Effect of Elongation of a Rod on Strain Inhomogeneity and Shape Change During the Compression-Type Forming Process

The influence of elongation on the strain inhomogeneity and shape change in twinning-induced plasticity steel rod is systematically investigated to understand the macroscopic shear band (MSB) formation mechanism and to decrease the strain inhomogeneity during the compression-type forming processes. Specimens fabricated by rod flat rolling with elongation (3D rod) and by plane compression without elongation (2D rod) are compared using both finite element analysis and experiment. Despite the similar final product shape, the 2D rod presents a lower effective strain at the surface region than the 3D rod, leading to a high strain inhomogeneity. The higher effective strain at the surface region of the 3D rod is mainly attributed to the elongation of the 3D rod during the rolling. In contrast, the 2D rod exhibits strong dead metal zones owing to the lack of elongation of the specimen. Therefore, the formation of MSBs or strain inhomogeneity of a specimen can be reduced by increasing the elongation of the specimens during the forming process. Both the contact width and lateral spread of the 3D rod are lower than those of the 2D rod because of the elongation of the 3D rod originating from the slip effect at the rod–roll interface during the rolling process. The small frictional effect at the rod and roll interface increased the elongation of the rod, leading to a decrease in the strain inhomogeneity and lateral spreading in the 3D rod.