restraint and a solution that works in both North America and Rest of the World is needed. 1.2 Objective Most of the work related to CRS was done in vehicles crashes. Currently, there is not appropriate and sufficient data on performance of CRS for children in buses and couches. This 2

19 work evaluated the CRS safety in mass transit buses and recommended interior design guidelines that will decrease the fatalities and injuries of the occupants during a crash event. Interior components were evaluated against crashworthiness requirements from the Federal Motor Vehicle Safety Standards (FMVSS) [5] and the Standard Bus Procurement Guidelines [6]. The performance standards of CRS in United State are defined by FMVSS 213. The main objectives of this project were as follows: To review the database and literature for accident statistics in order to identify the number of fatalities, injuries. Provide high and low energy impact level test data required to validate Finite Element and Multibody numerical models: - Frontal, side, and rear impact configurations - Occupant: 12 month, 3 YOLD, 5th, 50th and 95th percentile. To generate a Multibody (MB) model of the sled and Infant Seats (Up to 12 month Old) and Convertible Seats (3-year-old) child with child restraint and validate it against the sled results. To study the occupant position because position of seating occupant affects the child injuries. Comparison between child restraint system attachments LATCH and ISOFIX. 1.3 Project Outline Figure 1.1 shows the schematic representation of outline of the complete transit bus crashworthiness project. This project covers the outlined section, including creating the MB model, followed by sled testing and validation of the MB model. Next step is to compare LATCH attachment with ISOFIX attachment, followed by occupant position analysis. 3

20 Figure 1.1 Transit bus crashworthiness methodology 4

21 CHAPTER 2 BACKGROUND AND LITURATURE REVIEW 2.1 Background Performance standard for Child Restraint System (CRS) in United States are defined by FMVSS 213 which required that any marketed child seat for use in a vehicle should be designed to restrain and protect children in the event of crash. The performance criteria include protection from serious injury to head, chest and legs. The lack of occupant restraint use by motorists is a significant factor in most fatalities resulting from motor vehicle crashes. Of the 2,787,000 passenger vehicle occupants injured in crashes in 2001, only 12 percent (324,000) were reported as unrestrained. The rates are about the same for child occupants. For children ages 0-10 years old, an estimated 147,000 were injured in motor vehicle traffic crashes in 2001, and 12 percent (18,000) of these children were unrestrained. Of the 59,000 child occupants less than 5 years of age who were injured, 11 percent (6,000) were unrestrained. In 2001, 202 child occupants under 5 years of age were killed while restrained in child restraints, and another 32,000 were injured [7]. Child restraints are highly effective in reducing the likelihood of death and/or serious injury in motor vehicle crashes. National Highway Traffic Safety Administration (NHTSA) estimates ("Revised Estimates of Child Restraint Effectiveness," Hertz, 1996) that for children less than 1-year-old, a child restraint can reduce the risk of fatality by 71 percent when used in a passenger car and by 58 percent when used in a pickup truck, van, or sport utility vehicle. Child restraint effectiveness for children between the ages 1 to 4 years old is 54 percent in passenger cars and 59 percent in light trucks [7]. 5

22 Notwithstanding the effectiveness of child restraints certified to FMVSS No. 213, the agency is continuing to examine whether the safety of children in child restraints can be enhanced even further. In 2001, 202 child occupants under 5 years of age were killed while restrained in child restraints, and another 32,000 were injured. On November 27, 2000, NHTSA published a planning document that defined the agency s vision for enhancing child passenger safety over the next 5 years (65 FR 70687). The plan contained the agency s views on implementing three strategies for enhancing the safety of child occupants from birth through age 10: increasing restraint use; improving the performance and testing of child restraints; and improving mechanisms for providing safety information to the public. The agency requested comments on the plan and received suggestions on the various initiatives (Docket NHTSA 7938) [7]. Many commenter s responded to the second of the three strategies, making suggestions as to how they believed FMVSS No. 213 should be improved to further enhance child restraint performance. There was general concurrence with the agency's plan to undertake rulemaking with regard to the dynamic test and test seat assembly, child dummies used in this testing, and the criteria used to evaluate these tests. There was no objection to the agency's then-announced intention to improve side impact protection as a measure that would be pursued internationally in concert with other government and industry bodies. However, it was apparent from the few comments received on the subject that that commenter s considered child side impact protection to be a long-term project requiring several years of research and development [7]. Definitions of two types of fixing mechanisms that are used in the present study are presented here. National Highway Traffic Safety Administration (NHTSA) has recognized the difficulties that parents experience in securely attaching a CRS to a vehicle and has addressed 6

23 this issue in 1999 by establishing a uniform child restraint attachment system known as LATCH ( Lower Anchors and Tethers for CHildren ) by amending FMVSS 213, Child Restraint Systems and issuing FMVSS 225, Child Restraint Anchorage Systems, effective September 1, 2002 [21]. Among the standards for safety installations and restraint systems, one of the most widely known is the system for the connection of child restraint systems to vehicles, commonly referred to as ISOFIX. The standard covering this system is ISO Road vehicles - Anchorages in vehicles and attachments to anchorages for child restraint systems. In the present study the effectiveness of these two fixing mechanisms on the child occupants injury levels are evaluated. 2.2 Statistical Data This section gives the information about the statistical data of number of fatalities, patterns of crash regarding to motor vehicle accidents, as there is not enough statistical data on buses or couches. Each year, more than 5,800 children die, nearly 120,000 are permanently disabled, and more than 14 million are hurt seriously enough to require emergency medical care due to unintentional injury [8]. According to NHTSA misuse of child restraints is high, and failure to restrain children remains the most important problem in child occupant crash protection. In 2000, there were 528 deaths and about 67,000 injuries among passenger vehicle occupants younger than 5 (NHTSA, 2000a, b). Among those fatally injured, 35 percent were completely unrestrained. It is not known whether nonuse of child restraints and incorrect use are due to difficulties in installing the restraints, but it is clear that nonuse and, to a lesser extent, misuse contribute to child injuries [19]. NHTSA s Fatal Accident Reporting System (FARS) database shows the data on collision since 1991 to 1999 in Figure 2.1. Data presented below is based on the impact zone and shows 7

24 the fatalities of children below 8 years. More than 50 % of fatalities are due to Frontal impact, and followed by that Side Impact with 40 % of fatalities, rest of 9% is due to Rear Impact. Figure 2.2 Crash data analysis FARS [10] The figure 2.2 indicates the crash data for a year 1999 for the children ages from 0 through 10. 1,135 children ages from 0 through 10 killed in year 1999, out of that more that 50 % fatalities were unrestrained. The rate of death was 3 children per day and number of injured children are 500. Child occupant fatality rate was 3/100, 000 [9]. Figure 2.1 Crash data analysis child passenger safety 1999 FARS [10] 8

25 Motor vehicle crashes remain the leading cause of accidental injury-related death among children ages 14 and under. Seventy-five percent of motor vehicle crashes occur within 25 miles of home, and 60 percent of crashes occur on roads with posted speed limits of 40 mph or less [11]. Figure 2.2 Causes of accidental injury-related death for children 14 and under 2004 [11] In 2003, an estimated 220,000 children ages 14 and under were injured as occupants in motor vehicle-related crashes. In 2003, 1,591 child occupants ages 14 and under died in motor vehicle crashes. The motor vehicle occupant death rate among children ages 14 and under declined 25 percent from 1987 to In addition to physical trauma, motor vehicle injuries can have long-lasting psychological effects. One study showed that 25 percent of children, who suffered from traffic injuries, and 15 percent of their parents, were later diagnosed with post-traumatic stress disorder. As of January 1, 2004, 141 children have been killed by passenger air bags. Approximately 92 percent of these deaths were among children either unrestrained or improperly restrained at the time of the crash, including 23 infants in rear-facing car seats in front of passenger air bags. 9

26 The total annual cost of motor vehicle occupant-related death and injury exceeds $17.8 billion for all children ages 14 and under. National Highway Traffic Safety Administration s (NHTSA) National Center for Statistics and Analysis (NCSA), provides insight into fatalities and injuries to passenger vehicle occupants, based on a variety of impact attributes. Variables examined include restraint use, injury severity, crash type, vehicle type, seating position, and passenger age. The analysis was based on 1998 through 2002 data from NCSA s Fatality Analysis Reporting System (FARS), a census of fatal motor vehicle crashes; and NCSA s National Automotive Sampling System General Estimates System (GES), which collects data regarding injuries resulting from motor vehicle crashes. The report of NSTSA for NCSA concluded that: In single vehicle fatal crashes, unrestrained children in either passenger cars or light transport vehicles (LTVs) were between 2 and 3 times as likely to have been fatally injured as compared to restrained children. In multi- vehicle fatal crashes, unrestrained children in LTVs were from 2.5 to 5.4 times as likely to have been fatally injured as children who were restrained; comparatively, for children in passenger cars, being unrestrained made the child 1.6 to 1.8 times as likely to have been fatally injured. In single vehicle fatal crashes, restrained children in passenger cars were roughly 1.5 times as likely to have been fatally injured as restrained children in LTVs. In multi- vehicle fatal crashes, restrained children in passenger cars were roughly 2.5 times as likely to have been fatally injured as restrained children in LTVs. In fatal crashes, restrained children in the front seat were roughly 1.5 times as likely to have been fatally injured compared to restrained children in the second seat. 10

27 In multi- vehicle fatal crashes, unrestrained children in passenger cars were more likely to have been fatally injured than unrestrained children in LTVs; however this difference was much less than the difference seen among restrained children. In fatal crashes, the relative protection provided by traveling in the second seat (compared to the front seat) was lessened when the passenger is unrestrained. In two- vehicle fatal crashes, a much larger percentage of passengers in the struck vehicle were fatally injured (50 percent) compared to passengers in the striking vehicle (22 percent) [12]. 2.3 Literature Review Galganski R., Hatziprokopiou I., Pateel V., Arumugasundaram S., and Patra A. [13] studied about the selected differences between old (213O) and newly revised FMVSS 213 (213N). These variations were analyzed by conducting experimental tests and computer modeling. The experiment consist of three sled pulses, a midrange laboratory sled test pulse from the original safety standard (213O), and the lower and upper bound curves prescribed by the new standard (213N) and last one is a representative crash test pulse obtained from NHTSA s New Car Assessment Program (NCAP). The report made by them utilizes a MADYMO computer model and data from sled testing and crash testing to explore CRS certification outputs for occupant injury tolerance measures for above three pulses. Comparison of relevant model predicted occupant injury criteria indicated that the 213N lower bound test condition may not be a satisfactory measure of child seat injury protection. But in summing up, this experiment indicated that updated FMVSS is very vital first step in designing more robust realistic measure CRS crash protection performance [13]. 11

