Experimental measurement of crack opening and closure loads for 6082-T6 aluminium subjected to periodic single and block overloads and underloads

Crack closure and opening stresses have been determined for 6082-T6 aluminium, subjected to single and block overloads and single and block overloads and underloads, using an optical method. The distance between the overloads was varied in order to investigate the effect that crack growth distance between overloads has on crack growth rate. The optical method provided high magnification allowing crack closure away from the crack tip to be determined and the crack advance to be monitored dynamically. The data obtained gives insight into the significance of periodic overloading and underloading as well as what effect interactions, such as crack branching, have on crack growth retardation. The results obtained also enable numerical and analytical codes to be evaluated.