There is considerable experimental evidence that over length scales of the order of microns and smaller the plastic response of crystalline metals differs from the predictions of conventional continuum plasticity. In particular, the plastic response of crystalline metals is often size dependent over this length scale. The size dependence arises in a variety of contexts; e.g. micro-and nano-indentation and the grain size dependence of the flow strength of polycrystals. There are also a variety of mechanisms that lead to this size dependence including imposed plastic strain gradients and geometrically necessary dislocations, and the discreteness of dislocation sources. Recent discrete dislocation plasticity analyses of various plastic flow processes are used to illustrate a range of size effects and the scaling, both with respect to size and with respect to material properties, that emerge from the calculations.
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