Abstract

The crashworthiness enhancement of vehicle structures is a very challenging task during the vehicle design process due to complicated nature of vehicle design structures that need to comply with different conflicting design task requirements. Although different safety agencies have issued and modified standardized crash tests to guarantee structural integrity and occupant survivability, there is continued rise of fatalities in vehicle crashes especially the passenger cars. This dissertation research explores the applicability of a crash energy management system of providing variable energy absorbing properties as a function of the impact speed to achieve enhanced occupant safety. The study employs an optimal crash pulse to seek designs of effective energy absorption mechanisms for reducing the occupant impact severity. The study is conducted in four different phases, where the performance potentials of different concepts in add-on energy absorbing/dissipating elements are investigated in the initial phase using a simple lumped-parameter model. For this purpose, a number of performance measures related to crash safety are defined, particular those directly related to occupant deceleration and compartment intrusion. Moreover, the effects of the linear, quadratic and cubic damping properties of the add-on elements are investigated in view of structure deformation and occupant`s Head Injury Criteria (HIC).
In the second phase of this study, optimal design parameters of the proposed add-on energy absorber concept are identified through solutions of single- and weighted multi-objective minimization functions using different methods, namely sequential quadratic programming (SQP), genetic algorithms (GA) and hybrid genetic algorithms. The solutions obtained suggest that conducting multiobjective optimization of conflicting functions via genetic algorithms could yield an improved design compromise over a wider range of impact speeds. The effectiveness of the optimal add-on energy absorber configurations are subsequently investigated through its integration to a full-scale vehicle model in the third phase. The elasto-plastic stress-strain and force-deflection properties of different substructures are incorporated in the full-scale vehicle model integrating the absorber concept. A scaling method is further proposed to adapt the vehicle model to sizes of current automobile models. The influences of different design parameters on the crash energy management safety performance measures are studied through a comprehensive sensitivity analysis.
In the final phase, the proposed add-on absorber concept is implemented in a high fidelity nonlinear finite element (FE) model of a small passenger car in the LS-DYNA platform. The simulation results of the model with add-on system, obtained at different impact speeds, are compared with those of the baseline model to illustrate the crashworthiness enhancement and energy management properties of the proposed concept. The results show that vehicle crashworthiness can be greatly enhanced using the proposed add-on crash energy management system, which can be implemented in conjunction with the crush elements.