Parametric Analysis of Factors Influencing Stiffness and Crashworthiness of a Ladder Frame

Abstract

During a vehicle crash, a major portion of the energy is absorbed by the frame structure. In general, stiffness and durability are considered as the primary criteria for design; but, not the crashworthiness of a frame structure. The purpose of this study is to evaluate the crash worthiness of a ladder frame structure. The effect of variation of bending stiffness and torsion stiffness of the ladder frame on the crashworthiness, specific energy absorption (SEA) and the peak load is investigated. Numerical analysis for frontal crash and stiffness of the ladder frame is done using LS DYNA® and CATIA®-Structural analysis software respectively. The numerical model for the frame frontal crash is validated by benchmarking the results obtained in this work with literature data. The height and the thickness of the frame side member (FSM) which absorbs most of the energy are taken as the design variables. The cross section of the FSM and cross members are taken as rectangular tubes with 90 mm height and 2 mm thickness as the base model dimension. The optimization is done to maximize the SEA of the frame with stiffness as the constraint. An optimized combination of design variables is identified using the response surface method. It is seen that the optimal point is found to be with the maximum height and minimum thickness; it is inferred that the crashworthiness parameters are bounded by the stiffness target set for the frame. Parametric analysis is done to investigate the influence of the design variables on the crash performance of ladder frame. The results show that increase in height by 50% from the base model will result in 4% increase in SEA and 60% reduction in peak loads when compared to a case with 50% increase in thickness. Torsion and bending stiffness was found to be 8% lesser and 62% higher respectively in case of 50% increase in height.