A COMPARISON OF DIFFERENT METHODS TO DETERMINE THE THRESHOLD OF FATIGUE-CRACK PROPAGATION

Three different methods for determining the threshold value for fatigu e crack growth - the load-shedding technique, the stepwise increase of load amplitude on specimens precracked in cyclic compression, and dec rease of stress intensity range at a constant maximum stress intensity - were applied to a high-strength aluminium alloy. The load-shedding technique tended to lead to higher values of the threshold, especially at low R-ratios. The threshold determined with decreasing stress inte nsity range at a constant maximum stress intensity was larger than the effective threshold determined with stepwise increasing of load ampli tude on specimens precracked in cyclic compression.