Ref HAL: hal-02569130_v1
Ref Arxiv: 1912.06416
DOI: 10.1103/PhysRevMaterials.4.025603
WoS: 000515722500007
Ref. & Cit.: NASA ADS
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Résumé:

Amorphous solids display a ductile to brittle transition as the kinetic stability of the quiescent glass is increased, which leads to a material failure controlled by the sudden emergence of a macroscopic shear band in quasi-static protocols. We numerically study how finite deformation rates influence ductile and brittle yielding behaviors using model glasses in two and three spatial dimensions. We find that a finite shear rate systematically enhances the stress overshoot of poorly-annealed systems, without necessarily producing shear bands. For well-annealed systems, the non-equilibrium discontinuous yielding transition is smeared out by finite shear rates and it is accompanied by the emergence of multiple shear bands that have been also reported in metallic glass experiments. We show that the typical size of the bands and the distance between them increases algebraically with the inverse shear rate. We provide a dynamic scaling argument for the corresponding lengthscale, based on the competition between the deformation rate and the propagation time of the shear bands.

Ref HAL: hal-02563236_v1
Ref Arxiv: 1910.06181
DOI: 10.1016/j.jnoncrysol.2020.119895
WoS: 000519653700018
Ref. & Cit.: NASA ADS
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Ref HAL: hal-02563181_v1
DOI: 10.1063/1.5142605
WoS: 000519911600001
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Résumé:

We adapt and apply a recently developed optimization scheme used to obtain effective potentialsfor aluminosilicate glasses to include the network former boron into the interaction parameter set.As input data for the optimization, we used the radial distribution functions of the liquid at hightemperature generated by ab initio molecular dynamics simulations, and density, coordination andelastic modulus of glass at room temperature from experiments. The new interaction potentials areshown to reproduce reliably the structure, coordination and mechanical properties over a widerange of compositions for binary alkali borates. Furthermore, the transferability of these newinteraction parameters allows mixing to reliably reproduce properties of various boroaluminateand borosilicate glasses.

Ref HAL: hal-02540128_v1
Ref Arxiv: 1908.01484
DOI: 10.1021/acs.macromol.9b02166
WoS: 000526399500029
Ref. & Cit.: NASA ADS
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1 Citation
Résumé:

In order to determine in polymeric systems the geometrical mesh size ξ, we simulate a solution of coarse-grained polymers with densities ranging from the dilute to the concentrated regime and for different chain lengths. We determine the monomer density fluctuation correlation length ξc from the monomer structure factor as well as the radial distribution function, showing that the identification ξ = ξc is not justified outside of the semidilute regime. In order to better characterize ξ, we compute the pore size distribution (PSD) following two different definitions, one by Torquato et al. and one by Gubbins et al. We find that the mean values of the two distributions, ⟨r⟩T and ⟨r⟩G, display the behavior predicted for ξ by scaling theory, and argue that ξ can be identified with either one of these quantities. This identification allows to interpret the PSD as the distribution of mesh sizes, a quantity which conventional methods cannot access. Finally, we show that it is possible to map a polymer solution on a system of hard or overlapping spheres, for which Torquato’s PSD can be computed analytically and reproduces accurately the PSD of the solution. We give an expression that allows ⟨r⟩T to be estimated with high accuracy in the semidilute regime by knowing only the radius of gyration and the density of the polymers.