Stress intensity factors for spot welds and associated kinked cracks in cup specimens

In this paper, the stress intensity factors for spot welds in cylindrical-cup and square-cup specimens are investigated by finite element analyses. Axisymmetric and three-dimensional finite element models are developed for circular plates and cylindrical-cup specimens to establish the finite element meshes needed to obtain accurate global stress intensity factor solutions. The global stress intensity factors are compared with the existing analytical solutions for circular plates. Then a three-dimensional finite element model based on the finite element mesh for cylindrical-cup specimens is established to obtain the global stress intensity factors for square-cup specimens. Based on the computational results, a closed-form stress intensity factor solution is suggested for square-cup specimens. Next, based on the experimental observations of kinked crack growth mechanisms in square-cup specimens under cyclic loading conditions, axisymmetric finite element models are established to investigate the local stress intensity factor solutions for kinked cracks emanating from the main crack. Both circular and rectangular shaped notch tip and a sharp crack tip are considered for the main crack. Various kink lengths are considered. The local stress intensity factor solutions for kinked cracks are obtained. The results show that the local stress intensity factors for kinked cracks with finite kink lengths are much higher than those based on the closed-form solutions for kinked cracks with vanishing kink length. Finally, the implications of the local stress intensity factor solutions for kinked cracks on fatigue life prediction are discussed.