异质金属车身接头碰撞失效机理及优化研究

The development of the heterogeneous metal materials mixed body has become an important way for automotive lightweighting. Different from the traditional completely welded all-steel body, the heterogeneous metal material mixed body uses a lot of new connections including riveting, bonding and bond-riveting. The change in the way of material and connection directly influences the body structure dynamic response and failure modes during the crash process, and puts forward new challenges for body crashworthiness design. Due to the lack of reasonable crash equivalent elements for heterogeneous materials joints, the existing finite element models of the heterogeneous metal material body are not able to predict the body response correctly, and this greatly affects body crash safety design. In this project, first of all, the crash equivalent elements under high strain rate and the failure criteria for heterogeneous metal material joints are going to be established based on experimental data. Secondly, the effects of the combinations of heterogeneous metal materials and the connection modes on body crashworthiness will be studied. After decomposing the body crashworthiness target into the design goals of various key components, the collaborative optimization will be carried out for designing the connection layout parameters, material properties and the panel thicknesses, by using the crash equivalent elements of the joints including riveting, bonding and bond-riveting. The goal is to improve the crashworthiness of the heterogeneous metallic materials mixed car body.

异质金属材料混合车身已成为实现汽车轻量化的重要途径。与传统全钢车身完全采用焊接不同，异质金属车身大量采用SPR铆接、粘接和SPR铆粘复合等新型连接方式。材料和连接方式的改变直接影响车身动态响应和碰撞失效模式，对车身耐撞性设计提出了新的挑战。由于缺少合理的异质材料接头碰撞等效单元，现有的异质金属车身碰撞仿真有限元模型无法正确预测车身响应，极大地制约了车身的碰撞安全设计。本项目首先基于实验数据，建立SPR铆接、粘接和SPR铆粘连接的异质金属接头碰撞等效单元模型和失效准则；在此基础上，建立包含接头碰撞等效单元的异质金属车身碰撞仿真模型，分析板材厚度、材料强度和接头布置等参数对车身耐撞性的影响。最后，对包含异质金属接头的车身前纵梁和B柱进行基于耐撞性的多目标优化设计。本项目研究可为异质金属车身耐撞性设计提供理论支撑，助力异质金属轻量化车身的开发与产业化应用。

对拉剪工况和剥离工况下试件的动态拉伸性能进行分析，建立铆接的异质金属接头碰撞等效单元模型。为了提高接头等效单元仿真的精度，更准确地模拟冲击载荷下的异质金属结构失效，提出自冲铆接头等效单元韧性失效的建模方法。结合异质金属前纵梁试验验证接头等效单元的适用性和准确性，研究铆接点位置对异质金属前纵梁各面板之间的动力学关系的影响，发现在铆接点间距变化范围内，初始峰值力随着铆接点间距减小而增大，当铆接点间距减小至一定范围时，其对初始峰值力的影响作用不明显。反应在异质金属前纵梁上就是较大的铆接点间距使其前端刚度和强度较低，能够降低行人和乘员受伤的几率。变化较大的铆接点间距和布置位置，同时显著改变异质金属结构的变形量、总吸能等耐撞性指标。从铆接的异质金属双帽型薄壁梁的抗弯性能入手研究连接方式对汽车B柱和保险杠在横向冲击下的失效模式影响，在此基础上研究了结构参数对异质金属结构横向弯曲耐撞性的影响。基于RBF代理模型，利用NSGA-Ⅱ方法对多种材质组合的结构进行多目标优化并得到Pareto前沿，得到了异质金属梁的最佳参数以及比吸能和初始峰值力的理想值。与均质梁相比，异质金属梁的Pareto曲线占主导地位且更接近“乌托邦点”，这意味着钢铝异质金属结构在横向载荷下的耐撞性明显优于单一材料结构。在此基础上，研究了铝泡沫填充对异质金属结构耐撞性的影响，发现铝泡沫填充的异质金属梁能承受更大的横向冲击。尽管铝泡沫填充梁较重，但其整体结构比吸能优势明显，显示出更高的重量效率。无填充异质金属梁的抗弯性能对加载位置敏感，而铝泡沫填充异质金属结构的横向冲击下的耐撞性受加载位置影响较小。在此基础上，研究了横向冲击下铝泡沫填充异质金属结构耐撞性的四维多目标优化问题。