Reducing the weight of vehicles is a key challenge to reduce energy consumption in many fields. Polymers can be a lighter replacement to metal in a lot of structural applications.
The structure of amorphous polymers is complex and the macroscopic behavior may exhibit different properties than the local ones. Modeling and understanding the amorphous phase is key to describe and predict the properties of these materials. Weak non-linearity under creep is the main focus of this work.
Since two decades, it has been recognized that amorphous polymers exhibit dynamical heterogeneities. They may be seen as a tiling of different zones, each one with a Maxwell-like behavior, with its own relaxation time. The relaxation time is varying throughout the zones, bringing dynamical heterogeneities to the material. The time distribution spans over more than 4 decades. Given these heterogeneities, amorphous phase, near its glass transition can be seen as a multi constituent system [Masurel et al. Macromolecules 2015, 48, 18, 6690–6702]. The nonlinearity in creep is characterized by an acceleration of the strain time evolution as compared to the linear one. The observed difference in time to reach a given compliance is defined as the acceleration of creep. This acceleration is measured experimentally and compared to theoretical models.
Previous work done with stress relaxation experiments have shown that the nonlinear response is not the same locally and at the macroscopic level [Belguise et al. Phys. Rev. Mater., Volume 5 (2021), 033601]. At opposite, this work shows that for a low creep, the nonlinear response is similar at the macro scale and the local scale. The measured responses have been compared to theoretical calculations, as well as a simple modeling with Maxwell model and finite elements modeling.