Abstract: Stress Intensity Factor (SIF) analysis is the basis for crack propagation analysis and fatigue life prediction of structures with Multiple Site Damage (MSD). It is difficult for joint structures based on simplified models to consider factors such as secondary bending and rivet deformation. In this paper, the three-dimensional finite element models of butt-joints with MSD are established, followed by analysis of the distribution and variation of SIFs at each crack tip with different damage modes, design configurations and constraint conditions. The results show that K_I is dominant, while K_II and K_III are negligible. Due to the secondary bending, the SIF increases approximately linearly from the outer surface to the inner surface. Strong interference exists between the MSD cracks, increasing the SIF, and the shorter the distance between the cracks, the stronger the interference. With the increase of the splice plate thickness, the SIF values increase first and then decrease because of the effect of the splice plate stiffness and the rivet flexibility on the load transfer ratio of the rivet. The value of SIFs with countersunk rivets is higher than that with flat head rivets, with an increased difference between the inner and outer surfaces. While the anti-bending constraint has little effect on the average value of the SIF at the crack tip, it can significantly reduce the variation of the SIF on the thickness direction.

Key words: multiple site damage (MSD), butt-joints, stress intensity factor (SIF), 3D finite element, riveted joints