Following the discussion of cyclic deformation in ductile single crystals, we now direct attention to polycrystalline metals and alloys. Firstly, experimental observations are discussed to show how the cyclic deformation of single crystals oriented for multiple slip can be correlated with that of polycrystalline aggregates. Continuum characterization of cyclic hardening and softening of polycrystals is addressed, along with the effects of slip characteristics, alloying and precipitation. The Bauschinger effect is then introduced, wherein both microscopic and continuum viewpoints are presented to rationalize the dissimilar yield responses seen in tension and compression during load reversals. Continuum models for uniaxial and multiaxial cyclic deformation, which are of interest for engineering structures, are the focus of subsequent sections. Lower bound and upper bound theorems for elastic shakedown under cyclic loading are presented, and the origins of cyclic creep and ratchetting are then examined. The chapter concludes with the derivation of critical temperatures which signify distinct transitions in the cyclic deformation characteristics of particle-reinforced metal-matrix composites and layered materials. While this chapter confines attention to ductile crystalline solids, the cyclic deformation characteristics of brittle solids as well as semi-crystalline and noncrystalline solids are taken up in Chapters 5 and 6.

Effects of grain boundaries and multiple slip

The mechanisms of cyclic damage observed in ductile single crystals are also known to be generally applicable to the deformation of near-surface grains in polycrystalline metals of high purity.