Constant intermittent flow of dislocations: Central problems in plasticity

Plastic flow is never a continuous process either in time or in space, yet it continues to be modelled in this way. In this review, plasticity is discussed from the perspective of self-organised criticality (SOC). The following topics are discussed: slip bands and models for them; how crystallographic is slip?; distributed sources and collective motion of dislocations; the triumph and the failure of the Taylor model; long range stress does not contribute directly to the flow stress, so the forest rules; the perils of coarse-graining and the relationship between smoothed engineering variables and intermittently fluctuating physical variables; work-hardening of a slip band; what controls the structure of slip bands?; interpretation of precursor and exhaustion phases; relationship to other recent theories; consequences which follow from a sound theory of plastic flow. Brief appendices present algebraic results for slip bands modelled as ellipsoids.