Study on the out-of-plane deformation of the Portevin-Le Chatelier band by using digital shearography

摘要

The out-of-plane deformation of the Portevin-Le Chatelier (PLC) band is investigated during tensile tests in an Al alloy using digital shearography for the first time. The fringe patterns, which reflect the out-of-plane displacement gradient, indicate that the PLC bands also appear in the out-of-plane deformation field corresponding to the serrations in the stress-strain curve. Unlike the results obtained from other methods, the true bandwidth is determined by subtracting the shearing amount from the observed bandwidth. The continuous propagation of type-A PLC bands is traced at three different shearing amounts. The out-of-plane displacement of a PLC band is obtained based on the gray-level distribution in a frame of fringe pattern. The maximum displacement is approximately 250 nm in an interval of 1/15 s during a continuous propagation. The displacement gradient is greater in the front of the PLC band than in the back. Moreover, the position change process of the PLC band is presented, i.e., a band disappearing and a new band forming concurrently in another place. The inclination transition process, such that the inclination direction of the PLC band turns from the "/'' direction to the "'' direction, is also shown in detail. The results prove that the vibrations-proof and high sensitivity digital shearography is a valuable and important method in the investigation of the out-of-plane deformation of the PLC band. (C) 2015 Elsevier Ltd. All rights reserved.