Thermal Stress Values Research Articles

Study on the Temperature and Thermal Stress of the Slag Layer Cooling Process in a Membrane Wall Entrained-Flow Gasifier

The pulverized coal gasification was performed in a bench-scale membrane wall entrained-flow gasifier, and properties of coal ash and slag were analyzed. A three-dimensional mathematic model of the membrane wall was developed for the temperature and thermal stress analysis of the slag layer. The temperature and thermal stress of the slag layer were simulated, and the contribution of the phase change of slag during the cooling process was also investigated. The simulation results indicate that remarkable temperature gradients are observed in the slag layer and the temperature field is also influenced by the stud. The phase change of the molten slag significantly influences the stress distribution and variation during the cooling. The thermal stress mainly reveals to be compressive in the initial solid slag layer. Its value is larger in the region with a higher temperature, while the thermal stress acts as tension in the slag solidified, and a greater value is observed in the region with a lower temperature. Furthermore, the value of thermal stress decreases in the initial solid slag but increases in the slag solidified with the decreasing temperature during the cooling.

Heating Steady Thermal Stresses in an Al1100/Ti-6Al-4V/SiC 2D-FGM Plane Four-Side Clamped Plate

The steady thermal stress problems under linear temperature load on upper surface in an Al1100/Ti-6Al-4V/SiC 2D-FGM plane four-side clamped plate are analyzed by the FEM. When the variation of the material composition in y-direction is linear, the plane thermal stress distributions with the changes of composition shape distribution coefficient mx and porosity coefficient Ax in x-direction are obtained. The results show that compressive stresses of the metal side reduce and the compressive stresses increase on the ceramic side with the increasing of the mx. Except for lower surface, when mx =0.5, the thermal stress values of the 2D-FGM plane plate are smaller than those of the 1D-FGM plate. Compared with the maximum thermal stress value of the 1D-FGM plate, that of the 2D-FGM plane plate reduces by 815MPa. The thermal stress curve surface has more and more obvious convex trend and has smaller thermal stress gradient with the increasing of the Ax, especially it is when =0.1~0.5, =0.2~0.5, and other places have no variation. By comparison with the minimum thermal stress of Ax=0.0, that of Ax=3.99 reduces by 47.3% at =0.3. The results provide more comprehensive and concrete foundation of calculation for design and optimization of the 2D-FGM plane plate.

Numerical Simulation Optimization and Preparation of Cu/ZrW<sub>2</sub>O<sub>8</sub> Functionally Graded Films

A mathematical model for the Cu/ZrW2O8 functionally graded films was established using a finite element method. The effects of the parameters, such as the layer number (N) and composition distribution index (P), on the thermal stress fields of the Cu/ZrW2O8 functional graded films were discussed. It shows that when N=5 and P=2, the maximum thermal stress in the functional graded films is decreased. And the maximum value of thermal stress appears in the internal layers of the functionally graded films. The phase composition, the surface morphology and the thermal stress of the films were analyzed by the XRD, SEM and X-ray stress tester, respectively. The results show that the thermal stress distribution is similar to that from the numerical calculation. The maximum value of the thermal stress decreases to 72% of the original coating without the functionally graded films, and appears in the internal layers of the functionally graded films.

Simulation and Analysis of the Thermal Stress in Concrete under Temperature Fluctuation Condition

The temperature field distribution and thermal stress distribution in concrete has been studied by finite elements method to establish the relationship between the thermal stress and the temperature in this paper. The results show that the maximum thermal gradient and the maximum thermal stress in the concrete appears on the direction of greater structural dimension, and the thermal stress value is positively correlated with thermal gradient or saying temperature difference and elastic modulus, and is negatively correlated with the water content and air content.

Optimum zoned fuel gas supply to the coil of an ethane pyrolysis furnace

The calculated results from the mathematical simulation of an industrial ethane pyrolysis process carried out at the Ethylene-Polyethylene Works in Sumgait under the average constant thermal stress of radiant coil were compared with the results calculated for the same process but using the suggested method of zoned fuel gas supply. The derived mathematical description of the industrial feedback process is given. The optimum thermal stress values calculated from the mathematical model for each zone were used to calculate the optimum fuel gas supplies to each zone, providing the maximum yields of the target products. The results of the comparison of the suggested method of conducting the process with that accepted in industry are evidence of the advantages of the fuel gas supply by the coil zones. This essentially saves fuel gas and provides a higher yield of the target products and results in a higher profit for the company. An expression is given to calculate the optimum fuel gas supply to each zone, even under variable reactor inlet conditions (loading and inlet temperature), which allows for the effective control of the process.

