Amorphous solids lack long-range order. Therefore identifying structural defects -- akin to dislocations in crystalline solids -- that carry plastic flow in these systems remains a daunting ...challenge. By comparing many different structural indicators in computational models of glasses, under a variety of conditions we carefully assess which of these indicators are able to robustly identify the structural defects responsible for plastic flow in amorphous solids. We further demonstrate that the density of defects changes as a function of material preparation and strain in a manner that is highly correlated with the macroscopic material response. Our work represents an important step towards predicting how and when an amorphous solid will fail from its microscopic structure.
We report our atomic-scale computations for the static depinning threshold of dislocations in Al(Mg) solid solutions. The interaction between the dislocations and the isolated obstacles is studied ...for different types of obstacle, i.e. single solute atoms situated at different positions, and solute dimers with different bond directions. Part of this work is used to apply different standard analytical theories for solid solution hardening, the predictions of which are finally compared with our direct atomic-scale simulations (AS) for dislocation depinning in random Al(Mg) solid solutions. According to our comparisons, the dislocation statistics in our AS is qualitatively well described by the Mott-Nabarro-Labusch theory. In agreement with earlier results about a different system, namely Ni(Al), the depinning thresholds are similar for the edge and for the screw dislocations.
Understanding the role played by the microstructure of materials on their macroscopic failure properties is an important challenge in solid mechanics. Indeed, when a crack propagates at a ...heterogeneous brittle interface, the front is trapped by tougher regions and deforms. This pinning induces non-linearities in the crack propagation problem, even within Linear Elastic Fracture Mechanics theory, and modifies the overall failure properties of the material. For example crack front pinning by tougher places could increase the fracture resistance of multilayer structures, with interesting technological applications. Analytical perturbation approaches, based on Bueckner–Rice elastic line models, focus on the crack front perturbations, and hence allow for a description of these phenomena. Here, they are applied to experiments investigating the propagation of a purely interfacial crack in a simple toughness pattern: a single defect strip surrounded by homogeneous interface. We show that by taking into account the finite size of the body, quantitative agreement with experimental and finite elements results is achieved. In particular this method allows to predict the toughness contrast, i.e. the toughness difference between the single defect strip and its homogeneous surrounding medium. This opens the way to a more accurate use of the perturbation method to study more disordered heterogeneous materials, where the finite elements method is less adequate. From our results, we also propose a simple method to determine the adhesion energy of tough interfaces by measuring the crack front deformation induced by known interface patterns.
Metamaterials enable the emergence of novel physical properties due to the existence of an underlying subwavelength structure. Here, we use the Faraday instability to shape the fluid-air interface ...with a regular pattern. This pattern undergoes an oscillating secondary instability and exhibits spontaneous vibrations that are analogous to transverse elastic waves. By locally forcing these waves, we fully characterize their dispersion relation and show that a Faraday pattern presents an effective shear elasticity. We propose a physical mechanism combining surface tension with the Faraday structured interface that quantitatively predicts the elastic wave phase speed, revealing that the liquid interface behaves as an elastic metamaterial.
The propagation of dislocations in random crystals is evidenced to be governed by atomic-scale avalanches whose the extension in space and the time intermittency characterizingly diverge at the ...critical threshold. Our work is the very first atomic-scale evidence that the paradigm of second order phase transitions applies to the depinning of elastic interfaces in random media.
Cracks in random brittle solids Patinet, S.; Vandembroucq, D.; Hansen, A. ...
The European physical journal. ST, Special topics,
10/2014, Letnik:
223, Številka:
11
Journal Article
Recenzirano
Odprti dostop
Statistical models are essential to get a better understanding of the role of disorder in brittle disordered solids. Fiber bundle models play a special role as a paradigm, with a very good balance of ...simplicity and non-trivial effects. We introduce here a variant of the fiber bundle model where the load is transferred among the fibers through a very compliant membrane. This Soft Membrane fiber bundle mode reduces to the classical Local Load Sharing fiber bundle model in 1D. Highlighting the continuum limit of the model allows to compute an equivalent toughness for the fiber bundle and hence discuss nucleation of a critical defect. The computation of the toughness allows for drawing a simple connection with crack front propagation (depinning) models.
On the basis of the classical dislocation theory, the Solid Solution Hardening (SSH) is commonly ascribed to the pinning of the edge dislocations. At the atomic level, the theoretical study of the ...dislocation cores contrasts with such a prediction. Using the static molecular simulations with some interatomic effective potentials, we demonstrate numerically that the critical resolved shear stress associated to a screw dislocation in a random Ni(Al) single crystal has same order as the edge one. Such a result is imposed by the details of the dislocation stacking fault and the core dissociation into Shockley partials. The SSH statistical theory is employed to tentatively predict analytically the data acquired through our atomistic simulations at different Al concentration.
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