Subsequent Yield Surfaces for Annealed Mild Steel Under Dead-Weight Loading: Aging, Normality, Convexity, Corners, Bauschinger, and Cross Effects

Subsequent yield curves covering all four quadrants of axial stress-shear stress space were experimentally determined for SAE 1017 steel. Initial-yield test results for six different specimens under various combinations of axial load and twisting moments for dead-weight loading exhibited too much scatter to provide a definitive surface. However, after initial yielding of one to five percent a family of small-offset multiple probe yield curves was determined for each specimen. Subsequent curves in a given family of curves were derived from the preceding curves by either strain aging or loadings into the plastic range. Plastic stream increment vectors for zig-zag loading paths were determined. In general, natural aging and plastic straining resulted in smooth yield curves. There was some evidence to support occasional formation of well-rounded blunt corners under combined axial and shear loading. Subsequent yield surfaces underwent translation and changes in shape, and exhibited considerable Bauschinger and cross effects. In agreement with the maximum plastic work inequality all yield curves were convex and normality was obeyed.