Results 1 - 10 of 2041
Results 1 - 10 of 2041. Search took: 0.021 seconds
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[en] The speed-stress relation for gliding edge dislocations was experimentally measured for the first time. The experimental system used, a two-dimensional plasma crystal, allowed observation of individual dislocations at the ''atomistic'' level and in real time. At low applied stress dislocations moved subsonically, at higher stress their speed abruptly increased to 1.9 times the speed of shear waves, then slowly grew with stress. There is evidence that immediately after nucleation dislocations can move faster than pressure waves.
[en] Based on the fundamental equations of magnetoelectroelastic material and the analytic theory, and using the Muskhelishvili-introduced well-known elastic techniques combined with the superposition principle, the closed form solution of the generalized stress field of the interaction between many parallel screw dislocations and a semi-infinite crack in an infinite magnetoelectroelastic solid is obtained, on the assumption that the surface of the crack is impermeable electrically and magnetically. Besides, the Peach–Koehler formula of n parallel screw dislocations is given. Numerical examples show that the generalized stress varies with the position of point z and is related to the material constants. The results indicate that the stress concentration occurs at the dislocation core and the tip of the crack. The result of interaction makes the system stay in a lower energy state. (paper)
[en] The explicit expressions for critical stress intensity factors are derived for edge dislocation emission from an elliptically blunt crack with surface effects under mode I and mode II loadings. The influence of surface effects on dislocation emission criterion is analyzed. The result indicates the impact of the surface stress becomes remarkable for nanoscale blunted cracks and some particular materials, which cannot only affect the value of the critical stress intensity factors for dislocation emission, but also alter the emission angle.
[en] Experimental results on the dislocation dynamics in a two-dimensional plasma crystal are presented. Edge dislocations were created in pairs in lattice locations where the internal shear stress exceeded a threshold and then moved apart in the glide plane at a speed higher than the sound speed of shear waves, CT. The experimental system, a plasma crystal, allowed observation of this process at an atomistic (kinetic) level. The early stage of this process is identified as a stacking fault. At a later stage, supersonically moving dislocations generated shear-wave Mach cones
[en] There are two distinct approaches to the description of dislocations in solids. Often discrete dislocation modelling is too time-consuming and computationally intensive, whereas the solution of the equivalent problem in a continuum approximation can be obtained relatively easily. Although such solutions can provide information about the macroscopic stress it cannot be applied at the scale of the separation between neighbouring dislocations. We have already provided robust proof of the interconnection between continuum and discrete approaches to dislocation description and suggested a methodology for analyzing pile-ups of screw and edge dislocations in a uniform material and a pile-up of screw dislocations near an interface in a bimetallic solid. Here it is developed further to derive the equilibrium distribution of n edge dislocations in a linear pile-up stressed against an interface in a bimetallic solid. As n → ∞ the dislocation positions are located with sufficient accuracy that the stress distribution can be evaluated by a simple computational procedure. The stress is determined from a lumped discretisation of superdislocations away from the interface. We present an example in which a hundred dislocations can be replaced by just four superdislocations with only 1% error in the computation.
[en] The interaction between an edge dislocation and a crack emanating from a semi-elliptic hole is dealt with. Utilizing the complex variable method, closed form solutions are derived for complex potentials and stress fields. The stress intensity factor at the tip of the crack and the image force acting on the edge dislocation are also calculated. The influence of the morphology of the blunt crack and the position of the edge dislocation on the shielding effect to the crack and the image force is examined in detail. The results indicate that the shielding or anti-shielding effect to the stress intensity factor increases acutely when the dislocation approaches the tip of the crack. The effect of the morphology of the blunt crack on the stress intensity factor of the crack and the image force is very significant. (condensed matter: structure, thermal and mechanical properties)