An experimental study on fatigue crack growth in lap joints with multiple fastener holes

Although a lot of studies have been conducted on the multi-site damage (MSD) problems, most of them focus on the strength of plates with MSD and the phenomenon of MSD seems to be not fully clarified yet. In this study, fatigue crack growth tests were conducted using bolted lap joint specimens with multiple fastener holes in order to investigate the phenomenon of MSD. Crack growth data were generated using notched and unnotched specimens at different clamping force levels. The results of fatigue tests revealed that the existence of initial notches at fastener holes was an important factor for the occurrence of MSD in this type of specimen. Furthermore, the stress distribution of the lap joint specimen was analyzed by an infrared stress imaging system to understand the nature of fatigue crack initiation and fatigue crack growth. Good agreement was obtained between the crack initiation sites and the highest stress regions in the unnotched specimen.