Crack closure measurement at elevated temperatures using laser interferometric gage and fatigue threshold

A laser interferometric strain/displacement gage (ISDG) was developed and used to investigate the fatigue crack growth at elevated temperatures. The technique was modified so as to enable continuous measurement of crack closure during the fatigue crack growth tests. Only the numbers of interference fringes were used instead of the movement of those fringes as an input information in the present system developed in this study in order to calculate the crack opening displacement. The fatigue crack growth test were performed in SUS304 stainless steel compact tension specimens at several temperature up to 500degC. Crack closure monitoring was successful for all the tests in this study. A discussion was included on the influence of compressive stressing on the fatigue crack growth rate and closure. (author)