Investigation of the fatigue life and crack growth in torque tightened bolted joints

The fatigue crack initiation and fatigue crack growth life estimations have been numerically investigated and the total estimated fatigue lives have been compared with available experimental fatigue test results for a single plate of aluminum 7075-T6 bolted with different applied torques. To do so, pre-stresses around the hole due to the torque tightened bolt and stress concentration factor of the combined longitudinally applied load and bolt clamping force were determined using 3D finite element simulations results. The calculated pre-stresses and stress concentration factors for different bolt clamping forces were employed in AFGROW computer package to predict fatigue crack initiation and fatigue crack growth lives. The results show that there is good agreement between the numerically predicted total fatigue lives and available experimental fatigue test results. The numerical results also show that bolt clamping force increases both fatigue crack initiation and fatigue crack growth lives individually.