Strain characterization of propagative deformation bands

An experimental study on the formation and evolution of strain inhomogeneity in the form of deformation bands on the surface of polycrystalline sheet metals is presented. A whole field in-plane deformation measurement technique based on computer vision has been applied for in situ monitoring the development of plastic deformation patterns in annealed Al-5 % Mg and recovered AA5182 aluminum sheet metals. The strain inhomogeneity over a rectangular area about 5 mm x 3 mm on the sheet metal surfaces is found to increase steadily with increasing elongation during a uniaxial tensile test. Propagative deformation bands have been detected in both aluminum alloys by incremental strain mapping although no band-like deformation patterns can be identified by direct visual observation of Al-5% Mg specimen surfaces. The effect of plastic deformation patterns on surface finish, tensile ductility, and formability of sheet metals are elucidated. The approach and results of this experimental investigation can be valuable to physically-based multiscale plasticity modeling of sheet metal forming. (C) 1998 Elsevier Science Ltd. All rights reserved.