Transient Thermal Stress Distribution Research Articles

Design and performance evaluation of a multi-disc magnetorheological fluid brake for A00-class minicars

This paper presents the design and performance evaluation of a multi-disc magnetorheological fluid (MRF)-based brake (MRB) for A00-class minicars. The braking performance of the MRB is studied by means of theoretical analysis and experimental verification. Firstly, the MRB is designed according to the shear model of the MRF, and the structure optimization is carried subsequently. Secondly, multi-physical simulations of the MRB are conducted to investigate the transient temperature field, thermal stress and thermal strain distribution of the MRB under different braking models; Finally, a performance evaluating testbed is built to experimentally assess the braking performance of the MRB. The results indicate that the theoretical braking torque of the MRB fulfills the target value. The thermal strain-induced deformation of the disc is minimal and has a negligible effect on the torque output. In addition, the MRB is experimentally validated to exhibit excellent braking performance in terms of sufficient torque output capacity, rapid response, low temperature rise characteristic, as well as favorable velocity following property.

A multi-tier layer-wise thermal management study for long-scale wire-arc additive manufacturing

High heat input during layer-wise deposition in the Gas Metal Arc-based Wire-Arc Additive Manufacturing (GMA-WAAM) process leads to significant defects such as high residual stress and distortion. However, the choice of layer-wise heat input is constrained due to the requirement of an optimal set of weld parameters. It is essential to study the effect of heat input on the evolution and control of residual stress in the long-scale WAAM fabricated components. Therefore, this study investigates a novel multi-tier heat input strategy represented by four levels for a GMA-WAAM fabricated long-scale thin-walled component. Accordingly, a layer-wise single-, two-, three-, and four-tier heat input strategy in a twelve-layered long-scale thin-walled component is investigated for transient thermal and residual stress distributions through Finite Element Modelling (FEM). Further, a set of validation experiments was performed, which agreed with the predicted results. It is concluded that a reduced heat input during successive layer deposition greatly influences the cumulative heat input into the system. The two-tier heat-input (case 2) system is found suitable among proposed case studies as an appropriate thermal management system with a variation of 6.98% in peak (melt pool) temperature and 198.4 °C increase of minimum temperature during complete deposition. Also, the four-tier heat input (case 4) produced the component's lowest longitudinal and transverse stresses by 13.07% and 25.83%, respectively.

Numerical Model of the Railway Brake Disk for the Temperature and Axial Thermal Stress Analyses

Abstract Increases in travel speeds and traffic density in railway sector impose challenges on the modern disk-pad brake systems such as higher temperatures and stresses resulting in cracks/hot spots and a degraded system performance. The prediction of disk thermal behavior under challenging conditions has become an important engineering issue. In this study, a model is developed using the finite difference method with realistic time-dependent boundary conditions and different experimental convection correlations with non-uniform time-step size features. A previous numerical/experimental study on the thermal behavior of railway disk brake is partly adopted and enhanced. The results of the developed model agree well with the results of the previous study. A practical prediction method for thermal stresses in the disk is applied using the axial temperature distributions at several time instants from locations with highest temperature. Apart from that, same configuration of the disk with the pad is modeled in simcenter star-ccm+ which is a well-validated commercial computational fluid dynamics software to compare the results and computation times with that of the developed model. Using this model, an investigation has been conducted on the effect of temperature-dependent material properties on thermal behavior of the disk. The developed numerical model can simulate the conditions experienced by a railway disk in a relatively new standard (EN 14535-3) considering the transient thermal behavior and axial thermal stress distribution with relatively low computational time and reasonable accuracy. Also, in this study, valuable insights are obtained on the effect of variable thermal properties of the disk and convection correlations on the disk thermal behavior.

Evaluation of the Performance of Published Point Defect Parameter Sets in Cone and Body Phase of a 300 mm Czochralski Silicon Crystal

Prediction and adjustment of point defect (vacancies and self-interstitials) distribution in silicon crystals is of utmost importance for microelectronic applications. The simulation of growth processes is widely applied for process development and quite a few different sets of point defect parameters have been proposed. In this paper the transient temperature, thermal stress and point defect distributions are simulated for 300 mm Czochralski growth of the whole crystal including cone and cylindrical growth phases. Simulations with 12 different published point defect parameter sets are compared to the experimentally measured interstitial–vacancy boundary. The results are evaluated for standard and adjusted parameter sets and generally the best agreement in the whole crystal is found for models considering the effect of thermal stress on the equilibrium point defect concentration.

