On the direct interactions between heat transfer, mass transport and chemical processes within gradient elasticity

The behaviour of complex material systems often results from the combined effects of several multi-scale mechanisms and simultaneously occurring coupled physical processes. In this paper, we focus on such complex response of a class of geomaterials in which heat conduction, mass diffusion, chemical reactions and gradient-type elastic strain mechanisms interact. Our purpose is to develop within a formal thermodynamic framework a complete set of constitutive equations which account for most of the possible aforementioned direct couplings and the associated relevant size effects in a unified phenomenological way. For the sake of simplicity, the volume element is described at the macroscopic scale as a classical homogeneous continuous mixture of chemically active species. Based on theories of second-gradient elasticity endowed with the concepts of both nonlocality residual and constitutive insulation condition, a thermo-diffuso-chemo-elastic formulation is proposed in the restricted case of small perturbations. Coupling terms entering the relevant constitutive relations are discussed throughout the paper. Then, the model is applied to a simple one-dimensional situation, in which only the mechanical response is reported. The implementation of such modelling in a finite element code should enable us to address more specific problems, such as the stress solution phenomenon in hollow cylinders subjected to external loading.