A Study of Stress Intensity Factors in Lozenge Pattern of Joints

Riveted joints are very crucial in many industrial applications. Several studies have been carried out to understand the response of lap joints and butt joints with single and double row of rivets emphasizing on total fatigue life and residual stress evaluation. Studies that deal with initial crack and stress intensity factors (SIF) during its progress are very less. In addition, there is very less data on joints formed with Lozenge pattern. The present work aims to bridge this gap with studies on the Lozenge pattern of rivets with focus on the SIF in strap plates, given the fact that the initial cracks appear on them when the strap thickness is less than or equal to the plate thickness. The strap plate considered has six joints in Lozenge pattern in 3-2-1 fashion. Cracks were induced at different joint locations and variation of the stress intensity factor with progress in crack size was evaluated using Finite Element Analysis. Studies were conducted for various interference levels of practical interest. The most critical location of the crack and the most beneficial levels of interference were identified. Limits of interference, beyond which SIF increases drastically, were identified. Combined influence of interference and neighboring geometrical aspects such as holes and boundaries was recorded. Studies were also conducted to evaluate if there is a need for uniform interference at all joint locations. Also, to simulate the real world scenario, several combinations of random interference were induced at the joints and the SIF results were compared with that of uniform interference values. Finally, the effect of change in back pitch of the joints was also studied.