Transient thermal stress analysis of functionally graded annular fin with free base

The present study aims to provide a deeper understanding for the transient thermal stress distributions of an annular fin made of FGM. The material properties of annular fin are assumed to be graded along the fin radius as a power-law function while the Poisson’s ratio is taken to be constant for simplicity. The energy balance equation is solved on Laplace domain by using exponential like solution introduced by Keller and Keller and Gauss quadrature method. The transformation to time domain achieved by using Durbin fast Fourier transformation method. The temperature distribution and thermal stresses are presented in graphical form for FG annular fin that is pure ceramic in the base and pure metal on the tip.

Effect of additional holes on crack propagation and arrest in gas turbine casing

Gas turbines casings are susceptible to cracking at the edge of eccentric pin hole, which is the most likely position for crack initiation and propagation. This paper describes the improvement of transient thermal fatigue crack propagation life of gas turbines casings through the application of additional holes. A series of finite element patterns were developed and tested in ASTM-A395 elastic perfectly-plastic ductile cast iron. The effect of arrangement of additional holes on transient thermal fatigue behavior of gas turbines casings containing hole edge cracks was investigated. ABAQUS finite element package and Zencrack fracture mechanics code were used for modeling. Thermal fatigue test was performed. The result shows that the fractured surfaces of the failed specimen are in good agreement with the stress concentration areas and cracked areas of the casing. The effect of the reduction of transient thermal stress distribution around the eccentric pin hole on the transient thermal fatigue crack propagation life of the gas turbines casings was discussed. The result shows that transient thermal fatigue crack propagation life could be extended by applying additional holes of larger diameter and decreased by increasing the vertical distance, angle, and distance between the eccentric pin hole and the additional holes. The results from the numerical predictions were compared with experimental data.

Influence of a Coil Bobbin on Transient Thermal Stress in a REBCO Pancake Coil

It has been often reported that a superconducting property of a coil wound by a coated conductor is degraded by epoxy impregnation. The degradation is considered that a superconducting layer or a buffer layer is peeled from a metal substrate by thermal stress. The steady thermal stress in the winding at the operating temperature is examined frequently. However, the transient thermal stress in a cooling process becomes larger than the steady thermal stress due to the difference of heat contraction of each material and temperature distribution, since heat contraction is dependent on a temperature. In this study, by using finite-element analysis, we examined the transient temperature distribution and the transient thermal stress distribution inside a coated conductor's coil winding with epoxy impregnation, when the cooling process with liquid nitrogen was considered. The transient one at the edge of the winding with a glass fiber rein-forced plastic bobbin is more than twice as large as the steady thermal tensile stress and is greater than the cleavage stress strength. Moreover, we have found that it is desirable to use a material with a smaller thermal expansion coefficient and larger heat transfer as the coil bobbin in order to reduce the transient thermal stress in the winding. The effectiveness of the stainless steel bobbin to reduce the transient thermal stress in the winding was showed. Furthermore, it was shown that sufficient precooling was required for reduction of transient thermal stress when a bobbin material with smaller thermal conductivity is used.

Experimental study on cool down characteristics and thermal stress of cryogenic tank during LN2 filling process

During the filling processes of large-scale tanks with cryogenic liquids, the tanks experience non-uniform cool down processes and could suffer from significant thermal stress. An experimental study is performed to investigate the cool down characteristics and transient thermal stress distribution of an aluminum tank during LN2 filling processes with different feeding rates. The varying wall temperatures and induced thermal strains during filling processes are measured, and the local thermal stresses are evaluated. Test results indicate that when LN2 is fed into the tank, remarkable temperature gradient exists in the local wall region at the liquid level. The thermal stress at each point experiences a tension-compression cycle as the liquid level passes by. The maximum thermal stress at each point is proportional to the local maximum cooling rate, and the peak value emerges at the bottom of the tank. Moreover, the non-uniformity of the temperature distribution and the thermal stress level within the tank wall increase with the LN2 feeding rate. Under the largest feeding rate (0.08 kg/s) in this study, the peak value of thermal stress is about 41 MPa. This work could be beneficial to the design and safe operation of cryogenic tanks.

Numerical analysis of transient conjugate heat transfer and thermal stress distribution in geothermal drilling with high-pressure liquid nitrogen jet

This paper presents a numerical analysis of heat transfer and thermal stress in bottomhole rocks during geothermal drilling with high-pressure liquid nitrogen jet. The simulation is conducted by a three-dimensional model in transient state. The conjugate heat transfer method is employed to compute heat transfer between solid and liquid. The thermo-physical properties of liquid nitrogen and rocks are considered in detail. The results indicate that high velocity and turbulence kinetic energy of liquid nitrogen jet at impingement surface enhance heat transfer efficiency between cryogenic fluid and hot rock. Huge tensile stress is generated adjacent to the solid-liquid interface, which is favorable for rock breaking on bottomhole. The primitive rock temperature has a significant impact on maximal stress value. A set of experiments is conducted to validate the effects of thermal stresses on rock breakage. The thermal stresses diminish significantly under laboratory conditions without effective constraint on rock boundaries. In our experiments, the coal rather than other types of rock, was selected as working specimen due to its well-developed natural cracks and small tensile strength. Our results would shed light on the geothermal drilling with high-pressure nitrogen jet.