28 Langwieder K., Hummel and Roselt T. [1] stated that in conventional CRS, there are some problems with the anchorage system with the passenger seat belt causes problems leading to major misuse of the CRS. New German Insurance Association (Gesamtverband der Deutschen Versicherungswirtschaft ev - GDV) Institute of Vehicle Safety s research indicated that still serious misuse occurs about 30 % of CRS in the practical use. But ISOFIX has encountered these problems and performs as a robust and permanently correct anchorage of CRS resulting in easier handling and misuse reduction. Their research also involves number of test comparing conventional CRS and ISOFIX systems using ECE test benches and Car seats. The ISOFIX system hasn t shown more benefits compared to Conventional CRS using ECE test bench. While tests using real car seats showed that ISOFIX system performed well and the injury measurements were clearly below legal limits and those measurements were better than those for ECE test benches. The research further carried out by them using the additional top tether attachment, that tether values showed improved values with some problems regarding high chest acceleration and high neck moments. They conclude that ISOFIX offers an opportunity for a completely new process of optimizing child safety in motor vehicles. ISOFIX is not the only solution for conventional CRS but one can find something completely new safety solution with the help of an ISOFIX system. Comité de liaison européen des fabricants d equipements et de pièces automobiles CLEPA, European association of automotive suppliers [14], conducted study on the side impact and ease of use between ISOFIX and LATCH, they found that There is transverse and rotational movement of entire seat assembly towards the impacted side with Latch. 12

29 Head containment reduced with Latch by increased side movement and rotation about vertical axis. They found ISOFIX results to be superior to LATCH. Marius-Dorin Surcel and Michel Gou [15] conducted experiment with child dummy and its restraint system. The main purpose of this research was to develop numerical model to simulate the behavior of child passenger restraint system in case of side impact taking in to account the deformation of vehicle. The dummy is composed of multibody and side of restraint system is made up by FE to get better contact between vehicle body and the restraint system to study the deformation pattern also between child body and restraint system. The various attachments vehicle safety belts, Upper tether attachment, ISOFIX system and lower anchorage attachment were used to simulate the test and to study injury criteria for child dummy and the deformation of vehicle body because head injury criteria is much more dependent upon the intrusion. The results showed that the ISOFIX system performed the best protection for head followed by and lower flexible anchorage and vehicle safety belts. Intrusion has negligible influence on chest acceleration three of the installation showed same results. The model was offering a lot of possibilities of improvement, development and exploitation and other developments aim to evaluate different child dummies responses in the case of various side impact and frontal collision configurations. Hulme K., Patra A., Vusirikala N. and Galganski R. [16] developed visualization module for Madymo based CRS simulation model. They developed the module called NYSCEDII CRS Visualization Module (NCVM), it serves as add on component of Madymo. That research describes the features of the NCVM. It uses different finite element model of a recent-production 13

30 child restraint system (CRS) with three-year-old dummy in a modified FMVSS 213 sled test data. CVM features include the following: Kinematics, interaction between child dummy and CRS also between CRS vehicle structures. For structural analysis point of view its shows contours of stresses for the CRS and its restraint straps and vehicle structure. The simulation is seen as either a forward-continuous animation or backwardcontinuous animation with frame by frame. Stephen R. Kratzke [18] presented the issue about revision of FMVSS 213 CRS. The purpose of that study is to improve the safety of CRS. They considered two scenarios of impact, side and rear. That proposed rule was based on following considerations: Dynamic Tests: The procedure consisted with comparison of sled pulse of FMVSS 213 and 208 for different vehicles. From NHTSA revised FMVSS 213 pulse and seat bench assembly. Adoption of scaled injury criteria performance level similar to FMVSS 208. Improvement of protection from head injuries in side and rear impact crashes. Development of New Test Dummy: They developed new Hybrid III 10 year-old dummy and also widened the range of children dummy including 10 years old also the weight of 6 years old dummy was increased to 62 pounds. Modification in weights: Upper weight limit of FMVSS No. 213 s risen from 50 to 65 pounds. Adoption of weighted 6-years-old dummy for testing child restraints certified for use by children weighing more than 50 pounds. 14

31 Liang Tang, Meng Luo and Qing Zhou [20] optimized CRS for 10 year old dummy in their research. They optimized the booster seat and adult belt load limiting function. The whole model is built in MADYMO simulator. Several parameters are modified to get minimum injury criteria in accordance with ECE Regulation 44. The tool used for optimization is particle swarm algorithm, and then the results were compared with AutoDOE to validate optimization approach. It s been seen that in some cases particle swarm algorithm works better than the AutoDOE. When it came across the computational efficiency, particle swarm algorithm did better than AutoDOE. 2.4 Child Seat Classification CRS are designed taking in to considerations physical change in child by age. Some of restraint systems are explained in this section [22] Infant Seat Infants, from birth to at least age one, and at least 20 pounds should ride in the back seat in a rear facing safety seat. Installation should be like explained below: Figure 2.3 Infant seat [22] Harness straps should be at or below the infant s shoulders. Harness straps should fit securely. The straps should lie in a relatively straight line without sagging. 15

32 The harness chest clip should be placed at the infant s armpit level. Such a way it keeps the harness straps positioned properly. Infants weighing 20 pounds or more before one year should ride in a convertible child safety seat rated for heavier infants (most convertible seats are rated up to pounds rear facing) Convertible Seats Children over one year and at least 20 pounds may ride in a forward facing child safety seat in the back seat. Children should ride in a safety seat with full harness until they weigh about 40 pounds. Installation should be like explained below: Figure 2.4 Convertible seats [22] Harness straps should be at or above child s shoulders. Harness straps should be threaded through the top slots, in most cases. Harness should be snug. Straps should lie in a relatively straight line without sagging. Harness chest clip should be at the child s armpit level, which helps keep the harness straps positioned properly on the child s shoulders. 16

33 2.4.3 Booster Seats All children who have outgrown child safety seats should be properly restrained in booster seats until they are at least 8 years old, unless they are 4 9 tall. Belt-positioning boosters can only be used with both the lap and shoulder belt across the child. The shoulder belt should be snug against the child s chest, resting across the collar bone. The lap belt should lay low across the child s upper thigh area. Boosters should be used as in between safety restraints for children over 40 pounds who have outgrown a forward-facing child seat and are not yet ready for the adult safety belt. High back booster seats with 5 point harness (Figure 2.6.b) are recommended for children between pounds. Built in harness straps should be used with proper precautions. High Back belt positioning seats position (Figure 2.6c) the child for proper use of the lap shoulder belts and also give support to the head. These seats should always be used with lapshoulder belts and not with just one of the belts. Figure 2.5 Booster seats [22] 2.5 Child Seat Dimensions The typical child seat dimensions listed in Table 2.1 were the actual measurements taken before the sled testing. 17

34 2.5.1 Infant Seat Generic Dimensions TABLE 2.1 CHILD SEAT DIMENSIONS Type Height (In) Width (In) Depth (In) Convertible Convertible Booster Infant The figure 2.7 shows the dimensions for an infant seat. The infant seats are used to restrain 12 month child that child the restraint system should be rear facing. The figure 2.7 (I) is the baby carrier and figure 2.7 (II) is the base on baby carrier is placed. Figure 2.6 Rear facing infant seat (I) and (II) [29] Convertible Seat Generic Dimensions Convertible seats (Figure 2.8) are used to restraint 3 year old child. This restraint system should be placed in forward facing position. It has 4 point harness belt system to keep child in place. It can be used with both ISOFIX and LATCH system as per availability of attachment method on vehicle seat. 18

35 18 in 16 in 18 in 19.5 in 13.5 in 11.5 in Figure 2.7 Forward facing convertible seat [29] 2.6 Standard Bus Procurement Guidelines For petition of offers and contracts for supplying of transit buses, Standard Bus Procurement Guidelines (SBPG) [6] are used as a model. The SBPG are organized in following sections: 6 Request for Proposals, Offer, and Award (to be used in competitive negotiation) 7 Solicitation, Offer, and Award (to be used for sealed bids) 8 General Contractual Provisions 9 Quality Assurance Provisions 10 Warranty Provisions 11 Technical Specifications According to SBPG, 12 years or 500,000 miles whichever comes first should be the life of bus. It should be used for wide range of passengers including, children, adults, the elderly, and persons with disabilities. A section 6 gives the detailed technical specifications for transit buses. The detailed dimensions of the seat arrangement are shown in figure

36 Figure 2.8 Seating dimensions and standard configuration [6] The width, W, of the seat shall be 35 inches ± 1 inch. The length, L, shall be 17 ±1 inches. The seat height, H, shall be 17 ± 1 inches. For the rear lounge (or settee) and longitudinal seats, and seats located above raised areas for storage of under floor components, a cushion height of up to 18 ±2 inches will be allowed. This shall also be allowed for limited transverse seats, but only with expressed approval of the Procuring Agency. The seat back height, B, shall be a minimum of 15 inches. The seat cushion slope, S, shall be between 5 to 11. The seat back slope, C, shall be between 8 to 17. The hip to knee room, K, shall be 26 inches minimum. The pitch, P, is shown as reference only. 20

37 2.7 Attachment Methods Attachment method is the way to secure the child restraint system with vehicle seats in vehicles or buses. There are different ways of attachments are used. In automobile adult belts are used to restraint the CRS. But now days two attachments methods are being used widely and effectively, LATCH and ISOFIX. Also in this research LATCH and ISOFIX attachments were used and studied. The two attachment methods LATCH and ISOFIX are explained below in detail LATCH The Lower Anchors and Tethers for Children (LATCH) System is designed to make Standard installation of child safety seats easier by requiring child safety seats to be installed without using the seat belt system. As of September, 1999, all new forward facing child safety seats (excluding booster seats) meet stricter head protection requirements, which, in most cases, call for a top tether strap. Two sets of small bars, called anchors are located between a vehicle s seat cushion and seat back. LATCH-equipped CRSs have an adjustable strap which is attached to the child safety seat. It has a hook for fastening the seat to these vehicle lower anchors. As of September, 2000, most new cars, minivans, and light trucks have this tether anchor. As of September 1, 2002, two rear seating positions of all cars, minivans and light trucks are equipped with lower child safety seat anchorage points located between a vehicle s seat cushion and seat back. Also as of September 1, 2002, all child safety seats have two attachments which will connect to the vehicle s lower anchorage attachment points. This whole setup with lower anchors and upper tethers forms LATCH system. LATCH is designed to make car seat installation easier. It eliminates the need to use the vehicle's seat belt system, which is a common source of misuse. It uses anchors found between 21

