Characterization of the deformation behaviors associated with the serrated flow of a 5456 Al-based alloy using two orthogonal digital image correlation systems

The spatio-temporal characteristics associated with the Portevin–Le Chatelier (PLC) effect in a 5456 Al-based alloy were investigated by employing two orthogonal digital image correlation systems. This investigation yielded the first-ever experimental observations of the strain localization in the thickness direction, which was measured to be homogenous along the thickness of the specimen. In fact, this localization was more severe in the thickness plane than in the widthwise plane. This confirmed that the assumption of a plane-stress state is invalid for specimens, which are susceptible to the PLC effect. With respect to the deformation mode of the PLC bands, the localized region in the thickness and widthwise planes were actually in an unequal biaxial stress state and a state of simple shear, respectively. The deformation continuity of the boundary corresponding to the widthwise and thickness planes was discussed on the basis of the experimental data. Moreover, two different fracture modes, i.e., the shearing-to-opening mode and the pure shearing mode, were proposed. The aforementioned observations can provide new insights into the deformation behaviors of the plastic instabilities, especially as it relates to the numerical modeling of the morphology and propagation of the PLC band.