Substitutional Al solute interaction with edge and screw dislocation in Ni: a comparison between atomistic computation and continuum elastic theory

Molecular static simulations have been performed to study the interaction between a single dislocation and a substitutional Al solute atom in a pure crystal of Ni. When the Al solute is situated at intermediate distance from the slip plane, we find that both edge and screw dislocations experiment a non-negligible binding energy. We show that for such length scale the description of the elasticity theory can be improved by taking into account the spreading of dislocation cores via the Peierls-Nabarro model

Quantitative prediction of effective toughness at random heterogeneous interfaces

The propagation of an adhesive crack through an anisotropic heterogeneous interface is considered. Tuning the local toughness distribution function and spatial correlation is numerically shown to induce a transition between weak to strong pinning conditions. While the macroscopic effective toughness is given by the mean local toughness in case of weak pinning, a systematic toughness enhancement is observed for strong pinning (the critical point of the depinning transition). A self-consistent approximation is shown to account very accurately for this evolution, without any free parameter

Cracks in random brittle solids: From fiber bundles to continuum mechanics

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.Comment: The European Physical Journal Special Topics Special Topics, 201

From depinning transition to plastic yielding of amorphous media: A soft modes perspective

A mesoscopic model of amorphous plasticity is discussed in the context of depinning models. After embedding in a d + 1 dimensional space, where the accumulated plastic strain lives along the additional dimension, the gradual plastic deformation of amorphous media can be regarded as the motion of an elastic manifold in a disordered landscape. While the associated depinning transition leads to scaling properties, the quadrupolar Eshelby interactions at play in amorphous plasticity induce specific additional features like shear-banding and weak ergodicity breakdown. The latters are shown to be controlled by the existence of soft modes of the elastic interaction, the consequence of which is discussed in the context of depinning

Dislocations pinning by substitutional impurities in an atomic-scale model for the Al(Mg) solid solutions

International audienceWe report our atomic-scale computations for the static depinning threshold of dislocations in the Al(Mg) solid solutions. The interaction between the dislocations and the isolated obstacles is studied for different types of obstacle, i.e., the single solute atoms situated at different positions and the solute dimers with different bond directions. A 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 the dislocation depinning in the 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

Atomic-scale avalanche along a dislocation in a random alloy

International audienceThe 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

Local yield stress statistics in model amorphous solids

We develop and extend a method presented in [S. Patinet, D. Vandembroucq, and M. L. Falk, Phys. Rev. Lett., 117, 045501 (2016)] to compute the local yield stresses at the atomic scale in model two-dimensional Lennard-Jones glasses produced via differing quench protocols. This technique allows us to sample the plastic rearrangements in a non-perturbative manner for different loading directions on a well-controlled length scale. Plastic activity upon shearing correlates strongly with the locations of low yield stresses in the quenched states. This correlation is higher in more structurally relaxed systems. The distribution of local yield stresses is also shown to strongly depend on the quench protocol: the more relaxed the glass, the higher the local plastic thresholds. Analysis of the magnitude of local plastic relaxations reveals that stress drops follow exponential distributions, justifying the hypothesis of an average characteristic amplitude often conjectured in mesoscopic or continuum models. The amplitude of the local plastic rearrangements increases on average with the yield stress, regardless of the system preparation. The local yield stress varies with the shear orientation tested and strongly correlates with the plastic rearrangement locations when the system is sheared correspondingly. It is thus argued that plastic rearrangements are the consequence of shear transformation zones encoded in the glass structure that possess weak slip planes along different orientations. Finally, we justify the length scale employed in this work and extract the yield threshold statistics as a function of the size of the probing zones. This method makes it possible to derive physically grounded models of plasticity for amorphous materials by directly revealing the relevant details of the shear transformation zones that mediate this process

Expériences de mixités vécues par les enseignants d’éducation physique et sportive : lien entre vigilance et équité sexuée

La présente étude se propose de décrire, dans une perspective psychophénoménologique, les différentes expériences de mixités vécues par les enseignant-e-s lors des cours d’éducation physique et sportive (EPS). Derrière le vécu subjectif des enseignant-e-s opèrent des logiques intrinsèques qui participent à l’orientation d’une attention plus ou moins tournée vers l’équité. Les enseignant-e-s ne sont pas sans conscience pré-réfléchie des actes professionnels amenant à plus d’émancipation ou de renforcement des rôles sociaux conventionnellement attribués à un sexe. Mais cette conscience pré-réfléchie se traduit rarement en une véritable vigilance envers l’équité. La recherche montre également en quoi certaines formes de mixité sont des impasses pour être attentif à l’égalité des sexes.Based on a psychophenomenological approach, the present study describes the various experiences of coeducation lived by physical education teachers. Behind the teachers’ subjectivity, intrinsic rationales contribute to orienting attention to equity. Teachers are aware of the professional acts towards more emancipation or the intensification of conventional gender roles. But few behavioural types show a real awareness of gender equity. The research also shows why some forms of coeducation are not the correct answers as far as being attentive to gender equity is concerned