Assessment of effective stress intensity factors using thermoelastic stress analysis

It has been demonstrated that thermoelastic stress analysis (TSA) can provide accurate information about the real crack-driving force for fatigue crack growth. Experiments were conducted using aluminium 2024 compact tension specimens which were initially pre-cracked to different crack lengths at a constant R (R = 0). Subsequently, thermoelastic images were captured at increasing R values from 0 to 0.5 and Delta K values from 3 to 6 MPa m(0.5) were calculated. The images showed a dramatic change in the stress pattern ahead of the crack tip as R decreased which was always associated with an increase in phase difference (loss of adiabatic conditions) ahead of the crack tip. This indicates that the technique is able to account for the change in conditions that arise from contact between the crack faces. To support this observation, thermoelastic results have been compared with those obtained using compliance methods. The results showed a very good level of agreement, illustrating the ability of TSA to infer successfully the effective Delta K.