Thermal Stress Analysis Research Articles

EXAMINATION OF THERMAL STRESSES OCCURRING IN CIRCULAR DISCS BY FINITE ELEMENT METHOD

In this study, thermal stress analysis on discs consisting of two different materials was analyzed analytically. Disc materials were selected SiC/6061 Al Alloy composite and Al-7075 respectively. Assuming that the elasticity module does not change with temperature, thermal stress analysis was performed under constant temperature distributions in the area from the inner surface of the disc to the outer surface. Thermal stress analysis was performed under constant temperature distribution. A computer program was developed for the calculation and the ANSYS finite element program was used. The values obtained from the analysis are presented in tables and graphs. There have been differences in radial and tangential stresses that occur because the elasticity modules and thermal expansion coefficients of the materials that make up the discs are different. The radial stress value has always been determined as zero on the innermost and outermost surfaces of the discs. Tangential stresses under constant temperature distribution from the inner surface to the outer surface occurred as pressure on the inner part of the disc and tensile stress on the outer part. It is concluded that the stresses occurring in the SiC /6061 Al alloy composite material are greater than those of AL-7075.

Thermal stress analysis in a hemispherical shell made of transversely isotropic materials under pressure and thermo‐mechanical loads

AbstractThis article deals with the study of thermal stress in a hemispherical shell made of transversely isotropic material under the effect of thermal, pressure and mechanical load. Seth's transition theory and generalized strain measure are used for finding the governing equation. Mathematical modelling is based on stress–strain relation and equilibrium equation. Analytical solutions are presented for the hemispherical shell made of transversely isotropic material and isotropic material. The effects of different pertinent parameters (i.e., temperature, pressure and load) are considered for the spherical shell made of transversely isotropic material. The behaviour of stress distribution, mechanical load, pressure rise, and temperature distribution are investigated. From the obtained results, it is noticed that carbon fiber material hemispherical shell requires higher pressure at the internal surface in comparison to magnesium/polypropylene material. With the introduction of mechanical load, the value of pressure decreases at the internal surface, but reverse results are obtained in the case of thermal condition for the hemispherical shell made of carbon fiber/magnesium/polypropylene material. By applying thermal condition, the hemispherical shell made of carbon fiber material requires maximum hoop stress at the external surface as compared to the magnesium/polypropylene material. The transversely isotropic material hemispherical shell more convenient than that of isotropic material hemispherical shell. Results have been discussed numerically and graphically.

Comparison of approximation schemes for three-dimensional thermal stress analysis and applications to cracks with fluid flowing

In this paper, we first present an approximate scheme for thermal problem with heat sources varying with time (time-varying). It is different from one that the authors used previously. Both schemes use series of stepwise constant heat sources to approximate the continuously varying heat source. But the constant sources of the two schemes are different. The previous scheme divides the time period from the initial time to the solution time, at which the solutions are sought, into some time-steps and assumes that each of the series of constant sources is applied at the start time of the time-steps and all the constant sources last to the solution time. The new scheme assumes that each of the constant sources starts at the start time of a time-step but lasts only for one step of time. When solutions for temperature, displacement and stress are sought at multiple time instants or the boundary conditions are obtained step by step from other problems, it is easier and computing efficient to use the new scheme. If the solution is required at just one time instant, then computations of the two schemes are basically the same. The schemes are compared for the thermal effects caused by time-varying temperature on surface of a spherical cavity in an infinite body and the results of the two schemes agree very well. Comparison of the two schemes is also done for the temperature change in rock due to fluid flowing through a fracture inside the rock.

A unified modelling and simulation for coupled anomalous transport in porous media and its finite element implementation

This paper presents an unified mathematical and computational framework for mechanics-coupled “anomalous” transport phenomena in porous media. The anomalous diffusion is mainly due to variable fluid flow rates caused by spatially and temporally varying permeability. This type of behaviour is described by a fractional pore pressure diffusion equation. The diffusion transient phenomena is significantly affected by the order of the fractional operators. In order to solve 3D consolidation problems of large scale structures, the fractional pore pressure diffusion equation is implemented in a finite element framework adopting the discretised formulation of fractional derivatives given by Grunwald–Letnikov (GL). Here the fractional pore pressure diffusion equation is implemented in the commercial software Abaqus through an open-source UMATHT subroutine. The similarity between pore pressure, heat and hydrogen transport is also discussed in order to show that it is possible to use the coupled thermal-stress analysis to solve fractional consolidation problems.

