Electron microscopic observations, of the distribution of dislocations around non-deformable particles in a matrix of plastic crystalline metal, revealed a clear transition from laminar plastic flow to so-called rotational flow at a critical strain which depended mainly upon the particle size; with larger particles exhibiting smaller critical strains. These patterns were produced by plastic relaxation of the internal stresses caused by deformation. Although there seemed to be no certain method for predicting the patterns on the basis of continuum mechanics or dislocation mechanics, it was possible to devise simple models (involving a combination of dislocation theory and continuum patterns of flow) which helped to explain the transition and to predict the distribution of misorientations in the rotational structures. The results had important implications for the understanding of recrystallization phenomena and work-hardening behaviour. It was suggested that indentation plasticity might behave similarly.

Transition from Laminar to Rotational Motion in Plasticity. L.M.Brown: Philosophical Transactions of the Royal Society, 1997, 355, 1979-90