A study on wear resistance and microcrack of the Ti 3Al/TiAl + TiC ceramic layer deposited by laser cladding on Ti–6Al–4V alloy

Laser cladding of the Al + TiC alloy powder on Ti–6Al–4V alloy can form the Ti 3Al/TiAl + TiC ceramic layer. In this study, TiC particle-dispersed Ti 3Al/TiAl matrix ceramic layer on the Ti–6Al–4V alloy by laser cladding has been researched by means of X-ray diffraction, scanning electron microscope, electron probe micro-analyzer, energy dispersive spectrometer. The main difference from the earlier reports is that Ti 3Al/TiAl has been chosen as the matrix of the composite coating. The wear resistance of the Al + 30 wt.% TiC and the Al + 40 wt.% TiC cladding layer was approximately 2 times greater than that of the Ti–6Al–4V substrate due to the reinforcement of the Ti 3Al/TiAl + TiC hard phases. However, when the TiC mass percent was above 40 wt.%, the thermal stress value was greater than the materials yield strength limit in the ceramic layer, the microcrack was present and its wear resistance decreased.

Numerical study of thermal stress during different stages of silicon Czochralski crystal growth

In this paper, the influence of various crystal heights to the crystal/melt interface shape and thermal stresses distribution in the large diameter (300 mm) of the silicon single crystal growth in a Czochralski process was studied numerically. A tow dimensional fluid flow and heat transfer with solidification model was developed. The Navier-Stoks and energy equations in melt and the heat conduction equation in crystal are solved using the control volume-based finite difference method. The thermal elastic stress fields for different stages are calculated from the temperature field by adopting the plane strain model in an axi-symmetric geometry of a cylindrical crystal. It was found that the melt/crystal interface shape becomes more concave and the maximum value of thermal stress in the crystal reduces as the crystal grows. A good agreement between our numerical simulations and those found in the literature is obtained.

Thermo-elastic stress of a metal-matrix composite disc under linearly-increasing temperature loading by analytical and FEM analysis

In this study, the elastic stress analysis of a composite disc with aluminium matrix subjected to a linearly-increasing temperature distribution has been carried out. The values of tangential and radial stress components that have occurred under the effect of the temperature from the inner surface of the disc towards the outer surface have been obtained by two different methods, numerical and analytical. In the analytical analysis, a computer program has been developed to get the values of thermal stresses. But in the numerical study carried out with the finite-element method, Abaqus 6.8 package program has been used. As a result of these analyses, it has been observed that the stress values obtained from both methods support each other. It has been determined under this temperature distribution that tangential stress components are always on the condition of compression in the inner surface of the disc and of tensile in the outer surface. It has also been found out that radial stress components are always in the state of tensile along the whole profile of the disc. Finally, the stress analysis of the same composite disc subjected to this temperature distribution, but with a reduced mass, has also been examined numerically.

Electrochemical corrosion behavior, Vickers microhardness, and microstructure of Co–Cr and Ni–Cr dental alloys

Electrochemical corrosion behaviors, Vickers microhardness, microstructure, and electrical properties of Magnum H50 (Co=64.5%, Cr=29%, Mo=6.5% ) and Nikkeli–Kromi–Polttosekoitus (Ni=65.2%, Cr=22.5%, Mo=9.5%, X=2.8% Nb, Si, Fe, and Mn) dental alloys have been investigated. The corrosion potential for the Co64.5Cr29Mo6.5 alloy in HCl was higher than that of the Ni65.2Cr22.5Mo9.5X2.8 alloy. The corrosion rate with 0.5 M HCl for the Ni65.2Cr22.5Mo9.5X2.8 alloy was measured as being high and the corrosion resistance as being small as compared with the values for the Co64.5Cr29Mo6.5 alloy. Vickers hardness of the Co64.5Cr29Mo6.5 alloy was higher than that of the Ni65.2Cr22.5Mo9.5X2.8 alloy. Also Vickers hardness values of the used alloys were decreased by increasing indentation load. The thermal conductivity and minimum shear stress values of the used alloys are calculated.

