17 research outputs found
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
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
martensiteĀ formation