The Study of Local Stress Intensity Factors for Kinked (and Branched) Cracks in Commonly Used Spot Weld Specimens

Local stress intensity factors (LSIFs) for kinked (and branched) cracks of spot welds in lap-shear (LS), cross-tension (CT), U-shaped (US), and coach-peel (CP) specimens were investigated by three-dimensional (3D) finite element analyses (FEA). Models of spot welds without and with kinked (and branched) cracks were developed to derive global SIF (GSIF) and LSIF, respectively. Kinked (and branched) cracks with semielliptical shapes were assumed. Two dominant cracking modes were considered for each specimen. Note that fine mesh size and reasonable mesh design for crack tip regions were adopted to improve the computation accuracy. GSIFs for main crack were obtained to derive local SIFs for infinitesimal kinked cracks. LSIFs for finite kinked (and branched) cracks were then obtained. The computational results show that the LSIF solutions of the four specimens have similar general trends. As kinked (and branched) crack length increases, mode I LSIF solutions gradually increase and then decrease, while mode II LSIF solutions show inverse trends. Finally, applications of local SIFs for fatigue life estimations of spot welds were discussed.