Investigation and Computational Modelling of Variable TEG Leg Geometries

In this work, computational modelling and performance assessment of several different types of variable thermoelectric legs have been performed under steady-state conditions and the results reviewed. The study conducted has covered geometries, not previously analysed in the literature, such as Cone-leg and Diamond-leg, based on the corresponding thermoelectric generator leg shape structure. According to the findings, it has been demonstrated that the inclusion of a variable cross-section can have an impact on the efficiency of a thermoelectric generator. It has been concluded that the Diamond configuration generated a slightly larger voltage difference than the conventional Rectangular geometry. In addition, for two cases, Rectangular and Diamond configurations, the voltage generated by a TEG module consisting of 128 pairs of legs was analysed. As thermal stress analysis is an important factor in the selection of TEG leg geometries, it was observed based on simulations that the newly implemented Diamond-leg geometry encountered lower thermal stresses than the traditional Rectangular model, while the Cone-shape may fail structurally before the other TEG models. The proposed methodology, taking into account the results of the simulation carried out, provides guidance for the development of thermoelectric modules with different forms of variable leg geometry.

Temperature compensated diaphragm based Fiber Bragg Grating (FBG) sensor for high pressure measurement for space applications

A temperature compensated diaphragm-type Fiber Bragg Grating (FBG) sensor for high pressure measurement, with a maximum pressure up to 700 bar, has been developed and packaged for different applications including space. In this device, a pressure sensitive FBG is bonded at the centre of a Martensitic Stainless Steel (APX-4) diaphragm and a temperature compensation FBG is bonded in the strain-free region of the same diaphragm. The experimental results obtained indicate a pressure sensitivity of 3.64 pm/bar and a non-linearity + Hysteresis error of 0.75% of full-scale pressure in the range of 0 to 700 bar, with a correlative coefficient of 99.99%. Structural and thermal stress analyses of the diaphragm and strain transfer analysis from the diaphragm to FBG have been carried out using Comsol Multiphysics software, to validate the experimental results. Shock tube and vibration tests have also been carried out to study the dynamic characteristics and stability of the sensor. The pressure sensor developed, can be used to measure both static/dynamic pressures of cryogenic propellants as well as pneumatic pressure in rockets, missiles and launch vehicles.

Simulation and Analysis of Thermal Stress and Sintering Warpage of Planar Solid Oxide Fuel Cells

Solid oxide fuel cell (SOFC) is one of the new energy conversion technologies producing electricity and heat from fuel and oxidant through an electrochemical reaction. The high operating temperature has many advantages including high efficiency, flexible fuel adaptability and low emissions. However, it has also some drawbacks, e.g., thermal expansion mismatches among the involved materials, particularly when the temperature reaches around 1400 oC during the sintering process, which may cause non-uniform distribution of thermal stress and even further deformation and warpage observed in the cell manufacturing steps.A three-dimensional CFD (computational fluid dynamics) simulation model is developed to study the thermal stress distributed in the sintered function layers of the anode-supported planar SOFC unit cells (10×10 cm2) using a finite element method. Five layers are included, i.e., cathode and its separation layer (GDC/LSCF, 70 µm), anode support and active layers (Ni/YSZ, 550µm), and electrolyte layer (YSZ, 30 µm) between them. In terms of the thermal stress and deformation, the predicted results are presented and discussed for the sintered unit cells with different angels located around the four cornels.It is found that the maximum thermal stress occurs at the interface between the electrode and electrolyte; the magnitude and distribution of thermal stress at the interfaces are closely related to the material thermal properties; the maximum deformation about 13 mm in the thickness direction is predicted for the 90-angel shaped cornels at the sintering temperature 1400 oC, which is bigger than that for the case with the circular shaped cornels; the deformation magnitude depends not only on the maximum thermal stress, but also the difference between the maximum and minimum thermal stress. The findings and predicted results may be applied for optimization of design and sintering conditions for SOFC unit cells.AcknowledgementsThis work is supported by the National Key Research and Development Project of China (2018YFB1502204, 2018YFB1502203, 2018YFB1502205), the Ningbo major special projects of the Plan “Science and Technology Innovation 2025” (2018B10048). Figure 1

