Fracture Fatigue Entropy Research Articles

Microstructure-sensitive estimation of fatigue life using cyclic thermodynamic entropy as an index for metals

A technique for fatigue life prediction of metals is presented based on a microstructure-sensitive estimation of plastic strain energy per cycle. The approach enables rapid prediction of temperature evolution, estimation of cyclic plastic energy, and fracture fatigue entropy. Theoretical and experimental results are presented for low-carbon steel 1018 and aluminum 7075-T6 specimens. It is shown that the approach realistically predicts the fatigue life of metallic specimens.

In-situ Technique for Fatigue Life Prediction of Metals Based on Temperature Evolution

This article offers a technique for predicting the fatigue life of metals by monitoring its surface temperature. The method is based on the examination of the cooling characteristics of a specimen once its temperature becomes steady and actuation halted. It is shown that the cooling curve is unique for a specific material and geometry regardless of the operating conditions such as the loading type, amplitude, and frequency. Using this finding along with the concept of fracture fatigue entropy (FFE), a technique is introduced to readily predict fatigue life in-situ. Results of extensive sets of experiments for cyclically actuated fully-reversed bending and tension-compression (TC) types of loadings, at different frequencies, and for various specimens’ geometries are presented to test the validity of the technique.

Investigation of internal friction and fracture fatigue entropy of CFRP laminates with various stacking sequences subjected to fatigue loading

The heat dissipation caused by internal friction plays an important role during fatigue property prediction based on self-heating data but it is still unclear for Carbon Fiber Reinforced Polymer (CFRP). In this paper, fatigue tests and thermal data analysis are carried out in order to investigate internal friction and Fracture Fatigue Entropy (FFE) of CFRP laminates with various stacking sequences. The fatigue limit is firstly estimated based on an improved graphic method developed by our previous study and then used to mark the beginning of fatigue damage occurs. It is found that the relationship between internal friction and applied stress amplitude is non-linear which is different from metals. Quadratic function is employed to characterize the internal friction region below fatigue limit and the trend line is used to separate heat dissipation related to damage and internal friction beyond fatigue limit. Results show that the internal friction effect of cross-ply laminates is significantly greater than that of unidirectional laminates. FFEs estimated by the heat dissipation related to damage are found to be independent of applied stress amplitude, which can be used to predict S–N curve of CFRP laminates efficiently and precisely.

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

AbstractA 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.

Experimental determination of entropy and exergy in low cycle fatigue

Recent works in mechanical fatigue consider that a threshold of entropy exists, the fracture fatigue entropy. In this paper, we observe the existence of a threshold of entropy and exergy in low cycle fatigue for a flat Al-2024 specimen measuring the heat generated during a fatigue test. Results are compared considering various hypotheses (1D heat dissipation with convection and radiation considered as complementary parts, and, heat transfer from a fin with convection and radiation as boundary conditions) to an empirical mechanical model known in the literature and deviations between them are discussed.

On the application of fracture fatigue entropy to variable frequency and loading amplitude

A nondestructive fatigue model is developed that utilizes the thermographic methodology and the concept of entropy production to predict the residual life of a component subjected to variable amplitude loading. The applicability of the model is investigated using a set of experiments on stainless steel 304 covering both low- and high-cycle fatigue regimes. Results are also presented that compare the predictions of the residual life with those obtained by applying the Miner’s rule, quantitative thermographic methodology, fatigue driving stress, and the fatigue driving energy approaches. The results show that the maximum and average errors of the present approach are much lower than the above-mentioned methods. Also presented are the results of a series of variable-frequency fatigue experiments that are successfully predicted by the present methodology.

On the evaluation of fracture fatigue entropy

Fatigue is an irreversible degradation process wherein entropy increases until its accumulation reaches a critical failure value referred to as the fracture fatigue entropy (FFE). An experimentally-verified analytical approach for determining the entropy generation is presented that illustrates how the concept of FFE can be applied to analyze both low- and high-cycle fatigue. It is shown that the analysis should properly consider the contribution of internal friction, which does not contribute to the fatigue fracture. This parameter plays a significant role in high-cycle fatigue.

