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Diamond films were synthesized on a Mo substrate using combustion flame. During the cooling process, most diamond films delaminated. From previous work it was shown that diamond films delaminated at a synthesis temperature less than 1300K (low temperature), and films did not delaminate at synthesis temperature more than 1400K (high temperature). In this study, to clarify the influences on the delamination of the interface, films synthesized at high temperature and low temperature were investigated by SEM and X-ray diffraction. The results show that in the case of low temperature, diamond films were synthesized on the Mo substrate, case of high temperature, Mo₂C and diamond phases were synthesized on the Mo substrate. Thermally induced interfacial stress occurs due to the thermal expansion mismatch between the synthesized film and the Mo substrate. The interfacial stress by high temperature and low temperature was determined as the cause of the delamination. Thus, the interfacial stress of each synthesized temperature was calculated by a finite element method. The results show that the interfacial stress in the film synthesized by high temperature was smaller than that by the low temperature. As the buffer phases prevent the delamination, synthesized films by high temperature will be useful as hardcoating layer for a metal surface.

Steel bridges increased considerably since 1960's in Japan. That is due to the lightness and long trend in bridge construction. Bridges, which are damaged by an increase in vehicle load, corrosion, earthquake, and so on, need repairing or strengthening. Repair procedures of steel bridge generally include cutting, bolting and welding procedures. These procedures, cutting, bolting and welding, occasionally bring about a stress concentration within the limit range. So, a chain of confirmation against the safety of structure is necessary. A safety evaluation method, which has regard to heat effect, is necessary to repair damaged structure with welding. Generalized welding residual stress is useful employ, to estimate the safety of structure during the repair work with welding. This research investigates the features of thermal stress generated by welding. The pattern of welding residual stress distribution was classified according to the ratio between length and width of plate. With those results, the features of residual stress generated by welding were generalized.

Graphite is applied to structural material of the high temperature reactor and nozzle of high energy rocket engine. The excessive vibration and stress field can be occurred for this material due to the severe thermal condition. In this study, the thermal stress and vibration characteristics of ATJ graphite under high temperature condition are investigated by finite element analysis (FEA). The specimen is designed as a disk shape in order to simulate the rocket nozzle combustion condition. The experiment of thermal heat is also conducted using by CO₂ laser.

In-situ observation of thermal stresses in thin films deposited on a silicon substrate was made by synchrotron radiation. Specimens prepared in this experiment were nano-size thin aluminum films with SiO₂ passivation. The thickness of the films was 10 nm, 20 nm and 50 nm. Synchrotron radiation revealed the diffraction intensities for these thin films and make possible to measure stresses in nano-size thin films. Residual stresses in the as-deposited state were tensile. Compressive stresses were developed in a heating cycle up to 300°C and tensile stresses were developed in a cooling cycle. The thermal stresses in the 50 nm film showed linear behavior in the first heating stage from room temperature to 250°C followed by no change in the stress at 300°C, however, linearly behaved in the second cycle. On the other hand, the thermal stresses in 20 nm and 10 nm films almost linearly behaved without any hysteresis in increasing and decreasing temperature cycles. The mechanism of thermal stress behavior in thin films can be explained by strengthening of the nano-size thin films due to inhibition of dislocation source and dislocation motion.

The thermal conductivity of single-crystal silicon was investigated by using Raman spectroscopy. The laser simultaneously acted as an excitation source and a heating source. The correlations between Raman spectra with both temperature and laser power for single-crystal silicon, which has a potential relationship with the thermal conductivity, were estimated. The results showed the localized compressive stress caused by laser heating would underestimate Raman peak shift. So, the temperature was determined based on the variation of linewidth. The predicted thermal conductivity of single-crystal silicon is 125 W/m ⋅ K, which is comparable to the theoretical value.

The organic thin film transistor (OTFT) on flexible substrate electroplated electrodes has many advantages as in the fabrication of low cost sensors, e-paper, smart cards, and flexible displays. In this study, we simulated the mechanical and electrical characteristics of the OTFT with various voltage conditions by using COMSOL. The model consisting of a channel, source and drain was employed to investigate the temperature distribution and thermal stress concentration. The channel length is 40 µm and the voltage ranged between -20V and -40V. The OTFT was fabricated using pentacene as a semiconducting layer and electroplated Ni as a gate electrode. Mechanical properties of the fabricated OTFT were characterized by thermal stress which was predicted with the result of stress distribution.

