高强钢热冲压成形中高温损伤和开裂行为研究

How to accurately predict and control of damage and fracture behaviours at elevated temperature (DFBETs) is a key fundamental issue needed to be solved urgently in order to realize precise forming of high strength steel (HSS) during hot stamping. In the project, the typical characteristic structure in the fracture areas of hot-stamped parts is taken as object of study, and numerical simulation combined with expetiment and analytic theory is taken as method of study. The fracture criterion at elevated temperature (FCET) for HSS is established accounting for both temperatur and strain rate, the user material subroutine incorporating the FCET is developed, the FCET suitable for the loading condition of hot stamping is determined, and thus the finite element based method for prediting DFBETs in hot stamping of HSS is established; the characteristics of DFBETs and their relationships with thermodynamic control parameters (TCPs) are revealed; the effects of both forming parameters and their coupling on DFBETs are clarified, and the TCPs based method for controlling DFBETs is established. The study can not only provide a basis for the research on damage and fracture problems for complex hot-stamped parts, but also is of practical value for promoting the manufacturing level of the new technique in the Chinese automobile industry.

如何可靠地预测和控制高温损伤和开裂行为是实现高强钢热冲压精确成形亟需解决的关键基础问题。本项目拟以热冲压件开裂区的典型特征结构为研究对象，采用数值仿真、实验和理论解析有机结合的方法，建立考虑温度和形变率效应的高强钢高温开裂准则，开发嵌入高强钢高温开裂准则的用户材料子程序，确定适用于热冲压加载条件的高强钢高温开裂准则，从而建立高强钢热冲压成形中高温损伤和开裂行为的有限元预测方法；揭示该成形过程中高温损伤和开裂行为的特征及其与热力学控制参数之间的关联性；阐明成形参数及其耦合作用对高温损伤和开裂行为的影响规律和影响机制，建立高强钢热冲压成形中基于热力学控制参数的高温损伤和开裂行为的控制方法。这不仅为复杂热冲压件的损伤和开裂问题研究奠定基础，而且对提升该新技术在我国汽车产业中的制造水平具有重要的实用价值。

高强钢热冲压技术在实现车身轻量化的同时能保证整车的碰撞安全性，在汽车等领域得到了日益广泛的应用。如何可靠地预测与控制高强钢热冲压成形中的高温损伤和开裂行为是该技术研究和发展中亟需解决的关键基础问题。本项目以汽车高强钢热冲压件的典型特征结构为研究对象，利用自主建立的试验线开展高强钢热冲压实验，探索了该过程中传热、变形和相变的特征与规律；在解决板料-模具界面等效接触换热系数反演等关键建模技术问题的基础上，构建了高强钢热冲压全过程传热-变形-相变耦合三维有限元建模方法，探明了多场多因素耦合作用下板料应力应变场、温度场、回弹、微观组织及模具温度场的演变规律及其随成形条件的变化。采用平板高温单拉实验，并结合有限元仿真和理论解析，建立了考虑温度/形变率效应的高强钢B1500HS的高温开裂准则，并将其通过用户材料子程序嵌入ABAQUS/Explicit中，实现了对B1500HS热冲压成形中损伤和开裂的预测，通过与实验结果的对比，确定了适用于热冲压加载条件的高温开裂准则，从而建立了高强钢热冲压成形中高温损伤和开裂行为的有限元预测方法。采用该方法揭示了B1500HS热冲压成形中高温损伤演变和开裂行为的特征及其与热力学控制参数之间的关联性。在阐明关键参数对高温损伤和开裂的影响规律和机制的基础上，以提高板料成形极限为目标，建立了通过几何和工艺设计的协同优化以控制高温损伤和开裂行为的方法。本项目研究结果对发展高性能轻量化汽车零部件热冲压精确成形理论与技术具有重要的科学意义和应用价值。