A NOTE ON YIELD CURVES IN CYCLIC WORK SOFTENING

Cyclic work softening is a transient behavior which occurs at the beginning of fatigue tests and reduces the mechanical strength of the material. Softening is likely to occur in hard materials under low cycle fatigue conditions. A method is described by which cyclic softening or hardening can be predicted from the monotonic properties of the material. The mechanisms which produce softening are not completely understood but appear to vary depending on the mechanisms which produce the hardening of the material. Since cyclic softening is an unstable behavior, it cannot be described by any stable material models. Tests on 1100-H14 aluminum indicate that the material softens under cyclic torsion and that the softening causes only a very small reduction in the tensile strength.