汽车车身点焊接头及整车疲劳断裂完整实体分析

电阻点焊广泛应用于汽车车身等薄板结构的装配工艺中。点焊接头在其周围构成一个外裂纹，疲劳断裂是其主要失效形式。点焊结构疲劳性能评价依赖焊点附近的应力计算精度。有限元法用板、壳、梁等单元模拟焊点，计算模型在几何形状和拓扑连接上都与实际结构相差甚远，应力精度很低，以致点焊结构的应力分析一直是其疲劳断裂研究中的难点。本项目拟以直接在CAD几何模型上进行应力分析的边界面法，对点焊结构进行完整实体应力分析，避免结构几何上的抽象和简化，将点焊接头视作裂纹，精确计算接头局部应力及应力强度因子。项目研究内容包括：全自动的点焊接头几何建模和网格划分技术；基于边界面法的CAD与CAE真正的无缝连接技术；高效高精度的超奇异和近奇异积分技术；边界积分方程的大规模快速算法；并行算法和基于GPU等硬件加速技术。目标是在普通工作站上的求解规模达到300万自由度以上，从而实现包含数千个裂纹（焊点）的整车身完整实体应力分析。

Resistance spot welding is the most widely used method for connecting metal sheets in automotive and many other industrial assembly operations. From the point view of its geometric shape, spot-welded joints constitute outside cracks around them, thus are usually the weakest parts of structures leading to fatigue failure under fluctuating loads. The fatigue life prediction for spot welds depends on the accurate computation of stresses near the joints. In FEM analysis，the spot welds are usually modeled by beam and shell elements, the accuracy for stress is so poor that stress analysis is kept the main difficultly in the fatigue crack study. In this project, we will perform complete solid stress analysis directly on their CAD model by the Boundary Face Method, treating the joints as outside cracks and avoiding any geometric modification, to accurately evaluate the local stress and stress intensity factor. Our study includes completely automatic geometric model and meshing; truly seamless integration of CAD and CAE; effective and accurate hyper-singular and nearly singular numerical integration; fast methods for large scale BIE; parallel algorithms and acceleration algorithms by GPU. Our research goal aims at large scale computations up to three million dofs, and thus the entire Automotive body containing several thousands of spot welds can be performed on a work-station.