Thermal Stress Field Research Articles

An integrated analytical model for the forecasting of the molten pool dimensions in Selective Laser Melting

Selective laser melting (SLM) is one of the most promising processes in the Additive Manufacturing of metals because of the possibility to fabricate complex geometry parts with a wide range of materials. The molten pool dimensions are notoriously crucial for the production of high quality parts, in terms of mechanical properties and roughness, and to control the ‘balling’ phenomenon. In the past, several studies have been conducted to monitor temperature gradient and thermal history, stress and deformation field, balling occurrence, effect of volume shrinkage and the effect of process parameters on temperature evolution. Up to now, very few works are available in literature on the effects of the process parameters on the molten pool shape and dimensions: moreover, they also neglect the simultaneously effect of various physical factors. In this work, an integrated analytical model, consisting of three sub-models (thermal, optical and melting sub-models), with the purpose to forecast the molten pool dimensions in terms of width and depth, was developed. An experimental plan has been carried out, processing the 18 maraging 300 steel, to demonstrate the capability and the accuracy of the presented model. The obtained results demonstrate that the integrated analytical model led to optimal forecasting.

Analysis of thermal stresses in FGM-Matrix medium induced by constant heat flux at the far field

The thermal stress due to heat flux at the far field is derived for an infinitely extended elastic medium which contains a spherical inclusion made of functionally graded materials (FGM). The material properties in the inclusion phase are assumed to vary linearly while the material properties in the matrix phase are uniform. As FEM is not appropriate for this type of analysis, a semi-analytical approach is employed in which the temperature distribution for the entire medium and the thermal stress field in the matrix phase are obtained analytically while the thermal stress field in the FGM phase is obtained semi-analytically by solving a set of ordinary differential equations. The present method is preferred over FEM in that all the geometric and material parameters are kept in the formulations and the cost of computation is minimal. The von Mises stress is shown to be continuous at the FGM-matrix interface which underscores the advantage of using FGMs over conventional composites.

Residual thermal stress prediction for continuous tool-paths in wire-arc additive manufacturing: a three-level data-driven method

ABSTRACT Continuous tool-path is often chose to improve the deposition efficiency and surface accuracy of metal additive manufacturing, while it also causes large residual thermal stress, which will result in part deformation and performance degradation. This paper focused on wire-arc additive manufacturing (WAAM) with arbitrary part geometries and continuous tool-paths, and proposed a three-level data-driven method to predict the residual thermal stress filed accurately and rapidly. The first two-level of the proposed method predict the thermal field history of the whole WAAM process. The third level of the proposed method realises the residual thermal stress field prediction of WAAM based on above prediction results. Each level is based on a machine learning method, and their data were obtained based on the finite element method. The prediction accuracy of the proposed method exceeded 92%, and the time cost of one prediction process was only at the second level.

Thermal stress analysis of disc brake using analytical and numerical methods

This article presents study of the thermal stress development in brake disc and the associated life cycle of the disc. The thermal stress analysis of disc brake under the first brake application and the influences of thermal loads on stress development of the disc have been investigated. The temperature distribution was conducted as a function of disc thickness and braking time. The study was done on the disc brake of Sports Utility Vehicle with a model of DD6470C. Partial solution approach was used to solve analytical temperature distribution through the thickness. The model was done using representative areas of the disc exposed to high temperature whose distribution result was obtained as a function of disc thickness and braking time. The solutions of coupled thermal transient fields and stress fields were obtained based on thermal-structural coupled analysis. Based on the model developed for the study, the positions of high and low stress formations were investigated, and it has been observed that thermal stress and temperature gradient show similar behavior through the thickness of disc. Generally, high temperature and stress components were found on the rubbing surfaces of the disc.

Dual Laser Beam Asynchronous Dicing of 4H-SiC Wafer.

