Thermoelastic Characteristics Research Articles

Thermo-elastic Characteristics of Thermal Barrier Coating in a Gas Turbine Combustion Chamber with an Intermediate FGM Layer

This study is focused on the analysis of thermos-elastic characteristics of a gas turbine combustion chamber, where the inner surface experiences a higher temperature while the outer region of the wall should be thermally conductive to dissipate the heat of combustion. Using a single material is not suitable to ensure the above two requirements simultaneously. Instead of using a single material, a layered combustion chamber with high-temperature material at the inner region and thermally conductive material at the outer region can be a solution. This produces the problem of a sharp interface where disbonding occurs due to high thermal stresses. The problem of sharp interface can be eliminated by using a functionally graded material (FGM) layer in between the inner and outer layers of the combustion chamber. The present study considers a gas turbine combustion chamber consisting of three layers: the inner layer is used as a thermal barrier coating, the intermediate layer is a smooth transition from the inner layer to the outer layer, and the outer layer is a thermally conductive material. ANSYS simulation is used for the analysis of thermos-elastic characteristics of the combustion chamber with homogeneous and FGM intermediate layers. The effect of linear and nonlinear material distributions in the FGM layer on the thermos-elastic characteristics is studied. A comparison of results reveals that thermal stress smoothly changes from the inner layer to the outer layer in the case of the FGM intermediate layer compared to the homogeneous intermediate layer. This suggests that a combustion chamber with an FGM intermediate layer is more reliable than a homogeneous intermediate layer.

Сравнительный анализ термоупругих характеристик керамоматричных композиционных материалов, определенных по различным модельным представлениям структурно фазового состава матричного материала

A comparative analysis of thermoelastic characteristics of ceramic matrix composite materials (CMC) obtained by liquid and gas phase technologies, reinforced with two types of carbon fibers (CF), is carried out based on different model structural phase composition of the obtained matrix material. It is noted that when implementing the liquid phase siliconizing and using high modulus carbon fibers with high negative values of the absolute value of the coefficients of linear thermal expansion (CLTE), a simplified model of the matrix material consisting of only one SiC phase can be correctly used. When implementing PIP and CVI technologies, CMC with low modulus CF and CF with low negative CLTE values show the greatest sensitivity to an increase in matrix porosity. For CMC based on CF T800, the change in the longitudinal CLTE was about 66% with a porosity of 20%. An increase in porosity leads to a decrease in all elastic characteristics of the CMC, to the greatest extent for the transverse modulus of elasticity and the shear modulus.

A novel model of nonlocal photoacoustic and plasmaelastic heated by laser pulsed excitation of nanoscale semiconductor medium

The study takes into account the diffusion of photo-excited carriers in the presence of a laser pulse and theoretically investigates photoacoustic wave propagation in the thermoelastic domain. In a nonlocality medium, the phenomena of thermomechanical and acoustic wave interaction are considered. Thermoelasticity, photothermal, and photoacoustic theories provide the controlling formulas. Photoacoustic waves are not dependent on electron–phonon or electron–hole thermalization processes; rather, they are produced by thermoelastic stress resulting from the temperature increase induced by the laser. The optical, elastic, and thermoelastic characteristics of nanoscale semiconductor materials are taken into account and photoacoustic signals are predicted by solving a thermal diffusion issue and a thermoelastic problem in combination. The mathematical model can be solved using the harmonic wave approach. By obtaining numerical solutions, all the physical fields of the physical domain, such as thermal, acoustic, mechanical, and carrier density diffusion, as well as displacements and temperatures, can be derived. The influences of nonlocal parameters, thermal delay, and laser pulse effect are investigated and compared using two- and three-dimensional visual representations, corresponding to two-dimensions and three-dimensions domains, respectively.

