冲压成型速率是影响车身用“先焊后冲”双相钢激光拼焊板高周疲劳性能及断裂失效部位的关键因素，接头疲劳失效行为存在“危险预变形速率区间”。本项目拟通过实验测试与理论分析相结合的方式，系统研究预变形时接头各区域微观组织结构演化、残余应力分布、微区应变分布演化过程的变形速率相关性，阐明接头高周疲劳损伤行为存在预变形速率依存性的微观机制，揭示接头疲劳裂纹萌生、失效部位发生迁移的本质，建立“先焊后冲”双相钢激光焊接板高周疲劳损伤“成形速率依存关系”的控制机理。该研究结果不仅能进一步深化对金属材料“瞬态高速载荷”变形行为的理论认识，而且可以服务于“以实际服役力学行为评价为基础”的车用先进高强钢激光拼焊板“先焊后冲”结构设计和工艺技术的创新，为加快我国以“节能减排和保障安全”为标志的新一代汽车用先进高强钢的应用发展提供切实的科学依据。

Deformation rate of stamping forming is one of the key factors affecting the high cycle fatigue properties of laser tailor-welded dual-phase (DP) steel joints for automotive applications when stamping forming after welding and the fatigue failure behavior of the welded joints exists a dangerous deformation rate range. The project aims to systematically study the dependence of evolution of the microstructure, residual stress and strain distribution of subregions in the welded joints on the deformation rate during pre-deformation, and clarify the micromechanisms for deformation rate dependency of high cycle fatigue damage behavior of the welded joints through a combination of the experimental test and theoretical analysis. Furthermore, it aims at revealing the nature of the migration of fatigue crack initiation and failure location of the welded joints and establishing the controlling mechanism for dependence of high cycle fatigue damage behavior of the laser welded DP steel joints on the deformation rate when stamping forming after welding. The research results can not only further deepen the understanding of deformation behavior of metallic materials under the transient load at high speeds, but also serve to the innovation of structure design and process technology for DP steel when stamping forming after welding based on the mechanical behavior evaluation in the actual service. It will provide a practical scientific basis for accelerating the development and application of advanced high strength steel for the new generation of automobiles marked by energy saving, emissions reduction and safety.