SiC wafers, due to their hardness and brittleness, suffer from a low feed rate and a high failure rate during the dicing process. In this study, a novel dual laser beam asynchronous dicing method (DBAD) is proposed to improve the cutting quality of SiC wafers, where a pulsed laser is firstly used to introduce several layers of micro-cracks inside the wafer, along the designed dicing line, then a continuous wave (CW) laser is used to generate thermal stress around cracks, and, finally, the wafer is separated. A finite-element (FE) model was applied to analyze the behavior of CW laser heating and the evolution of the thermal stress field. Through experiments, SiC samples, with a thickness of 200 μm, were cut and analyzed, and the effect of the changing of continuous laser power on the DBAD system was also studied. According to the simulation and experiment results, the effectiveness of the DBAD method is certified. There is no more edge breakage because of the absence of the mechanical breaking process compared with traditional stealth dicing. The novel method can be adapted to the cutting of hard-brittle materials. Specifically for materials thinner than 200 μm, the breaking process in the traditional SiC dicing process can be omitted. It is indicated that the dual laser beam asynchronous dicing method has a great engineering potential for future SiC wafer dicing applications.

Non-Fourier Heat Conduction and Thermal-Stress Analysis of a Spherical Ice Particle Subjected to Thermal Shock in PEM Fuel Cell at Quick Cold Start-Up

Quick start at low temperature is one of the key bottleneck technologies that restrict the large-scale commercialization of proton exchange membrane (PEM) fuel cell vehicles. Ice and devices in battery systems based on thermal deicing are inevitably subjected to thermal shock. In order to study this problem, a non-Fourier heat conduction model is established to study the temperature response of a spherical ice particle subjected to thermal shock with different boundary conditions on the surface. Furthermore, distribution of thermal stress in the particle is obtained using the calculated temperature field, and the effect of thermal relaxation time and boundary conditions on the temperature response as well as the thermal stress field are also analyzed. The results, which are significantly different from that obtained using Fourier law of heat conduction, show that the mechanical stresses and the serious expansion of the ice particle may lead to the severe deformation of the devices connected to the ice during the cold start-up, imposing a great challenge in controlling structural reliability of PEM fuel cells. The numerical results are expected to provide a scientific theoretical basis for PEM fuel cell design and low-temperature start-up control.

Three-dimensional exact analytical solutions of transversely isotropic plate under heat sources

An accurate and efficient calculation method for the transversely isotropic thermoelastic plates plays an important role in exact design and quality control of the engineering structures. In this study, the three-dimensional (3D) thermal stress field of transversely isotropic plates under arbitrary heat source is obtained using Green’s function method. To achieve the purpose, the 3D Green’s function solutions of transversely isotropic plate under a point heat source are firstly derived based on the general solutions which are presented in potential functions. The concise harmonic potential functions are constructed in simple functions with undetermined constants by mirror image principle. Then, the Green’s functions are achieved by substituting the harmonic functions into the general solution. All temperature and stress components can be analytically expressed using simple functions which are convenient to use. The present method without simplifying assumption of dimensions has the applicability and reliability to analysis plate structures with arbitrarily thickness. Numerical calculations show the good convergence and high efficiency of the method. This study presents a high precision and efficiency predesign method for the thermos elastic plate structures. The numerical results provide theoretical guideline for the accurate design and quality control of plate structures.

Influence of Initial Stress and Variable Thermal Conductivity on a Fiber-Reinforced Magneto-Thermoelastic Solid with Micro-Temperatures by Multi-Phase-Lags Model

This paper presents the theory of multi-phase-lags thermoelasticity that was used to study the wave propagation on a fiber-reinforced thermoelastic medium with micro-temperatures. The medium was considered to be homogeneous, isotropic and thermal conductivity as a linear function of thermodynamic temperature. The Fourier transform and Laplace transform are employed to solve the governing equations and obtained the solution of the physical quantities. The graphical illustrations of the impact that initial stress, variable thermal conductivity, magnetic field, and the phase-lags have on the field functions are presented. The variable thermal conductivity, initial stress, and magnetic field have a good impact in all the physical quantities.

