Stress Analysis in Automotive Chassis Using Analytic Hierarchy Process

Transcription

1 Volume 117 No , ISSN: (printed version); ISSN: (on-line version) url: ijpam.eu Stress Analysis in Automotive Chassis Using Analytic Hierarchy Process 1 N.V. Dhandapani, 2 T. Soundharya and 3 R. Arulmurugan 1 Karpagam College of Engineering, Coimbatore. 2 Karpagam College of Engineering, Coimbatore. 3 Karpagam College of Engineering, Coimbatore. Abstract In this paper a methodology for stress analysis involving optimization technique is presented. In particular, stress analysis and topometry are coupled with decision making approach. The methodology is applied to the stress analysis of a heavy duty dump truck off road vehicle chassis. The objective of this analysis is to find the root cause of failure in horse collar area. The result demonstrates the applicability of methodology (decision making approach) for obtaining the hierarchies of the factors considered which is distributed on the vehicle structure. The numerical model shows a root cause failure of horse collar region due to maximum principle stress and shear stress by Analytic Hierarchy Process. Key Words:Automobile chassis, stress, analytic hierarchy process, structural analysis. 569

2 1. Introduction The chassis is the key structural member of a vehicle upon which all the other systems and its components are mounted. It is the most crucial element that gives strength and stability to the vehicle under different conditions. Chassis should be firm enough to bear up the shock, twist, vibrations etc. Alongside the strength, a significant concern in chassis design is to have enough bending and torsional stiffness for better usage characteristics. So, strength and stiffness are two essential criteria for the design of chassis. For heavy duty trucks, the preferred type of chassis is of the ladder frame type. It is named as ladder frame since it resembles a ladder. It usually consists of two longitudinal members which are connected by several horizontal members. The longitudinal members resist bending forces while the horizontal members provide torsional stiffness. Though an I section member has better bending resistance than a C-section frame, the longitudinal members are generally fabricated from a C-section or a rectangular section channel since it is widely available and also provides a better platform for mounting the components when compared to a circular cross-section. 2. Need for Stress Analysis in Chassis Design As described in the earlier section, chassis of a vehicle plays a vital role and carries out functions of critical importance. Hence, it becomes necessary that a chassis is designed with a very high factor of safety so that it does not fail. Failure of a chassis leads to irreparable damage leading to vehicle recall and cause a huge setback in terms of safety and economy for manufacturers as well as the users.the chassis structure is made of channels, either C-type or of box type channels. The dimensions of this channel are determined by the load this structure needs to withstand. As the load increases, the thickness of the metal and overall dimensions of the channel section increases. In general, with increase in payload, the weight of the channel required to be used also increases. The weight of the payload of a vehicle, especially a heavy duty truck acts majorly on the rear two-thirds of the vehicle and only the comparatively lighter operator cabin is positioned in the front portion of the vehicle. Due to this, the component which is lying in the middle is subjected to failure by various factors like Ductility, Fatigue, % elongation, Maximum principle stress, Total deformation, Shear stress, Factor of safety etc. The analysis is carried out to find the root cause for failure using a decision making approach called Analytic Hierarchy Process so that it can be rectified in future. 3. Literature Survey The judgment of the stresses in a truck chassis before developed is important for 570

3 the design improvement and it is investigated [1]. The stress analysis of chassis using finite element analysis was performed using ANSYS. The same finite element model is used for fatigue analysis of the chassis [2]. The structural analysis of the chassis frame is performed to check the vulnerable points having high magnitude stress at static load condition [3].The stress analysis of heavy dump truck chassis was investigated for fatigue examination and life forecast of components to find out the critical point having high stress [4, 5].The analysis of chassis frame was done to improve its payload by adding stiffener at maximum stress region of chassis [6].The load characteristics of chassis were investigated using finite element method [7, 8].S. S. Sane et al. [9] performed stress analysis of a light commercial vehicle chassis by using finite element method. Initially analysis of the actual chassis of the vehicle was performed and values of the stress and deflection were gathered. A total of nine different load cases were considered for the analysis of the chassis. To reduce the stress values stiffeners of changing height were added at the critical locations. The analytical stress analysis of a platform incorporated structure mounted on vehicle chassis designed for nontraditional type of loading prototype was described [10]. 4. Methodology The AHP method The Analytic Hierarchy Process (AHP) decomposes a complex MCDM problem into a system of hierarchies. The final step in the AHP deals with the structure of an m*n matrix (Where m is the number of alternatives and n is the number of criteria). The matrix is constructed by using the relative importance of the alternatives in terms of each criterion. Analytic Hierarchy Process is an multi criteria decision making method based on priority theory. It deals with complex problems which involve the consideration of multiple criteria/alternatives simultaneously. Its ability to incorporate data and judgement of experts into the model in a logical way, to provide a scale for measuring intangibles and method of establishing priorities to deal with interdependence of elements in a system. The methodology is capable of violating a complex, unstructured situation into its component parts, arranging these parts into a hierarchic order (criteria, subcriteria alternatives etc.) Assigning numerical values from 1 to 9 to subjective judgements on the relative importance of each criterion based on the characteristics Synthesizing the judgements to determine the overall priorities of criteria/sub-criteria/ alternatives. Four major steps of using the AHP technique are: 1. Develop a hierarchy of factors influences the final decision. This is known as the AHP decision model. 2. Obtain pair wise comparisons between the factors using inputs from Users/managers. 3. Calculate relative importance weights at each level of the hierarchy. 571

