Research On Experimental Design Method And Applications For Autobody Lightweight Design

Energy saving and environmental protection are two main problems for the world automobile industry and vehicle lightweight is an effective way to realize these two problems. Weight reduction of body structure plays a rather important role in lightweight of full vehicle, for body structure weights about 40 percent of full vehicle. Autobody lightweight design is an optimization procedure with multiple parameters and constraints which should firstly satisfy crashworthiness performance. Traditional design via finite element analysis and"trial and error"method has the disadvantages of huge computational cost and slow convergence, then the optimization design in which approximation model is employed in lieu of finite element simulation becomes a crucial and hot research topic. The approximation model which is built by experimental design and approximation method can express the relationship between design variables and responses. Nowadays the selection of these methods which are used to build approximation model is to some extent arbitrary and uncertain, so this problem should be considered properly for the autobody lightweight design. This dissertation presents a systemic study on autobody lightweight design based on theories of approximation model and optimization method. The purpose of the lightweight design is to achieve weight reduction of the original body structure meanwhile meeting both stiffness and crashworthiness requirements. The studying work is summarized as follows:1) In the view of high nonlinear characteristics of crashworthiness responses, the comparison of three types of experimental design methods in terms of their capability to generate accurate approximation models for crashworthiness indicators is conducted based on Support Vector Regression method. The result reveals that uniform design integrated with Support Vector Regression method can provide the most accurate approximation model while the number of sample points is limited into the"small scale range"which is suitable for autobody lightweight design.2) A feasible flow for autobody lightweight design based on approximation model is proposed. In the design flow, approximation model which is built by uniform design and Support Vector Regression method will ensure its global accuracy. The adaptive optimization procedure will improve the local accuracy of approximation models around the optimal result. The proper engineering modification will ensure the feasibility of lightweight result. According to the design flow, a lightweight design for car door structure is conducted which not only realizes the weight reduction effect of 6.72%, but also proves the feasibility of the design flow.3) The full vehicle structure is a complex system and it contains various performances which have different levels of nonlinearity. The lightweight design for full vehicle body structure considering both stiffness and crashworthiness is conducted by optimizing the sheet thickness and the corresponding material parameters of body components. As a result, the reduced weight of body structure is 9.1kg which realizes the weight reduction effect of 5.44%.