An improved thermo-parameters method for dynamic shakedown analysis of railway subgrade

To ensure the safety and stability of train operation, a reasonable evaluation of long-term durability of railway subgrade subjected to large number of cyclic train loads is necessary. With the concept of controlling safety margins against excessive inelastic deformation, shakedown theory provides an effective approach for the analysis of long-term performance of geotechnical structures. In this paper, an improved thermo-parameters method (TPM) is proposed to carry out dynamic shakedown analysis on the railway subgrade. Mathematically, the method is formulated as an optimization problem, in which the objective function is the dynamic shakedown limit and variables are the shakedown residual stresses defined through the distribution of hypothetical thermal stress field and further described by the Non-Uniform Rational B-Splines (NURBS) surface. The presented solution procedure was incorporated to the finite element (FE) model and numerical examples were presented to demonstrate its effectiveness for different cases. An in-situ test conducted in a fill section of railway subgrade was used for numerical modeling and further result validation. The results indicated that the dynamic shakedown limits varied with the loading frequency and showed smaller values than the quasi-static shakedown limit, especially at the natural frequency of structure. The current findings may be beneficial to the further understanding of the long-term durability and stability of subgrade under dynamic loading, and provide useful information for the shakedown design of the railway subgrade.

Visualizing structural changes of egg avidin to thermal and electric field stresses by molecular dynamics simulation

Eggs are one of the most common ingredients used by human beings due to their nutritional attributes and health benefits. However, eggs also contain an anti-nutrient known as avidin, which forms an avidin-biotin complex, resulting in biotin unavailable in the body for absorption. In the present study, molecular dynamics (MD) simulation was used to evaluate the effect of external stresses, including thermal and oscillating electric field (0.05 V/nm, 2450 MHz) at 300–353 K on the structural properties of avidin. The modeling was performed using a GROningen MAchine for Chemical Simulations (GROMACS) software. The alteration in conformation of avidin was evaluated in terms of the number of hydrogen bonds, root mean square deviation, the radius of gyration, and solvent accessible surface area. The application of thermal stress and electric field resulted in conformational changes in the avidin protein. The results also showed that hydrogen bonds have a significant influence on the stability of alpha-helices, which are responsible for the compactness of the molecule. Change in the hydrogen bonds can increase the surface area and hence the surface properties of avidin significantly. Thermal combined with electric field showed an application in inhibiting the activity of avidin present in egg white.

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.

Effect of deformation of diamond anvil and sample in diamond anvil cell on the thermal conductivity measurement* *Project supported by the National Key Research and Development Program of China (Grant No. 2018YFA0702700) and the National Natural Science Foundation of China (Grant Nos. 11674404 and 11774126).

Studies show that the sample thickness is an important parameter in investigating the thermal transport properties of materials under high-temperature and high-pressure (HTHP) in the diamond anvil cell (DAC) device. However, it is an enormous challenge to measure the sample thickness accurately in the DAC under severe working conditions. In conventional methods, the influence of diamond anvil deformation on the measuring accuracy is ignored. For a high-temperature anvil, the mechanical state of the diamond anvil becomes complex and is different from that under the static condition. At high temperature, the deformation of anvil and sample would be aggravated. In the present study, the finite volume method is applied to simulate the heat transfer mechanism of stable heating DAC through coupling three radiative-conductive heat transfer mechanisms in a high-pressure environment. When the temperature field of the main components is known in DAC, the thermal stress field can be analyzed numerically by the finite element method. The obtained results show that the deformation of anvil will lead to the obvious radial gradient distribution of the sample thickness. If the top and bottom surfaces of the sample are approximated to be flat, it will be fatal to the study of the heat transport properties of the material. Therefore, we study the temperature distribution and thermal conductivity of the sample in the DAC by thermal-solid coupling method under high pressure and stable heating condition.

