Research On Simplified Method Of Thin-walled Beams For Crashworthiness Design

Vehicle passive safety is one of key problems for the automobile industry. How to improve the crashworthiness of vehicles has been the key issue of the automotive safety. The thin-walled metallic components, as the most conventional and effective energy-absorbed device, have been widely used in automotive design and manufacture.Nowadays, most of the FE models are modeled using shell elements, which are called detailed models. The using of shell elements can promise a high fidelity to the real model's physical geometry and design features and is therefore very useful for the product design and evaluation at a detailed level. Despite the advances in computer technology, the enormous computational cost associated with the complex nonlinear crashworthiness analysis renders it to be impractical to rely exclusively on computer simulations for crashworthiness design. Therefore, for the crashworthiness optimization design problems, how to avoid the sensitivity analysis of large complex systems becomes the key step. To optimize the dynamic impact problem for crashworthiness optimization of design, response surface method is a fast, efficient approximate solution method. Using response surface method to construct the approximate model, the approximate function must be determined first. Then, using statistical experimental design choices enough design points in the design space, and finally, using least square method to get approximation model for fitting analysis results of design points.In fact, in the conceptual design process of autobody, users always want to spend less time on the simplified model construction. At the same time, the analysis of a simplified model can save a lot of computer time and resources. At present, the research of autobody structure is mainly taken in the detailed design and manufacture and improves the product stage. In the conceptual design stage, this work is completed very little. But when the autobody structure needs to be modified; the entire development phase needs to be redesigned, which will greatly increase the costs. Therefore, a proper method on the construction of simplified model which can well describe the crashworthiness parameters is necessary.First, the collapse mechanisms of straight thin-walled beams and nonlinear spring characteristics of axial deformation are reviewed and simplified methods for such beams based on their axial collapse mechanisms are introduced. Then, classic theories about the crash behavior of curved beams are reviewed and applied. A detailed model for a thin-walled rotational straight beam is created, and the nonlinear spring element is used in the resulting simplified models to simulate the rotating behavior. In each section, detailed models for the box section beams are presented first. Next, similar crash analyses are performed on both the simplified and the detailed models via computer simulation. The efficiency of the simplified models is then verified by comparing the results.The collapse behaviors of thin-walled beams with channel and hexagon cross sections are studied, and then the reliable simplified models are developed. Meanwhile, the bending behaviors of these two kinds of beams are predicted accurately. Based on bending characteristics, a new non-linear spring element is developed, and then detailed model and simplified model are used in the same crash analyses. The dynamic results are compared with those from the corresponding detailed models to validate the developed nonlinear spring elements and the derived bending resistance.The curved rail and crash box those thin-walled beams of autobody structures with different cross section shape are simulated to construct the simplified model for crash analysis. As a result, these segments connected by translational and rotational nonlinear springs show an acceptable consistent relationship with the initial detailed models. According to the analysis results, this simplified model can help the designers modifying the structural parameters of key components according to the crashworthiness demands to save a lot of time and effort. Therefore, the achievement of this work is to enrich and perfect the simplified autobody model for the BIW production design.The meta-model method is applied to solve the crashworthiness problems of complex detailed model. First of all, uniform design and central composite design have been applied in the selection of sampling points and RSM has been used to construct the meta-models. After obtaining the meta-models, genetic algorithm and particle swarm optimization method are respectively used to solve the crashworthiness optimization problem, i.e. the crashworthiness of the crash box. Finally, the optimized results show that the internal energy of structure increases. Meanwhile, the maximal crash force and total mass of structure decrease. Specially, there is no violation of constraint conditions which can prove that the crashworthiness optimization problem has been solved well.