パンチ穴材引張過程中のせん断き裂の変形におけるせん断影響域の作用

抄録

We investigate the occurrence and growth behavior of the semicircular cracks caused by shear (hereinafter referred to as "shear cracks"), which is the first stage of tensile fracture of hole steel plates subjected to punch process (hereinafter referred to as "punched materials"). Punched material is widely used for automobile because of its low cost. When a punched material is subjected to a tensile load, a shear affected zone (SAZ) by the punch process exists within a certain depth range near the punched hole edge, and make the strength characteristics of the punched materials be worse than those holed materials by drilling and hole inner surface polishing (hereinafter referred to as "ideal materials"); particularly, punched materials of some steel types can be brittlely fractured. And then, different from the ideal material, no matter the fracture types be a ductile failure or be a brittle fracture, in the initial stage of the fracture of the punched material, there is a semi-elliptical crack occurred by shearing at an inclination with the tensile direction, which is called "shear crack." In this research, we used the punched material which was reported to be brittle fracture at the static strain rate, the results of both ductility and brittleness were obtained by tensile tests at several strain rates. Shear cracks in both the ductile and the brittle fracture surfaces occurs in multiple stages. The timing and driving force of these several stages were considered, the fracture process of both ductility and brittleness was clarified, and the factors that influence the process were also clarified.