Pre-tensioning effect on fatigue life of bolted shear joints

A number of experimental studies have demonstrated that pre-tensioning fasteners significantly increases the fatigue life of shear joints. Fatigue life prediction for clamped joints is still a complex and unresolved issue because of the mixed nature of load transfer, which partly occurs by frictional forces. This article presents a calculation method based on a multiaxial-type critical-plane criterion, which determines the fatigue life and fatigue crack initiation site. For this purpose, the values of hydrostatic pressure and amplitude of maximum alternating shear stress on a critical octahedral plane are determined at each point of the structure and for each loading increment, and are used to predict the fatigue life of the joint. A dedicated experimental study was conducted within materials & processes airbus laboratory to validate the numerical results. In addition, a dimensionless parameter Rs is introduced to quantify the proportion of load transferred by friction and by bearing of the bolt, and allows the optimal preload to be approximated, above which value more clamping should not give further improvement. This value characterizes the shift of the crack location from the net section to the outside of the compressed area.