Subsequent Yield Surfaces for Annealed Mild Steel Under Servo-Controlled Strain and Load Histories: Aging, Normality, Convexity, Corners, Bauschinger and Cross Effects

Abstract

Initial-yield results on SAE 1017 steel are presented for: four different specimens under combined axial load and twisting moment for servo controlled loading; and six different specimens under various combinations of servo controlled axial strain and shear strain. Subsequent yield curves determined by small strain offset multiple probes on a given specimen are presented covering all four quadrants of axial stress-shear stress space. The resulting families of subsequent yield curves allows conclusions to be drawn concerning the effects of plastic strain and strain aging. All curves were found to be convex and normality of the plastic strain increment vector was obeyed. The response to plastic straining allowed discussion of corner formation, translation, rotation, Bauschinger and cross effects of subsequent yield curves and formation of a limit curve. A comparison is made between the experiments and the Prager kinematic hardening model and the Ziegler modification.

Concerning Cusps and Vertices on the Yield Surface of Annealed Mild Steel

“…It may also be noted that the loadings (straining) employed in [2, 31 to disturb the yield surface after the first loading involved plastic strains of the order of 0.000,35. These strains are of the same order of magnitude as those used by GUPTA and LAUERT in probing the yield surface yet the plastic strainings in [2,3] caused considerable translations and changes in shape of the subsequent yield surface as reported in [Z, 31. On the other hand, GUPTA and LAUERT [ l ] reported no effect on the subsequent yield curve of probes involving off-set strains even 10 times as much as the plastic strains involved in [2].…”

“…I n several instances in [2,3] straining was performed by alternate steps of tension then torsion. The accompanying strain increment vector generally showed no marked change in direction with change in loading direction as would be expected if the loading produced a rounded nose rather than a pointed vertex.…”

“…Considerable strain aging was observed t o occur after 24 t o 72 hours following loading. This aging resulted in an expansion of the subsequent yield curve with some translation of the center of the yield curve in a direction opposite t o the direction of prior loading in the several examples in [3]. Figure 2 shows one example which, however, involved yielding on unloading prior to aging.…”

“…A total of 46 subsequent yield surfaces were determined on 11 specimens using a small-strain technique with dead weight load control in [ 2 ] and both servo-hydraulic load and strain control in [3]. The probes, load or strain increments, were controlled manually by either precise load increments with dead weight or careful servo-control.…”

Stress analysis and testing of the outer capsule design for the Strontium Heat Source Development Program

“…However, details of the experimental conditions and materials involved were insufficient to draw any general conclusions. Michno and Findley (1975) have conducted extensive experiments on SAE-1017 steel. All data were generated for biaxial stress states.…”