Vegetable insulating oil, with advantages such as high safety and environmental friendliness, is a good substitute for traditional mineral oil. However, thermal failure is one of the important factors affecting the safe operation of oil-immersed electrical equipment. This study focuses on soybean vegetable oil as the research subject and establishes a simulation model for soybean insulating oil to investigate the influence of thermal stress at different temperatures ranging from 1000K to 2000K on system decomposition and gas generation characteristics. The results indicate that, under elevated temperatures, the decomposition of soybean vegetable insulating oil predominantly occurs through decarboxylation reactions, leading to the generation of CO₂ and hydrocarbon radicals. The hydrocarbon radicals further decompose and react with other species, resulting in the formation of characteristic gases. It was observed that CO₂ and C₂H₄ serve as stable thermal decomposition by-products. Increasing temperatures significantly enhance the generation rates of various characteristic products and broaden the variety of such products. For instance, H₂ and CH₄ are characteristic gases produced at different temperature ranges. Studying the decomposition and gas generation characteristics of vegetable insulating oil under thermal stress holds crucial significance for transformer design and operation.

Tooth pain, especially tooth thermal pain, is one of the most important symptoms and signs in dental clinic and daily life. As a special sensation, pain has been studied extensively in both clinic and experimental research aimed at reducing or eliminating the possible negative effects of pain. Unfortunately, the full underlying mechanism of pain is still unclear, because the pain could be influenced by many factors, including physiological, psychological, physical, chemical, and biological factors and so on. Besides, most studies on pain mechanisms in the literature are based on skin pain sensation and only few are based on tooth pain. In this paper, we present a comprehensive review on both neurophysiology of tooth pain mechanism, and corresponding thermal, mechanical, and thermomechanical behaviors of teeth. We also describe a multiscale modeling approach for quantifying tooth thermal pain by integrating the mathematic methods of engineering into the neuroscience. The mathematical model of tooth thermal pain will enable better understanding of thermal pain mechanism and optimization of existing diagnosis and treatment in dental clinic.

A new thick shell element is used to study the thermoelastic behavior of functionally graded structures made from shells and plates. The element accounts for the varying elastic and thermal properties across its thickness. It also accounts for the thickness change, normal stresses and strains. The nonlinear heat transfer equations governing the through-thickness thermal distribution are treated using the Rayleigh-Ritz method. Prescribed temperatures as well as convection conditions are imposed on both faces of the shell. Three examples involving functionally graded beams, circular plates and spherical shells are examined. The effect of the volume fraction of the constituent materials and the through-thickness integration order are also investigated.

An improved aerothermoelastic flutter model of an infinitely long isotropic panel is proposed to investigate the complex dynamic behaviors of panel structures in supersonic flow. Considering the history effects of aerodynamic heating, a new model suitable for numerical computation of the temperature distribution in the panel is presented and proved mathematically. Then, the internal force and moment in the panel induced by thermal stress are accurately introduced into the existing panel flutter model. Finally, some numerical analyses based on the Galerkin procedure are presented, in combination with the presented aerothermoelastic model which is based on von Karman large deflection plate theory. From the numerical results, it is found that the effects of the aerodynamic heating and its history are significant and complicated, since they can induce, intensify, or change the oscillation behaviors of the panel. Furthermore, a rich variety of nonlinear dynamic behaviors, such as instabilities and chaos in the panel flutter model, are captured and analyzed, by bifurcation analysis and the maximum Lyapunov exponent in nonlinear dynamics. As a conclusion, it can be drawn that the model presented could be used to study the aerothermoelastic dynamics accurately and feasibly.

An accelerated explicit method and GPU parallel computing program of finite element method (FEM) are developed for simulating transient thermal stress and welding deformation in large scale models. In the accelerated explicit method, a two-stage computation scheme is employed. The first computation stage is based on a dynamic explicit method considering the characteristics of the welding mechanical process by controlling both the temperature increment and time scaling parameter. In the second computation stage, a static equilibrium computation scheme is implemented after thermal loading to obtain a static solution of transient thermal stress and welding deformation. It has been demonstrated that the developed GPU parallel computing program has a good scalability for large scale models of more than 20 million degrees of freedom (DOFs). The validity of the accelerated explicit method is verified by comparing the transient thermal deformation and residual stresses with those computed by the implicit FEM and experimental measurements. Finally, the thermal stress and strain in an automotive engine cradle model with more than 12 million DOFs were efficiently computed and the results are discussed.