Flow features and thermal stress evaluation in turbulent mixing flows

The present paper depicts a numerical study of flow and thermal features in T-junctions with circular cross-section. The numerical simulation is based on the experimental validated wall-resolved Large-Eddy Simulation method. The Reynolds number in the warm main pipe flow covers a range of Rem=27000 to Rem=134000 and the temperature difference of the mixing fluids is up to ΔT=249 K. The location of maximum fluctuations does not change due to a nearly identical flow pattern type in all simulations. This condition allows the investigation of the flow evolution, mixing process and heat transfer for the same thermal flow pattern type. The numerical simulations are coupled with the heat conduction in the structure due to the thermal fluid-structure-interaction. Further, this study offers a deeper insight into the hidden physics of turbulent mixing flows and the transport as well as damping of thermal fluctuations in the near-wall fluid/solid region. Our study considers also thermal stress analysis by Finite-Element Method by utilizing the wall temperature distribution of previously performed numerical simulations. Therefore, fatigue damage is evaluated based on the stress received from the Finite-Element analysis. The results show that the highest Reynolds number case corresponds to the highest flux intensity and turbulence. This affects the flow field and the thermal features in the core flow and the transport of fluctuations close to the wall. The locations with peak fluctuation intensity in the fluid generates also high fluctuating temperature areas in the structure. The finite element analysis demonstrates that the highest temperature difference case leads to the highest alternating stress intensity which has potential for thermal fatigue. The generated maximal alternating stress is coupled with the flow conditions of the mixing fluids. With an increasing Reynolds number of the main and branch pipe flow as well as temperature difference raises also the resulting maximum alternating stress intensity.

The influence of dynamic loading and thermal conditions on tram track slab damage resulting from subgrade differential settlement

To guarantee the operation safety of the tram in typical soft soil area, the damage characteristics of tram track slabs due to subgrade differential settlement, dynamic train loads and environmental issues are investigated in this work. A three-dimensional (3D) finite element analysis (FEA) model is utilized to calculate the additional track vertical profile irregularity due to the subgrade differential settlement. The overall rail vertical profile irregularities are employed as excitations of a tram vehicle-track-subgrade coupling model to calculate the dynamic pad forces. After that, a sequentially coupled thermal-stress analysis procedure is proposed to evaluate the initial stress-damage field of the slabs resulting from environmental temperature variation. The plastic damage theory is adopted to investigate the damage characteristics of tram track slabs due to multiple issues. According to the damage factors calculated from this model, the criterion of subgrade differential settlement of the tram track is proposed. The damage state of the tram track is suggested to be a key factor of the subgrade differential settlement control system.

Studies on the silver-coated patch with spot welding for the ITER Thermal Shield

ITER Thermal Shield (TS) reduces radiation heat loads from vacuum vessel and cryostat to superconducting magnet structure. One of the key process among the fabrication of TS is the silver electroplating to reduce the emissivity. Requirement on emissivity of TS surface after silver coating is below 0.05 at the room temperature. In practice, inevitable non-coated areas exist due to the intrinsic geometry of TS. These local defects can be repaired by attaching thin silver coated patch with spot welding. This paper treats structural characteristics on the spot welding of silver coated plates. Strength of spot welding is measured by tensile shear test. Distances between spot welding are verified by finite element analysis considering temperature deviation between TS surface and patch. Finally, thermal stress analysis for the several applications to TS main components are presented.

Numerical simulation and thermal stress analysis of direct internal reforming SOFCs

ABSTRACT Hydrocarbon fuels such as CH4 can be converted into H2 and CO by direct internal reforming (DIR) processes within the anode of solid oxide fuel cells (SOFCs). DIR-SOFCs can reduce system complexity and capital cost due to the elimination of external reformers. However, the strong endothermic reforming reactions at the cell entrance may result in large thermal stress, leading to premature failure. In this study, a numerical simulation study was carried out to analyze the effect of operating conditions and cell structures on temperature, composition and thermal stress distributions in DIR-SOFCs. A two-dimensional axisymmetric model was developed by considering the coupling effects of the chemical/electrochemical reactions; transport processes of mass, charge, or heat; and thermal mechanical stress. The failure probability of the cell was estimated by stress distributions. Simulation results show that the increase of the steam-to-carbon ratio and operating voltage leads to higher thermal stresses and higher failure probability. The introduction of a metal supportive layer may release the thermal stress problem at severe DIR-SOFC operation conditions, which leads to a flatter temperature distribution and smaller failure probability compared to anode-supported SOFCs.