38 the vehicle's back seat cushions and buckles or hooks on child safety seats. The two parts snap together to secure the child safety seat to the vehicle seat. In addition, all new vehicles have top anchor points that connect to a child safety seat's top tether strap. Together, these components are intended to make safety seat installation easier for parents. Figure 2.9 LATCH attachment [22] ISOFIX ISOFIX stands for "International Standards Organization FIX". It is a standard for installing child seats into cars and is intended to secure child restraint to vehicle seat quick and simple. This attachment is done by securing the toe rigid attachments at the bottom of the child seat to two fixed points on vehicle seat. It also has top tether to avoid the rotation of the child restraint system. [23] Figure 2.11 shows the lower attachment for ISOFIX. When cars are manufactured, ISOFIX points are built into them. Child seat manufacturers also build ISOFIX fitting points on their child seats. This will enable ISOFIX child seats to be simply plugged into the ISOFIX points in the car. ISOFIX is an essential development because many people find it difficult to fit child seats correctly, and many surveys have found that a high proportion of the child seats are not fitted securely enough. 22

39 Figure 2.10 Lower attachments for ISOFIX CRF [29] Most child seats are currently secured using a car's adult lap and diagonal seat belt. However, car seats design, seat belts, and their anchorages are different for different vehicle models. All these factors make it virtually impossible to make a child car seat that fits all cars, and sometimes tricky to fit a child car seat correctly. ISOFIX is designed to solve all these problems. The ultimate aim is that any ISOFIX child car seat you buy will fit your car simply by plugging it into the ISOFIX points. The other benefit of ISOFIX is that it will create a rigid link between the child seat and the car to provide extra solidity. This system provides the more rigid coupling of CRS to the vehicle offering the best performance in side impact crashes. 2.8 General Injury Mechanisms in Crash Scenarios In crash scenarios, three types of collision forces can cause injury. 1. First is due to external collision between motor vehicle and another object. 2. Second is due to the collision between interior of motor vehicle and passenger body. 3. Last is due to the internal collision of body parts inside the occupant body. The later two forces are very important from fatal injury point of view. Therefore the consistent uses of safety measure are required. 23

40 2.8.1 Head Injury Injuries to the head are divided into three different sections as follows: Skull injuries Brain injuries Scalp injuries. 2.9 Injury Criterion Head Injury Criterion (HIC) The head injury criterion (HIC) is used in case of head injury. Values greater than 1,000 suggest that there are chances of serious head injury. HIC is calculated as 2.5 t 2 1 HIC = max a() t dt ( t2 t1 ) t2 t (2.1) 1 t1 where, t1, t2 = arbitrary instants of time when head experiences acceleration or deceleration. a (t) = resultant linear acceleration at the center of gravity of the head [24] Neck Injury Criterion Neck injury occurs from compressive or tensile forces along the axis of the neck or shear forces acting perpendicular to the neck axis. The duration of the load which acts on the neck is also important as it affects the level of injury. Neck injuries can even occur due to moments. A limiting value of 504 in-lb and 1,680 in-lb is set for moments in extension and flexion, respectively. (SI equivalent of 1 lb-f is N and in 1 in-lbf is N-m) [24]. 24

41 2.9.3 Thoracic Trauma Index The thorax consists of some vital organs like the heart, and the chest which are vulnerable to rapid changes in the acceleration pulse. In cadaver tests, the peak lateral acceleration on the struck side of the rib and lower thoracic spine highly influences the injury to the thorax [24] FMVSS 208 Injury Criteria The FMVSS 208 standard was developed to reduce the number of fatalities and number of severity of injuries to occupants involved in frontal crashes. This standard also specifies the injury criteria for various ATD s. This standard is used for estimating the fatalities from frontal impacts. Parameters from FMVSS 208 are used to compare results obtained from MADYMO model of a frontal impact involving a transit bus. Injury criterion is shown in Table 2.2. TABLE 2.1 FMVSS 208 INJURY CRITERIA FOR VARIOUS ATDS [6] Injury Criterion Performance Limits ICPL's 50th %ile 3Y Old CRABI (12 Month Old) HIC Chest Resultant Acceleration (3ms) in G's Chest Deflection (mm) NA Femur Load (N) NA NA Neck Peak Tension (N) Neck Peak Compression (N) Neck Criteria Nij Neck Flexion (Nm) Neck Extension (Nm) Neck Shear (N) Not Mandated (Due Care) 25

42 CHAPTER 3 TESTING PROCEDURE AND STANDARDS This chapter gives the overview of the testing standards required for testing and the whole testing procedure. There are several standards for testing are available in the world but in this chapter only those standards are discussed which are followed in North America only. The standards discussed are North American standard FMVSS 213 for child restraints use in automobile and airplane, also the standard FMVSS 225 for strength requirement for anchorages. All these three standards are summarized below. 3.1 FMVSS 213 Standards This standard describes the requirements for child restraint systems used in motor vehicles and aircraft. The scope of this standard is to reduce the number of children killed or injured in motor vehicle crashes and in aircraft. The applications of this standard are passenger cars, multipurpose passenger vehicles, trucks and buses, and to child restraint systems for use in motor vehicles and aircraft. [24] Terms and Definitions This standard involves some terms and their definitions about child restraint system that are described in short below. 1. Add on CRS Any portable CRS. 2. Backless CRS CRS other than belt-positioning seat, having a seating platform that does not extend to support the child s back or head and has a structural element designed to restrain forward motion of the child s torso on impact. 3. Built in CRS - A CRS that is designed to be an integral part and permanently installed in a motor vehicle. 26

43 4. Belt Positioning Seat- CRS that positions a child on a vehicle seat to improve the fit of vehicle type 2 II belt systems and lacks any structural component to restrict the forward motion of the child s torso in forward impact. 5. Booster Seat Either a backless CRS or belt positioning seat. 6. Car Bed A restraint system designed to restrain or position a child on a continuous flat surface. 7. CRS Any device except TYPE I or TYPE II seat belts designed for use in a motor vehicles or aircraft to restrain, seat or position children who weigh 50 pounds or less. 8. Contactable Surface Any CRS surface (except the belt hardware) that may contact any part of the head or torso of the appropriate test dummy specified in S7 when the system is tested in accordance with S Harness Combination of pelvic and upper torso CRS that consists primarily of flexible material and that does not include a rigid seating structure for the child. 10. Rear Facing CRS CRS, except a car bed that positions a child to face in the direction opposite to the normal direction of travel of the motor vehicle. 11. Child Restraint Anchorage System A vehicle system that is designed for attaching the child restraint system to a vehicle at a particular designated seating position. 12. Torso The portion of the body of a seated anthropomorphic test dummy, excluding the thighs that lie between the top of the child restraint system seating surface and the top of the shoulders of the test dummy. 13. Specific Vehicle Shell- The actual shell means the actual vehicle model part into which the built in child restraint system is or is intended to be fabricated, including the complete surroundings of the built in CRS. 27

44 14. Factory Installed CRS Built in CRS that has been or will be installed permanently in a motor vehicle before that vehicle is certified as a completed or altered vehicle in accordance with part Rear Facing CRS The CRS except a car bed that position a child to face in the direction opposite to the normal direction of travel of motor vehicle. 16. Torso The portion of the body of a seated anthropomorphic test dummy, excluding the thighs that lie between the top of the CRS seating surface and the top of the shoulders of the test dummy [24] Test Conditions and Procedure The test conditions described in section below apply to the dynamic systems test. The test procedure for the dynamic systems test is specified in The test dummy is placed in the test specimen (child restraint), clothed and positioned Test Device 1. Add-on Restraint System - This test device is a standard seat assembly consisting of a simulated vehicle bench seat, with three seating positions. The assembly is mounted on a dynamic test platform so that the center SORL of the seat is parallel to the direction of the test platform travel and so that movement between the base of the assembly and the platform is prevented. 2. Built in CRS - The specific vehicle shell or the specific vehicle is used for testing the built in CRS. 28

45 Dynamic Test Condition The tests are frontal barrier impact simulations of the test platform or frontal barrier crashes of the specific vehicles as specified in S5.1 of section for following two test configurations I and II. 1. Test Configuration I These tests are carried out at a velocity change of 48 km/h (30 miles/h) with the acceleration of the test platform entirely within the curve shown in Figure 3.1 (for child restraints manufactured before August 1, 2005) or in Figure 3.2 (for child restraints manufactured after August 1, 2005), or for the specific vehicle test with the deceleration produced in a 48 km/h (30 miles/h) frontal barrier crash. Figure 3.11 Acceleration function for test configuration I [29] Figure 3.2 Acceleration function for test configuration I (Upper and Lower Bound) [29] 29

46 2. Test Configuration II The test are set at a velocity change of 32 km/h (20 miles/h) with the acceleration of the test platform entirely within the curve shown in Figure 3.3, or for the specific vehicle test, with the deceleration produced in a 32 km/h (20 miles/h) frontal barrier crash. Figure 3.3 Acceleration function for test configuration II [29] Dynamic Test Procedure A. Activate the built-in child restraint or attach the add-on child restraint to the seat assembly as described below: 1 Test Configuration I i. Child restraints other than belt-positioning seats - Install the child restraint system at the center seating position of the standard seat assembly, in accordance with the manufacturer s instructions as specified in these standards, except that the standard lap belt is used and, if provided, a tether strap may be used. ii. Belt positioning seats A belt positioning is seat is attached to either outboard seating position of the standard seat assembly in accordance with the manufacturers instructions provided with the system using only the standard vehicle lap and shoulder belt and no tether. 30

47 iii. In case of each built in child restraint system, activate the restraint system in specific vehicle, in accordance with manufacturer s instructions. 2 Test Configuration II i. In the case of each add-on child restraint system which is equipped with a fixed or movable surface or a backless child restraint system with a top anchorage strap, install the add-on child restraint system at the center seating position of the standard seat assembly using only the standard seat lap belt to secure the system to the standard seat. ii. In the case of each built-in child restraint system which is equipped with a fixed or movable surface or a built-in booster seat with a top anchorage strap, activate the system in the specific vehicle shell or the specific vehicle in accordance with the manufacturer s instructions. B. Dummy is to be selected according to standards specified in S7. The dummy is assembled, clothed and prepared as specified in S7 and S9 and part 572 [24]. C. Place the dummy in the child restraint. Position it, and attach the child restraint belts, if appropriate, as specified in S10 [24]. D. Belt adjustment i. Add-on systems other than belt positioning seats Tighten the shoulder and pelvis belt until a 9 N force is applied to the webbing at the top of shoulder and to the pelvic the pelvic webbing 50 mm on either side of the torso midsagittal plane pulls the webbing 7 mm from the dummy. 31