In this study, 3D thermal stresses in composite laminates under steady-state through thickness thermal conduction are investigated by means of a stress function-based approach. One-dimensional thermal conduction is solved for composite laminate and the layerwise temperature distribution is calculated first. The principle of complementary virtual work is employed to develop the governing equations. Their solutions are obtained by using the stress function-based approach, where the stress functions are taken from the Lekhnitskii stress functions in terms of in-plane stress functions and out-of-plane stress functions. With the Rayleigh–Ritz method, the stress fields can be solved by first solving a standard eigenvalue problem. The proposed method is not merely computationally efficient and accurate. The stress fields also strictly satisfy the prescribed boundary conditions validated by the results of finite element method (FEM) results. Finally, some of the results will be given for discussion considering different layup stacking sequences, thermal conductivities and overall temperature differences. From the results, we find that the thermal conductivity greatly affects the stress distributions and peak values of stresses increase linearly for the present model. The proposed method can be used for predicting 3D thermal stresses in composite laminates when subjected to thermal loading.

The human head is one of the most sensitive parts of human body due to the fact that it contains brain. Any abnormality in the functioning of brain may disturb the entire system. One of the disturbing factors of brain is thermal stress. Thus, it is imperative to study the effects of thermal stress on human head at various environmental conditions. For the thermoregulation process, the human head is considered to be a structure of four layers viz.; brain, cerebrospinal fluid (CSF), skull and scalp. A mathematical model has been formulated to estimate the variation of temperature at these layers. The model is based on radial form of bio-heat equation with the appropriate boundary conditions and has been solved by variational finite element method. The rate of metabolic heat generation and thermal conductivity in this study have been assumed to be heterogeneous. The results were compared with the experimental studies for their coincidence and it has been observed theoretically and experimentally that the human head has greater resistance to compete with the thermal stress up to large extent.

Stretchable microelectrode is applied in various fields, such as sensory skins for soft robotics and wearable electronics for biomedical patches, etc. The structural quality of the stretchable microelectrode is a significant factor since it influences the thermo-mechanical characteristics. In order to improve the structural quality of the electrode, a serpentine-patterned configuration with various curvature angles of 60${}^{\circ }$, 90${}^{\circ }$ and 120${}^{\circ }$ were applied to the film of each electrode. In addition, thermal stress was applied at certain voltages to demonstrate the thermo-mechanical characteristics of the serpentine-patterned microelectrode. The numerical analysis on von Mises stress and thermal stress of the electrode was conducted with a commercial code, COMSOL Multiphysics ver. 5.3a. The results were graphically described by showing stress distributions of each case and the microelectrode having highest thermo-mechanical characteristics was derived.

Thermoelectric (TE) modules for power generation usually operate under high temperatures and large temperature differences, which inevitably introduce thermal stress in the modules. Suppressing the thermal stress is then one of the important issues for improving the service reliability of TE modules. In the past decades, various approaches have been developed for the design optimization of TE module primarily being focused on the enhancement of conversion efficiency, while the influence of structural factors on the module’s mechanical reliability is often overlooked. In this work, we proposed a multi-objective optimization strategy by using the finite element method to evaluate the structural reliability of a TE module, which integrates the module mounting mode, configurational structure of ceramic substrates, thickness of ceramic substrates and electrodes, cross-sectional shape of TE legs, and gaps between $p$- and $n$-type legs. As a typical sample, the thermal stress of an 8-pair skutterudite (SKD)-based TE module with the framework dimensions of 20 × 22 × 12 mm³ was well studied under the service conditions. The results reveal that a split structure of ceramic substrates and a pressing mounting mode with 2 MPa pressure on the module’s hot-side can significantly reduce the thermal stress in the module. Meanwhile, increasing the gap distance between $p$- and $n$-type legs, rounding the square column shaped legs, using thin ceramic substrate and thick electrode also can relieve the thermal stress somewhat. The simulation gives a comprehensive solution to reduce the thermal stress and enhance the module’s service reliability for the practical applications through structure optimization.

