Research On Simplified Method For Plastic Deformation Characteristics Of Top-hat And Double-hat Section Thin-walled Beams

Vehicle crashworthiness is an important design attribute which designers strive to improve. However, design for structural crashworthiness is a difficult task. Accident analyses have shown that two-thirds of the collisions in which car occupants have been injured are frontal collisions. Despite worldwide advances in research programs to develop intelligent safety systems, frontal collision remains to be the major source of road fatalities and serious injuries for decades to come. For improved frontal car safety it is necessary to design a structure that absorbs enough energy in each realistic crash situation. To protect the occupants, the passenger compartment should not be deformed and intrusion must be avoided too. Moreover, to prenent excessive deceleration levels, the available deformation distance in front of the passenger compartment must be used completely. Owing to good energy absorption capacity, controllability of deformation mode and high efficiency from the point of view of minimum weight for given strength, thin-walled beams have been used in design of vehicle structures. Top-hat and double-hat section thin-walled structures are widely used in energy absorbing device of vehicle body.In view of the importance of crashworthiness, is necessary to study it in the conceptual design phase of vehicle. In this phase, only simplified model of vehicle body can be given. Therefor, research on the modified models of top-hat and double-hat section thin-walled beams under plastic deformation is very significant. The outline of the dissertation is summarized as:In the first chapter, the engineering background and significance of the study in this dissertation is introduced. The status of research on the simplified models of thin-wall beam under plastic deformation are showed by summing up the literatures.The research contents of this paper are presented here.In the second chapter, two simplified models about crushing and bending collapse of thin-walled rectangular section columns are introduced and researched. Bacause of the good accuracy and availability, the two simplified models are applied and improved by many researchers in the world and the work of this paper is based on them too.In the third chapter, the simplified models of top-hat and double-hat section thin-walled beams under axial collapse are introduced. The paper presents a simplified model of two cell double-hat thin-walled beam under axial collapse based on the double-hat section model. The numerical simulations are performed for the axial collapse process of the top-hat, double-hat and two cell double-hat secton thin-walled beams using the finite element method. The result of numerical simulations verifys the accuracy of these models. Then the paper compares the crashworthiness of the three kinds of thin-walled beams by the theoretical formulas of the simplified models and the numerical simulations.In the fourth chapter, based on the experimental study in the literatures, this paper discusses the bending deformation mode of the top-hat and double-hat section thin-walled beams and indicated the similarity of the bending deformation mode between rectangular section and top-hat section thin-walled beams. Then, the paper presents a new simplifed model of double-hat section thin-walled beam under bending collapse. Some numerical examples are given to verify the accuracy of the model.Finally, the main content is summarized and prospects for the futher work is predicted.