Study of Geometric Interference Parameters on the Stress Distribution and Fatigue Crack Growth in Pin Loaded Lug Joint

Lug-Bush-Pin joints are extensively used in almost all the disciplines of mechanical engineering design as structural members. Due to their simplicity and highly efficient load-bearing characteristics, lug joints are extensively used in aircraft for the attachments of flaps, ailerons, and engine pylons. These joints are sensitive to fatigue and hence their fatigue strength dictates the life of the entire structure. In the current study, a typical lug and bush are joined through an interference fit and the pin is considered to be snugly fit initially in the assembly. Interference level varying from 0.1 to 0.5% of bush diameter was considered for the lug-bush interface. Wear of pin is generally allowed by design resulting in pin-bush clearance, which in turn can affect the stress distribution of the joint. Typical clearances ranging from 0.1 to 0.5% of pin diameter were considered. The joint was analyzed for static and fatigue performance using a nonlinear elastic-plastic finite element analysis. A total of 56 geometric cases, involving clearance of bush with the lug in combination with snug fit pin and varying levels of clearance fit at the pin were examined. The fatigue life is estimated for each of the bush-pin fit combinations. Unstructured Mesh Method (UMM) and Separating, Morphing, Adaptive, and Re-meshing Technology (SMART) are employed to ascertain Fatigue Crack Growth analysis. The results suggest a good correlation with analytical solutions within the 2.5% variation of accuracy. Fatigue crack growth rate response was also studied for the bush and Pin joint at the locations of high-stress.