Mechanothermodynamic Entropy and Analysis of Damage State of Complex Systems (original) (raw)

Thermodynamic entropy generation model for metal fatigue failure

2018

Fatigue damage is comprehensively determined by thermodynamic entropy generation as the damage precursor. For fatigue mechanism, time rate of thermodynamic entropy generation is defined as ratio of plastic strain energy density rate per specimen’s temperature. Recent researches claim that entropy generation is constant at the time of crack initiation, directly related to the type of material, independent of loading and surrounding conditions. In this study, an analytical solution is proposed to evaluate the temperature of specimen during the fatigue test while the Morrow equation employed as plastic strain energy density. Result leads to derive new analytical-empirical model for calculating entropy generation. It is shown that temperature obtained from analytical solution is in good agreement with experimental data. In the next section, uncertainty and sensitivity analysis are accomplished based on proposed model. Monte-Carlo simulation and sigma-normalized derivative methods are em...

On the Development of Mechanothermodynamics as a New Branch of Physics

Entropy

This paper aims to substantiate and formulate the main principles of the physical discipline-mechanothermodynamics that unites Newtonian mechanics and thermodynamics. Its principles are based on using entropy as a bridge between mechanics and thermodynamics. Mechanothermodynamics combines two branches of physics, mechanics and thermodynamics, to take a fresh look at the evolution of complex systems. The analysis of more than 600 experimental results allowed for determining a unified mechanothermodynamical function of limiting states (critical according to damageability) of polymers and metals. They are also known as fatigue fracture entropy states.

Mechanothermodynamical system and its behavior

Continuum Mechanics and Thermodynamics, 2012

An attempt to formulate the basic principles of mechanothermodynamics of systems is made. The notion of tribo-fatigue entropy generated in a mechanical system is introduced similarly to thermodynamic entropy governed by matter and energy exchange. Interrelation of motion, damage, and information is found. It is shown that motion generates new information in the system if its damageability index is non-zero. The information is positive if the system is hardened and negative if it softened. It leads one to perceiving the principal feature of interaction of irreversible damages (effective energies and entropy) generated by effects of different nature (mechanical loads, heat flows, etc.), viz. dialectic character of interaction. Two principles of thermodynamics are formulated.

On the Role of Entropy Generation in Processes Involving Fatigue

Entropy, 2011

In this paper we describe the potential of employing the concept of thermodynamic entropy generation to assess degradation in processes involving metal fatigue. It is shown that empirical fatigue models such as Miner's rule, Coffin-Manson equation, and Paris law can be deduced from thermodynamic consideration.

Thermomechanics of damage and fatigue by a phase field model

Journal of Thermal Stresses, 2016

In the paper we present an isothermal model for describing damage and fatigue by the use of the Ginzburg-Landau (G-L) equation. Fatigue produces progressive damage, which is related with a variation of the internal structure of the material. The G-L equation studies the evolution of the order parameter, which describes the constitutive arrangement of the system and, in this framework, the evolution of damage. The thermodynamic coherence of the model is proved. In the last part of the work, we extend the results of the paper to a non-isothermal system, where fatigue contains thermal effects, which increase the damage of materials.

Measures of Entropy to Characterize Fatigue Damage in Metallic Materials

2019

This paper presents the entropic damage indicators for metallic material fatigue processes obtained from three associated energy dissipation sources. Since its inception, reliability engineering has employed statistical and probabilistic models to assess the reliability and integrity of components and systems. To supplement the traditional techniques, an empirically-based approach, called physics of failure (PoF), has recently become popular. The prerequisite for a PoF analysis is an understanding of the mechanics of the failure process. Entropy, the measure of disorder and uncertainty, introduced from the second law of thermodynamics, has emerged as a fundamental and promising metric to characterize all mechanistic degradation phenomena and their interactions. Entropy has already been used as a fundamental and scale-independent metric to predict damage and failure. In this paper, three entropic-based metrics are examined and demonstrated for application to fatigue damage. We collec...

An Irreversible Thermodynamics Theory for Damage Mechanics of Solids

The entropy production is a non-negative quantity based on irreversible thermodynamics and thus serves as a basis for the systematic description of the irreversible processes occurring in a solid. In this paper, a thermodynamic framework has been presented for damage mechanics of solid materials, where entropy production is used as the sole measure of damage evolution in the system. As a result, there is no need for physically meaningless empirical parameters to define a phenomenological damage potential surface or a Weibull function to trace damage evolution in solid continuum. In order to validate the model, predictions are compared with experimental results, which indicates that entropy production can be used as a damage evolution metric. The theory is founded on the basic premise that a solid continuum obeys the first and the second laws of thermodynamics.

An exergetic approach for materials fatigue

International Journal of Exergy, 2017

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 Approach to Fatigue Failure Analysis in Metals and Composite Materials

2011

Fatigue is a dissipative process and must obey the laws of thermodynamics. In general, it can be hypothesized that the degradation of machinery components is a consequence of irreversible thermodynamic processes that disorder a component, and that degradation is a time dependent phenomenon with increasing disorder. This suggests that entropy-a fundamental parameter in thermodynamics that characterizes disorder-offers a natural measure of component degradation. The majority of the existing methods for prediction of fatigue are limited to the study of a single fatigue mode, i.e., bending or torsion or tension-compression. Further, the variability in the duty cycle in a practical application may render many of these existing methods incapable of reliable performance. During this research, we put forward the idea that fatigue is a degradation process and that entropy is the most suitable index for assessing degradation. That is, tallying irreversible entropy is more reliable and accurate than many of the other methods presented in the existing papers. We show that in processes involving fatigue, for a given material (metal and composite laminate), there exists a unique threshold of the cumulative thermodynamic entropy beyond which fatigue fracture takes place. This threshold is shown to be independent of the type of the fatigue process and the loading history. This exciting result is the basis of the development of a Fatigue Monitoring Unit (FMU) described in this research. We also propose a general procedure for assessment of damage evolution based on the concept of entropy production. The procedure is applicable to both constant-and variable amplitude loading. Empirical relations between entropy generation and damage evolution for two types of metals (Alumunium 6061-T6 and Stainless steel 304) and a woven Glass/Epoxy composite laminate are proposed and their potential for evaluation of fatigue damage are investigated.

A Model of Mechanothermodynamic Entropy in Tribology

Entropy

A brief analysis of entropy concepts in continuum mechanics and thermodynamics is presented. The methods of accounting for friction, wear and fatigue processes in the calculation of the thermodynamic entropy are described. It is shown that these and other damage processes of solids are more adequately described by tribo-fatigue entropy. It was established that mechanothermodynamic entropy calculated as the sum of interacting thermodynamic and tribo-fatigue entropy components has the most general character. Examples of usage (application) of tribo-fatigue and mechanothermodynamic entropies for practical analysis of wear and fatigue processes are given.