A Model of Mechanothermodynamic Entropy in Tribology

Abstract

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.Keywords: entropy; mechanothermodynamics; tribo-fatigue; tribology; fatigue; damage Thermodynamic EntropyThe following functions are used to describe the state of thermodynamic systems [1]:where temperature T, volume V, and number of moles of chemical components N k are the macroscopic state variables. In the general case of an open system, the change dU of internal energy U is presented [1] as:where dQ is the amount of heat; dA is the amount of mechanical energy; dU sub is the amount of substance, which the system exchanged with the environment for a time interval dt; p is the pressure; the µ k 's are the chemical potentials. Planck especially emphasized that dU in Equation (2) is an infinitely small difference, whereas dQ, dA, and dU sub are the infinitely small amounts. It follows from (2) that entropy S change in a thermodynamic system (subscript T) is: Abstract: 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 tribofatigue 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.

An Entropy Based Low-Cycle Fatigue Life Prediction Model for Solder Materials

“…The material parameters of SAC305 solder joints aging at different temperatures (at 77 K, 223 K, 293 K and 453 K) for 72 hours and different experimental conditions (with strain amplitude of 4%, 6%, 8% and electrified condition) are summarized in Table 2. It should be noted that Equation (19) cannot be directly applied because the samples in the current experiments are not standard uniaxial specimen, thus the stress and strain cannot be directly used in the model. In additional, the defects introduced during the manufacturing process and microstructure distribution of intermetallic compound produced during the reflow process cannot be neglected.…”

“…It should be noted that Equation (19) cannot be directly applied because the samples in the current experiments are not standard uniaxial specimen, thus the stress and strain cannot be directly used in the model. In additional, the defects introduced during the manufacturing process and microstructure distribution of intermetallic compound produced during the reflow process cannot be neglected.…”

“…The material constant for different Al alloys and steel alloys [32] were adopted to calculate the change of entropy. The material parameters are summarized in Table 1: Based on Equation (19), the increment of entropy after the plastic damage can be obtained, as shown in Figure 1a,b. It is noted that for different materials, the entropy increment process are quite different.…”

“…From Equation (19), the increment of entropy during the fatigue process after the initiating of plastic damage can be calculated. The material constant for different Al alloys and steel alloys [32] were adopted to calculate the change of entropy.…”

“…Researches have been performed on Mechanothermodynamics for the complex systems working under mechanical fatigue, thermal loading, friction and wear conditions [19][20][21][22]. In these works the specific entropy is assessed as the ratio between the effective energy components and limiting energy.…”