Analysis of thermal stresses in FGM-matrix media induced by a constant heat generation

The three-dimensional thermal stress field is derived for an elastic medium that contains a spherical inclusion made of an functionally graded material (FGM) embedded in a matrix phase. The material properties in the inclusion phase are assumed to vary linearly while the material properties in the matrix phase are uniform. The presence of a uniform heat source in the inclusion introduces the temperature distribution which generates thermal stresses. The temperature distribution is derived analytically by solving the heat conduction equation. Based on the temperature distribution, the differential equations for the displacement field are derived for both the inclusion and matrix phases. The displacement for the matrix phase is solved analytically while the displacement for the FGM inclusion phase is solved semi-analytically using the method of weighted residuals. Only a single differential equation needs to be solved. To the authors’ best knowledge, this is the first attempt to express the thermal stress field semi-analytically. Unlike the conventional two-phase composite materials in which the von Mises stress is discontinuous at the interface of the inclusion and the matrix, the von Mises stress in this model shows continuity at the interface.

Simulation and Analysis of Thermal Stress and Sintering Warpage of Planar Solid Oxide Fuel Cells

Due to mismatching of thermophysical properties between involved materials, a non-uniform distribution of generated thermal stress may result in a deformation and warpage in the cell sintering steps for SOFC (solid oxide fuel cell). A three-dimensional CFD (computational fluid dynamics) model is developed to study the displacement and thermal stress distribution within the SOFC sintered functional layers. It is found that the thermal stress is concentrated on the interface between the anode and the electrolyte layers; the warpage is larger during the co-sintering of anode and electrolyte layers (i.e., half-cell sintering). A parameter study is also conducted for the thickness variation of the anode, as well as for the four corners being chamfered. Considering effects of microscopic structure evolution on the cell shrinkage, a correlated method is developed to evaluate the thermal expansion coefficients varied with the sintering temperature. It is found that the difference becomes bigger in the correlated thermal expansion coefficients between the YSZ and anode layers, which leads to even larger displacement predictions. The findings and predicted results may be applied for optimization of the material designs and the sintering parameters for SOFC.

Thermal behaviour of annular hyperbolic fin with temperature dependent thermal conductivity by differential transformation method and Pade approximant

The current paper explores the steady-state heat transfer and thermal stress analysis of a hyperbolic annular fin with temperature dependent thermal conductivity. The framed equations are articulated in terms of non-linear ordinary differential equations. The domination of non-dimensional parameters on the thermal gradient of the fin has been analysed graphically by using Runge–Kutta Fehlberg fourth-fifth order (RKF-45) process and DTM-Pade approximant. Here, differential transformation method (DTM)-Pade approximant has been implemented to find the analytical solution for the non-linear ordinary differential equations. The RKF-45 method is used to obtain numerical outcomes for different non-dimensional parameters. Further, the obtained numerical results are compared with the results achieved from DTM-Pade approximant solution. This relation demonstrates that numerical outcome obtained by DTM-Pade approximant are nearer to that of numerical results. Outcome results exposes that, the escalating values of thermal conductivity parameter upsurges the thermal distribution. The growing values of the radius ratio elevate the thermal distribution in the fin. Further, the radial stress and tangential stress distribution varies for larger values of dimensionless parameters.

Fire damaged box girder inspection and assessment and strengthening treatment

Based on a fire accident in a bridge of the Jinan-Qingdao high-speed railway, the preliminary damage assessment of the box girder was conducted through surface inspection, concrete strength testing, concrete carbonation depth testing and reinforcement protective layer thickness testing methods. Then a corresponding numerical model of the fire damaged box girder was created by the Midas software, and the heat transfer analysis and thermal stress analysis were carried out. The results showed that the fire damaged level of the box girder were Grade II (moderate damage). Finally, the corresponding reinforcement measures were recommended.

