Stress intensity factor solutions and fatigue estimation for dual phase and low-carbon steel spot weld

In this paper, stress intensity factor solutions of kinked crack for unequal thickness resistance lap-shear specimens of advanced high strength steel and low carbon steel are investigated for fatigue life estimation. The global stress intensity factor solutions for the main cracks in the lap-shear specimens are developed via finite element analyses and analytical solutions, and the finite element solutions are in good agreement with the analytical solutions. The local stress intensity factor solutions for kinked cracks and the effects of crack shape, crack length and kinked angle to the local stress intensity factors are investigated via finite element analyses. The mode I stress intensity factor of kinked crack shows a smooth increase as the kinked length is less than 30 percent of sheet thickness, and it increases sharply as the kinked length exceeds 50 percent of sheet thickness. An equivalent stress intensity factor of the three dimensional kinked crack and a fatigue life estimation method based on the equivalent stress intensity factor are proposed in the present study. The crack propagation of through-thickness is divided into several sections and subsection integral based on the equivalent stress intensity factor is applied to estimate the fatigue life of lap-shear resistance specimens. Compared with the fatigue test, the fatigue estimation based on subsection integral of local equivalent stress intensity factor for the lap-shear resistance specimens agrees well with the experimental results.