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Register a new userMarkov Property of Continuous Dislocation Band Propagation
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Added by
Arnomitra Chatterjee
Publication date
2008
fields
Physics
and research's language is
English
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Tensile tests were carried out by deforming polycrystalline samples of substitutional Al-2.5%Mg alloy at room temperature for a range of strain rates. The Portevin-Le Chatelier (PLC) effect was observed throughout the strain rate regime. The deformation bands in this region are found to be of type A in nature. From the analysis of the experimental stress time series data we could infer that the dynamics of type A dislocation band propagation is a Markov process.
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We study the formation of frequency band gaps in single column woodpile phononic crystals composed of orthogonally stacked slender cylinders. We focus on investigating the effect of the cylinders local vibrations on the dispersion of elastic waves along the stacking direction of the woodpile phononic crystals. We experimentally verify that their frequency band structures depend significantly on the bending resonant behavior of unit cells. We propose a simple theoretical model based on a discrete element method to associate the behavior of locally resonant cylindrical rods with the band gap formation mechanism in woodpile phononic crystals. The findings in this work imply that we can achieve versatile control of frequency band structures in phononic crystals by using woodpile architectures. The woodpile phononic crystals can form a new type of vibration filtering devices that offer an enhanced degree of freedom in manipulating stress wave propagation.
We employ the methods of atomistic simulation to investigate the climb of edge dislocation at nanovoids by analyzing the energetics of the underlying mechanism. A novel simulation strategy has been demonstrated to estimate the release of surface energy of the nanovoid during the void induced climb. The curvature of the pinned dislocation segment is found to play a key role in mediating this unique mechanism of dislocation climb. Our study reveals that the kinetics of void-induced climb process is fundamentally distinct from the conventional diffusion-mediated climb.
Pinning of dislocations at nanosized obstacles like precipitates, voids and bubbles, is a crucial mechanism in the context of phenomena like hardening and creep. The interaction between such an obstacle and a dislocation is often explored at fundamental level by means of analytical tools, atomistic simulations and finite element methods. Nevertheless, the information extracted from such studies has not been utilized to its maximum extent on account of insufficient information about the underlying statistics of this process comprising a large number of dislocations and obstacles in a system. Here we propose a new statistical approach, where the statistics of pinning of dislocations by idealized spherical obstacles is explored by taking into account the generalized size-distribution of the obstacles along with the dislocation density within a three-dimensional framework. The application of this approach, in combination with the knowledge of fundamental dislocation-obstacle interactions, has successfully been demonstrated for dislocation pinning at nanovoids in neutron irradiated type 316-stainless steel in regard to both conservative and non-conservative motions of dislocations.
The classical motion of gliding dislocation lines in slip planes of crystalline solid helium leads to plastic deformation even at temperatures far below the Debye temperature and can affect elastic properties. In this work we argue that the gliding of dislocations and plasticity may be the origin of many observed elastic anomalies in solid He-4, which have been argued to be connected to supersolidity. We present a dislocation motion model that describes the stress-strain $tau$-$epsilon$ curves and work hardening rate $dtau/depsilon$ of a shear experiment performed at constant strain rate $dot{epsilon}$ in solid helium. The calculated $dtau/depsilon$ exhibits strong softening with increasing temperature due to the motion of dislocations, which mimics anomalous softening of the elastic shear modulus $mu$. In the same temperature region the motion of dislocations causes dissipation with a prominent peak.
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