Variational coarse-graining of lattice energies for crystal defects: Applications to partial dislocations and stacking faults

Ziel

Defects are omnipresent in crystalline materials and the understanding of their emergence and interaction is essential for the prediction of the macroscopic material behaviour. Thus, there is a huge interest to pass in a rigorous mathematical way from atomistic models for crystal defects to macroscopic models, e.g. for crystal plasticity. From a variational viewpoint this can be addressed by deriving effective limiting energies from lattice energies when the lattice spacing vanishes. A powerful method to carry out such a variational coarse-graining procedure is Gamma-convergence. In this framework we address here the variational coarse graining of lattice energies which capture the formation and interaction of defects of different dimension, namely partial dislocations and stacking faults. The splitting of dislocations into partial dislocations resulting in a stacking fault is a typical phenomenon of closed-packed crystalline structures. Thus, on the one hand we aim at proposing and analysing a suitable discrete model for partial dislocations and stacking faults in HCP, on the other hand we will embed this result into a broader context by investigating in a general framework the emergence of fractional vortices and string defects in XY-model type energies. Eventually, we will characterise geometric properties of minimisers for the coarse-grained energies.

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