| Interfaces are explicitly accounted for, within gradient plasticity, by assigning a finite thickness to the interface or grain boundary and by differentiating between the constitutive properties of the "grain boundary" phase and the adjacent "bulk" phase. The present model is applied to consider the deformation of micro- and nano- crystalline materials under constant load or constant displacement rate conditions. The corresponding stress-strain curves exhibit serrations as observed experimentally during nanoindentation or microtensile tests: "plateaus" or "strain bursts" in the case of a constant load rate and "serrations" or "stress drops" in the case of a constant displacement rate. Such a genuine and routinely observed phenomenon when the deformation process is experimentally monitored by sufficiently sensitive devices in a variety of material classes is the main feature of the present contribution; a feature that has not been captured theoretically before with a simple analytical gradient plasticity model. |
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