Anisotropic strain localization in tensile prestrained sheet steel

Abstract

Multiple forming operations are often needed to stamp complex shapes out of sheet metal. Large changes in strain path can occur from such operations. This study examined the effects of a particular strain path change, tensile-tensile, on the mechanical properties of an aluminum-killed steel. Large tensile specimens were prestrained various amounts in one direction followed by machining smaller tensile specimens at 0, 45, and/or 90 deg to the prestrain direction. The smaller samples were then pulled to failure. For samples pulled in the same direction as the prestrain, the residual strength and ductility were equivalent to those obtained from an interrupted tensile test. In contrast, both the 45 and the 90 deg prestrained specimens showed a larger than expected flow stress and an abrupt change in the nature of the residual ductility at prestrains of 7.5 pct and larger. At 7.5 pct prestrain, the uniform strain, as measured by the maximum-load point on the load vs elongation tensile curve, decreased abruptly. The decrease was accompanied by a corresponding increase in the post-uniform strain. This unusual behavior is explained in terms of a rapid increase in strain-hardening with strain.