Thermodynamic entropy as a marker of high‐cycle fatigue damage accumulation: Example for normalized SAE 1045 steel

Abstract

A nondestructive thermographic methodology is utilized to determine the fracture fatigue entropy for evaluating the fatigue damage in metals within the high-cycle fatigue regime. Thermodynamic entropy is shown to play an important role in the fatigue process to trace the fatigue damage as an irreversible degradation of a metallic material being subjected to cyclic elastic-plastic loading. This paper presents a method to evaluate fatigue damage in the normalized SAE 1045 steel being based on the concept of thermodynamic entropy and its nonlinearities. The procedure looks to be applicable to constant and load increase tests proven by experiments.

A Review of Damage, Void Evolution, and Fatigue Life Prediction Models

“…s ≥ 0), J q the heat flux, T the surface temperature, W p the cyclic plastic energy per unit volume, N f is the final number of cycles when failure occurs, b and c are curve fitting parameters, b is fatigue strength exponent and c is fatigue ductility exponent, ε f is the fatigue ductility coefficient, σ f denotes the fatigue strength coefficient. Similar work was also done by Teng et al [90] for normalized SAE1045 steel.…”

Nonlinear fatigue life prediction model based on the theory of the S‐N fatigue damage envelope

“…This highlights the need for further research within the field regarding damage accumulation, at which several attempts have been made both from the viewpoint of theoretical approaches or reflections regarding the S-N curve and regarding the measurement of fatigue damage. [14][15][16][17][18][19][20][21][22][23][24] Examples of this might be such as the double linear damage rule (DLDR), developed by Manson et al, [25][26][27] on the basis of the suggestion by Grover, 28 which shows good agreement with experimental results. The principle in Manson's work is to apply two linear damage rules, which were first categorized as crack initiation and propagation but later categorized as Phase I and Phase II.…”

Microcellular Ethylene–Vinyl Acetate Copolymer Foam: Life Prediction Under Reciprocating Compression

“…In the actual fitting, the elastic deformation is ignored and the plastic deformation is directly fitted. [32,34,35] The law of change is similar to the power function, [33,36] assuming that the stress (σ)-strain (ε) change law is Equation (2), the origin software has used to fit the stress-strain curves of the five specimens in different cycles with Equation (2). The fitting results are shown in Figure 5 and Table 4.…”