REPRESENTATIVE VOLUME AND EFFECTIVE MATERIAL CHARACTERISTICS OF PERIODIC AND STATISTICALLY UNIFORMLY REINFORCED FIBER COMPOSITES

In the deformable solid mechanics, there are concepts associated with continuum points (displacements, relative elongations, shifts) and a set of continuum points – an elementary volume (mass, energy, stresses). The role of such volume in the mechanics of composite materials is played by the representative volume element (RVE).This concept was first introduced by R. Hill (1963). Modern authors use the W.J. Drugan, J.R. Willis (1996) formulation. Based on the analysis of the RVE concept, we formulated its essential features: RVE is the minimum possible sample for numerical tests to determine the effective material parameters of the composite; under any RVE loading, its macroscopic stress-strain state is uniform. Its significance for the mechanics of composite materials is revealed: the existence of RVE for a composite is a criterion for applying the effective modulus theory to the analysis of its stress-strain state; the dehomogenization of a stressed-state composite material at a point is a solution to the micromechanics problem of the RVE stress-strain state determination; the characteristic size of RVE limits the size of the sampling grid in the numerical study. An iterative algorithm for constructing a representative volume of a periodic structure composite and its effective material thermoelastic characteristics is proposed. It is shown that the geometric shape of such a composition is a rectangular parallelepiped. The RVE construction algorithm for periodic compositions is extended to the composites statistically uniformly reinforced with continuous fibers. A method for modeling such materials with a following regular structure is suggested described: in the section perpendicular to the fibers, fiber centers should be located at the vertices of regular triangles. Examples of constructing RVE and thermoelastic material characteristics of specific compositions are given. The calculation results are compared with the data obtained using certified software products.

Investigation of mechanical properties of composite materials reinforced with carbon fibers

Theoretical and experimental methods for obtaining and investigating effective thermomechanical characteristics - residual stresses and deformation in panels made of nanomodified materials with asymmetrical reinforcement scheme have been developed in this paper. The study of the residual stress-strain state of structural elements made of carbon plastic using the values of thermoelastic characteristics of composite monolayers identified on the basis of the developed methods meade it possible to reveal the possibility of reducing the residual stress-strain state in structures with asymmetric reinforcement schemes.

A BRIEF OVERVIEW OF STATIONARY TWO-DIMENSIONAL THERMOELASTIC STATE MODELS IN HOMOGENEOUS AND PIECEWISE-HOMOGENEOUS BODIES WITH CRACKS

Purpose. A two-dimensional mathematical model of the problem of thermo-elasticity for piecewise-homogeneous component plate containing a crack has been built. The stress intensity coefficients in the vertices of the crack increase affecting strength of the body significantly. This leads to the growth of a crack and, as a result, to further local destruction of a material. Therefore, such a model reflects, to some extent, the destruction mechanism of the elements of engineering structures with cracks. Methodology. Based on the method of the function of a complex variable we have studied the two-dimensional thermoelastic state for the body with crack as stress concentrators. As result, the problem of thermoelasticity was reduced to a system of two singular integral equations (SIE) of the first and second kind, a numerical solution of which was found by the method of mechanical quadratures. Findings. The two-dimensional mathematical model of the thermoelastic state has been built in order to determine the stress intensity factors at the top of the crack and inclusion. The systems of singular integral equations of the first and second kinds of the specified problem on closed (contour of inclusion) and open (crack) contours are constructed. The influence of thermophysical and mechanical properties of inclusion on the SIF sat the crack types was investigated. The dependences of the stress intensity factor which characterizes the distribution of the intensity of stresses at the vertices of a crack have been built, as well as its elastic and thermoelastic characteristics of inclusion. This would make it possible to analyze the intensity of stresses in the neighborhoods of crack vertices depending on the geometrical and mechanical factors. As a result, this allows to determine the critical values of temperature in the three-component plate containing a crack in order to prevent the growth of the crack, as well as to prevent the local destruction of the body. It was found that the appropriate selection of mechanical and thermophysical characteristics of the components of a three-component plate containing a crack can be useful to achieve an improvement in body strength in terms of the mechanics of destruction by reducing stress intensity factors at the crack’s vertices. Originality. The solutions of the new two-dimensional problem of thermoelasticity for a specified region due to the action of constant temperature as well as due to local heating by a heat flux were obtained. The studied model is the generalization of the previous models to determine the two-dimensional thermoelastic state in a piecewise homogeneous plate weakened by internal cracks. Practical value. The practical application of this model is a more complete description of the stress-strain state in piecewise homogeneous structural elements with cracks operating under temperature loads. The results of numerical calculations obtained from the solution of systems of equations and presented in the form of graphs can be used in the design of rational modes of operation of structural elements. This takes into account the possibility of preventing the growth of cracks by the appropriate selection of composite components with appropriate mechanical characteristics.