2D Quasi-Static Accurate Solutions for Isotropic Thermoelastic Materials with Applications

Thermally induced stress is an important scientific problem in engineering applications. In this paper, an accurate and efficient method for the two-dimensional quasi-static thermal elastic problem is established to explore the thermal stress problem. First, the compact quasi-static two-dimensional general solution is derived in terms of simple potential functions. The general solution is simple in form and can be derived for arbitrary boundary problems subjected to a line heat load. This is completely new to the literature. Second, Green’s function solutions of an infinite plane under the line pulse heat source based on the general solutions are presented to analyze the thermal stress field. Lastly, numerical results are taken into account to study the temperature and stress field induced by the dynamic heat source load. The corresponding analysis can constitute to reveal the mechanism of thermal elastic problems and provide some guidance for experiments or engineering structural design in the future work.

ZrB2 – SiC ceramics: Residual stresses and mechanical properties

The stress-strain state of ZrB2-SiC ultra-high-temperature ceramics, produced using commercial powders with different impurity levels, was investigated by X-ray diffraction. Upon analysis of ZrB2 and SiC diffraction lines shift, the level of thermal stresses (strains) of the different phases was determined. An increase of internal stresses in ceramics with rising viscous-brittle transition temperatures, Tve, was attributed to increased grain boundary strength. Ceramics, for which high Tve and high level of internal stresses were estimated, exhibited high strength, up to 700 MPa at 1400 °C. A field of compressive thermal stresses in the matrix phase resulted to be necessary for achieving high strength at low-temperatures. On the contrary, the presence of low-melting impurities at the grain boundaries negatively impacted on the stress level in ZrB2 boundaries in the high temperature regime.

Creep-Fatigue Experiment and Life Prediction Study of Piston 2A80 Aluminum Alloy.

In order to improve the reliability and service life of vehicle and diesel engine, the fatigue life prediction of the piston in a heavy diesel engine was studied by finite element analysis of piston, experiment data of aluminum alloy, fatigue life model based on energy dissipation criteria, and machine learning algorithm. First, the finite element method was used to calculate and analyze the temperature field, thermal stress field, and thermal–mechanical coupling stress field of the piston, and determine the area of heavy thermal and mechanical load that will affect the fatigue life of the piston. Second, based on the results of finite element calculation, the creep–fatigue experiment of 2A80 aluminum alloy was carried out, and the cyclic response characteristics of the material under different loading conditions were obtained. Third, the fatigue life prediction models based on energy dissipation criterion and twin support vector regression are proposed. Then, the accuracy of the two models was verified using experiment data. The results show that the model based on the twin support vector regression is more accurate for predicting the material properties of aluminum alloy. Based on the established life prediction model, the fatigue life of pistons under actual service conditions is predicted. The calculation results show that the minimum fatigue life of the piston under plain condition is 2113.60 h, and the fatigue life under 5000 m altitude condition is 1425.70 h.

Size effect on heat conduction and associate thermal fracture behavior of thin ceramic plates

Thermal barrier materials used in gas-turbine engines and aerospace vehicles have to resist large thermal gradients or high heat fluxes. The existence of high temperature gradient results in nonlocal effect of heat conduction, especially in very small time and space scale, the size effect of heat conduction is significant. In this work, a nonlocal dual-phase-lag heat conduction model is adopted to analyze the thermal shock fracture problem of thin cracked plates under sudden thermal shock. By using Laplace transform and inverse transform, the temperature field and the thermal stress field are obtained first. Then through the principle of superposition, the formulation results in a mode I crack problem. In the numerical part, the effects of different heat conduction models, thermal nonlocal parameters, and crack geometry parameters on the transient responses are discussed. By comparison analysis, the results show that taking the size effect into account is crucial in the assessment of thermal shock fracture of ceramic plates at micro/nano scale. The stress intensity factor first increases and then decreases with the increase of crack geometry parameters, indicating that the cracked plate exhibits crack growth resistance behaviour.