4 4. Mix relative importance weights to obtain an overall ranking of the various alternatives. While comparing two criteria we follow the simple rule as recommended by Saaty (1980). Thus while comparing two attributes X and Y we assign the values in the following manner based on the relative preference of the decision maker. Table 1: Scale Used for Pair wise Comparison INTENSITY OF PROBLEM DESCRIPTION IMPORTANCE 1 Equal importance 3 Weak importance of one over other 5 Strong Importance 7 Demonstrated Importance 9 Absolute Importance 2,4,6,8 Intermediate values Reciprocals of the above If activity i has one of the above numbers assigned to it when compared with activity j, then j has the reciprocal value when compared with i. The seven factors that are considered for chassis analysis: Ductility. Fatigue. % elongation. Maximum principle stress. Total deformation. Shear stress. Factor of safety. Table 2: Weights of Criteria Ductility Fatigue Maximum % Total Shear Factor Elongation principle deformation stress of safety stress Bumper Front rail structure Horse collar Front suspension mounting point Rear rail structure Torque tube Rear suspension mounting point

5 Determination of Criteria Weights Iteration 1 Iteration 2 Criteria Weight 573

6 Results Obtained from Pair Wise Comparison 574

7 5. Results and Discussion The analytic hierarchy process is used to find the root cause failure of the horse collar area. Firstly the weights of each criterion are calculated and the pair wise comparison is made for each part of the vehicle structure. From the analytical model, it is clear that the maximum principle stress influences more when comparing with the alternatives chosen. 575

8 6. Conclusion The existing vehicle chassis of heavy duty truck is taken for analysis with box type cross section is performed. After analysis, the comparison between the analytic model and FEM shows that the root cause of failure is by maximum principle stress acting along the horse area. It can be rectified by increasing the cross section gradually along the component and can eliminate the failure by distributing the stresses over the entire area rather than concentrated upon surface of the component. References [1] Patil H.B., Kachave S.D., Deore E.R., Stress analysis of automotive chassis with various thicknesses, IOSR Journal of Mechanical and Civil Engineering 6 (1) (2013), [2] Dubey A., Dwivedi V., Vehicle chassis analysis: Load cases & boundary conditions for stress analysis, in: NaCoMM 2003, IIT Delhi, India, (2003). [3] Paul I.D., Sarange S.M., Bhole G.P., Chaudhari J.R., Structural analysis of truck chassis using finite element method, International Journal of Multi disciplinary Research and Advances in Engineering 4 (I) (2012) [4] Abd. Rahman R., Tamin M.N., Kurdi O., Stress analysis of heavy duty truck chassis as a preliminary data for its fatigue life prediction using FEM, Journal Mekanikal 26 (2008), [5] Murali G., Subramanyam B., Naveen D., Design improvement of a truck chassis based on thickness, in Altair Technology Conference, India, (2013). [6] Dhandapani N.V., Mohan Kumar G., Debnath K.K., Static & Dynamic Analysis of Heavy Vehicle Frame Structure using FEA, International Conference on Innovative Research In Engineering & Technology (ICIRET 2010), Park College of Engineering and Technology, (2010). [7] Kotari S., Gopinath V., Static and dynamic analysis ontatra chassis, International Journal of Modern Engineering Research 2 (1) (2012), [8] Dhandapani N.V., Rajasekaran K., Effective design and development of automotive interior door analysis, 2nd International Conference on Advanced Engineering and Technology for Sustainable Development (ICAETSD-2016), on 19th & 20th February, at Karpagam College of Engineering, Coimbatore, (2016). 576

9 [9] Rajappan R., Vivekanandhan M., Static and modal analysis of chassis by using FEA, The International Journal of Engineering and Science 2 (2) (2013), [10] Patel T.M., Bhatt M.G., Patel H.K., Analysis and validation of Eicher chassis frame using Analysis, International Journal of Emerging Trends & Technology in Computer Science 2 (2) (2013), [11] Sane S.S., Ghanashyam J., Anandraj H., Stress Analysis of a Light Commercial Vehicle Chassis by FEM, Piaggio Vehicles, HTC 08 (2013), 1-5. [12] Deulgaonkar V.R., Matani A.G., Kallurkar S.P., Advanced mathematical analysis of chassis integrated platform designed for unconventional loading by using simple technique for static load, International Journal of Engineering and Innovative Technology 1 (3) (2012), [13] Dhandapani N.V., Mohan Kumar G., Debnath K.K., Fatigue analysis of heavy vehicle frame structure using FEA, International Conference on DIGITAL FACTORY (ICDF 2008), organized by Coimbatore Institute of Technology from 11th to 13th (2008). [14] Ramana Naiketal B., Strength Analysis on Automobile Chassis, IJMETMR 2 (11) (2015), [15] Navnath V. Paldeetal, Design improvement and analysis of car chassis for Static and Dynamic Characteristics, International Journal of Engineering Research (2015), [16] Dhandapani N.V., Mohan Kumar G., Debnath K.K., Modelling Design and Analysis of 60 Ton Load Carrying Dump Truck Frame Structure Using HYPER MESH 9.0, International Conference of South Asia on Global Manufacturing Systems & Management (IGGMSM-2011), Coimbatore Institute of Technology, (2011). [17] Bhuwanesh S., Finite Element Analysis of Truck Chassis, Emerging trends in Engineering & Management for Sustainable Development, ETEMSD , (2016). 577

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