Structure and Strength of Dislocation Junctions: An Atomic Level Analysis

The quasicontinuum method is used to simulate three-dimensional Lomer-Cottrell junctions both in the absence and in the presence of an applied stress. The simulations show that this type of junction is destroyed by an unzipping mechanism in which the dislocations that form the junction are gradually pulled apart along the junction segment. The calculated critical stress needed for breaking the junction is comparable to that predicted by line tension models. The simulations also demonstrate a strong influence of the initial dislocation line directions on the breaking mechanism, an effect that is neglected in the macroscopic treatment of the hardening effect of junctions.Comment: 4 pages, 3 figure

Mesoscopic Analysis of Structure and Strength of Dislocation Junctions in FCC Metals

We develop a finite element based dislocation dynamics model to simulate the structure and strength of dislocation junctions in FCC crystals. The model is based on anisotropic elasticity theory supplemented by the explicit inclusion of the separation of perfect dislocations into partial dislocations bounding a stacking fault. We demonstrate that the model reproduces in precise detail the structure of the Lomer-Cottrell lock already obtained from atomistic simulations. In light of this success, we also examine the strength of junctions culminating in a stress-strength diagram which is the locus of points in stress space corresponding to dissolution of the junction.Comment: 9 Pages + 4 Figure

Dislocation Plasticity of Al Film on Polymer Substrate Studied by In-situ TEM Tensile Testing

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Size-dependent martensitic transformation path causing atomic-scale twinning of nanocrystalline

Nanocrystalline \chem{NiTi} alloys were processed by devitrification of an amorphous phase to elucidate the impact of the nanocrystallinity on the thermally induced martensitic phase transformation. Forced by a size-dependent strain energy barrier, atomic-scale twinning leads to a unique path of the martensitic phase transformation. The observed twin boundaries of very low energy facilitate arrays of compound twins on atomic scale to overcome the strain energy barrier of the nanograins thus violating the hitherto well-established theory of martensite formation