Investigation of Bolt Clamping Force Effect on T-stress in Mixed Mode Fracture

As the cracks and notches in structures may exist in various angles with respect to the loading direction, crack growth and final fracture occur under combined condition of loading i.e. mixed mode fracture condition. Therefore, studying factors that affect material’s fracture strength under mixed mode loading is important. In this study, In order to investigate the effect of bolt clamping force, resulting from torque tightening, on fracture strength, stress intensity factors and T-stress of a rectangular center cracked specimen under mixed mode I/II loading condition, experimental and numerical studies have been carried out. Fracture experiments were conducted on four types of polymethyl methacrylate (PMMA) specimens with crack length ratio a/w of 0.5. Complete range of mode mixities from pure mode I to pure mode II was created by placing the specimens in a modified Arcan fixture and their fracture strength under different loading directions were obtained using a static tensile machine. To give explanations for the obtained results from fracture tests by using mixed mode fracture theories, finite element simulations of the experimental tests were performed to compute mode I and mode II stress intensity factors and also T-stress. The results revealed that bolt clamping force has positive effect on fracture strength of the specimens in all loading directions. Also it was shown that bolt clamping force has a considerable effect on increasing T-stress values.