Simulation-based evaluation of the effectiveness of fiber-optic sensing in monitoring and optimizing water circulation in next-generation enhanced geothermal systems

The success of multi-stage hydraulic fracturing technology in unconventional oil and gas reservoir development has attracted much attention from the geothermal community. Some pilot field experiments have been conducted to investigate the multi-stage hydraulic stimulation along horizontal or high-deviated wellbores in geothermal reservoirs (denoted as next-generation enhanced geothermal systems). One common output of such stimulation is that the created hydraulic fractures show various conductive capabilities, which could potentially lead to undesirable flow localization, early thermal breakthrough, and low cold water sweep efficiency. Monitoring the water circulation between horizontal wellbores connected through hydraulic fractures becomes important in avoiding early severe producing temperature reduction in practical operations. In this study, we investigate the effectiveness of distributed temperature sensing (DTS) and distributed strain sensing (DSS) in identifying dominant flow paths in geothermal reservoirs with multi-stage hydraulic stimulation and horizontal well completion designs. A coupled thermo-poro-elastic model for general-purpose geothermal reservoir simulation is developed and solved using a combined finite volume/finite element method, together with a fully implicit sequential coupling scheme. The temperature and strain responses along horizontal production wells are simulated and analyzed during water circulation. Reservoir temperature reduces in the area that is close to the water flow paths, which induces thermal contraction. These thermoelastic characteristics can be monitored by fiber-optic sensing, forming distinct signatures for flow-localization identification. DTS data may be dominantly influenced by the fractures with higher conductivity, ‘masking’ the signals related to fractures in the downstream, but DSS data can provide additional information for accurate identification of high conductive fractures. Successful mitigation strategies, for example plugging the dominant fractures illustrated in this study, could substantially increase the producing fluid temperature. The analyses in this study show that fiber-optic sensing is an effective technology to monitor and optimize water circulation in next-generation enhanced geothermal systems.

Thermoelastic characteristics of moving viscoelastic nanobeams based on the nonlocal couple stress theory and dual-phase lag model

Thermal behavior of a moving viscoelastic nanobeam under the influence of periodic thermal load is considered in the framework of Kelvin-Voigt viscoelastic model with fractional operators. The equation of motion for axially moving nanobeam is modeled by employing the Eringen’s nonlocal elastic theory in conjunction with the couple stress hypothesis and the conventional Euler–Bernoulli beam model. The thermoelastic features is then established by employing the generalized dual phase-lag heat conduction model. After utilizing the Laplace transform, the thermomechanical equations are coupled and solved. The current results are validated by presenting numerical examples and comparing with previous solutions obtained by traditional theories in the literature. According to the provided numerical simulations, the deflection of the axially moving nanobeam as well as its temperature change reduce with the axial velocity and the influences of small scale and nonlocal parameters are also revealed and discussed.

A numerical homogenization method for the determination of the thermal bowing of a masonry wall exposed to fire: Application to natural stone masonry

Thermal bowing is one of the major concerns when analysing the structural behaviour of masonry walls in fire conditions, along with the loss of resistance due to material degradation. This contribution proposes a new homogenization method aimed at determining the thermal deformed shape of a masonry wall exposed to fire. First, the homogenized thermo-elastic characteristics of a natural stone masonry wall are determined taking into account the material properties of stone and mortar as functions of temperature increase, as well as the geometrical characteristics of their assembly. As a result, membrane and bending stiffness coefficients, as well as thermal-induced efforts, of the wall modelled as a homogenized plate are obtained. Such homogenized thermo-mechanical characteristics make it possible to determine the deformed shape of the wall after a certain time of fire exposure, through the formulation and the resolution of a finite element plate problem, making use of the previous homogenized stiffness characteristics. Numerical simulations show that the presence of joints has little influence on the deformed shape of the masonry wall compared to a homogeneous stone-only wall. They appear to be in rather good agreement with previous full-scale experimental tests carried out on limestone masonry walls, therefore providing a first validation of the proposed method, even though further improvements could be envisaged as regards a more reliable determination of the temperature gradient across the wall thickness.