48 ii. Add-on belt positioning seats and Built-in child restraint systems The lap portion of Type II belt systems is tightened to the tension not less than53.5 N and not more than 63 N while that of shoulder portion not less than 9 N and not more than 18 N. E. Accelerate the test platform to simulate frontal impact in accordance with Test Configuration I or II, as appropriate. F. Determine conformance with the requirements in S5.1 [24] Injury Criteria and Occupant Excursion Limits 1. HIC36 (Head Injury Criteria) should be less than Head excursion limit 720 mm (28.34 inch) max, 813 mm (32 inch) without tether. 3. Knee excursions limit 915 mm (36 inch) max. 4. Resultant chest acceleration limit is 60 G s regardless of whether equipped the child restraints with a top tether. 5. Seat back angle shall not exceed 70 degree. 3.2 FMVSS 225 Standards Federal Motor Vehicle Safety Standard (FMVSS) 225 specifies requirements for Child Restraints Anchorage Systems, to ensure the securement of add-on child restraints to vehicle seats and also to improve the strength of anchorage system. This standard describes the use of a universal attachment system for child restraints, at two seating positions, and also it makes sure that the child restraints be fitted with some means of attaching to those systems. This standard applies to passenger vehicles and trucks with gross weight rating (GWVR) of 8500 pounds or less and to busses with GWVR of pounds or less [25]. 32

49 3.2.1 Terms and Definitions 1. Child Restraint Anchorage Any part of the vehicle that is involved in transferring loads generated by CRS to the vehicle structure other than Type I and II seat belts. 2. Child Restraint Anchorage System A vehicle system having CRS to a vehicle at a particular designated seating position, consisting of two lower anchorages a tether anchorage. 3. Child Restraint Fixture - The fixture shown in figure 3.4 that simulates the dimensions of a CRS, and that is used to determine the space required by the CRS and the location and accessibility of the lower anchorage. 4. Seat Bight The area close to and including the intersection of the surfaces of the vehicle seat cushion and seat back. 5. Tether Anchorage - A permanently installed vehicle system that transfers loads from a tether strap through the tether hook to the vehicle structure and that accepts a tether hook. 6. Tether Hook - A device, used to attach a tether strap to a tether anchorage. Figure 3.4 Child restraint fixtures [25] 33

50 7. Tether Strap - A strap that is secured to the rigid structure of the seat back of a CRS, and is connected to a tether hook that transfers the load from that system to the tether anchorage Lower Anchorage Specifications Figure 3.5 shows the detailed specification for lower anchorage system. The lower anchorage shall consist of two bars that are 6mm ± 0.1mm in diameter. They should be straight, horizontal and transverse and axes are collinear. The length should not be less than 25mm and should not exceed 60mm The centre distance between two anchorages should be d = 280mm Those two anchorages should be permanent and integral part of vehicle. Anchorages shall not deform more than 5mm under the application of load of 100N in any direction. Figure 3.6 Lower anchorage specifications [25] Lower Anchorage Location It should not be more than 70mm behind Z point (Figure 3.6). Not less than 120mm behind the vehicle seating reference point measured along vertical longitudinal plane. 34

51 Figure 3.7 Lower anchorage locations [25] Strength of the Lower Anchorage If the lower anchorages are tested according to testing requirements, it will not allow X point on SFAD 2 as shown in figure 3.6 to be displaced horizontally as follows: When a force of N is applied in the forward direction in a vertical longitudinal plane, it should displace more than 175mm. When a force of 5000 N is applied laterally 75±5 degree to either side of vertical longitudinal plane parallel to vertical longitudinal plane, it should displace more than 150mm Test Requirements for Lower Anchorages Vehicle shall meet the strength requirement of the lower anchorage explained above with test requirements explained below: Place SFAD 2 in the vehicle seating position and attach it to the two lower anchorages of the child restraint anchorage system. Do not attach the tether anchorage. 35

52 a. Forward force direction: Apply preload force of 500 N at point X. Increase the force to 11,000 N within 30 seconds with onset rate not exceeding 135,000 N per second and maintain the 11,000 N loads for 10 seconds. b. Lateral force direction: Apply preload force of 500 N at point X. Increase the force to 5,000 N within 30 seconds with onset rate not exceeding 135,000 N per second and maintain the 5,000 N loads for 10 seconds[29]. Figure 3.8 ISO static force application device 2 (SFAD 2) [25] 36

53 CHAPTER 4 BASELINE SLED TEST 4.1 Overview of Sled Program To evaluate the passenger safety one has to study the factors affecting the injury to the passenger and to evaluate those injuries multiple tests have to carry out to do some engineering analysis to reproduce the dynamic conditions of real world. There are three methods to achieve this engineering analysis. Full-scale vehicle crash testing To obtain the acceleration data or sled pulse Dynamic sled testing To obtain injury values used for validation MB modeling of crash scenarios For validation and further studies. It is not possible to carry out full vehicle crash tests using whole set up environment. The complex and destructive nature of conducting these crash tests makes them very expensive, it will touch the expenses of sky. Often, engineering analysis requires multiple tests wherein occupant motion or vehicle component performance comparisons are made when subject to specific dynamic conditions. For all these situations there arises the concept of sled testing. This sled test produces same dynamic condition for full scaled vehicle crash test in controlled environment with minimum level of cost. The particular part of vehicle is made to test the real world conditions. This reduces the cost of full vehicle and the cost of second vehicle. This is achieved by giving the acceleration pulse to sled on which all vehicle compartment setup is fixed by external energy source like hydraulic system. The sled and buck can then be subjected to accelerations representative of a particular crash environment. This controlled acceleration is commonly referred to as a sled pulse which is obtained from the FE simulation of the complete vehicle (bus) structure crash against other vehicles or rigid wall. 37

54 4.2 Approach to Sled Test Program The preliminary task of the project and the sled program is to generate a Numerical Model of typical mass transit bus interior. Previously created Body in White (BIW) of the vehicle (vehicle buck) [27] by analyzing and studying available database and U.S. reports on traffic safety for sled test is used with additional changes in the seat structures of the bus. This BIW was used for validation of some critical configurations (Figure 4.1) identified in previous phase with a series of the sled tests. Figure 4.1 Final design of sled test BIW (Configuration I and II) In Kansas state transit buses are not having child restraint anchorage system to restrain the child seats. By analyzing and studying the FMVSS 225 for child restraint anchorage system, as explained in section 3.2. To reduce the complexity in installing CRS in bus only lower anchorage system was designed, tether attachment was not designed. (Figure 4.2) This BIW was the open frame construction with several high speed cameras installed on it to capture the kinematics and occupant interaction. 38

55 Figure 4.2 Child seat anchor attachment method (FMVSS 225) 4.3 Methodology Sled Test Device All sled tests were performed by means of the MTS Inc. system accelerator sled facility at the National Institute for Aviation Research (NIAR) Crash Dynamics Laboratory. The system houses a servo hydraulic MTS Model Crash Simulator. The system, an acceleration crash sled, allows the impact to take place first and uses the sled to decelerate to a safe level of speed. Figure 3.3 shows NIAR s sled test facility. Figure 4.3 Sled test facility at NIAR 39

56 4.3.2 Test Anthropomorphic Test Devices For this study five types of ATDs Hybrid III 95 th percentile, Hybrid III 50 th percentile, Hybrid II 50 th percentile, Hybrid III 3-year-old dummy, and CRABI 12-month-old dummy were used. Table 4.1 gives the summarized information of those ATDs. All the dummies used were calibrated and instrumented based on the requirement and availability of the data channels. TABLE 4.1 DATA FOR HYBRID III FAMILY USED IN THE PRESENT STUDY ATD Parameter 12 mo CRABI 3 YO Child 50% Male 95% Male Weight (lbs.) Stature (in.) Sitting Height (in) Instrumentation Data channels used for each sled test were varied according to the number of ATDs used in the test because of the limited availability of the data channels. Figure 4.4 shows the general positions of data channels. Figure 4.4 Locations of data channels in ATD 40

57 Accelerometers at head, torso and pelvis giving linear accelerations in X, Y and Z directions, were available for the all the ATD s used. Upper neck load cell for upper neck forces (X, Y and Z) and upper neck moments (X, Y and Z), were used for critical dummies according the impact and sitting position and child dummies only. Femur load cells in left and right femur were mounted for critical ATDs according the impact condition and sitting position. Two accelerometers were used pan and back of the CRS to measure the acceleration in X. Chest deflection potentiometer for chest deflection for critical ATDs according the impact condition and sitting position Data Processing Measurement data were recorded by means of an onboard system. The sampling rate of the transducer data was 10 khz. Four SpeedCam VISARIO high-resolution ( x 1024 pixel resolution) cameras were used to record the test sequence. The locations of few high speed cameras were not fixed, location of cameras were changed according to the impact conditions and configuration of sled. One camera was mounted in the side of the sled to show the movement from the side; the other was mounted directly onboard on the sled fixture to show the relative movement in more precisely. For some tests two cameras were mounted onboard to get closer look at kinematics and interaction between CRS and occupant and between occupant and occupant. One camera was positioned at the top of the testing area. Once sled is prepared with placing ATDs at appropriate places, Position and profiles of ATDs and interior structure were recorded in terms of data points with the help of a FARO arm coordinate measuring machine (CMM) for further validation of the tests using computer 41

58 simulations. Then photos were taken before and after the test, to get idea of initial position of ATDs and other interior structure while doing validations through computer simulations also to see the interaction point between occupant and occupant and between occupant and CRS. This process was repeated for every single test and validations were done. The ATD data were processed according to SAE J211. The ATD data processing filters are shown in Table Frontal Impact Test TABLE 4.2 ATD DATA PROCESSING FILTERS Data Channel SAE J211 Filter Sled Acceleration CFC 60 Head Accelerometer CFC 1000 Chest Accelerometer CFC 180 Pelvis Acceleration CFC 1000 Chest Deflection CFC 600 Neck Forces CFC 1000 Neck Moments CFC 600 Femur Force CFC 600 Figure 4.5 General sled test configuration I for frontal impact tests 42

59 Figure 4.5 shows the general set up for frontal impact sled test ( to ). The sled was equipped with two rows of front facing seats. It didn t has side facing seats due to absence of occupant on side facing seat and no interaction of occupants with side facing seats. A divider panel was fastened to the sled in front of first row of the front-facing seat. This whole setup represents a typical bus interior structure. Figure 4.6 shows the general set up for frontal impact sled test ( and ). The sled was equipped with two side facing seats. A wheel well cover was fastened to the sled in front of right side facing seat. This whole setup represents a typical bus interior structure. Figure 4.6 General sled test configuration II for frontal impact tests Maximum Acceleration = 11.1 g s Change in Velocity V = 10.9 mph Figure 4.7 Frontal impact sled test sled pulse 43

