【作者】 王金轮；

【导师】 兰凤崇；

【作者基本信息】 华南理工大学 ， 车辆工程， 2011， 博士

【摘要】 大量事实表明,高强度钢板已成为颇具竞争力的汽车轻量化材料,它在抗碰撞性能、加工工艺和材料成本方面较其他材料具有较大的优势。由于高强度钢板的力学性能与普通钢板相比差异较大,一方面导致车身板件成形性能变差且容易出现开裂、起皱等缺陷;另一方面回弹量大是高强度钢板在车身上应用时一直没有得到很好解决的主要问题,尺寸精度难以控制,严重影响了汽车产品的装配精度。另外,各种级别的高强度钢板在车身上应该怎样合理地分布,具体到哪些部件可以用高强度钢板替代,不同部件间高强度钢板如何匹配,需要在保证车身结构整体性能不受影响的前提下,有选择的进行替换,以便在满足整车原有性能及降低自重的基础上节约材料成本,发挥合理的材料用于合适部位的优势。(1)针对高强度激光拼焊板成形性差的问题,系统地研究了差厚同材、同厚异材、差厚异材三种材料匹配对其成形性能的影响规律及内在机理,包括材料流动、焊缝移动及应变路径的变化等,为车身拼焊板件的选材提供依据。同时针对差厚同材拼焊板,研究了厚/薄两侧压边力分布对其成形极限深度、焊缝移动和危险点应变路径的影响规律,为车身拼焊板件成形的压边力控制提供依据。(2)针对高强度激光拼焊板回弹量大的问题,建立了一种以破裂准则而非起皱准则设计的台阶式变压边力,可以在成形件未出现破裂的前提下增大有效塑性应变区域,减小回弹量;以前纵梁拼焊式内板为例,结合随位置和行程变化的变压边力,利用正交试验设计确定了各参数对回弹量大小的影响程度,优化方案表明合理的变压边力参数对高强度拼焊板侧壁和法兰回弹角的控制效果比较显著。(3)针对目前汽车抗撞性的CAE分析已经达到相对成熟阶段,模拟精度的继续提高受到多方面制约。在比较一步逆成形法与增量法成形精度的基础上,利用增量法成形和网格映射技术,将成形工艺引起的材料性能变化如厚度减薄、塑性硬化等引入到碰撞仿真分析中,分析了成形效应对单帽形件及整车结构变形、吸能率及加速度等的影响规律,考虑成形效应的仿真结果与实验结果更趋一致,精确碰撞仿真需要考虑成形工艺过程引起的材料性能的变化。(4)建立了变形量控制下碰撞仿真过程的理想加速度-位移历程曲线,以此为设计目标进行耐撞性研究,以某款自主品牌SUV车前纵梁为例,建立了前纵梁耐撞性问题的简化模型和拼焊板前纵梁焊缝位置的优化原则,以保证拼焊板前纵梁在碰撞过程中合理的压溃顺序吸收更多的碰撞动能;设计了质量最轻和吸能最优两种优化方案,建立了不同设计方案的数学优化模型,利用试验设计、近似模型及自适应响应面法相结合,得到了符合耐撞性要求的拼焊板轻量化设计优化解。(5)在白车身模态实验和实车100%正面碰撞实验验证有限元模型精度的基础上,建立了兼顾效率和精度要求的100%正面碰撞前端吸能结构的简化模型,考虑了材料的变形路径和应变率效应,基于多目标遗传算法得到了轻量化与耐撞性多目标问题的Pareto优化解集,优化后的零部件厚度、材料分布更加合理,使整车100%正面碰撞的安全性有了明显的提高,从而验证了基于多目标遗传算法的轻量化与耐撞性多目标优化的可行性。本文研究涉及材料匹配对成形回弹的影响以及材料匹配对结构耐撞性的影响等,目的是为车身结构的轻量化选材提供方法和依据,促进高强度钢板在自主品牌车型上的应用。更多还原

【Abstract】 Facts showed that high-strength steel (HSS) has become quite competitive automotive lightweight materials, which has greater advantages on anti-collision performance, processing technology and material cost than other materials. As the mechanical properties of HSS are quite different from ordinary steel, which leading to poor forming performance of autobody panels; on the other hand, large rebound of HSS is a major problem when applied on autobody that hasn’t been solved yet, and dimensional accuracy is difficult to control, which seriously affects the assembly precision of automotive products. In addition, how should a reasonable distribution of various levels of HSS on autobody, which parts can be replaced with HSS, and how to match HSS between different components, that need to be replaced selectively in the premise of ensuring the overall performance of autobody unaffected, in order to take the advantage of the proper material selected for the right part based on meeting the original performance and reducing the autobody weight.(1) With HSS tailor-welded cylindrical pieces as an example, the influence of material matching law on formability including material flow, weld-line movement and strain path changes was divided into three cases: 1) different thickness with the same material, 2) the same thickness with different materials and 3) different thickness with different materials, which provides the basis for material selection on autobody tailor-welded blank (TWB). While with the 1st case considered, the influence of blank holder force (BHF) distribution on thick/thin sides on its forming limit, weld-line movement and strain path at the cracking point was studied, which provides the basis for BHF control on TWB forming.(2) A step-BHF based on rupture criterion rather than wrinkle criterion was presented to increase effective plastic strain region and reduce the amount of springback with no rupture appeared; with TWB-front rail inner panel as an example, orthogonal experimental method was used to determine the influence of various BHF parameters on the amount of springback, the optimization results showed that the control effect is very significant for HSS TWB-sidewall and flange springback angle.(3) As the CAE simulation of crashworthiness has reached a mature stage relatively, the simulation accuracy to continue to improve subjected to many constraints. On the basis of precision comparison of one-step forming method and incremental method, material property changes such as thinning and plastic strain hardening were included into crash simulation analysis by incremental forming method and grid mapping technology. The influence of forming effects on structure deformation, energy absorption rate and acceleration, etc of a single cap-shaped pieces and the whole vehicle was studied, the simulation results considering forming effects were more consistent with experimental results, the changes of material properties during forming process should be considered in accurate crash simulation.(4) The ideal acceleration-displacement curve under deformation control of crash simulation was proposed. With a certain own-brand SUV front rail as an example, a simplified model of front rail on crashworthiness problem was established; the weld-line location of TWB front rail was optimized to obtain a reasonable crushing order and absorb more impact energy; two design cases and mathematical optimization models of lightest and optimal energy absorption were proposed, experimental design, approximation model and adaptive response surface method were combined to obtain the optimal TWB lightweight solution while satisfying the crashworthiness requirements.(5) With the accuracy of the CAE model verified through modal experiments of body in white and real 100% frontal crash test, a simplified model of the frontal energy-absorbing structures was established with efficiency and accuracy both taken into account, with the material deformation path and strain rate effect considered, the Pareto optimal solution set was obtained through multi-objective genetic algorithm base on lightweight and crashworthiness optimization. As the optimized thickness and material distribution more reasonable, the 100% frontal crash safety was greatly improved, thus verified the feasibility of multi-objective optimization of the lightweight and crashworthiness issue based on multi-objective genetic algorithm.This study involved the influence of material matching on forming, springback and structural crashworthiness; the purpose is to provide material selection method for structural lightweight, and promote the application of HSS on own-brand autobody.更多还原