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

• The out-of-plane displacement within the PLC band is firstly obtained.
• The displacement gradient is greater in the front of the PLC band than in the rear.
• There is a slight relative torsion around tensile axis when the PLC band appears.
• The process of position changing of the PLC band is firstly presented.
• The transition process of inclination direction of the PLC band is shown in detail.

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.