耦合制造工艺因素的功能梯度热成形车身结构优化设计研究

Functional gradient structure fabricated by hot forming (FGS-HF) can improve the automobile crashworthiness and lightweight simultaneously since its compound distribution characteristics of soft & hard zones. This composite structure is one of the research hotspot in the automotive body manufacturing field for lightweight. However, the performance of the FGS-HF is significantly affected by the technological variables of hot forming, and local failure and fracture behavior occurs easily in the collision process. It is difficult to predict accurately the dynamic crash process by means of traditional simulation methods, and further implement effectively the global optimization considering with the manufacturing process parameters and structure design variables. Thus, an optimization design method for automotive FGS coupling with technological variables of hot forming process is proposed in this program. The failure criterion of the quench-hardenable boron steel considering damage accumulation and the closed-loop optimal control strategy are firstly established by means of the theoretical deduction and experimental investigation to realize the local failure prediction efficiently and improve simulation accuracy. Subsequently, the technological variables of hot forming including manufacturing process parameters and forming history variables are introduced into the crashing simulation coupling with the multi-objective optimization process. A multi-objective and multi-constrained optimization framework with independent variables of manufacturing process factors, crashworthiness and lightweight indexes is constructed to realize the integrated optimization of structure design and manufacturing for hot-forming FGS. Finally, the rationality and availability of proposed optimized design method are further verified by an engineering case. The research results can provide theoretical and technical support for the application of hot-forming functional gradient structure in automobiles. The research results can provide strong theoretical foundation and technical support for predicting accurately crashworthiness of FGS-HF as well as the optimizing the processing technology.

功能梯度热成形结构因其具有软-硬复合分布的特征，在提高碰撞安全性的同时实现车身轻量化，是目前汽车车身轻量化制造领域的前沿研究方向之一。然而其性能受热成形制造工艺因素影响显著且易于在碰撞过程中发生局部破裂失效，采用传统仿真方法无法准确表征其碰撞模拟过程，难以有效地实现其制造工艺与结构设计参数的全局最优化。本项目提出一种耦合制造工艺因素的梯度强度热成形车身结构优化设计方法。通过建立考虑损伤累积的淬硬热成形钢失效准则及闭环优化控制策略，将热成形工艺因素与成形历史变量与碰撞仿真及多目标优化决策进行耦合和集成，建立一套以制造工艺参数为优化自变量，抗撞性和轻量化指标为优化目标的多目标、多约束闭环控制优化框架；最后，通过实例验证该方法的合理性和有效性。研究成果将为准确预测梯度强度热成形结构的抗撞性能、优化工艺提供有力的理论依据和技术支撑。

面向汽车车身轻量化制造领域的软-硬复合功能梯度热成形结构，针对其难以有效实现制造工艺与结构设计协同优化的问题，采用理论、实验和仿真优化相结合的方法，研究了差异化淬火温度、差异化模具温度等定制化热成形制造工艺，建立了淬硬钢的硬度/淬火温度-应力-应变3D曲面模型，获得了不同硬度等级、不同预制损伤的淬硬热成形钢的GISSMO失效准则；. 以汽车前纵梁为原型，采用差异化淬火温度工艺，制备了均一强度和梯度强度的淬硬钢单帽型薄壁结构；通过将所建立的GISSMO失效模型引入仿真，验证了GISSMO模型应用于典型零件的适用性和准确性；通过开展耦合热成形过程的薄壁结构碰撞仿真建模研究，分析了热成形损伤及耦合硬度、厚度、残余应变分布等对抗撞性能研究的影响；. 最后，以车身前部常见的S形前纵梁为原型，基于差异化模具温度工艺，开展了梯度热成形S梁的热成形试验和仿真，研究了模具温度、合模压力等工艺因素对结构性能梯度分布的影响；通过耦合制造工艺的抗撞性能建模研究，建立了一套耦合制造工艺因素的梯度强度热成形结构多目标优化设计方法，实现了以制造工艺为优化变量的功能梯度热成形S梁结构的优化设计;. 项目发表/录用学术论文10篇，其中SCI论文8篇；为完善热成形加工理论和技术、提升功能梯度热成形钢结构的优化设计理论、助推功能梯度热成形结构从理论走向产业应用有积极贡献。