A Method of Determining the Stress Effective during Lüders Band Propagation

Abstract

IN materials which exhibit a well-defined yield-point drop followed by non-uniform yielding at a nearly constant stress, this stress is given by the Patch equation¹ as: where σ_y is the lower yield stress, σ_i is the friction stress, k_y is a term originally thought to be associated with an unlocking stress and 2d is the grain diameter. It is desirable to have an accurate value of the macroscopic stress, σ_y, in order that the slope of the lower yield stress vs. grain size curve, k_y, be as meaningful as possible. In addition, the dependence on temperature of the lower yield stress is an important property in theoretical considerations. Difficulties may arise, however, in determining what value of the lower yield stress to use in such situations. This communication describes a method which can be used to determine, at least in an approximate manner, whether the magnitude of any corrections to the nominal yield stress is sufficiently large to warrant consideration.