On the thermodynamic entropy of fatigue fracture

Abstract

Entropy production during the fatigue process can serve as a measure of degradation. We postulate that the thermodynamic entropy of metals undergoing repeated cyclic load reaching the point of fracture is a constant, independent of geometry, load and frequency. That is, the necessary and sufficient condition for the final fracture of a metal undergoing fatigue load corresponds to a constant irreversible entropy gain. To examine validity, we present the results of an extensive set of both experimental tests and analytical predictions that involve bending, torsion and tension-compression of aluminium 6061-T6 and stainless steel 304 specimens. The concept of tallying up the entropy generation has application in determining the fatigue life of components undergoing cyclic bending, torsion and tension-compression.

Acoustic Entropy of the Materials in the Course of Degradation

“…The extension of their approach to electrical and chemical properties is also published in [30][31][32]. Naderi et al [33] also reported experimental results on the existence of a entropic limit at the time of the fatigue failure.…”

“…This hints of a possible existence of an information entropic limit to the acoustic entropy generated in the course of the fatigue failure of the materials. Previously, research by Naderi et al [33] showed that there exists a critical limit in the cumulative thermodynamic entropy generation (known as fatigue fracture entropy) beyond which fracture occurs. The evolutionary trend of the acoustic entropy, under various operating conditions tested in this study, also reveals a persistent trend over the course of the fatigue degradation.…”

A Model of Mechanothermodynamic Entropy in Tribology

“…[35] is normalized with respect to the FFE value for SS 304. These results have two important implications [35,37]: (a) fatigue damage accumulation is independent of load, frequency, and geometry; and (b) damage behavior under variable loading has no knee point and independent of multistage loading and loading sequence. As damage progresses towards the final fracture, the accumulated entropy monotonically increases to the fracture fatigue entropy (FFE) which is unique for a given material [37].…”

“…According to [35,37] entropy continuously increases simultaneously with the rise of degradation, towards the fatigue fracture entropy (FFE). Research shows that regardless of the type of the mechanical fatigue process (bending or torsion, tension-compression) FFE is constant unique to the material.…”

“…Processes of accumulation of fatigue damage are analyzed in a number of other works [35][36][37][38][39][40][41] by Khonsari, Amiri and Naderi basing on the traditional concept of entropy. One of these approaches presented in [35,36] is discussed below.…”