Thermal Stresses in Bodies with Random Initial Temperature Distribution

This paper describes a stochastic analysis in the one-dimensional uncoupled linear thermoelasticity. The autocorrelation functions of transient temperature and thermal stresses are analytically obtained in seven simple geometries: infinite plate, infinite strip, hollow sphere, infinite body with a spherical cavity, infinite hollow cylinder, annular disk and infinite body with a cylindrical hole, which have a random initial temperature distribution. Numerical calculations are performed for some geometries under the condition that the randomness in the initial temperature is given as a homogeneous white noise. The transient behavior of the mean square temperature and thermal stresses is illustrated and it is observed in objects confined to a finite region that whereas the maximum value of the mean square thermal stresses occurs within the objects shortly after the heat flow begins, it appears at a lateral surface after a length of time has elapsed.

Analysis of Thermal Stress in Asphalt Overlay Based on Thermal-viscoelasticity Theory

AbstractThe thermal stress responses of various structural asphalt pavement under different cooling conditions were analyzed considering thermal-viscoelasticiy of asphalt pavement mixture by using finite element software. The influence of cooling speed, initial temperature, cooling range, pavement thickness, base modulus and thermal shrinkage ratio on temperature stress were represented. The results indicate that (1) the cumulated value of thermal shrinkage stress in asphalt pavement is low under high temperature; (2) the initial temperature and cooling speed distinctly effect the thermal stress of asphalt pavement; (3) the reflective crack is more easily occurred in thin asphalt overlay than the thick one, while the up-down crack is more easily happened in thick asphalt overlay than the thin one; and (4) too large base modulus is unsuitable.

Engineering extruded collagen fibers for biomedical applications

AbstractExtruded collagen fibers constitute a promising biomimetic scaffold for tissue engineering applications. In this study, we compared the structural, thermal, and mechanical properties of fibers produced from either NaCl or poly(ethylene glycol) with a number‐average molecular weight of 8000 (PEG 8K), the only two coagents that have been used in the fabrication process. As novel, we report the fabrication of fibers with properties similar to native or synthetic fibers using other coagents. NaCl derived fibers were characterized by higher thermal stability (p < 0.026), stress (p < 0.001), and modulus (p < 0.0025) values than PEG 8K, whereas the latter yielded more extendable fibers (p < 0.012). Poly(ethylene glycol)s with number‐average molecular weights of 200 and 1000 produced fibers with similar mechanical properties (p > 0.05) that were thinner (p < 0.033), stiffer (p < 0.022), and less extendable (p < 0.0002) than those of PEG 8K. Poly(vinyl alcohol) (PVA) with a number‐average average molecular weight of 9–10,000 and PEG 8K yielded fibers with similar diameters and stress‐at‐break values (p > 0.05); however, the poly(ethylene glycol) derived fibers were more extendable (p < 0.0003), whereas the PVA fibers were stiffer (p < 0.029). Gum‐arabic‐ and soluble‐starch‐derived fibers were of similar tensile strength, extendibility, and stiffness (p > 0.05). In this in vitro study, the thickest (p < 0.011) and the weakest (p < 0.0066) fibers were produced in the presence of sodium sulfate. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008

Numerical simulation of liquid-encapsulant float zone growth of indium phosphide crystals in zero gravity

Numerical simulation for flow, heat transfer and thermal stress for a 3 in. diameter liquid-encapsulated float zone growth of single-crystal InP is conducted by using the finite-element method under zero gravity condition. The results show that the crystal and feed rod rotation rate has a notable influence on the flow pattern in the melt. It also shows that the melt/crystal interface shape becomes more convex and the maximum value of thermal stress in the crystal reduces with increasing encapsulant thickness, decreasing pulling rate and decreasing the length of the melting zone.

Modelling of particle breakage during drying

An advanced theoretical drying model of single wet particle is proposed. The temperature profile in both crust and wet core regions is described by partial differential equations with appropriate boundary conditions. A Stefan-type vapour diffusion through the crust pores and its convection to the drying ambient has been assumed. The results of model validation for of whole milk droplet drying are presented. The reasons of wet particle possible cracking/rupture are analysed for silica drying. It is concluded that the values of thermal stresses in the crust have decisive importance for the silica particle cracking/rapture during drying. Finally, the results of thermal stresses calculation for silica drying under different conditions are presented.

