考虑损伤耦合的高强度钢热成形极限预测方法研究

Hot forming technology of high strength steel is an important method for structure lightweight of Auto-body. With the complicated thermal-mechanical feature which coupling damage evolution behavior in hot forming, the damage effect with temperature and strain rate sensitivity has put the HSS forming limit precise prediction forward to new requirements and challenges. This project focuses on the damage mechanism of HSS high temperature rheological behavior, method to establish theoretic model of forming limit coupling with damage factors in hot forming. In this study, the accurate description of high temperature deformation behavior and the precise calibration of void damage for HSS with different temperature and strain rate are to be investigated. The damage void coalescence criterion and high temperature hardening law are employed to deduce the modified GTN mesoscopic damage model and develop high temperature incremental visco-plastic constitutive equation combined damage. Based on M-K instability model for reasonable modification and improvement, the influence rules of damage characteristic parameters for HSS hot forming limit is also investigated. Furthermore, a novel theoretic model of 3D forming limit diagram coupling with damage evolution for hot forming will be established and insure the accuracy & high reliability by the improved high temperature NAKAJIMA forming limit experiment. These research objects above mentioned include, but not limited to the 3rd generation advanced high strength steel and other metal blanks. The achievement is significant for the hot forming process optimization as well as the improvement of the formability simulation method of metal for provide theoretical and technical support.

高强度钢板热成形技术是实现车身轻量化的重要途径。热成形过程伴随复杂的热-力耦合损伤演化行为，温度、应变率影响下的损伤效应对高强度钢板热成形极限的准确预测提出了新的要求和挑战。本项目主要聚焦高强度钢高温流变行为下的损伤机理和建立耦合损伤的热成形极限预测方法，完成如下研究：考虑温度和应变率影响下的高强度钢板高温流变行为及孔洞损伤演化规律，结合孔洞损伤聚合准则及高温硬化法则，建立适用于热成形的GTN细观损伤模型，并推导耦合损伤的高温粘塑性增量本构方程；进一步通过对M-K失稳模型进行合理修正，建立耦合损伤的热成形极限预测方法，研究损伤参数对高强度钢板热成形极限的影响规律，并结合高温NAKAJIMA热成形实验获得高强度钢三维热成形极限图，确保理论预测结果的精确性和可靠性。研究成果可为包括第三代先进高强度钢在内的金属板材热成形工艺优化及数值模拟方法提供系统的理论和技术支撑。

本项目按照计划针对高强度硼钢/铝合金高温变形过程中的损伤演化行为和耦合损伤的热冲压成形极限预测方法开展研究。采用理论、实验和数值建模相结合的方法，阐释了工艺因素对高强度钢板/铝合金高温变形行为及孔洞损伤演化的协同影响机理，建立了耦合损伤的高温金属板材热冲压成形极限预测方法。本项目按计划顺利执行。测定了温度和应变率影响下的高强度钢板高温流变行为及孔洞损伤演化规律，推导了耦合损伤的高温弹塑性本构方程，对M-K失稳模型进行必要修正，进而建立了一套可靠的耦合损伤的热冲压成形极限预测方法。进一步开展了Nakazima高温胀形实验和仿真研究，建立了22MnB5在不同温度下的高温成形极限TFLD。最后，通过开展实际汽车B柱热冲压实验和仿真模拟，验证了相关TFLD与建模策略对实际零部件热冲压成形预测结果的有效性和准确性。项目相关研究成果得到了国有科研院所、汽车零部件制造企业的关注，其中关键部件的制备、仿真建模技术及高温成形极限测试仪器已经应用到了相关单位实际热成形产品开发与工艺优化中。