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 g rowth thresholds for branch cracks has been studied for AISI 316 stain less steel and BS4360 50D under mixed mode I/II loading. The work has examined: (1) the influence of precrack length; (2) the influence of s tress intensity factor range at the final stage of precracking; (3) th e influence of precracking load R-ratio; and (4) the influence of prec racking unloading schemes. A computer controlled precracking test syst em has been set up in the current investigation and comparisons have b een made between the results of computer controlled work and those pub lished previously using a manually controlled technique. The results s how that a computer controlled precracking method generally gives more conservative and more repeatable growth threshold values for branch c racks than a manually controlled precracking procedure.