Numerical Simulation of Temperature Field and Thermal Stress Field of Work Roll During Hot Strip Rolling

Based on the thermal conduction equations, the threedimensional (3D) temperature field of a work roll was investigated using finite element method (FEM). The variations in the surface temperature of the work roll during hot strip rolling were described, and the thermal stress field of the work roll was also analyzed. The results showed that the highest roll surface temperature is 593 °C, and the difference between the minimum and maximum values of thermal stress of the work roll surface is 145. 7 MPa. Furthermore, the results of this analysis indicate that temperature and thermal stress are useful parameters for the investigation of roll thermal fatigue and also for improving the quality of strip during rolling.

Investigation of Analytical Solutions for Bonded Structures by Photomechanical Methods

Abstract: In this paper, both photoelasticity and moiré interferometry were successively incorporated with finite element method to investigate the predicted thermal stresses and lateral displacement of bonded structures calculated from different theories. It was found that the distributions of moment and transverse force play significant roles in making different values of thermal stresses in the adherends by authors’ and Suhir's 1986 theories. On the other hand, the values of lateral displacement obtained from different theories are almost identical.

Transient thermal stress analysis of CeO 2 thin films on Ni substrates using finite element methods for YBCO coated conductor

The effect of residual stresses of CeO 2 buffer layers on Ni substrate for YBCO coated conductors is considered. CeO 2 films were fabricated on Ni tape substrate from the solutions prepared from alkoxide precursors, solvent, chelating agent and modifying liquid material by using a reel-to-reel sol–gel technique. SEM observation showed that CeO 2 buffer layers had crack-free, pinhole-free and continuous structures and the characteristic feature of the films was grain boundary grooves. Finite element method (FEM) was used to compute the temperature and stress fields of the sample with CeO 2/Ni configuration. The solution was obtained by ANSYS 5.4 analysis programme. The effect of time and residual stresses of the films with different thickness was examined in terms of the FEM results. It was found that the positions of the improved temperature and thermal stresses were considerably affected material properties, time and film thickness for CeO 2 buffer layers and the thermal stresses values increased upon increasing the film thickness.

Heat transfer and thermal stress analysis in grooved tubes

Heat transfer and thermal stresses, induced by temperature differences in the internally grooved tubes of heat transfer equipment, have been analysed numerically. The analysis has been conducted for four different kinds of internally grooved tubes and three different mean inlet water velocities. Constant temperature was applied from the external surface of the tube. Energy and governing flow equations were solved using finite difference scheme. Finite element method (FEM) was used to compute the thermal stress fields. Grooving effects on the thermal stress ratio have been discussed. As a result, maximum thermal stress occurs in the case ofp =d for all water inlet velocities. The maximum thermal stress ratio positions inside the tube have been indicated as MX for all investigated cases. In the light of the thermal stress values, various designs can be applied to reduce thermal stress in grooved tubes.

Effects of WC size and amount on the thermal residual stress in WC–Ni composites

Effects of WC particle size and volume fraction on the magnitude and distribution of thermal residual stresses (TRS) in WC–Ni cemented carbide composites were studied by neutron powder diffraction. Samples of high (0.3) and low (0.1) Ni volume fraction and coarse (1.7μm) and fine (0.5μm) WC particle size were employed. Thermal residual strain and stress values were obtained at temperatures between 100 and 900K. The magnitude of the mean (compressive) WC stress increased as WC fraction decreased, while the mean (tensile) Ni stress did the opposite. For both phases, stresses were highest for fine WC particles, reaching over 3GPa in Ni. Elastic strain distributions, due to the sharp edges and corners of WC particles, were characterized by analyzing diffraction peak widths. The range of stress increased with the magnitude of the TRS. Even though the mean TRS is compressive in WC, regions of tension exist, and, for Ni, regions of compression are present.

Microscale computational simulation and experimental measurement of thermal residual stresses in glass–alumina functionally graded materials

Glass–alumina functionally graded materials are new attractive composite materials, that can achieve peculiar mechanical properties due to their gradual compositional variation. Nevertheless, the difference between the coefficients of thermal expansion of the constituent phases may result in significant thermal residual stresses in service or during fabrication. A proper glass formulation can minimize the mismatch in thermo-mechanical properties, thus relevantly reducing the mean value of the resultant thermal stresses. However, it is a crucial requirement to evaluate the effect of microstructural discreteness and randomness on the actual stress distribution in functionally graded materials. With this aim, a computational model which applies the finite element method at the microscale is used. The careful modelling of the real microstructural details enables to accurately predict the local stress values and distribution. In order to verify the reliability of the computational simulations, the residual thermal stresses were also experimentally measured by means of a piezo-spectroscopic technique. The comparison between the numerical and the experimental results validate the microstructure-based model.