Modeling Corrosion & Fatigue In Bcc Metals With Unified Mechanics Theory
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Corrosion and fatigue are critical degradation mechanisms in metallic structures. 1 This study presents a novel model, based on the Unified Mechanics Theory (UMT), to predict the fatigue life of pre-corroded steel samples with a body-centered cubic (bcc) crystal structure. UMT offers an ab initio unification of Newton's laws and the Boltzmann-Planck formulation of the second law of thermodynamics. 2 Critically, UMT incorporates entropy as an independent variable within the equilibrium differential equation, eliminating the need for empirical degradation/dissipation/aging functions or potentials. 2 Entropy at a material point is directly calculated from the material's thermodynamic fundamental equation, derived analytically from physical chemistry. This equation encapsulates all atomic mechanisms responding to external disturbances, going beyond the limitations of Newtonian continuum mechanics, which solely considers displacement/strain. UMT recognizes that atoms utilize various mechanisms beyond displacement, such as heat generation, to respond to external forces. The generated entropy is then used to calculate the Thermodynamic State Index (TSI), a linearly independent axis alongside the Newtonian space-time axes. 1 TSI ranges from zero to one at failure, allowing for non-zero derivatives of displacements with respect to entropy. The model's predictions demonstrate excellent agreement with experimental fatigue life measurements of pre-corroded steel samples, validating the UMT-based approach for accurately predicting very high cycle fatigue without relying on empirical curve fitting2. REFERENCES [1] Cemal Basaran, Introduction to Unified Mechanics Theory with Applications, second editions, Springer, 2023 [2] Hsiao Wei Lee, Hamidreza Fakhri, Ravi Ranade, Cemal Basaran, Halina Egner, Adam Lipski, Michał Piotrowski, Stanisław Mroziński, Modeling fatigue of pre-corroded body-centered cubic metals with unified mechanics theory, Materials & Design, Volume 224, 2022, 111383,
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