Abstract
In this paper, to confirm the validity of a new determination method of ductile fracture material parameters using bore expanding test, strain in the necking area is evaluated qualitatively. Bore expanding test specimen with fine grids on the surface is used to measure the strain in the necking area. The grid length by micro scope is measured, and radial strain, circumferential strain and equivalent strain are obtained to evaluate necking evolution. In addition to qualitative evaluation of strain in the necking area, validation of the proposed method is confirmed through fine detail observation on neck initiation and its evolution by a digital laser microscope. Compared between the shift of strain values and fine observation of surface, necking behavior near the bore edge is discussed.
