ACOUSTIC-EMISSION MEASUREMENT OF FATIGUE-CRACK CLOSURE

The COD and BFS methods show relatively good agreement with each other and measure the through-thickness mean value of crack closure loads. In the plane strain condition, the crack closure levels obtained by the COD and BFS methods were lower than those by the AE and surface strain gage methods. The data obtained by the surface strain gage method must be interpreted carefully, because the shape of the compliance curves is affected by the location relative to the crack tip. The intrinsic fatigue life curve ( da dN vs. ΔKeff) obtained by the AE technique fitted well with the curve of high stress ratio (R = 0.8) test at high ΔK, suggesting that the AE technique is sensitive to local crack-tip behavior on a microscopic scale and can be considered as a reliable measurement method for crack closure phenomena under repetitive loads. © 1995.