Modeling Material Degradation Due to Moisture and Temperature

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The mechanical response, serviceability, and load bearing capacity of materials and structural components can be adversely affected due to external stimuli, which include exposure to a corrosive chemical species, high temperatures, temperature fluctuations (i.e., freezing-thawing), cyclic mechanical loading, just to name a few. It is, therefore, of paramount importance in several branches of engineering – ranging from aerospace engineering, civil engineering to biomedical engineering – to have a fundamental understanding of degradation of materials, as the materials in these applications are often subjected to adverse environments. In this dissertation, we study degradation of materials due to an exposure to chemical species and temperature under large-strain and large-deformations. In the first part of our research work, we present a consistent mathematical model with firm thermodynamic underpinning. We then obtain semi-analytical solutions of several canonical problems to illustrate the nature of the quasi-static and unsteady behaviors of degrading hyperelastic solids. As second part, we propose several non- dimensional parameters that characterize chemo-thermo-mechanical coupling. These parameters will provide insights on the strength and the nature of various couplings in different types of coupled multi-physics processes. We will also discuss about the importance and the effect of the coupling term (i.e., grad[μ] • h), which accounts for mass/chemical species transfer in the balance of energy using canonical problems. Last but not least, the computational framework based on staggered scheme and monolithic scheme, are depicted in the paper and compared. Several numerical case studies have been done using five different methodologies, Newton-Raphson method with regular mesh and metric-based mesh, standard Galerkin method with regular mesh and metric-based mesh, and non-negative formulation with regular mesh. Furthermore, the behavior of degrading 3D spherical shell and slabs are studied. The limitations of typical semi-inverse solutions, which are commonly employed in practice, will be highlighted. We will also illustrate the proposed model and computational framework on a transient, large deformed, three-way coupled degradation problem.

Degradation, Three-way coupled
Portions of this document appear in: Xu, C., Mudunuru, M. K., and Nakshatrala, K. B., 2016. “Material degradation due to moisture and temperature. Part 1: Mathematical model, analysis, and analytical solutions”. Continuum Mechanics and Thermodynamics, 28, pp. 1847–1885.