A method for determining r-value of aluminum sheets with the Portevin-Le Chatelier effect

Lankford coefficient (r-value) is an important parameter for metal sheet. For sheet metals with obvious Portevin-Le Chatelier (PLC) effect, the r-values are difficult to measure owing to the occurrence of inhomogeneous deformation. In this paper, the PLC bands of AA3104-H19 sheet were investigated by uniaxial tensile test with digital image correlation (DIC) technology. The result showed that inclination of the PLC band keeps invariable with respect to loading direction with straining. The constancies of PLC band angle and r-value are result from the limit of texture evolution during tensile test. Additionally, an analytic relationship between the PLC band inclined angle and r-value was derived based on the observation of zero-expansion along the PLC band direction. Accordingly, a novel r-value determining method based on the PLC band was proposed. The accuracy of the new method was evaluated by comparing with the extensometer method, DIC method and crystal plasticity simulation.