Unified Mechanics of Metallic Structural Materials

Unified mechanics theory (UMT) unifies Newton׳s universal laws of motion and the second law of thermodynamics at the ab-initio level. As a result, governing differential equation of any structural system directly includes entropy generation in the system. The linearly independent thermodynamic state index axis (TSI) of the unified mechanics theory maps the entropy generation rate at a material point between zero and one, according to the thermodynamic fundamental equation of the material. Then, the thermodynamic lifespan of any closed system travels between zero and one along the TSI axis according to the second law of thermodynamics as formulated by Boltzmann. Because entropy generation is directly included in the differential equation of the structure, there is no need for empirical dissipation potential obtained by curve-fitting a function to dissipation/degradation test data. However, the thermodynamic fundamental equation of the material must be derived analytically based on fundamental principles of physics and chemistry. In this chapter, some recently developed models for metallic structural material’s fatigue, corrosion, and hydrogen embrittlement behavior as well as, the temperature and strain rate-dependent flow stress modeling are presented.