Carbon fiber structural batteries, which combine structural and functional properties, have good energy storage capacity while bearing loads have received attention from scholars at home and abroad in recent years as a new type of energy storage device. However, in the process of use, temperature changes will lead to the occurrence of thermal stresses, which may cause structural failure under multiple cycles. In this paper, the thermal-stress coupled model of structural batteries was established first using the temperature and thermal stress models of structural batteries, considering the heat exchange with the external environment of structural batteries. Then based on the coupled model, the thermal stress in the structural battery was simulated and analyzed in COMSOL considering different charge and discharge rates and ambient temperatures of the structural batteries. The results show that: (1) The higher the charging and discharging rates, the higher the temperature of the structural battery, resulting in greater thermal stress. (2) The higher the ambient temperature of the structural battery, the longer its discharge time and the lower the voltage at which discharge terminates, which is beneficial for the electrochemical performance of the battery. But the higher the ambient temperature, the greater the temperature change inside the structural battery, which is not conducive to the mechanical performance of the structural battery. This study can provide reference for the safety analysis of structural batteries in thermal environments.

Metal matrix composites (MMCs) have been regarded as one of the most principal classifications in composite materials. The thermal characterization of hybrid MMCs has been increasingly important in a wide range of applications. The coefficient of thermal expansion is one of the most important properties of MMCs. Since nearly all MMCs are used in various temperature ranges, measurement of coefficient of thermal expansion (CTE) as a function of temperature is necessary in order to know the behavior of the material. In this research paper, the evaluation of thermal expansivity has been accomplished for Al 6061, silicon carbide (SiC) and Graphite (Gr) hybrid MMCs from room temperature to 300°C. Aluminum (Al)-based composites reinforced with SiC and Gr particles have been prepared by stir casting technique. The thermal expansivity behavior of hybrid composites with different percentage compositions of reinforcements has been investigated. The results have indicated that the thermal expansivity of the different compositions of hybrid MMCs decreases by the addition of Gr with SiC and Al 6061. Few empirical models have been validated for the evaluation of thermal expansivity of composites. Using the experimental values namely modulus of elasticity, Poisson's ratio and thermal expansivity, computational investigation has been carried out to evaluate the thermal parameters namely thermal displacement, thermal strain and thermal stress.

This paper develops a model to identify the effects of thermal stress on temperature distribution and damage in human dermal regions. The design and selection of the model takes into account many factors effecting the temperature distribution of skin, e.g., thermal conductance, perfusion, metabolic heat generation and thermal protective capabilities of the skin. The transient temperature distribution within the region is simulated using a two-dimensional finite element model of the Pennes’ bioheat equation. The relationship between temperature and time is integrated to view the damage caused to human skin by using Henriques’ model Henriques, F. C., Arch. Pathol.43 (1947) 489–502]. The Henriques’ damage model is found to be more desirable for use in predicting the threshold of thermal damage. This work can be helpful in both emergency medicines as well as to plastic surgeon in deciding upon a course of action for the treatment of different burn injuries.

The thermal characterization and analysis of composite materials has been increasingly important in a wide range of applications. The coefficient of thermal expansion (CTE) is one of the most important properties of metal matrix composites (MMCs). Since nearly all MMCs are used in various temperature ranges, measurement of CTE as a function of temperature is necessary in order to know the behavior of the material. In this research paper, the evaluation of CTE or thermal expansivity has been accomplished for Al 6061, silicon carbide and graphite hybrid MMCs from room temperature to $300^{\circ }$C. Aluminium-based composites reinforced with silicon carbide and graphite particles have been prepared by stir casting technique. The thermal expansivity behavior of hybrid composites with different percentage compositions of reinforcements has been investigated. The results have indicated that the thermal expansivity of different compositions of hybrid MMCs decrease by the addition of graphite with silicon carbide and Al 6061. Empirical models have been validated for the evaluation of thermal expansivity of composites. Numerical convergence test has been accomplished to investigate the thermal expansion behavior of composites.

The thermo-mechanical behavior of functionally graded (FG) panels is investigated in supersonic air flow. The three-node triangular element based on the Mindlin plate theory is employed to account for the transverse shear strains, and the von-Karman nonlinear strain–displacement relation is utilized considering the geometric nonlinearity. The effective material properties of the FG material are assumed to vary through the thickness according to simple power law distribution. The aeroelastic equation is established using the first-order piston theory, the linear rule of mixture and the principle of virtual work. A multi-mode approach is utilized to form the reduced-order model. Nonlinear flutter response is obtained by solving the reduced-order aeroelastic equation in time using the Runge–Kutta fourth-order method. Numerical simulation reveals that the multi-mode reduced-order model has a good convergence property. By using the 24-mode model the variation of flutter amplitude with dimensionless dynamic pressure, and the route of nonlinear flutter response from simple harmonic limit cycle oscillation (LCO) to non-harmonic periodic oscillation are examined.