Analysis and comparison of safety of children and adult passenger in car based on crash tests results

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1 Key Engineering Materials Online: ISSN: , Vol. 597, pp doi: / Trans Tech Publications, Switzerland Analysis and comparison of safety of children and adult passenger in car based on crash tests results Bartosz Zdunek 1, a *, Michał Landowski 2, b, Stanisław Taryma 1, Ryszard Woźniak 1, Krystyna Imielińska 2, Artur Muszyński 3 1 Gdansk University of Technology, Faculty of Mechanical Engineering, Machine Design and Vehicles Department, 2 Gdansk University of Technology, Faculty of Mechanical Engineering, Materials and Welding Engineering Department ul. G. Narutowicza 11/12, Gdańsk, Poland 3 Military University of Technology, Faculty of Mechanical Engineering, Department Of Mechanics and Applied Computer Science ul. gen. Sylwestra Kaliskiego 2, Warszawa 49, Poland a zdunekmech@o2.pl, b mlandowski@gmail.com Keywords: safety, child seat, crash tests 1. Features car seat The main task of child seat is to provide safety for children during the trip. Safety should not be limited only to the best protection during an accident, but it is same important to ensure appropriate driving conditions, because of the specific body type of the child, and not a full-fledged backbone and muscular system. The seat beside the protection of the child in traffic should be safe for other passenger in everyday use as well as during a collision. It should not have sharp edges and outstanding rigid components. This is particularly important in the case of a side impact. When there is a significant risk of collision of fellow passenger seat. Seat belts allow for large displacement in the transverse direction to the axis of the vehicle. The side impact deformation occurs more passenger compartment due to the smaller deformation zone than in a frontal collision. The existing EKG ONZ Regulation No 44 is going to be update. On 9 July 2013, a new child seat safety regulation came into force. Known as Regulation 129 (Reg. 129), it will eventually replace the current regulation (Reg. 44), which is to be slowly phased out. Side impact collisions account for around 25% of road accidents in Europe. Despite this, the current regulation impact test takes no account of side impact protection. Crucially, the new regulation will include side impact testing, with separate tests being carried out for the smallest and largest size of child that will fit into the seat. To pass the test, seats must be able to absorb the energy from a side impact, while ensuring the child s head stays in the head rest. [1] Despite a significant increase in car passive safety, child safety problem is not finally solved. Car bodies better dissipate impact energy and the passenger compartments are more resistant. The interiors of vehicles are designed for people with an height of at least 150 cm. New safety systems are often not adjusted to the needs of the youngest passengers. Some of safety systems may be dangerous for children, such as airbag for the child if he is traveling rearward. Charging rate of airbag filling gas is so high that could cause a head butt in the back of the seat. Several manufacturers produce seats integrated into the rear seat car such as Mercedes Benz B- Class[2]. They provided a basic level of protection and were recommended for occasional use.[3] Most manufacturers decided to give this part of the market for specialized manufacturers of car seats. The seat is so an adapter that allows safe transport of children in a car which is not adjusted to kid dimensions. Appropriate level of comfort is the subsequent important aspect, otherwise the All rights reserved. No part of contents of this paper may be reproduced or transmitted in any form or by any means without the written permission of Trans Tech Publications, (# , Pennsylvania State University, University Park, USA-16/09/16,15:05:07)

2 200 Progress in Mechanical Engineering and Technology child will be tired and grumpy. Disruptive behavior of children affect on driver concentration and may cause of an accidents. 2. Integrated seat belts system Child seat from group 0+ and 1 for children weighing up to 18 kg usually are equipped with a five point seat belts with a central belt buckle (Fig. 1). Another option is to cross-belt system or of kind of bumper finished in foam with fixed to the seat in front. Figure 1: Cross-belt system on left[4], five point seat belt system on right [5] 3. Crash Test Crash test was made on the car Ford Windstar SE Sport Four mannequin were in the vehicle (Fig. 2): D - the driver, P2 - a passenger in the front seat, P3 - a child in the car seat in the back seat on the right side, P4 - a child in the car seat in the back seat on the left side. Figure 2: Indication of the places in the car.[6] On front seats were two identical mannequins with dimensions adult male, fasten three-point safety belts. On the back seat were fastened child seats by the car three-point seat belts. In those child seats two identical dummies were fastened. The dummies corresponded to the size of a three-year child The test consists of front-center hit of a car in undeformable wall at a speed of 56 km/h

3 Key Engineering Materials Vol Performed test with four mannequins allow the assessment of the safety level of the individual seats of the vehicle. Mannequins are arranged like a typical family in car. Adult travel in the front seats and children in the rear seat. The driver D and passenger P2 in the front seat is equipped with seat belts and airbags. Mounted in the back two child seats P3 and P4 are equipped with five-point safety belts. 4. Crash Test results analysis The characteristics present longitudinal acceleration of the passengers heads. For driver D (Fig. 5) increase of acceleration is observed at period from about 0.09 to 0.15 s and it obtains its peak value of 38 g at period between the 0.11 and 0.12 s. Figure 3: Displacement of a child dummy during crash test.[7] P2 is not holding hands on the steering wheel thus he did not absorb part of kinetic energy what affects higher acceleration value than driver (Fig. 4). There is no seat belt's pretensioners, so P2 move forward freely. He is later stopped by the belts and hit the airbag with higher speed. Because of higher speed the values of acceleration are increasing in compare to driver. The heads of mannequins P3 and P4 fastened in car seats accelerate to similar values (Fig. 5). The highest values, are between 0.1 are 0.18 s is due to the van deceleration lane as shown in Figure 3 in the pictures. Another phenomenon do not take place for passengers in the front seats is a clear peak at 0.23 s and 0.25 s peak is caused by hitting a child with a rigid back support car seat. It has a lower value than the first peak, as part of the absorbed energy was limited by safety belts and child seat mounting. Figure 4: A comparison of the longitudinal acceleration of the head D, P2 P4 [7]

