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

Area of Science:

• Thermodynamics
• Materials Science
• Mechanical Engineering

Background:

• Fatigue remains a critical failure mechanism in materials, impacting structural integrity and lifespan.
• Existing fatigue models often lack predictive accuracy under diverse environmental and loading conditions.

Purpose of the Study:

• To develop a novel, instantaneous fatigue model and predictor grounded in ab initio irreversible thermodynamics.
• To establish a robust framework for relating material fatigue to fundamental thermodynamic principles and environmental factors.

Main Methods:

• Integration of the first and second laws of thermodynamics with Helmholtz free energy.
• Application of the degradation-entropy generation theorem to link fatigue measures (stress, strain, cycles, time to failure) with loads, materials, and environmental conditions.
• Utilizing irreversible entropies generated by dissipative processes as a key indicator of material degradation.

Main Results:

• The formulated model demonstrated a near 100% agreement with experimental fatigue data for a steel shaft under bending and torsion.
• Successful prediction of fatigue life based on material properties, loading conditions, and environmental parameters.
• Introduction of new material and design parameters for enhanced fatigue characterization.

Conclusions:

• The developed irreversible thermodynamics-based fatigue model offers a highly accurate and predictive tool for material fatigue assessment.
• The model provides a fundamental understanding of fatigue mechanisms through the lens of entropy generation.
• This approach holds significant potential for improving material selection, design optimization, and predicting the service life of components.