Microscopic evaluation of plastic deformation during back-and-forth bending of polycrystalline pure titanium specimen with a pair of parallel grooves using arranged marks at lattice points

A single-cycle bending test of polycrystalline pure titanium was carried out using a rectangular specimen with a pair of parallel grooves. The plastic deformation in a long part between these grooves was observed at every quarter cycle of back-and-forth bending. Before the test, multiple square marks of gold were made at the lattice points having a mutual distance of 12.5 μm in the region of interest by ion-coater. The strain and rotation during the test were evaluated based on the displacement of these gold marks. The following results were obtained: (1) The region of interest between grooves showed plastic deformation during bending, and the deformation was mainly caused by slips. Twining was also observed in some grains. (2) The strain and rotation during the bending were not uniform grains to grains. The shearing strain was small compared with the normal strains and rotation. (3) The region, which showed a larger normal strain at the first quarter cycle, continued to show a relatively large strain at the following quarter cycles in an opposite direction. Rotation showed a similar behavior. (4) Crystal orientation analysis was performed for grains with clear slip lines. The plastic deformation of these grains seemed to occur mainly by the prismatic slip.