Non-uniform Deformation Behavior of Coarse-grained Ultralow Carbon Steel Measured Using Digital Image Correlation Method

In this work, non-uniform deformation behavior of coarse-grained ultralow carbon steel was investigated under uniaxial tension and cyclic simple shear. A digital image correlation method was used to measure strain fields at the grain level. Heterogeneous strain distribution appeared at the early stage of the process, and the heterogeneity remained almost unchanged in the subsequent deformation. Localized strain bands were observed under both uniaxial tension and simple shear, but the directions of the bands were different between the two deformation modes. It was hypothesized that the directions of the strain bands were correlated with the planes where the maximum or minimum shear stresses occurred. During cyclic simple shear, the heterogeneity of strain distribution and occurrence of strain bands depended on the shear direction. In contrast, the number of cycles had little effect on the heterogeneity of strain distribution. Comparing the grain boundaries and the strain distributions, it was observed that many of the strain-band boundaries occurred along the grain boundaries, but some of them appeared within grains.