Reverse shearing of shear bands in polystyrene

Abstract

Shear bands produced in polystyrene by compression can be reverse sheared by a second compression in a perpendicular direction. The net shear strain can be zero or negative. Like the forward shear, the reverse shear also produces a ridge on the surface. The height of the ridge seems to be proportional to the reverse shear strain. On the side surface the reverse shear produces a step whose height increases at an average rate of 1.17 mm sec⁻¹ (at a crosshead speed of 1 mm sec⁻¹), estimated by high-speed cinematography at 1000 frames sec⁻¹. During the reverse shear the second compression experiences a yield drop whose size increases with the forward strain due to the first compression. The implications of these results are discussed.