Influences of Boundary Temperature and Angular Velocity on Thermo-Elastic Characteristics of a Functionally Graded Circular Disk Subjected to Contact Forces

The behaviors of functionally graded (FG) engineering structures are influenced by various parameters, such as the boundary temperature, the angular velocity, variations in the thickness, the weight of the structure, and the loading state. The thermo-elastic characteristics of FG rotating circular disks under the loading of contact forces were investigated. Hooke’s law in plane stress problems was applied to derive a pair of partial differential equations and a finite volume method was developed due to the complexity of the governing equations. The thermo-elastic characteristics of the FG rotating disks were investigated according to the variations in their outer boundary temperature and angular velocity. The increase in the outer boundary temperature caused crack generation at the inner surface of the circular disk and on the opposite side to the loading point. The increase in the angular velocity caused unstable thermo-elastic behaviors near the area of the outer boundary surface, especially at 0.7<(r−a)/(b−a) < 0.9, and may have led to crack generation at the outer surface of the rotating disk. These results may be applied to the design of functionally graded circular cutters or grinding disks undergoing contact forces to produce proper and reliable thermo-elastic characteristics for practical applications.

Thermal plane waves in unbounded non-local medium exposed to a moving heat source with a non-singular kernel and higher order time derivatives

In this paper, the thermoelastic characteristics of a nonlocal unbounded viscoelastic medium due to an instantaneous heat source is investigated by considering a modified dual-phase-lag model with higher-order time derivatives. The fractional derivative and Eringen's non-local theory are also applied in the considered model. To extend the application of the classical Kelvin-Voigt model, a fractional derivative operator with non-single kernels based on the Atangana and Baleanu's concept is proposed. After applying the Laplace transform method, the governing systems of equations are expressed as vector-matrix differential form and solved by constructing an eigenvalue problem. Some comparative results are presented to analyze the effects of heat source velocity, nonlocal parameter, structural viscoelastic coefficients, phase lags, fractional and higher-order parameters on the behavior of physical fields.

Determination of the Deformed Shape of a Masonry Wall Exposed to Fire Loading by a Homogenization Method

The present contribution shows how it is possible to determine the homogenized thermo-elastic characteristics of a natural stone masonry wall, taking into account the material properties of stone and mortar as functions of temperature increase, as well as the geometrical characteristics of their assembly. Joints are incorporated in the analysis through a numerical homogenization procedure. As a result, membrane and bending stiffness coefficients, as well as thermal-induced efforts, of an equivalent plate are obtained. Such homogenized thermomechanical characteristics make it possible to determine the deformed shape of the wall after a certain time of fire exposure. As an example, the calculation procedure is performed on a particular configuration of infinitely wide wall, illustrating the influence of the joints on its thermal deformed shape. To assess the practical validity of this homogenization-based calculation procedure, results of the numerical homogenized model (incorporating joints) are compared to those of a homogeneous model (without joints), and to available experimental results obtained on a 3 m-high, 3 m-wide wall exposed to fire loading.