Three-dimensional quasi-static general solution for isotropic thermoelastic medium with applications

An accurate and efficient method for three dimensional quasi-static thermal elastic problems is established. The three-dimensional equations of isotropic quasi-static-thermo-elasticity are simplified by the introduction of two displacement functions. A general solution is derived by virtue of the Almansi's theorem, which is expressed in terms of three functions, satisfying harmonic functions and quasi-static heat conduction equation respectively. Exact and complete fundamental solution would be derived for arbitrary boundary problems subjected to a point heat load. The solution is concise in form which is completely new to the literature. In this paper, the 3D solutions of the isotropic quasi-static medium under dynamic point heat source based on the general solutions are presented by two newly functions. All components of the coupled field are expressed in terms of elementary functions which are convenient to use. The number results for two types of dynamic heat source show the change rules of the thermal stress field. The corresponding analysis can give some theoretical basis for revealing the mechanism of thermal elastic coupling problem and provide guidance for engineering structural design in the future work.

Computational Analysis of Laser Cladding of Preset MCrAlY Coating Based on ANSYS Ii-Stress Field

A finite element model of thermal coupling stress field during laser cladding plasma spraying of preset MCrAlY coating was constructed based on the finite element model of temperature field by using the indirect thermal coupling method in ANSYS finite element software. Moreover, stress field during laser cladding was analyzed. Through the constructed model, variation laws of stress field with time during laser cladding and cooling process could be mastered. Based on the stress field, the formation mechanism of cracks in laser cladding coating and influencing factors were further analyzed and some solutions to cracks of laser cladding coating were proposed.

Multi-layered structural designs of MoSi2/mullite anti-oxidation coating for SiC-coated C/C composites

The gradient and laminated multi-layered MoSi2-mullite coatings were prepared with similar thickness by supersonic atmosphere plasma spraying (SAPS) on SiC coated C/C composites to analyze the effects of the two multi-layered structure on the oxidation resistance of SAPS MoSi2 coating under high temperature environment. Unexpectedly, the gradient multi-layered design showed almost no positive effect on the protective performance improvement in comparison to the monolayer MoSi2 coating. The laminated multi-layered design remarkably improved the oxidation resistance at 1500 °C, up to 226 h, as well as the thermal shock resistance to 30 thermal cycles with only half the mass loss of the monolayer one. Such obvious improvement in the laminated MoSi2/mullite multi-layered coating was attributed to the effect of macroscopic interfaces on the auxiliary self-healing and the change of thermal stress field, which were conducive to hindering further crack prolongation.

Analysis of bimaterial singular regions for orthotropic and isotropic materials under thermal loading

A method to formulate an asymptotic elasticity solution for bimaterial singular regions in orthotropic materials is presented for the thermal case. In the vicinity of material and geometric singularities, approximate methods such as finite elements fail to converge and procedures to improve these solutions become necessary. The results presented herein can be used in conjunction with approximate numerical techniques for the determination of stresses and stress intensity factors in composite bonded joints, cracked bimaterial interfaces, or a junction of dissimilar materials under thermal loading. The thermal displacement and stress fields at the tip of a bimaterial wedge are developed by means of eigenfunction expansions including both singular and nonsingular terms. The thermal elasticity solution for isotropic materials as the limiting case of the orthotropic solution is also obtained. The formulations obtained are applicable to bonded joints with interfacial or interlaminar cracks, geometric and material discontinuities, and uniform thermal loading. The detailed formulation presented provides an essential component in the application of finite elements for the determination of generalized intensity factors and stresses in composites, bonded joints, or other dissimilar materials under thermal loading. Formulation results for orthotropic materials, including the limiting case of isotropic materials, are compared with published and closed form results that use different formulations, and excellent agreement is observed. Furthermore, the existence of logarithmic stress singularities of the form (k⋅ΔT⋅lnr) is investigated and discussed.