60 TABLE 4.3 TEST SUMMARY FRONTAL SLED TESTS 44 Tests Summary Pulse Bus 30 mph to Min Van 30 mph Seat Width 17.5" / mm Ground To Seat Pan Height 17.5" / mm Front Divider Panel to Seat Distance 11.0" / mm Test Number Forward Facing Seat Pitch 32.0" / " / " / " / mm mm mm mm - - Forward Facing Seat Hip to Knee 28.0" / " / " / " / Room mm mm mm mm - - Wheel Well None None None None 1 1 Divider Panel None None Impact Orientation Frontal Frontal Frontal Frontal Frontal Frontal Position 1 H III CRABI H III CRABI H III 3Y Old H III 3Y Old - - Position 2 H III 50th % H III 50th % H III 50th % H III 50th % H III 3Y Old H III 3Y Old Position 3 H III 95th % H III 95th % H III 95th % H III 95th % - - Position 4 H III 3Y Old H III 3Y Old H III CRABI H III H III CRABI CRABI H III CRABI Position H III 50th % H III 50th % Position H III 50th % H III 50th % Position Position S Position S Child Seat Attachment Method LATCH ISOFIX ISOFIX LATCH LATCH ISOFIX Configuration I I I I II II 44

61 Table 4.3 gives the summarized data for frontal impact sled tests performed. There were totally 6 frontal impact sled tests were conducted using both sled configurations (Figure 4.1) and both child attachments system. (Figure 2.10 and 2.11) The Sled pulse for frontal impact sled test was extracted from the simulation of the frontal impact of a bus traveling at 30 mph and mini van traveling at 30 mph. Figure 4.7 shows the acceleration sled pulse applied during frontal-impact for both configurations I and II. 4.5 Side Impact Test Figure 4.8 shows the general set up for frontal impact sled test ( and ). The seat configuration for the side impact sled tests was kept the same as in the previous frontal sled tests (Figure 4.5), except the side-facing seat row, and front wall were added. Figure 4.8 General sled test configuration I for side impact tests Table 4.4 gives the summarized data for side impact sled tests performed. There were totally 2 side impact sled tests were conducted using LATCH child attachments system (Figure 2.10). 45

62 TABLE 4.4 TEST SUMMARY SIDE SLED TESTS Tests Summary Pulse Bus 0 mph Large Truck 25 mph Seat Width 17.5" / mm Ground To Seat Pan Height 17.5" / mm Front Divider Panel to Seat Distance 11.0" / mm Test Number Forward Facing Seat Pitch 32.0" / mm 32.0" / mm Forward Facing Seat Hip to Knee Room 28.0" / mm 28.0" / mm Wheel Well None None Divider Panel 1 1 Impact Orientation Side Side Position 1 H III 50th % H III CRABI Position 2 H III CRABI H III 50th % Position 3 H II 50th % HIII 3Y Old Position 4 HIII 3Y Old H II 50th % Position 5 H III 50th % H III 50th % Position Position 7 H III 95th % H III 95th % Position S1 - - Position S2 - - Child Seat Attachment Method LATCH LATCH Configuration I I Maximum Acceleration = g s Change in Velocity V = mph. Figure 4.9 Side impact sled test sled pulse 46

63 The sled pulse for side-impact testing was extracted from the simulation of the sideimpact of a bus 0 mph (stationary) and a large truck traveling at 25 mph. Figure 4.9 shows the acceleration sled pulse applied during side impact testing. 4.6 Rear Impact Test Figure 4.9 shows the general set up for frontal impact sled test ( and ). The seat configuration for the rear impact sled tests was kept the same as in the previous frontal sled tests (Figure 4.5), except that side facing seat row was added and divider panel was removed from sled. (Figure 4.10) Figure 4.9 General sled test configuration I for rear impact tests Table 4.5 gives the summarized data for rear impact sled tests performed. There were totally 2 side impact sled tests were conducted using both child attachments system. (Figure 2.10 and 2.11) The sled pulse for rear-impact testing was extracted from the simulation of the rear impact of a bus at 0 mph (stationary) and a bus traveling at 20 mph. Figure 4.11 shows the acceleration sled pulse applied during rear-impact testing. 47

64 In all ten tests were conducted with frontal, side and rear impact. Tables 4.3, 4.4 and 4.5 give all the data about the ten sled test. Maximum Acceleration = g s Change in Velocity V = mph Figure 4.10 Rear impact sled test sled pulse TABLE 4.5 TEST SUMMARY REAR SLED TESTS Tests Summary Pulse Bus 0 mph Bus 20 mph Seat Width 17.5" / mm Ground To Seat Pan Height 17.5" / mm Front Divider Panel to Seat Distance 11.0" / mm Test Number Forward Facing Seat Pitch 32.0" / mm 35.0" / mm Forward Facing Seat Hip to Knee Room 28.0" / mm 32.0" / mm Wheel Well None None Divider Panel 1 1 Impact Orientation Side Side Position 1 H III CRABI HIII 3Y Old Position 2 H III 95th % H III 95th % Position 3 H III 50th % H III 50th % Position 4 HIII 3Y Old H III CRABI Position Position Position Position S1 - - Position S2 - - Child Seat Attachment Method LATCH LATCH Configuration I I 48

65 4.7 Comparison of LATCH and ISOFIX The one of the aim of this research was to study the effect of LATCH and ISOFIX attachment system and compare those to have best installation system. All the sled tests conducted were of either ISOFIX or LATCH attachment system. Three tests of each LATCH and ISOFIX attachment were conducted for frontal impact. From results of sled test plots in the form of bar charts were created which gives comparison LATCH versus ISOFIX attachment system. Figure 4.12 shows the injury values of CRABI and 3-year-old dummy for frontal impact with different configuration but at same position. Right column of figure shows the injury values for 3-year-old dummy and left column shows for CRABI. If we consider the 3-year-old dummy irrespective of position both attachments worked for best performance of reducing the injury values. There was only slight difference in injury values of both attachment systems about 5-10%. If we consider the CARBI, both attachment systems gave best performance reducing the injury values and difference is also small about 10-15% in both attachment systems. From the test videos it had been seen that the lateral moment of CRS is more with LATCH attachment than that of ISOFIX, but there was not that much differences in injury values of both. So in summing up all, we can say that ISOFIX and LATCH provide similar levels of performance for frontal impacts. Further analysis is required for side impact applications. 4.8 Occupant Interaction Analysis Another interesting aim of this research was to study the behavior of adult occupants with child dummies. The effect of adult dummies or structure on child dummies is explained next: 49

66 Figure 4.11 Comparisons of LATCH and ISOFIX attachment system Frontal Impact Test and Good performance with LACTCH and ISOFIX. There is no interaction between child and adult occupants. 50

67 P percentile Test and year-old with passengers seating behind may experience head to head contact Possible solutions: Bus seatback height modifications, and/or increase the seat pitch for locations behind future designated CRS locations Test and Acceptable performance for both the 3-year-old and the 12 month ATDs and also Side Impact acceptable interaction with other adult passengers Test th Hybrid III 95P P Neck Flexion (My+)/ Neck Extension (My-): Due to head to head contact between the 95th percentile and 3-year-old. 3-year-old Neck Extension (My-): Due to head to head contact between the Hybrid III 95P th and 3-year-old. 3-year-old Neck Compression (Fz-): Due to head to head contact between the Hybrid th III 95P P percentile and 3-year-old. th Hybrid III 95P P Femur Compression: Due to contact femur/seat structure. Note even though the injury values for the 12 month old are low there is a lot of interaction with the side facing seat occupant Possible Solutions: Avoid the use of CRS with passenger side facing seats or do not allow the use of CRS in aisle seats facing side facing passenger seats Test th Hybrid 95P P Femur Compression: Due to contact femur/seat structure. Acceptable interaction of the 3YOLD and 12 month old with other adult passengers. 51

68 4.8.3 Rear Impact Test Neck Extension (My-): (50th and 95th) Due to seatback design. The dynamic performance could be enhanced with improvements to the seatback stiffness and headrest design. 3-year-old, although the injury values are low special attention needs to be considered on seat pitch and seat back rotation of the seat in front of the CRS Test Neck Extension (My-): (50th) Due to seatback design. The dynamic performance could be enhanced with improvements to the seatback stiffness and headrest design 12 month old, although the injury values are low special attention needs to be considered on seat pitch and seat back rotation of the seat in front of the CRS Acceptable level of performance for the 3-year-old Note that the 12 month CRS Seat Base was detached during the test, also it should be th noted that this CRS behind the hybrid III 95P P percentile reduced seat back rotation th hence reducing the hybrid III 95P P percentile neck extension by 60 % when compared to the previous test. 52

69 CHAPTER 5 MADYMO MODEL DEVELOPMENT OF SLED STRUCTURE Overview of Simulation To study the safety of structure and occupants, laboratory sled testing has been conducted in automobile and aerospace industries, but they are very costly and requires lots of efforts to set up the scenario of different conditions. And in real life crashes are more complex which is not performed by sled testing. Computer simulations proved a vital role in crashworthiness of structure and occupants which can be used as replacement of laboratory sled testing in both industrial and research area. Main purpose of simulation is to reduce the time and cost of testing. In industries simulation used to check the design for crashworthiness before actual testing and launching the product in market. In research area simulation is used to optimize the existing or hypothetical scenarios or designs. Thus in all simulations help to reduce the cost of number testing, number of prototypes and design to be manufactured and tested also reduces time in the product development cycle. In simulations multibodies are validated against the sled tests results and been used for studying kinematics and biomechanics of occupants in various scenarios with varying accelerations pulses and other parameters which eliminates the need for carrying out the sled tests which are expensive and time consuming. 5.2 MADYMO Version MADYMO stands for MAthematical DYnamical Models. MADYMO is widely used for studying the vigorous safety and wide-ranging biomechanics. The input deck for MADYMO is in the form of.xml (extensible Markup Language). This deck allows user to define elements, their attributes and relationship between those. 53

