Host: The Iron and Steel Institute of Japan
Pages 173-176
The strain distribution within a final fracture region, i.e., necking deformation region, in the tensile test was visualized by using a combination of replica and digital image correlation methods, and then the relationship between inhomogeneous strain distribution and fracture behavior in martensitic steel was discussed. Strain was inhomogeneously distributed at an initial stage of tensile deformation (before necking deformation). The positions of high- and low-strain regions were maintained from the initial stage of deformation to just before fracture, indicating that more strain concentration occurs at high-strain regions with progressing tensile deformation. In several regions, the values of cumulative εMises were considerably high exceeding 0.8 at just before fracture. It suggests that a portion of the martensitic structure has a large ductility. Cracks nucleated during necking deformation, and the crack positions tended to be high-strain regions. Strain concentration owing to the crack is one of the reasons for this. However, the histogram of the ratio of the local εMises in crack nucleation regions to average εMises calculated from the εMises strain distribution map at a uniform strain revealed that the crack positions are located at high-strain regions even before crack nucleation. Thus, it can be concluded that crack nucleation is easy in high-strain regions and high strain is one of the factors for crack nucleation.
