抄録
Application of the unloading method to measure the elastic-plastic fracture toughness JIC of ductile iron was studied and the following results were obtained; the inclination of the load versus load line displacement curve at the initial loading period becomes somewhat smaller than those of the unloading lines of the early unloading times and it results in negative values in calculation on crack growth, however an appropriate R-curve can be obtained by shifting the entire curve following to the behavior of the crack growth calculated from each unloading compliance.
