Yielding of Thermal Amorphous Materials

Metallic glasses, colloidal gels, and glasses, foams, and emulsions represent a diverse set of examples of amorphous materials. Under small stresses, these materials deform as an elastic solid, while under large stresses, they deform plastically. A local yield stress, or an energy barrier, associated with each configuration exists. Therefore, the response of the amorphous materials to mechanical loading is governed by their complex energy landscape, i.e., a spectrum of local yield stresses or energy barriers. A fundamental question that has not been addressed is what happens if the energy barrier to rearrangements is only moderately larger than the thermal energy. We introduce the thermal soft glassy rheology model which takes the energy landscape as an input and models the microstructural rearrangements as thermally-mechanically activated processes. The interplay between mechanical loading and thermal hops out of the amorphous configurations leads to different regimes of structural relaxation. We will present the response of thermal amorphous materials to various tests such as start-up shear, oscillatory shear, and stress relaxation. Furthermore, we will show the role of shear history and how the encoded memory of previous deformation can alter the local stresses and macroscopic stress. We will connect the molecular physics information to the local energy barrier to feed into the thermal SGR model, ensuring the model has no fitting parameters.