Three-Dimensional Structure of Portevin-Le Chatelier Bands and Shear Bands in Strip Cast AA5754 Sheets Using Digital Image Correlation 2007-01-1381

Strip cast AA5754 sheets are of interest for automotive interior panel applications. However, Portevin-Le Chatelier (PLC) bands are seen in this material and cause surface quality concerns. Moreover, shear banding is the main failure mechanism of this material. However, the relationship between PLC bands and shear bands is still controversial in the literature. In order to delineate this problem, the digital image correlation (DIC) strain mapping technique is used to explore the three-dimensional structures of PLC bands and shear bands in AA5754 sheets.

Two-dimensional DIC measurements were carried out simultaneously on both of the sheet sample surfaces (front and back side) of an AA5754 tensile sample using a commercially available optical strain mapping DIC-based system (Aramis). DIC measurements were also conducted on the thickness direction. Based on the strain mapping results, the three dimensional structures of both PLC bands and shear bands are constructed. The results show that the PLC bands penetrate through the thickness and carry small strain increments (2-3%) higher than the nominal applied strain. The shear bands penetrate through the thickness with a more complex three-dimensional structure and are independent of prior PLC bands. The development of PLC and shear bands changes with tensile stress state (uniaxial tension and plane strain tension) and strain rate.