From microscopic to Macroscopic mechanical non-linearities of amorphous polymers near their glass transition

Proposition de stage M2 2020-2021

Laboratoire Sciences et Ingénierie de la Matière Molle, (SIMM)

Adresse: ESPCI, 10 Rue Vauquelin 75005 Paris

Directeur du laboratoire: Etienne Barthel

Responsables du stage: Helene MONTES (helene.montes (arobase) espci.fr), Francois Lequeux (francois.lequeux (arobase) espci.fr) Sabine Cantournet (sabine.cantournet (arobase) mines-paristech.fr)

Scientific description:
In the forthcoming years, polymer materials will become increasingly used in the particular field of high-performance materials, particularly in the field of transport and aeronautics. To predict their mechanical behavior, it is important to understand the physical properties that govern their mechanical behavior.
The latest advances in the physics of the glass transition suggest that these materials have a very heterogeneous dynamic that can be characterized by a distribution of the local relaxation time distribution. Dynamical disorder induces mechanical coupling resulting in subtle percolation-depercolation mechanism that drives the macroscopic response of the system in the glass transition, especially in the non linear regime.
The aim of this work is to understand the role of dynamical disorder on the weakly nonlinear response of glassy polymers. We expect different situations depending on the types of the mechanical solicitation undergone by the system like creep, stress relaxation, uniaxial stretching in traction and compression. The candidate will perform both mechanical experiments on model systems. Experimental responses will be compared to numerical predictions given by a mechanical model based on theoretically predicted dynamical heterogeneities that we already developed during the previous years and that is in operation. The advantage of the model is to give the state of the stress and strain fields at each step of the mechanical experiments as we already did for stress relaxation in the linear regime (see figure 1).

We expect to reveal specific scaling laws for the macroscopic nonlinear response that are related to the intrinsic mechanical response of heterogeneities and the mechanical coupling occurring at this length scale.

Figure 1 : Effect of disorder on the stress relaxation in the linear regime. The shear Modulus relaxation predicted by FE 2D model for a heterogeneous system (s=4.6) for a step of strain is compared to the response of an homogenous sample (s=0). Stress field maps are shown at different stages of the macroscopic relaxation. The corresponding time values are equal to : 10-5, 10-4, 10-3, 0.5, 1, 5, 50.

Keywords: polymer physics, mechanical properties, non linearities, experiment, simulations
Techniques/methods in use: rheology, Finite element simulations
Internship location: SIMM - ESPCI
Possibility for a Doctoral thesis: Yes

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Sciences et Ingénierie de la Matière Molle

Soft Matter Enginering and Science Laboratory - UMR 7615

10 rue Vauquelin
75231 PARIS CEDEX 05
FRANCE

  • Chair : E. Barthel
  • Vice Chairs : J.B. d’Espinose & G. Ducouret
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