汽车前部结构低速碰撞耐撞性与轻量化优化

Crashworthiness and Lightweight Optimization for Frontal Structure of Automobile Under Low-speed Impact

为解决低速碰撞下车身前端结构耐撞性和轻量化的矛盾,建立防撞梁、吸能盒、前纵梁总成一体化模型并进行整体碰撞分析优化。为避免优化中前纵梁因屈曲而出现大幅溃缩的数值结果,引入结构纵向位移溃缩量作为第3项评价指标,并将其与吸能量、峰值碰撞力共同作为优化模型的耐撞性约束条件,建立以6个部件板厚为设计变量的质量最小碰撞优化模型。提出将变量区间先分段再进行正交试验的组合正交试验设计采样方法,以保证总成结构遵循刚度逐级增强的压溃变形机制。结合响应面代理模型和含精英保留策略的遗传算法构造出针对目标函数和3项约束指标的惩罚函数对高度非线性碰撞问题进行优化。为简化优化计算流程,探索和对比了采用组件优化和分组均匀试验设计的优化过程。结果表明:经优化后,可实现吸能量增加10.1%,峰值碰撞力减小11.1%,溃缩量减少12.6%,减重15.1%;将溃缩量作为约束条件引入碰撞优化问题有助于综合控制优化结果;组合正交试验是解决变形次序紊乱的有效方法;所构造的惩罚函数可将多目标优化问题单目标化;组件优化和均匀试验设计可有效简化涉及较多变量的碰撞优化问题的求解过程。

In order to solve the contradiction between crashworthiness and lightweight for frontal structure of automobile body under low-speed impact, bumper, crash-box and front rail integrated model was established to conduct collision analysis and optimization as a whole assembly. To avoid the numerical results with large crumple distances because of frontal rail bulking in optimization, longitudinal structural crumple distance was introduced as the third indicator and was taken as one of constraint conditions of crashworthiness indicators with energy absorption and peak impact force, and minimum mass collision mathematical model was built based on the design variable of thicknesses of six parts. To ensure that the crush deformation of assembly structure follows the mechanism of stiffness enhancing step by step, the composite orthogonal experimental design （OED） was proposed which divided the variables intervals into several sections firstly and then carried on the orthogonal experiment. Response surface surrogate model method, genetic algorithm （GA） with elite strategy and penalty functions subjected to object function and three constraint conditions were employed to solve the highly nonlinear problem in collision. Components optimization and uniform experimental design （UED） were explored and compared to simplify optimization process during collision. The results show that after optimization, the results accomplish mass reduction of 15. 1% whereas energy absorption addition of 10.1%, peak force and crumple distance decrease of 11.1% and 12.6%, respectively. Introducing crumple distance into optimization as a constraint condition is very helpful for controlling the optimization results comprehensively~ composite orthogonal experimental design is an effective method to solve the deformation sequence in disorder; the established penalty functions can transfer the multi-objective optimization into single object problem, and components optimization method and UED can effectively simplify the solving process of crashworthiness optimization problems with multiple variables.