Investigation of the PLC Effect Using DIC

Abstract

In certain alloys non-homogeneous plastic flow is observed. A category of jerky flow, also called the Portevin-Le Chatelier (PLC) effect, is attributed to the competition between dislocation aging by solute atoms and plastic strain rate. In this study, the PLC effect was examined in an aluminum-magnesium alloy using digital image correlation (DIC) techniques. A cold rolling procedure was developed for Al5052-T0 specimens that resulted in repeatable jerky flow when tested in tension at nominal displacement rates that spanned three orders of magnitude. The tests were successful in producing repeatable propagating type bands of serrated flow, which resulted in serrations or stress drops on the stress versus time curve. Deforming specimens were photographed during testing, and the images were correlated using commercially available DIC software to determine local strains and local strain rates. The present study focuses upon type B, or hopping, bands. The DIC results revealed that the strain front moved along the length of the specimen and strains 1 to 2% higher were observed in the wake of the propagating bands. In addition, at least an order of magnitude increase in local strain rate corresponded to the band front as it moved through the specimen. At slower nominal displacement rates, the magnitude of the stress drops for type B bands was greater, but the number of stress drops was fewer for a given nominal displacement. The repeatability of this study shows that DIC provides an effective way to characterize this type of non-homogeneous or localized plastic flow.