[P1-72] Thermally Activated Creep and Constant Shear Rate Deformation in Amorphous Materials
In this contribution, we shall discuss two issues related to the deformation of amorphous materials.
The first issue concerns transient creep also called Andrade creep, characterized by strain slowly increasing algebraically with time, a regime interrupted by fluidization and eventually steady flow. Here we characterize creep and fluidization on the basis of a mesoscopic viscoplastic model that includes thermally activated yielding events and a broad distribution of energy barriers, which may be lowered under the effect of a local deformation. We relate the creep exponent observed before fluidization to the width of barrier distribution and to the specific form of stress redistribution following yielding events. We show that Andrade creep is accompanied by local strain hardening driven by stress redistribution and find that the fluidization time depends exponentially
on the applied stress, in qualitative agreement with experiments.
The second issue to be discussed concerns constant shear rate deformation of molecular glasses. Recent experiments on polymer glasses [2] have demonstrated enhanced mobility in the preyield regime accompanied by a narrowing of the distribution of segmental relaxation times. Yet, the mechanisms at play remain partially understood.
In the light of the mesoscopic model [1], we characterized the evolution of the distribution of energy barriers during constant shear rate deformation. Our simulation results account for enhanced mobility and the narrowing of the distribution of relaxation times. Good agreement is obtained with the experimental observations of Bending et al., without any adjustable parameter.
All the simulation results are interpreted in the light of a mean-field analysis, and should help in rationalizing the creep and deformation phenomenology as observed in disordered materials.
References
[1] S. Merabia and F. Detcheverry, Thermally activated creep and fluidization in flowing disordered
materials, EPL (2016)
[2] B. Bending, K. Christison, J. Ricci, and M. D. Ediger, Measurement of Segmental Mobility during Constant Strain Rate
Deformation of a Poly(methyl methacrylate) Glass, Macromolecules (2014)
The first issue concerns transient creep also called Andrade creep, characterized by strain slowly increasing algebraically with time, a regime interrupted by fluidization and eventually steady flow. Here we characterize creep and fluidization on the basis of a mesoscopic viscoplastic model that includes thermally activated yielding events and a broad distribution of energy barriers, which may be lowered under the effect of a local deformation. We relate the creep exponent observed before fluidization to the width of barrier distribution and to the specific form of stress redistribution following yielding events. We show that Andrade creep is accompanied by local strain hardening driven by stress redistribution and find that the fluidization time depends exponentially
on the applied stress, in qualitative agreement with experiments.
The second issue to be discussed concerns constant shear rate deformation of molecular glasses. Recent experiments on polymer glasses [2] have demonstrated enhanced mobility in the preyield regime accompanied by a narrowing of the distribution of segmental relaxation times. Yet, the mechanisms at play remain partially understood.
In the light of the mesoscopic model [1], we characterized the evolution of the distribution of energy barriers during constant shear rate deformation. Our simulation results account for enhanced mobility and the narrowing of the distribution of relaxation times. Good agreement is obtained with the experimental observations of Bending et al., without any adjustable parameter.
All the simulation results are interpreted in the light of a mean-field analysis, and should help in rationalizing the creep and deformation phenomenology as observed in disordered materials.
References
[1] S. Merabia and F. Detcheverry, Thermally activated creep and fluidization in flowing disordered
materials, EPL (2016)
[2] B. Bending, K. Christison, J. Ricci, and M. D. Ediger, Measurement of Segmental Mobility during Constant Strain Rate
Deformation of a Poly(methyl methacrylate) Glass, Macromolecules (2014)