EFFECT OF YIELD STRENGTH AND SINGLE TENSILE OVERLOAD CYCLES ON EFFECTIVE STRESS INTENSITY RANGE RATIO IN 6061-T6 A1-ALLOY

Crack closure experiments were conducted on 6061-T6 Al-alloy, using COD gauge for various overload ratios (1.67, 1.88 and 2.06) and different prestrains (0,3 and 6%). On the basis of these experiments some power laws are developed. The delay period after application of single overload is also increased as magnitude of overload increased. The retardation is less as percentage of prestrain increased for the same over-load ratio. After application of an overload cycle the decrease in U value is less in prestrain material as compared to as received material. Crack growth rate is also decreased after application of overload cycle. It attains the CAL crack growth rate after certain number of cycles.