70 P step P explicitly. MADYMO use numerical integrations methods to solve the equations of motions. There are three methods are available in MADYMO. Modified Euler method with a fixed time step. Runge-Kutta method with fixed time step. Runge-Kutta Merson method with variable time step. These all methods are based on one step explicit methods, in which solution at a time point tbnpb th is used to calculate the solution for tbn+1pb th Explicit Euler integration method with a fixed time step was used for this research study. 5.3 Test ATDs Specifications MADYMO ATD database describes the validated and calibrated dummies. It has three types of model ellipsoids, facets, FE model. Ellipsoidal models are based on rigid-body modeling features of MADYMO. This model is set up with use of ellipsoids, cylinders and planes. They are the most CPU time-efficient type of models. The recommended maximum time steps for the ellipsoid and facet models generally lie between 1.0e-4 s to 1.0e-5 s. The standard models of the adult and child Hybrid III dummies, 50th percentile male, 95th percentile male, three-year-old child, a 12 month old CRABI are used in the present study. In next section some of ATDs are briefly explained Hybrid III 3-year-old Child Dummy The Hybrid III 3 Year Old Child Dummy is used to study the effect of deploying side and frontal airbags to an out-of-position child of 3 years old. The dummy has recently been included in FMVSS 208 and is the recommended dummy to represent a 3 years old child in the ISO Outof-Position test procedures. Hybrid III 3-year-old dummy are scaled from the ellipsoid model of the Hybrid III 50th percentile dummy with exceptions as explained next [26]. 54

71 Figure 5.1 Ellipsoid model of hybrid III 3-year-old dummy [26] A three-pivot neck model has been implemented. The middle pivot is a revolute translational joint and the others are spherical joints with stiffness depending on the bending direction. Lumbar spine is modeled with two joints with mass and inertia distributed over both upper and lower spine bodies. The sternum stop, which limits the sternum to spine box displacement, is modeled by two separate point-restraints. A protected joint resistance model is used to model rib x-displacement CRABI 12 Month Old Dummy The CRABI (Child Restraint AirBag Interaction) 12 month old dummy is used to evaluate CRS in automobile in all impact scenarios with and without airbags. This dummy also th scaled down from Hybrid III 50P P percentile dummy with weight 10.0Kg and height of 747MM standing or 480 MM sitting. Geometry measurements on the physical dummy and existing information about mass distribution have been used as anthropometry source. This dummy is not th validated with additional tests as it is for Hybrid III 50P P percentile standing male [26]. 55

72 Figure 5.2 Ellipsoid model of CRABI 12 month old dummy [26] Hybrid III 50 th Percentile Dummy Hybrid III 50 th percentile male dummy is widely used within all dummies for automotive safety restraint systems in crash testing. This dummy is accepted in several standards like FMVSS 208, ECE R.94, and the European New Car Assessment Programme (NCAP). This dummy represents the American male with average size and weight. 37 ellipsoids with various joints are used in MADYMO to produce this dummy. Figure 5.3 Ellipsoid model of hybrid III 50 th percentile [26] 56

73 The neck has five kinematic joints located in the centre and on the rotation axis of the nodding joint (OC). The rib body represents the front of the rib cage (left and right), and the sternum body represents the compliant sternal region (center). The abdomen a separate body, is connected to the lower torso with a translational joint. The hip model is a combination of a spherical joint and a protected joint resistance model. The knee has flexion and the translational movement of the knee slider. The foot and ankle has approximately 45 degrees angular rotation has stopper to reduce tibia load peaks [26]. th Hybrid III 95P P Percentile Dummy th The biomechanical responses of this dummy are scaled form the standard hybrid III 50P P percentile dummy. This represents the larger size of adults. th Figure 5.4 Ellipsoid model of hybrid III 95P P percentile [26] 57

74 P 5.4 Description of Occupant Environment To validated MB model is used from the studies that have been done [21] and [27] with some modifications. Sled model was having child restraint systems. Detailed modeling of child restraint system is briefly explained in section This sled model was consisting of divider panel, wheel well, side and front facing seats, floor, side walls, and front walls. Out of which divider panel was made up of ellipsoids, while side walls, front walls and floor were made from planes and wheel well, seats were of FE model as facets. These each part was defined in different systems with appropriate characteristics and joints considering influence of interior on kinematics and injuries Dummy Selection The MADYMO database has wide number of dummies that can be used for simulations to represent their counterparts used in full scale or sled testing. But according to the position of occupant sitting, selection was made. For this research worst conditions were considered. The following validated dummy models from the MADYMO database were selected to represent their counterparts used in sled testing: Hybrid III 3-year-old dummy Hybrid III CRABI (12-month-old) dummy th Hybrid III 95P P percentile th Hybrid III 50P P percentile th Hybrid II 50P P percentile dummy dummy dummy As this research was based on worst conditions, there was an exclusion of hybrid III 5P percentile dummy. th 58

75 5.4.2 Modeling of Facet Child Restraint System Model Previously created [29] model of infant seat and convertible seat was used for this research work with some modifications in seat mesh model. Detailed modeling of seats can be found in [29]. The seats previously had fine mesh quality of element size 5mm which was taking time to run the simulation. So remeshing had been done with coarse mesh.. This was done by using Automesh option in 2D section. Mesh seed was created with element size as 15 mm. Element density is varied until satisfactory mesh obtained. Figure5.5 shows the meshed geometry of infant seat and convertible seat. Figure 5.5 Mesh Geometry of infant and convertible seats The occupant environment contains many FE models, like, child seats, bus seats, wheel well, seat supports etc to simulate the occupant environment, those FE parts should be converted into facet models. This is done with separating the quad and triad elements in two different parts retaining their connectivity. This is done because MADYMO defines two separate properties for quad and triad elements. The detailed description of bus environment is found in [27]. Figure5.6 and 5.7 show the facet model of infant seat and convertible seat respectively. 59

76 Figure 5.6 Rear facing infant seat Figure 5.7 Forward facing convertible seat 60

77 5.4.3 Joint and Property Selection Seats have revolute or revolute-translational joints at the center where seat back and seat pan meet to obtain kinematics correlating with sled test as discussed in [27]. But some modifications in characteristics were made as shown in figure 5.8. The values for loading and unloading functions were taken from the sled test and the damping coefficient used was Theses joints were defined between seat back and seat pan. Figure 5.8 Joints Stiffness Functions MADYMO simulation is primarily based on appropriate geometry, characteristics loads, joints and their characteristics, and properties. Contact properties are based on the facet force deflection characteristics. Contact characteristics are also vital attribute in MADYMO simulation when considering the validation to correlate kinematics and biomechanics from the sled test. Contact properties are depends upon force deflection, hysteresis, and coefficient of damping and friction. Those contact properties are generated by actual component testing or from finite element analysis or standard MADYMO model libraries. However, different contact characteristics are used for ellipsoid parts and for facet part. For defining the characteristics CHARACTERISTIC.CONTACT was used to define force-deflection properties to the parts. 61

78 MADYMO library is having three types of contact definitions as next: CONTACT.MB_MB between two multibodies. CONTAC.MB_FE between multibody and FE model (facet model) CONTACT.FE_FE between FE models (facet models) This research, rather MADYMO simulations were conducted with different types of contacts. Their Characteristics curves are shown in figure 5.9 and table 5.1 defines the parameters used for contact properties used for simulations. TABLE 5.1 CONTACT DEFINITIONS Contact ATD_ATD ATD to Seat ATD to CRS CRS to Seat Contact Definition Contact Type Function Name(Figur e 5.10) Damping Coefficient Friction Coefficient Hysteresis Model Hysteresis Slope CONTACT. MB_MB USER MID- POINT Body_to_Bo dy_contact CONTACT. MB_FE USER_SLA VE Seat_plane_C ontact_functi on CONTACT. MB_FE USER_MAS TER Contact_Char _Dummy CONTACT.F E_FE USER_SLA VE Seat_plane_c ontact_charac ter6 Seat to Seat Support CONTACT.F E_FE USER_SLA VE Rigid_metal_ contacts C 3C 3C 3.5E5-3.5E5 3.5E5 3.5E Modeling of Child Attachment System All the tests were carried out either with LATCH or ISOFIX attachment system. To simulate these attachments in MADYMO, translational and revolute-translational joints were used. 62

79 Figure 5.9 Contact property characteristics Figure 5.10 Translational characteristics For LATCH system translational joints are defined at the each end of the segment. Those joints were between bus seat and belt which secure CRS to bus seat. According to FMVSS 225, anchorage points should have 60 mm slack to secure every CRS to seat. To implement this, 63

80 Translational characteristics were locked on either side after 30 mm moment of belt segment by increasing the force suddenly after 30 mm on ether side as shown in figure 5.10(a). For ISOFIX system revolute-translational joints used at the center of the CRS. The characteristics curve for revolute joint used was as shown in figure 5.10(b) and same translational characteristics curve as shown in figure 5.10(a) was used ATD Inertial Load In all two acceleration pulses were applied to each dummy. One was gravitational acceleration pulse (Figure 5.11(a)) which was 9.81 m/s 2 to simulate the gravitational effect on dummies. Figure 5.11 ATD inertial loads 64

81 Second was sled pulse (Figure 5.11 (b,c,d)) according the impact conditions (frontal, side and rear respectively) was applied to each dummies. Later ones were extracted from the finite elemental simulations which are used for actual sled testing. Those are taken from the passenger compartment as passenger and child safety was being studied. Finally all these propertied and pulses were applied to whole bus setup as shown in Figure 5.13 and ran all simulations indicated in table 4.3 to MADYMO Bus Interior Model Figure 5.12 describes the bus interior set up configuration I for frontal impact test. This setup was used for test to It had two rows of forward facing seats with divider panel. Figure 5.12 MADYMO setup for frontal impact test configuration - I Hybrid III 50 th percentile dummy was on seat position 2 and hybrid III 95 th percentile dummy was on seat position 3 as shown in the figure 5.12 and that seat positions were same for all four tests but child dummies were interchanged. In test and CRABI was being on seat position 1 and hybrid III 3-year old dummy on seat position 4 while for test and CRABI was being on seat position 4 and hybrid III 3-year old dummy 65

82 on seat position 1. Attachment system used for Test and was LATCH while for test and test was ISOFIX. (Table 4.3) Figure 5.13 describes the bus interior setup configuration II for frontal impact test. It had two sets of side facing seats and a wheel well cover. This setup was used for test and The dummies positions were same for all tests except CRS attachment system. Hybrid III 50 th percentile dummy was on seat position 5 (figure 4.1) and seat position 6 as shown in the figure CRABI was being on seat position 4 and hybrid III 3-year old dummy was on seat position 2. Test had LATCH while had ISOFIX. (Table 4.3) Figure 5.13 MADYMO setup for frontal impact test configuration - II Figure 5.14 describes the bus interior set up configuration I for side impact test. This configuration had two row of forward facing seat with a divider panel and a set of side-facing seats. This setup was used for test and Hybrid III 50 th percentile dummy was on seat position 1 and 5, hybrid II 50 th percentile dummy was on seat position 3 and hybrid III 95 th percentile dummy on seat position 7 as shown 66