Mechanical and thermal stress analysis of hybrid ceramic and lithium disilicate based ceramic CAD-CAM inlays using 3-D finite element analysis

Objectives: The aim of this study was to analyze mechanical and thermal stresses of hybrid ceramic and lithium disilicate based ceramic of CAD/CAM inlays using 3D Finite element analysis. Material and Methods: A three dimensions finite element model of permanent maxillary premolar designed according to standard anatomy with class II cavity preparation for inlay restored with two different ceramic materials:- 1- Hybrid ceramic (Vita Enamic), 2- Lithium disilicate based ceramic (IPS e.max CAD). Totally six runs were performed on the model as: One loading case for each restorative material was tested in stress analysis; seven points of loading with 140N vertically applied at palatal cusp tip and cusp slop, marginal ridges and central fossa while the models base was fixed as a boundary condition in the two cases. Two thermal analysis cases were performed for each restoration material by applying 5ºC and 55ºC on the crown surface including the restoration surface. Results: The results of all structures were separated from the rest of the model to analyze the magnitude of stress in each component. For each group, maximum stresses on restorative materials, cement, enamel, and dentin were evaluated separately. Both ceramic materials generated similar stress distribution patterns for all groups when a total occlusal load of 140 N was applied. Conclusion: Thermal fluctuations of temperature have a great influence on the stresses induced on both restoration and tooth structure. IPS e.max CAD produced more favorable stresses on the tooth structure than Vita Enamic. KEYWORDS Ceramics; Finite element analysis; IPS e.max CAD; Lithium disilicate; Vita Enamic.

Structural analysis of large-scale SS collecting mirrors for ITER diagnostics

ITER is a nuclear fusion research and engineering project. It is supposed to be the first fusion device designed for testing the integrated technologies, materials, and physical aspects necessary for development of the commercially available fusion-power plant. One of the important components of the project is optical diagnostic systems with collecting mirrors. These mirrors have to provide stability of optical systems under severe loads of different types that could possibly arise in the tokamak. The collecting mirrors of several ITER diagnostics have a large scale and should be installed into diagnostic ports. Thermal stress analysis of the mirror updated design is aimed to obtain deformation and rotation values of the mirrors’ reflecting surfaces in order to conduct ray tracing analysis and to edit mirrors alignment to provide correct functioning of the optical systems. The maximum temperature values of the Divertor Thomson Scattering collecting mirrors were estimated for the normal operation mode. The FE model of the second mirror takes into account all the force boundary conditions, basic kinematic boundary conditions and constraints. Boundary conditions taken for the simulation were applied on surfaces contacting with the diagnostic rack. Thermally stressed state was calculated and corresponding displacement and rotation distributions were obtained.

Thermal Stress Analysis and Spatial Data Matching of Urban Underground Pipelines

The mining of thermal data of underground pipelines is very important for the construction of urban underground pipeline network data matching model and the proposal of large-scale pipeline spatial data matching mechanism. The existing temperature field calculation and stress field simulation methods for thermal pipelines are quite mature already, but they generally pay less attention to the overall connection features of the underground pipeline network and the local details of network nodes, and the deep-level sharing and utilization of the thermal stress data of pipelines is insufficient during the process of spatial data matching of the pipeline network. To this end, this paper conducted a research on thermal stress analysis and spatial data matching of urban underground pipelines. First, the paper gave a theoretical analysis on the temperature field and stress field of underground pipelines and obtained the simulation calculation results; then it elaborated on the calculation of the similarity of underground pipeline network information, proposed a method for spatial data matching, and gave the corresponding algorithm flow; at last, experimental results verified the reliability of the simulation calculation results of the thermal stress of underground pipelines and the effectiveness of the proposed spatial data matching method.

Tank Wall Thermal Stress Analysis and Risk Prevention and Control of Crude Oil Storage Tank

If the crude oil in storage tank is directly heated without considering its temperature distribution, several problems will occur, namely, the thermal expansion of crude oil, and the uneven thickness of the condensate layer, bringing difficulty to the safe management of crude oil storage and transport. However, few scholars have analyzed the temperature field distribution of crude oil storage tank (COST) under heating, or the internal force of COST under static force. Thus, this paper probes into the thermal stress of tank wall, and the risk prevention and control of COST. Firstly, the heat transfer properties of COST were analyzed, an energy balance model was constructed for COST, and several variables were selected to evaluate the heat transfer effect of the tank under different heating modes, including thermal design power, temperature rise rate, and heat energy utilization rate. Next, the cross-section of COST wall was selected for thermal stress analysis. Based on the extremes of circumferential and vertical thermal stresses, the weak parts of COST susceptible to risks like leakage were determined, and several measures and suggestions were presented for reducing the risks of crude oil storage and transport.

Transient Thermal and Mechanical Stress Analysis of 2D-Functionally Graded Finite Cylinder: A Truly Meshless Formulation

Transient Thermal and Mechanical Stress Analysis of 2D-Functionally Graded Finite Cylinder: A Truly Meshless Formulation