Ductile failure under combined shear and tension

The aim of this paper is to establish the extent to which materials can be deformed under shear-dominant loadings. Custom Al-6061-T6 tubular specimens are loaded under radial paths of tension and shear to failure. During the experiments, the deformation is monitored in a test section designed to have nearly uniform stress and deformation at large strains while providing minimum constraint to the development of localization that precedes failure. The recorded shear stress-rotation and axial stress-displacement responses exhibit maxima beyond which deformation localizes in a narrow band that is of the order of the 1 mm wall thickness of the test section. For the mainly shear dominated stress paths followed, deformation remained nearly planar allowing for the establishment of both the true stresses and the local deformation strictly from measurements. Results from thirteen radial path experiments show the strain at failure to monotonically increase as the mean stress decreases, a result that is in contrast with previously reported results for Al alloys. In addition, the measured failure strains are significantly larger than previously reported values. Furthermore, statistical grain-level strain estimates revealed a significant variation in strain across the macroscopically observed localization zone, with strains reaching 25–100% higher levels than the macroscopic values. This indicates that localization also occurs at a smaller scale than hitherto understood. Scanning electron microscopic evaluation of the failure zones showed that for this material, void formation and coalescence is delayed until the very end of the life of the deforming material.