Finite element analysis of double lap protruding head bolted joints in tension simulating aircraft joints

Since the inception of aerospace industry the emphasis has been laid upon safe and efficient design of aircraft. Use of bolted joints is widespread in aircraft industry due to high loading capability. They have higher tensile and fatigue strengths as compared to welded, riveted and pinned joints. Bolt pretension has a direct positive impact on joint behavior and its resistance to fatigue due to creation of positive stress conditions surrounding the hole. Double lap joints have improved strength as compared to single lap joints due to direct impact of pretension on double lap joints. This paper focuses on investigating the effects of fastener geometry in the absence of washers around the double lap single bolted aluminum alloy joint. The model comprises of 7075-T6 aluminum plates bolted by structural steel bolt. Elastic plastic multi linear kinematic hardening material behavior has been observed for the aluminum alloy. Bolt clamping force and tensile force on the middle plate has been applied in two steps and result solely for bolt clamping forces, combination of bolt clamping force & tensile force and for difference frictional coefficients between the contact surfaces have been analyzed. It has been observed that the increase in clamping force increases compressive stress around the plate. Moreover, in the presence of tensile loading the increase in clamping force decreases the tensile stress around the holes. This study also finds that the increase in frictional coefficient significantly decreases tensile and compressive stress distribution around the hole, therefore choice of proper frictional coefficient is of paramount importance for correct results. This research helps in analysis of compressive and tensile stresses induced as a results of force application on double lap joints with protruding heads. Moreover effects of frictional coefficients on joint loading has also been emphasized.