Effect of clamping force and friction coefficient on stress intensity factor of cracked lapped joints

Fatigue failure of steel connections is a well-known failure mechanism, especially for structures which sustain heavy cyclic loads like steel bridges. Reliable determination of stress intensity factors (SIFs) for cracks in bolted joints is required to evaluate their safety and fatigue life. The SIF is a traditional topic in mechanics and there have been many solutions for many different cases. The effect of clamping force and friction coefficient on SIF of a crack emanated from lapped joints has not been considered in the literature. The key contribution of the present paper is to evaluate such effect on SIF of cracked single or double lapped joints using 3D finite element method (FEM). Furthermore, the variation of stress concentration factor (SCF) through the thickness of uncracked lapped joints as a function of clamping force and friction coefficient was also studied. A group of 3D finite element models for steel lapped joint was constructed. Three clamping forces of 20, 100 and 200 kN were assumed. Coefficient of friction of 0.0, 0.3 and 0.5 were studied. observed that high clamping force causes a decrease in stress concentration for un-cracked connection. For cracked lapped joint, SIF decreases, i.e. increase in fatigue life, with increasing clamping force.