THE INFLUENCE OF PRECRACKING TECHNIQUES ON FATIGUE-CRACK GROWTH THRESHOLDS UNDER MIXED-MODE I/II LOADING CONDITIONS

The influence of precracking history on the subsequent fatigue crack growth thresholds for branch cracks has been studied for AISI 316 stainless steel and BS4360 50D under mixed mode I/II loading. The work has examined: (1) the influence of precrack length; (2) the influence of stress intensity factor range at the final stage of precracking; (3) the influence of precracking load R-ratio; and (4) the influence of precracking unloading schemes. A computer controlled precracking test system has been set up in the current investigation and comparisons have been made between the results of computer controlled work and those published previously using a manually controlled technique. The results show that a computer controlled precracking method generally gives more conservative and more repeatable growth threshold values for branch cracks than a manually controlled precracking procedure.