83 in the figure 5.14 and that seat positions were same for all two tests but child dummies were interchanged. In test , CRABI was being on seat position 1 and hybrid III 3-year old dummy on seat position 4 while for test CRABI was being on seat position 4 and Hybrid III 3-year old dummy on seat position 1. CRS attachment systems were also same that of LATCH (Table 4.4) Figure 5.13 MADYMO setup for side impact test configuration I Figure 5.12(d) describes the bus interior set up configuration I for rear impact test. It had same setup as for frontal impact with two rows of forward-facing seats but except divider panel. This setup was used for test and Hybrid III 50 th percentile dummy was on seat position 3 and hybrid III 95 th percentile dummy was on seat position 2 as shown in the figure 5.15 and that seat positions were same for all two tests but child dummies were interchanged. In test CRABI was being on seat position 1 and hybrid III 3-year old dummy on seat position 4 while for test CRABI was being on seat position 4 and Hybrid III 3-year old dummy on seat position 1. Attachment system used for Test and was LATCH. (Table 4.5) 67

84 Figure 5.15 MADYMO setup for rear impact test configuration - I 68

85 CHAPTER 6 VALIDATION OF NUMERICAL MODELS 6.1 Introduction This chapter discusses the comparison of simulation and test results validation methods utilized are discussion in. Validation is the vital part of this research and is a important part once simulations of numerical model have done to do further studies or implementation of that standard or rule. The meaning of validation is as its name explains to validate the numerical model with the actual sled test. In other words, it means to check or testify the process of simulation with the rules or standards. The data recorded form the actual sled test for all available channels were plotted and compared with the respective data from simulations. 6.2 Validation Approach In this research, three approaches were followed to validate the numerical model with the actual sled test. Dummy Kinematics Injury Parameters Profiles Matching and Quantitative comparison Validation of Dummy Kinematics The kinematics of dummies during crash is very important to study the safety performance, since it gives an idea about the behavior with the interior structure and the biomechanical responses of the dummy in particular crash condition. The sled tests were captured with high speed cameras from different sides. The animations of numerical models were compared with 69

86 those videos to study the kinematics of dummies in both cases. Figure 6.1 shows the kinematics of dummies in frontal impact condition Injury Parameters Injury values are also considered as important factor in validating the tests as it provides the reliability and accurateness of numerical model with actual sled test. From injury parameters one can easily understand the severity of the crash conditions. Each injury parameter has its standard injury criteria defined. Those are used as a basis for certification by many agencies. The simulated values must be within the tolerance range of those predicted by the actual tests. The injury values obtained from actual sled test were used for validations of numerical models. The various types of injury criteria studies in this research are as follows: Head injury criteria (HIC) Chest 3ms Pelvic 3ms Neck forces and moments Femur forces Profile Matching In this validation method the peak profiles of the head, chest and pelvis acceleration and neck forces and moment and femur forces were compared with the actual sled test. For this validation Sprague and Geers method was used. All the profiles of injury parameters mentioned above were compared and validation was done. To check quantitatively the uncertainty and accurateness of the excremental data validation or error matrices were used. These methods are based on the comparison of the experimental data with series of parameters to find the uncertainty 70

87 and the accuracy of the experimental data. Model accuracy and quality of the numerical model and test were evaluated with the help of the error matrices The Sprague and Geers method considers a magnitude error factor that is insensitive to phase discrepancies, a phase error factor that is insensitive to magnitude discrepancies. The total error factor or score is given by the following expressions [28]. Score = 2 2 M + P (6.1) Where, I gg M = magnitude error factor M = 1 I 1 P = phase error factor P = * ar cos π Where, ff I I ff fg * I gg IBffB = t 2 t2 1 2 t 1 * t1 f ( t) dt IBggB = t 2 t2 1 2 t 1 * t1 g ( t) dt IBfgB = t 2 1 t 1 * t2 t1 f ( t) * g( t) dt Where, tb1b<t<tb2b is the time span or evaluation period f(t) = benchmark history or reference data g(t) = candidate solution or data to compare [28]. 71

88 CHAPTER 7 RESULT AND DISCUSSION This chapter provides the detailed result and discussion part of research. In detail, three part of validations, dummy kinematics, profile matching and injury parameters are studied and explained in this chapter. 7.1 Comparison of Dummy Kinematics Frontal Impact (Configuration I) Figure 6.1 shows the frontal impact (Config - I) test comparing the kinematics of sled test and of MADYMO simulation. In this test the occupant kinematics were observed until 250 ms. The simulation results show the exact kinematics and same profile of dummies as compared to actual sled test, except some differences. The kinematics of hybrid III 50 th and 95 th were observed exactly. The time of contact between knees and divider panel was same also for 95 th dummy the position and time of impact of neck with head rest of front seat was same as that in actual sled test. The kinematics of CRS of 3-year-old dummy wasn t match exactly due to some lack parametric studies of belt properties and contact properties Frontal Impact (Configuration - II) Figure 6.2 describes the comparison of kinematics of actual sled test and MADYMO simulation of frontal impact (Config - II) test In this test the occupant kinematics were observed until 250 ms. The kinematics from simulation was matching with those of actual sled test as shown in figure 6.4. The adult dummies showed the exact time of contact with each other and with CRABI seat in sled test and simulation. But the position of legs of the adult dummy at position 5 in the last frame was different than that of in the test. 72

89 CRABI was shown exact time of head contact with the CRS in simulation as it was in actual sled test with less elastic deformation of CRS in simulation. The 3-year-old dummy showed same kinematics till 150 ms but after that the position of legs was different than those in actual sled test due to soft contact between CRS and legs. Figure 7.1 Kinematics of frontal impact test (Configuration - I) 73

90 Figure 7.2 Kinematics of frontal impact test (Configuration - II) Side Impact Figure 6.3 shows the side impact test comparing the kinematics of sled test and MADYMO simulation. Occupant kinematics was observed until 250 ms in this test. The simulation showed the exact correlation with the actual sled test. All dummy profiles were matching with sled test. For side facing dummies contact between knee and forward facing seats 74

91 was at the same time that of actual sled test. The contact of forward facing dummies with side wall is also at the same time in both test and simulation. Figure 7.3 Kinematics of side impact test The 3-year-old dummy also showed the same kinematics till 200 ms but after that lack of cushion geometry it didn t match with the actual sled test in last frame of 250 ms also in actual sled test elastic deformation of CRS was found but it wasn t found in simulation. The kinematics of CRABI (12-month-dummy) in simulation also didn t match with those of actual sled test. The 75

92 reason for this was the difference in location of center of gravity of CRABI seat in actual sled test and simulation. In real it had more mass in the front section of seat that was the reason of lifting and rotation of CRABI seat about Z-axis in actual sled test. This was not observed in MADYMO simulation. This problem can be overcome by adjusting the CG of seat at right location Rear Impact The Kinematics comparison of actual sled test and MADYMO simulation of rear impact test is shown in figure 6.3. In this test the occupant kinematics were observed until 250 ms. The comparison shows the matching of kinematics with some exceptions. The adult dummies in simulation were having same kinematics that of actual sled test, but the neck extension was greater in actual sled test than that in simulation little offset. This is because of the limitation of neck extension of dummies used in MADYMO database. The use of rear impact dummies can be remedy for this problem. The 3-year-old dummy also showed same kinematics till 150ms after that the path of hand was different for actual sled test and simulation. The rotational joint between back and pan of the rear seat was a stiff for 3-year old dummy. Therefore there was no contact between head of 95th percentile dummy at position 2 and hand of the 3-year-old dummy in simulation. The kinematics of CRABI was followed the same way as that of actual sled test till 100 ms after that it had problem of location of centre of Gravity (CG) as explained in section 7.12, but here in this test rotation was around Y-axis. 76

93 Figure 7.4 Kinematics of rear impact test Comparison of Injury Parameters The injury values of actual tests and simulation were plotted in the form of bar charts to get idea about the injury values. The injury values were plotted as normalized values. These normalized values were drawn form basic injury criteria based on FMVSS 208. Appendix C shows plots of all occupants for all sled tests. The simulation values are quite similar to the actual tests, except in some cases where the values were uncontrollable due to restrained free 77

94 dummy configuration. For child dummies the values for all injuries are way below the standard criteria. In all those occupants child dummies were too safe due to CRS Head Head Injury criteria (HIC) gives the head injury in the form of acceleration for all occupants. HIC for child dummies were very low well below 20% for each case providing better safety for child due to CRS. The values for all tests showed the HIC values laid well below the acceptance HIC values Chest Chest injury values were well below acceptance values. The chest acceleration was measure in time interval on 3 ms and was shown below 60 g s (acceptable value). Child chest values were also reduced with the use of CRS. Also the values for adult dummies were below safety value Neck Neck forces and moments are plotted for actual sled tests and simulation on same scale. It was shown that there were quite similar values for neck forces and moments. Neck tension, flexion, compression, and extension values for Child dummies were well within the range of the injury criteria. But for adult dummies it had shown the high values in simulation due to unrestraint and free dummies Femur Left femur and right femur forces of adult dummies were recorded and plotted for sled test and simulation as child dummies don t have channel for femur forces. The values for both forces showed below standard criteria. In all while summing up, it has been seen that child dummies were having very low injury values than those of adult occupants because the adult 78

95 occupants were unrestraint and free. But child dummies were restrained with either LATCH or ISOFIX attachments. Figure 7.5 shows the compassion of normalized injury values for actual sled test and simulation models. An appendix B contains the bar charts for other tests. Figure 7.5 Normalized Injury Values for Test (Frontal Impact) 7.3 Comparison of Profile All signals from actual sled test and simulations were plotted on same scale and compared the nature of signals for all the tests. The Appendix B shows the all the signals form all 10 tests from Test to and from to An appendix A contains the signals of head, chest and pelvis acceleration, neck forces and moments and femur forces. The comparison showed the matching of profiles, with some exceptions. Due to unrestraint occupant it s difficult to control the injury in turn profiles of signals. 79

96 CHAPTER 8 CONCLUSIONS AND RECOMMENDATIONS 8.1 Conclusions The research is to implement and evaluate the automotive child restraint system in mass transit buses. The objective of this research was to study the safety performance of child restraint system in mass transit buses and interaction between passenger and CRS. To achieve these objectives actual sled test for frontal, side, and rear impact were conducted with using different child restraint system (LATCH and ISPFIX) and adult passengers. These pulses were drawn from the study of finite element analysis of mass transit bus previously done. Injury values are evaluated for all the three cases using FMVSS 208 criteria. To validate the sled tests mutilibody analysis were done using MADYMO 6.3 ver. Results form mutiboby (MADYMO) model were extracted and validated with sled test. It has been observed that the kinematics was similar and the profiles of actual sled test and simulations were close. The injury profiles are within 20 %. For side impact some profiles like neck forces and moments are higher than 20 % due to head to head contact of adult occupant with child occupant. The kinematics of CRS was little offset from sled test after 200 ms, due to lack of detailed geometry. This problem can be solved by detailed geometry. Injury values of occupants were below the described FMVSS 208 criteria values. Following conclusions can be drawn from this research: The dynamics sled test results indicate that appropriately installed CRS improve significantly the level of safety for small children travelling in Mass Transit Buses during typical impact conditions 80

