A Unified Representation of Stress-Strain Curves in Reversed Direction of Prestrained Cell-Forming Metals

Abstract

A model of the Bauschinger effect for cell-forming metals is summarized, in which a strain in the reversed direction is caused by “unpiling” of dislocations dynamically piled up in the cell interior during prestraining. The model suggests that, if both stress, σ, and strain, ε_r, in the reversed direction are normalized by the prestress, σ_p, σ⁄σ_p vs ε_r⁄σ_p curves become coincident with one another.
Except after prestraining to small strains (<∼3%), the normalization by σ_p was found to be applicable to changes in prestrain and grain size in room-temperature deformation of aluminium and copper, the normalized curves for different prestrains and grain sizes becoming similar in shape. This indicates that the present model can explain the Bauschinger effect so far as the cell structure forms during prestraining. However, the normalization by σ_p⁄μ (μ: the shear modulus) failed for changes in deformation temperature and stacking-fault energy, namely for a change in the nature of dislocation structure (that is, for the conversion of cell structure to subgrain structure or to planar arrays of dislocations). For presenting a more widely applicable model, a quantitative change in a ratio of the number of dynamically stored dislocations during prestraining to that of total dislocations (namely, a fraction of reversely mobile dislocations) with dislocation structure must be taken into consideration.