Developing a new model to predict the fatigue life of cross-ply laminates using coupled CDM-entropy generation approach

In this paper, a new model based on thermodynamic entropy approach is proposed to predict the fatigue life of cross-ply laminates. The basis of the model is that, during fatigue loading, the accumulated entropy up to final failure that is generated because of damage in fiber and matrix is nearly constant and independent of the magnitude of loading and conditions. In the present study, for the first time, these values called the fracture fatigue entropy of fiber (FFE-F) and fracture fatigue entropy of matrix (FFE-M) which are considered as a final failure criterion in 0° and 90° layers, respectively. A CDM-based constitutive model is utilized to predict the damage energy in the fatigue degradation of composite laminates. FFE-F and FFE-M values are calculated using experimental results of available tension-tension fatigue tests. The validity of the proposed damage-entropy model in fatigue life prediction of T700/Cycom890 carbon/epoxy laminated composite is investigated and the obtained results are in good agreements with experimental ones. It is noted that the developed model can discriminate between different stacking sequences in fatigue loading and also is sensitive to the frequency of loading and different ambient temperature. In addition, the obtained results show that the proposed damage-entropy model is applicable in life prediction of specimens undergoing both high-cycle and low-cycle fatigue loading.

An exergetic approach for materials fatigue

An entropy approach has been recently developed, based on the irreversible thermodynamics and entropy production. It has been observed that, for low cycle fatigue, metals undergoing cyclic load reach fracture, at a certain level of entropy production called fracture fatigue entropy (FFE) (Naderi and Khonsari, 2010), solely dependent on the material. Until now, we only used the two principles of thermodynamics separately to follow the behaviour of a solid continuum problem as low cycle fatigue. We propose here to use the two laws of thermodynamics together via the Gouy-Stodola equation and the concept of exergy to provide a new description for metals undergoing low cycle fatigue.

An exergetic approach for materials fatigue

An entropy approach has been recently developed, based on the irreversible thermodynamics and entropy production. It has been observed that, for low cycle fatigue, metals undergoing cyclic load reach fracture, at a certain level of entropy production called fracture fatigue entropy (FFE) (Naderi and Khonsari, 2010), solely dependent on the material. Until now, we only used the two principles of thermodynamics separately to follow the behaviour of a solid continuum problem as low cycle fatigue. We propose here to use the two laws of thermodynamics together via the Gouy-Stodola equation and the concept of exergy to provide a new description for metals undergoing low cycle fatigue.

Thermodynamic analysis of fatigue failure in a composite laminate

We put forward a thermodynamic approach for analyzing fatigue failure in a composite laminate. We show that fatigue is an irreversible progression of increasing entropy that accumulates until it reaches a critical value called the fracture fatigue entropy (FFE) at the onset of failure. Extensive series of fatigue tests are carried out that involve load-controlled tension-tension, and displacement controlled fully-reversed bending fatigue with three different stress ratios as well as constant- and variable-loading. The role of hysteresis energy in the entropy generation is investigated. FFE values are calculated based the experimental data obtained for temperature and hysteresis energy of a woven Glass/Epoxy (G10/FR4) laminate. The concept of tallying entropy accumulation and the use of FFE are useful for determining the fatigue life of composite laminates undergoing cyclic loading.

A comprehensive fatigue failure criterion based on thermodynamic approach

In this work, stress curve and energy-based (linear elastic strain energy, and hysteresis loop energy) fatigue failure criteria are compared with a new, entropy-based model for the prediction of fatigue life in a woven glass/epoxy laminate. Extensive experimental results are reported that involve load-controlled tension–tension fatigue test with two different stress ratios as well as constant- and variable-loading of a woven glass/epoxy laminate with various load angles. The plot of fracture fatigue entropy vs. fatigue life is compared with the energy plotted vs. number of cycle and stress plotted vs. number of cycle (i.e., the so-called S–N curve) plots.

Cyclic deformation behavior of Cu16 at.% Al singles crystals. I. Strain burst behavior: Hong, S.I. and Laird, C. Mater. Sci. Eng. A Apr. 1990 A124, (2), 183–201

We put forward a thermodynamic approach for analyzing fatigue failure in a composite laminate. We show that fatigue is an irreversible progression of increasing entropy that accumulates until it reaches a critical value called the fracture fatigue entropy (FFE) at the onset of failure. Extensive series of fatigue tests are carried out that involve load-controlled tension-tension, and displacement controlled fully-reversed bending fatigue with three different stress ratios as well as constant- and variable-loading. The role of hysteresis energy in the entropy generation is investigated. FFE values are calculated based the experimental data obtained for temperature and hysteresis energy of a woven Glass/Epoxy (G10/FR4) laminate. The concept of tallying entropy accumulation and the use of FFE are useful for determining the fatigue life of composite laminates undergoing cyclic loading.