arXiv subjects

Martin Roman-Faure

Publications and source records attributed to Martin Roman-Faure.

4 recordsLinked to original sources

arXiv2026

Weakly non-linear creep of amorphous polymers near their glass transition, comparisons between models and experiment

The non-linear mechanics of amorphous polymers near the glass transition reveals a stress-induced acceleration of stress relaxation of nanometric sub-units. Recent theoretical work predicts that the local acceleration within these nano-domains should scale as the exponential of the squared local stress, a behavior now supported by experiments. However, this local dynamics has some complex consequences on the macroscopic mechanical response, as dynamical heterogeneities generate complex stress and strain fields in polymers close to the glass transition. In this study we consider the non-linear creep of an amorphous polymer near its glass transition and evaluate the relation between local and global acceleration and the emerging load-carrying structure, by comparing experimental data with predictions of three models of increasing complexity: a two-states (2S) model, a self-consistent (SC) model and a finite-element (FEM) model. The experimentally observed trend of accelerated creep under increasing applied stress is reproduced by the SC and FEM models, while the 2S model overestimates stress localization. The macroscopic, homogenized acceleration is predicted to be close to the microscopic one, albeit with an apparent yield stress that depends on compliance. The FEM model evidences the development of a load carrying sub-structure that occupies a small fraction of the total material volume driven by the interaction of sub-domains. This work shows that complexity and heterogeneity emerge due to non-linear interactions and that their adequate representation is essential for predicting the macroscopic mechanical response of amorphous polymers near their glass transition.

cond-mat.soft↗

arXiv2024

Weak non-linearities of amorphous polymer under creep in the vicinity of the glass transition

The creep behavior of an amorphous poly(etherimide) (PEI) polymer is investigated in the vicinity of its glass transition in a weakly non linear regime where the acceleration of the creep response is driven by local configurational rearrangements. From the time shifts of the creep compliance curves under stresses from 1 to 15~\si{\mega\pascal} and in the temperature range between $T_g -10K$ and $T_g$, where $T_g$ is the glass transition, we determine a macroscopic acceleration factor. The macroscopic acceleration is shown to vary as $e^{-(\Sigma/Y)^n} $ with $n=2 \pm 0.2$, where $\Sigma$ is the macroscopic stress and $Y$ is a decreasing function of compliance. Because at the beginning of creep, the stress is homogeneous, the macroscopic acceleration is thus similar to the local one, in agreement with the recent theory of Long \textit{et al.} (\textit{Phys. Rev. Mat.} (2018) \textbf{2}, 105601 ) which predicts $n=2$. For larger compliances, the decrease of the of $Y$ is interpreted as a signature of the development of stress disorder during creep.

cond-mat.soft↗

arXiv2024

Weak non-linearities of amorphous polymer under creep

The creep behavior of an amorphous poly(etherimide) (PEI) polymer is investigated in the vicinity of its glass transition in a weakly non linear regime where the acceleration of the creep response is driven by local configurational rearrangements. From the time shifts of the creep compliance curves under increasing applied stresses in the range 1-15~\si{\mega\pascal}, we determine a macroscopic acceleration factor. At the start of creep, the stress is homogeneous and the macroscopic acceleration can be assimilated to that of the local rearrangements which is shown to vary as $f=e^{-(\sigma/Y)^n} $ with $n=2 \pm 0.2$, where $\sigma$ is the local stress and $Y$ is a decreasing function of compliance. This experimental result is in agreement with the recent theory of Long \textit{et al.} (\textit{Phys. Rev. Mat.} (2018) \textbf{2}, 105601 ) which predicts $n=2$. From a mean field approximation, we interpret the variation of $Y$ with compliance as the result of the development of stress heterogneities during creep.

cond-mat.soft↗

arXiv2022

Soft coring: how to get a clarinet out of a flute?

Cutting mozzarella with a dull blade results in poorly shaped slices: the process occurs in a configuration so deformed as to yield unexpectedly curved surfaces. We study the rich morphogenetics arising from such process through the example of coring: when a thin cylindrical hollow punch is pushed into a soft elastomer, the extracted core is "clarinet-shaped", reaching diameters far smaller than those of the tool. With contributions from fracture mechanics and large strain theory, we build a simple yet quantitative understanding of the observed shapes, revealing the crucial role of friction.

cond-mat.soft↗