Optimal analysis of TSM fitting considering contact interface TECs of meshing gears

The pre-research project aims to propose a method of optimizing tooth surface modification (TSM) fitting under thermoelastic lubrication (TEL) conditions to reveal the most popular and concerned mechanism issues in the field of mechanical engineering. This is an exploratory study, mainly considering the gear comprehensive error and TSM state of TEL contact interfaces are extremely harsh, which complicates simulation analysis and optimal design. TSM simulation has fitted numerically agreement with optimized results obtained experimentally, which means that they can, whether isolated or by using a multiscale coupling method, start to be adopted to revise, and verify meta-models for thermoelastic characteristics (TECs) under TEL problems. This subject involves the TSM fitting of the theoretical teeth surface superimposed structure, and performs 3D and diagonal modification optimization design, obtains the modified surface position and normal vectors, according to load teeth contact analysis (LTCA), a variety of optimized modification models are established and complex curved surfaces are analyzed to fit the actual gear teeth surface thermoelastic contact numerical simulation, which has been further demonstrated and expressed in the type experiment combined with actual key working conditions and multiple influencing parameters, which is of great significance to the development of modern gear transmission system.

Neural Network-Based Prediction Model to Investigate the Influence of Temperature and Moisture on Vibration Characteristics of Skew Laminated Composite Sandwich Plates.

The present study deals with the development of a prediction model to investigate the impact of temperature and moisture on the vibration response of a skew laminated composite sandwich (LCS) plate using the artificial neural network (ANN) technique. Firstly, a finite element model is generated to incorporate the hygro-elastic and thermo-elastic characteristics of the LCS plate using first-order shear deformation theory (FSDT). Graphite-epoxy composite laminates are used as the face sheets, and DYAD606 viscoelastic material is used as the core material. Non-linear strain-displacement relations are used to generate the initial stiffness matrix in order to represent the stiffness generated from the uniformly varying temperature and moisture concentrations. The mechanical stiffness matrix is derived using linear strain-displacement associations. Then the results obtained from the numerical model are used to train the ANN. About 11,520 data points were collected from the numerical analysis and were used to train the network using the Levenberg–Marquardt algorithm. The developed ANN model is used to study the influence of various process parameters on the frequency response of the system, and the outcomes are compared with the results obtained from the numerical model. Several numerical examples are presented and conferred to comprehend the influence of temperature and moisture on the LCS plates.

Obtaining of Carbon Fibers Based Composite Materials and Study of Their Mechanical Properties

In this work, theoretical and experimental methods have been developed for obtaining and studying effective thermomechanical characteristics - residual stresses and deformations in panels made of nanomodified materials with an asymmetric reinforcement scheme. The study of the residual stress-strain state of structural elements made of carbon fiber reinforced plastic using the values ​​of thermoelastic characteristics of composite monolayers identified on the basis of the developed methods made it possible to reveal the possibility of reducing the residual stress-strain state in structures with asymmetric reinforcement schemes.

Phase relations and thermoelasticity of magnesium silicide at high pressure and temperature.

Within the exploration of sustainable and functional materials, narrow bandgap magnesium silicide semiconductors have gained growing interest. Intriguingly, squeezing silicides to extreme pressures and exposing them to non-ambient temperatures proves fruitful to study the structural behavior, tune the electronic structure, or discover novel phases. Herein, structural changes and thermoelastic characteristics of magnesium silicides were probed with synchrotron x-ray diffraction techniques using the laser-heated diamond anvil cell and large volume press at high pressure and temperature and temperature-dependent synchrotron powder diffraction. Probing the ambient phase of Mg2Si (anti-CaF2-type Mg2Si, space group: Fm3¯m) at static pressures of giga-Pascals possibly unveiled the transformation to metastable orthorhombic anti-PbCl2-type Mg2Si (Pnma). Interestingly, heating under pressures introduced the decomposition of Mg2Si to hexagonal Mg9Si5 (P63) and minor Mg. Using equations of state (EoS), which relate pressure to volume, the bulk moduli of anti-CaF2-type Mg2Si, anti-PbCl2-type Mg2Si, and Mg9Si5 were determined to be B0 = 47(2) GPa, B0 ≈ 72(5) GPa, and B0 = 58(3) GPa, respectively. Employing a high-temperature EoS to the P-V-T data of anti-CaF2-type Mg2Si provided its thermoelastic parameters: BT0 = 46(3) GPa, B'T0 = 6.1(8), and (∂BT0/∂T)P = -0.013(4) GPa K-1. At atmospheric pressure, anti-CaF2-type Mg2Si kept stable at T = 133-723 K, whereas Mg9Si5 transformed to anti-CaF2-type Mg2Si and Si above T ≥ 530 K. This temperature stability may indicate the potential of Mg9Si5 as a mid-temperature thermoelectric material, as suggested from previous first-principles calculations. Within this realm, thermal models were applied, yielding thermal expansion coefficients of both silicides together with estimations of their Grüneisen parameter and Debye temperature.

