Thermodynamics of Fatigue: Degradation-Entropy Generation Methodology for System and Process Characterization and Failure Analysis.

Osara Osara,Bryant Bryant

doi:10.3390/e21070685

Abstract

Formulated is a new instantaneous fatigue model and predictor based on ab initio irreversible thermodynamics. The method combines the first and second laws of thermodynamics with the Helmholtz free energy, then applies the result to the degradation-entropy generation theorem to relate a desired fatigue measure—stress, strain, cycles or time to failure—to the loads, materials and environmental conditions (including temperature and heat) via the irreversible entropies generated by the dissipative processes that degrade the fatigued material. The formulations are then verified with fatigue data from the literature, for a steel shaft under bending and torsion. A near 100% agreement between the fatigue model and measurements is achieved. The model also introduces new material and design parameters to characterize fatigue.

Highlights

All solids can yield or fail under continuous loading
Assessment of degradation leading to fatigue failure is complicated by various dynamic loads, material composition and load conditions
This study introduced the Degradation-Entropy Generation (DEG) domain, a multi-dimensional space that linearly characterizes a real system’s nonlinear phenomenological transformation paths

Summary

Introduction

All solids can yield or fail under continuous loading. Equilibrium and monotonic conditions facilitate evaluation of a component’s strength. Assessment of degradation leading to fatigue failure is complicated by various dynamic loads, material composition and load conditions. With metals under heavy structural loading, sudden failure can be catastrophic [1]. Cyclic loading causes about 90% of all metal failures [2,3,4,5,6,7]. Thermal cycle-induced stresses can fatigue electronic components

Methods

Discussion

Conclusion