Papers by Keyword: Dislocation Source

Abstract: As a result of the work of Frank-Read dislocation source the shear zone is formed. It is filled with deformation defects forming as a consequence of the dynamic features of the motion of dislocation loops and due to the interaction of shear forming dislocations with dislocations of non-coplanar slip systems. The accumulation of jogs on screw segments leads to the fact that the edge segments are moving faster than the screw segments so the shear zone is swept out generally by screw segments. The expressions of the intensities of the deformation defects accumulation in shear zones are given in the article. The point defects plays special role in the formation and evolution of misorientation substructures into deformed monocrystals, polycrystals and nanocrystals.

Abstract: This paper presents synthesis of acoustic-emission (AE) wave propagation in multi-layer materials and simulation of AE wave responses at free surface. In particular, the AE source is modelled as an arbitrary-orientation dislocation over an inclined-to-surface fault within one layer or at the layer-to-layer interface, while the materials are assumed as multi-layer media, each of which is homogeneous, isotropic and linearly elastic. With the use of the integral transformation approach, the three-dimensional wave propagation in the materials is solved in transformed or frequency-wavenumber domain. Subsequently, a closed-form solution for wave responses at free surface is found, which can then be converted in time-space domain. Numerical examples are finally provided for illustration.

Abstract: This paper presents synthesis of acoustic-emission (AE) wave propagation in multi-layer materials and simulation of AE wave responses at free surface. In particular, the AE source is modelled as an arbitrary-orientation dislocation over an inclined-to-surface fault within one layer or at the layer-to-layer interface, while the materials are assumed as multi-layer media, each of which is homogeneous, isotropic and linearly elastic. With the use of the integral transformation approach, the three-dimensional wave propagation in the materials is solved in transformed or frequency-wavenumber domain. Subsequently, a closed-form solution for wave responses at free surface is found, which can then be converted in time-space domain. Numerical examples are finally provided for illustration.

Abstract: Macroscopic mechanical response of metal polycrystal with mean grain diameter of 0.2 to 5 microns are simulated by a strain gradient crystal plasticity software code which incorporates some phenomenological models for dislocation accumulation and annihilation, as well as dislocation-grain boundary interactions. Obtained results of macroscopic stress-strain relation show significant increase of yield stress and strain hardening ratio for fine grained specimens.

Abstract: The deformation mechanism in the nanometer grain size range has been basically investigated from the results of microstructural observation after superplastic deformation in a Zn-Al eutectoid alloy in which a reverse grain size dependence of superplasticity was previously reported: flow stress increases and elongation decreases with decreasing grain size when grain size is markedly reduced to nanometer range. By controlling the aging condition after solution treatment and subsequent quenching, two specimens are prepared: the as-quenched specimen with ultrafine grains of 83nm in diameter and aged specimen with normally fine grains of 2.6μm. The elongation is confirmed to be smaller in the as-quenched specimen than in the aged specimen, although the flow stress is lower. As a result of TEM observation on the interior of the grains, dislocations are rare in the as-quenched specimen, while a significant density of dislocations are observed in the aged specimen. This result strongly supports the mechanism previously proposed by Mishra et al. that the accommodation process, i.e., the dislocation glide inside the grains, becomes more difficult with decreasing grain size in the nanometer grain size range, even though the grain boundary sliding as the major process becomes facilitated. Roughly assessed m-value was in accord with this mechanism.