97 Installation of CRS with Lower Anchorages provides a good level of protection for Rear Facing Infant and Convertible Seats The Upper tether was not used in order to reduce the modifications to the Mass Transit Bus interior, and to reduce the time it takes to secure CRS The strength of the Mass Transit Bus seat Lower Anchorages may be tested per FMVSS225 The use of CRS doesn t increases the risk of severe or fatal injuries to other Mass Transit Bus passenger for typical seating arrangements in a frontal impact scenario Placing CRS in a window seating position eliminates possible post accident evacuation issues Position 1 (Frontal Impact): 3-year-old may experience head to head contact with the passenger seating behind Position 2 and 4 (Side Impact): Avoid the use of CRS with passenger side facing seats or do not allow the use of CRS in aisle seats facing side facing passenger seats Position 2 and 4 (Side Impact): Although the injury values were low there is a lot of uncontrolled interaction with standing passengers Position 4 (Rear Impact): 3-year-old and 12 month although the injury values are low special attention needs to de consider on seat pitch and seat back rotation of the seat in front of the CRS Higher neck compression loads and neck flexion moments for adult occupants are observed in some case, for both the frontal and rear impact conditions while all the injury values for child occupants are way below FMVSS 208 criteria. 81

98 MB model was successfully developed and validated against the test results in all the three categories identified as dummy kinematics, injury values and time history data profiles Overall the MB models developed were found to be in good correlation with the test setup which can be used for further studies. CRS can be implemented in mass transit buses to improve the safety performance of children and passenger. 8.2 Recommendations Along with conclusion some recommendations were also drawn from this research. Those are as below: ISOFIX and LATCH provide similar levels of performance for frontal impacts. Further analysis is required for side impact applications. The recommended minimum seat pitch for CRS installations is 35 inches for Infant Seats (due to the size of the base with ISOFIX and LATCH configurations) and 32 inches for Convertible Seats. DOE studies can be conducted by considering type of attachments used, variation of seat pitch distance, changing the positions of dummies to do further study this research Further dynamic sled tests for side and rear impact need to be studied before releasing CRS/Mass Transit Bus layout and design recommendations. Structural analysis can be done on CRS to study the nature of forces present at the attachment. 82

99 REFERENCES 83

100 LIST OF REFERENCES [ 1 ] Langwieder K., Hummel T. and Roselt T., ISOFIX possibilities and Problems of New Concept for Child Restraint Systems, International Journal of Crashworthiness, Vol.8, No. 5, pp , January, [ 2 ] Weber K., Crash Protection for Child Passengers, UMTRI Research Review, Vol. 31, No. 3, July-September [ 3 ] National Transportation Statistics, Bureau of Transportation Statistic, U.S. Department of Transportation, Washington DC 20590, [ 4 ] Moore, C., National Transportation Statistics, Bureau of Transportation Statistic, U.S. Department of Transportation, Washington DC 20590, [ 5 ] Anon. Federal Motor Vehicle Safety Standards and Regulations, U.S. Department of Transportation, Washington, DC. [ 6 ] Anon., Standard Bus Procurement Guidelines 30-foot Low-floor Diesel Buses, American Public Transportation Association, [ 7 ] Child Restraint System Transportation Recall Enhancement, Accountability and Documentaion Act, National Highway Traffic Safety Administration, U.S. Department of Transportation, February [ 8 ] Docket No. NHTSA , Revisions to the Federal Motor Vehicle Safety Standard for Child Restraint Systems, Docket No. NHTSA , Potential Side Impact Protection Standard for Child Restraint Systems, National Highway Traffic Safety Administration Washington DC 20590, June 28, [ 9 ] Gotschall C., NHTSA s Draft Child Restraint System Safety Plan, National Highway Traffic Safety Administration, U.S. Department of Transportation, November 27, [ 10 ] Huntley M., Federal Motor Vehicle Safety Standard No. 213 Child Restraint Systems, National Highway Traffic Safety Administration, U.S. Department of Transportation, May, 15, [ 11 ] Facts About Injuries To Child Occupants In Motor Vehicle Crashes, Safe Kids Worldwide, [ 12 ] Child Passenger Fatalities and Injuries, Based on Restraint Use, Vehicle Type, Seat Position and Number of Vehicles in the Crash, National Highway Traffic Safety Administration, National Center for Statistics and Analysis, U. S. Department of Transportation, Washington DC 20590, April

101 [ 13 ] Galganski R., Hatziprokopiou I., Pateel V., Arumugasundaram S., and Patra A., Reexamination of FMVSS 213 Using New Car Assessment Program Test Data, [ 14 ] Side Impact and Ease of Use Comparison between ISOFIX and LATCH CLEPA Presentation to GRSP, Informal Document GRSP Geneva, May [ 15 ] Marius-Dorin Surcel, Michel Gou, Intrusion Influence on Child Occupant Behavior In The Case Of A Side Impact MADYMO Simulation, École Polytechnique de Montreal, Canada, pp [ 16 ] Hulme K., Patra A., Vusirikala N., Galganski R., Development of a Visualization Module for MADYMO-based Child Restraint System (CRS) Safety Simulation. [ 17 ] Child Restraint Use Survey LATCH Use and Misuse, National Highway Traffic Safety Administration, National Center for Statistics and Analysis, U. S. Department of Transportation, Washington DC 20590, Report No. DOT HS , December [ 18 ] Federal Motor Vehicle Safety Standards; Child Restraint Systems - Advance notice of Proposed Rulemaking (ANPRM), Federal Register, 49 CFR Part 571, Docket No , RIN 2127 AI83, National Highway Traffic Safety Administration (NHTSA), U. S. Department of Transportation,, Vol. 67, No. 84, Wednesday, May 1, [ 19 ] Safety Rating Program for Child Restraint Systems, Docket No. NHTSA , Notice 1, Insurance Institute for Highway Safety, January 7, [ 20 ] Liang Tang, Meng Luo and Qing Zhou, Optimaization of Child Restraint System by Using a Particle Swarm Algorithm, Computational Intelligence and Bioinformatics: Internation Conference on Intelligent Computing, ICIC 2006, Kunming, China, Pro, Vol. 4115, pp , September [ 21 ] Gowda A., Safety of Seated and Standing Occupants in Real Life Crash Scenarios of Mass Transit Buses, Wichita State University, October [ 22 ] Occupant Protection for Children Safety Information, URL: n1.pdf [cited 13 September 2005] [ 23 ] Economic Commission for Europe Regulation No. 16, Uniform Provisions Concerning The Approval Of: 1) Safety-Belts, Restraint Systems, Child Restraint Systems And ISOFIX Child Restraint Systems For Occupants Of Power-Driven Vehicles, 2) Vehicles Equipped With Safety-Belts, Restraint Systems, Child Restraint Systems And ISOFIX Child Restraint Systems. [ 24 ] Federal Motor Vehicle Safety Standards 213, National Highway Traffic Safety Administration, U. S. Department of Transportation. 85

102 [ 25 ] Federal Motor Vehicle Safety Standards 225, National Highway Traffic Safety Administration, U. S. Department of Transportation. [ 26 ] MADYMO Manuals, Version 6.3, Version 6.3, TNO Automotives, December [ 27 ] Thokade S., Passenger Safety in Real Life Crash Scenarios of Mass Transit Bus, Masters Thesis, Wichita State University, October [ 28 ] Sprague M. A. and Geers T. L. A Spectral-Element Method for Modeling Cavitation in Transient Fluid-Structure Interaction, International Journal for Numerical Methods in Engineering, Boulder, CO , USA, 2, January, 2004 [ 29 ] Patil A., Modeling and Evaluation of Child Safety Seat and Restraint System for Aerospace Application, Masters Thesis, Wichita State University, December

103 APPENDICES 87

104 APPENDIX A COPARISION OF PROFILES (SPRAGUE AND GEARS) A.1 Frontal Impact test A.1.1 Hybrid III CRABI 12-month old dummy Figure A.1 CRABI 12-month old dummy acceleration 88

105 Figure A.2 CARBI 12-month old dummy neck forces and moments 89

106 A.1.2 Hybrid III 50 th Percentile Dummy Figure A.3 Hybrid III 50 th percentile dummy accelerations 90

107 Figure A.4 Hybrid III 50 th percentile dummy neck forces and moments Figure A.5 Hybrid III 50 th percentile dummy femur forces 91

108 A.1.3 Hybrid III 95 th percentile dummy Figure A.6 Hybrid III 95 th percentile dummy accelerations 92

109 Figure A.7 Hybrid III 95 th percentile dummy neck forces and moments Figure A.8 Hybrid III 95 th percentile dummy femur forces 93

110 A.1.4 Hybrid III 3-year old dummy Figure A.9 Hybrid III 3-year old dummy accelerations 94

111 Figure A.10 Hybrid III 3-year old dummy neck forces 95

112 A.2 Side Impact Test A.2.1 Hybrid III 50 th percentile dummy at position 1 Figure A.11 Hybrid III 50 th percentile dummy accelerations 96

113 A.2.2 Hybrid III CARBI 12-month old dummy at position 2 Figure A.12 Hybrid III CRABI 12-month old dummy accelerations 97

114 Figure A.13 Hybrid III CRABI 12-month old dummy neck forces and moments 98

115 A.2.3 Hybrid II 50 th percentile dummy at position 3 Figure A.14 Hybrid II 50 th percentile dummy accelerations 99

116 A.2.4 Hybrid III 3-year old dummy at position 4 Figure A.15 Hybrid III 3-year old dummy accelerations 100

117 Figure A.16 Hybrid III 3-year old dummy neck forces and moments 101

118 A.2.5 Hybrid III 50 th percentile dummy at position 5 Figure A.17 Hybrid III 50 th percentile dummy accelerations 102

119 Figure A.18 Hybrid III 50 th percentile dummy neck forces and moments Figure A.19 Hybrid III 50 th percentile dummy femur forces A.2.6 Hybrid III 95 th percentile dummy at position 7 103

120 Figure A.20 Hybrid III 95 th percentile dummy accelerations 104

121 Figure A.21 Hybrid III 95 th percentile dummy neck forces and moment Figure A.22 Hybrid III 95 th percentile dummy femur forces 105