Fatigue life estimation after crack repair in 6061-T651 aluminum alloy using the stop holetechnique under mixed mode condition

The stop-hole method is a simple and accessible crack arresting method widely used to retard and even to stop the fatigue crack propagation in structural components that cannot be replaced as soon as the crack is observed. It is common to drill a hole at or near the crack tip to turn the crack into a notch, resulting in reduction of its stress concentration. The crack growth retardation is examined using an experimental and numerical study on the efficiency of stop holes under different mixed mode loading conditions. Compact tension specimens of 6061-T651 aluminum alloy were used to perform the crack arresting tests under mixed mode cyclic stress loading. A fatigue crack growth code for twodimensional elastic problems is developed to examine the efficiency of this method. To study the effectiveness of this repair method, the Paris equation is used to investigate the fatigue crack growth life and a classical strain based technique is adapted to explain the fatigue crack initiation life of several experiments carried out in the past on aluminum specimens. The crack initiation life was the number of fatigue loading cycles causing a 0.2 mm crack to initiate at the stop-hole edge. The numerical results reveal that, the presence of stop holes significantly decreases the stress concentration around the crack tip. Also the fatigue life extensions of mixed mode compact tension specimens underdifferent mode mixities are compared. The comparison between the experimental and the computational results shows that the fatigue life extension caused by the stop-holes can be effectively predicted using the fatigue life code.

Keywords:

fatigue crack growth , mixed mode , crack growth retardation , stop hole