Improved Method for ΔK decreasing Fatigue Crack Growth Test and Crack Closure Measurement－Toward Establishment of JIS Standard

Abstract

The effect of the applied force shedding rate on the da/dN-ΔK relationship near the threshold region was investigated using two types of metals, and it was found that the da/dN-ΔK relationship is independent of the applied force shedding rate for shedding interval of 50 μm and the shedding rate less than 2%. In the crack opening measurement by the compliance method, the crack opening point can be clearly identified and the effective stress intensity factor range ΔK_eff can be automatically determined by averaging the strains in loading and unloading, and using a normalized-strain and applied force relationship, where the normalized is accomplished by strain divided by the linear strain at the same applied force.