4 202 Progress in Mechanical Engineering and Technology Figure 5: Longitudinal acceleration of the head D, P2 P4 [7] Values of HIC (Head Injury Criterion): D 256, P2 516, P3 653, P4 606 [8] The values of HIC indicate a much greater chance of head injuries for children in child seats than adults in the front seats. Risk of injury of driver's head is smaller compare it to passenger P2, despite the half larger peak accelerations. The key is the time of acceleration impact. 5. Testing of energy absorbing materials For dynamical test, various kinds of materials were chosen, that were expected for good energy absorbing characteristic. Absorbing materials (see tab.1) are placed on flat piece of polypropylene cut from child s seat.

5 Key Engineering Materials Vol Tab.1. List of materials No Material No Material 1 balsa 8mm 13 Styrofoam I 40mm 3 Styrofoam 19mm 15 Styrofoam II 40mm 5 Styrofoam 30mm 19 balsa 15mm 7 Polyurethane foam 21 balsa 2x8mm 9 Polyurethane stiff foam 15mm 23 balsa 2x8mm glued together 11 kappa 10mm 25 balsa 2x8mm stretch wrapped Figure 5: Test setup Instron CEAST 9310 with anti-rebound system(left), specimen no.1 during test (right), balsa 8mm on child seat material (1), tup (2) The tests were made on dynamic droptower impact system Instron CEAST 9310 (fig.5). Impact tup had diameter 20 mm and was made of steel. The energy of impact was 10 J. The test was made in same conditions to compare materials energy absorbing characteristics. The materials with best characteristic would be used in crash test to verify their usefulness in child head protection. Figure 6: Selected courses of dynamic forces for 1 - balsa wood 8 mm, 7 - foam, 13 - Styrofoam, 21 - balsa wood 16 mm.

6 204 Progress in Mechanical Engineering and Technology The worst results were for 40 mm thick foam 7. The tested form was identical as the one used in child seat cover production. It is too soft, the impact hammer is just minimally decelerated. So the value of peak force is the biggest one and the course is unfavorable and steep (see fig.7). Best results were measured for 40 mm thick Styrofoam I 13 (see fig.6-8). It most reduce the peak force value, and make the force course more flat. It means the a smaller force act longer time what is more safe for child head then a big in short time. Unexpected good results had balsa wood especially it was only 1 - balsa wood 8 mm and 21 - balsa wood 16 mm thick (Fig. 6-8). Standard deviations of mean values was higher than others materials used in this test, which is caused by characteristic composite material structure. It makes the material interesting for use as energy absorber. The future tests will verify usefulness of balsa as energy absorber in child s seats. Figure 7: Peak forces for tested materials. Figure 8: Time of dynamic forces acting for tested materials. 6. Conclusions The car crash test with four dummies, including two car seats allowed a direct comparison of the security under the same conditions of children and passengers directly to the car seat. Analysis of acceleration and video from the test allows to understand the phenomena during the collision, the

7 Key Engineering Materials Vol air bags influence, collision child's occipital bone with seat backrest. The use of HIC ratio allows an approximate evaluation of the possibility of injuries. The phenomena of collision child's occipital bone with seat backrest in most of works is omitted. Development of child seats is focused on reduction of loads in the first phase, in forward movement. The collision during backward movement is very dangerous for a child, occipital bone may broke. To reduce the possibility of head injury should be used energy absorbing material, that would reduce the value of peak forces and would make courses of force to be more flat. The dynamic test let evaluated the usefulness of specific materials as energy absorbers. The stiffer foams and natural composite balsa gave better results, because they absorb more energy. It is supposed that this materials reduce risk of head injury. The studies will be continue to find material of best energy absorbing properties. That material would be used in crush tests with child mannequin to check assumptions. Most foam used nowadays in child seat cover is soft and absorb minimal part of impact energy. Longer time of acting force is probably better for child safety, because it let to distribute the same energy of impact and avoid big value of peak force. We must strive to use materials which absorb energy of impact in longest time. References [1]. TRL - Transport Research Laboratory, New Regulation for Child Restraints: centre/new_regulation_for_child_restraints.htm (actual at ) [2]. Mercedes-Benz Website: (actual at ) [3]. Paulina Zielińska: Foteliki dla dzieci w autobusach PolskiBus? (actual at ) [4]. Fotelik.info: Test fotelików dla TVN Turbo, (actual at ) [5]. Dino shop: Fotelik Ramatti Formula Classic + wkładka (9-18kg), (actual at ) [6]. Żuchowski A., Prochowski L.: Analiza stanu bezpieczeństwa pasażerów na tylnych siedzeniach samochodu osobowego podczas wypadku drogowego, X Międzynarodowa Konferencja Hamulcowa i Bezpieczeństwa (2011) [7]. NHTSA.: Vehicle Database Query Results - Test Detail Information, Test no (2001) [8]. Chichester, Charles, et al. A test methodology for assessing demining personal protective equipment (PPE). No. RM-1. ARMY COMMUNICATIONS-ELECTRONICS COMMAND FORT BELVOIR VA, (2001)