Thermoelastic Characteristics of Functionally Graded Circular Disk Models under the Loading of Contact Forces

A rotating functionally graded circular disk undergoing a contact load is taken into account to investigate the thermoelastic characteristics. By considering contact force, a pair of partial differential equations is induced as the governing equations based on Hooke’s law. The behavior of circular disk modes is described with the variations of contact force and homogeneous thickness. A finite volume model is introduced to obtain approximate solutions for the governing equations because of the complexity of the equations. Contact force is highly influential in the radial direction compared to the circumferential direction in the displacement distribution, while a large radial stress appears near the area of the contact point. In the strain distribution, the magnitude increases as the angle grows near part of the outer boundary in the circular domain. The radial distribution profiles are susceptible to the growth of contact force in nearby area of the outer boundary, whereas the influences on the circumferential direction profiles are trivial. The increase of homogeneous thickness dwindles the radial magnitude of displacement, stress, and strain distribution profiles over nearby area of the outer boundary of the circular domain. As a result, numerical approach demonstrates that contact force and homogeneous thickness are indispensable parameters and provide deep influence on the thermoelastic movements of a rotating circular disk. Thus, the results obtained may be useful to design an appropriate FGM circular disk model for the industrial area by controlling the above parameters.

Investigation of thermo-elastic characteristics in functionally graded rotating disk using finite element method

Abstract In this research paper, displacement, stresses and strains are presented for rotating FGM disk with variable thickness by using finite element method (FEM). Thermo-elastic material properties and thickness of FGM disk continuously vary as exponential and power law function in radial direction along radius of disk. The value of Poisson's ratio is taken as constant. The problem of thermo-elasticity is converted into second order governing differential equation in terms of radial coordinate. This conversion is based upon equilibrium equation for disk and stress-strain relationship. The influence of variable thickness, angular velocity and functionally graded materials is discussed on thermo-elastic characteristics of rotating disk for exponential variation of material properties. Further, these thermo-elastic characteristics of disk are plotted for various values of non-homogeneity parameter under power law distribution of material properties. Thus, the investigations done in this research paper may be useful for industrial area in construction an appropriate FGM disk by controlling above mentioned parameters.

Finite element method for stress and strain analysis of FGM hollow cylinder under effect of temperature profiles and inhomogeneity parameter

Abstract This study represents a numerical analysis of stress and strain in the functionally graded material (FGM) hollow cylinder subjected to two different temperature profiles and inhomogeneity parameter. The thermo-mechanical properties of a cylinder are assumed to vary continuously as power law function along the radial coordinate of a cylinder. Based on equilibrium equation, Hooke's law, stress-strain relationship in the cylinders, and other theories from mechanics second order differential equation is obtained that represents the thermoelastic field in hollow FGM cylinder. To find a numerical solution of governing differential equation, the finite element method (FEM) with standard discretization approach is used. The analysis of numerical results reveals that stress and strain in the FGM cylinder are significantly depend upon variation made in temperature profile and inhomogeneity parameter n. The results show good agreement with results available in the literature. It is shown that thermoelastic characteristics of the FGM cylinder are controlled by controlling the value of the above discussed parameters. Moreover, these results are very useful in various fields of engineering and science as FGM cylinders have a wide range of applications in these fields.

Effects of angular velocity and boundary temperature to thermo-elastic characteristics on homogeneous circular disks subjecting to contact forces

Effects of angular velocity and boundary temperature to thermo-elastic characteristics on homogeneous circular disks subjecting to contact forces