Improved Method for Δ<i>K</i> decreasing Fatigue Crack Growth Test and Crack Closure Measurement－Toward Establishment of JIS Standard

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 ΔKeff 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.