Effect of additional holes on transient thermal fatigue life of gas turbine casing

Gas turbines casings are susceptible to cracking at the edge of eccentric pin hole, which is the most likely position for crack initiation and propagation. This paper describes the improvement of transient thermal fatigue crack propagation life of gas turbines casings through the application of additional holes. The crack position and direction was determined using non-destructive tests. A series of finite element patterns were developed and tested in ASTM-A395 elastic perfectly-plastic ductile cast iron. The effect of arrangement of additional holes on transient thermal fatigue behavior of gas turbines casings containing hole edge cracks was investigated. ABAQUS finite element package and Zencrack fracture mechanics code were used for modeling. The effect of the reduction of transient thermal stress distribution around the eccentric pin hole on the transient thermal fatigue crack propagation life of the gas turbines casings was discussed. The result shows that transient thermal fatigue crack propagation life could be extended by applying additional holes of larger diameter and decreased by increasing the vertical distance, angle, and distance between the eccentric pin hole and the additional holes. The results from the numerical predictions were compared with experimental data.

Identification of the transient temperature and stress distribution in an atmospheric reentry capsule assuming temperature-dependent material properties

The purpose of this work is to develop a method for solving inverse transient-state thermal and strength non-linear problems in complex shapes. Non-linearity is caused both by the material temperature-dependent properties and radiation. The proposed algorithm reconstructs the whole transient temperature and thermal stress distribution based on temperatures measured in the element selected points. Measured transient temperature values are generated during a numerical simulation of aerodynamic heating on the atmospheric reentry capsule. Both constant and temperature-dependent properties of the material are assumed. A comparison is presented between the transient temperature distributions obtained based on the material constant and temperature-dependent properties. Finally, the developed method is used to identify the transient temperature and stress distribution in the atmospheric reentry capsule assuming temperature-dependent properties of the material. The proposed approach is expected to be a good solution for improving spacecraft structures.

Numerical analysis of the thermal and mechanical effects of laser windows of a high-power all-solid-state 2-μm laser system

The output window of a high-power laser system is vulnerable to damage, and this is the main limiting factor on the power scaling and structure integrity of the laser system. In endeavoring to obtain higher output powers from the laser system, the impact of the thermal and mechanical effects and the damage mechanism of the output window must be considered. In order to study these issues, a thermal model of the laser window is established based on the heat transfer and thermoelastic theories, and the expressions for the transient thermal and mechanical stress distributions of the output window are deduced in terms of the integral-transform method. Taking the infrared quartz window material as an example, the temperature and mechanical field distributions of a high-power all-solid-state 2-μm laser system window are simulated, and the laser-induced damage mechanism is deeply analyzed. The calculation results show that the laser window-induced damage is mainly caused by melting damage when the temperature exceeds the melting point of the material. The presented theoretical analysis and numerical simulation results are significant for the design and optimization of high-power laser windows. © The Authors. Published by SPIE under a Creative Commons Attribution 3.0 Unported License. Distribution or reproduction of this

Analytical treatment of transient temperature and thermal stress distribution in CW end pumped laser rod: Thermal response optimization study

The analytical solution of transient temperature distribution and Tresca failure stress in CW end- pumped laser rod has been derived using integral transform method. The analytical result is compared with numerical solutions presented by other works and good agreement has been found. Analytical solution with its clear physical meaning and its explicit form permits to predict the influence of various factors on the solution. The optical path difference which gives a valuable means to quantify the optical properties of laser material such as designed beam quality, will converge to a constant value as steady state temperature distribution is reached. One can obtain the dominate factors which affect the laser response to bring the laser rod to the thermal equilibrium; it has been found that fast response can be achieved by reducing pumping power, increasing extracted heat from the rod , choosing a crystal having high thermal diffusivity and decreasing laser rod radius while its volume remains constant. One final advantage of the analytical solution is that a fast result can be obtained where the numerical solution usually is a time consuming technique.

Numerical Simulation for Exhaust Manifold Based on the Serial Coupling of STAR-CCM+ and ABAQUS

This study aims to realize the serial coupling of STAR-CCM+6.04 and ABAQUS 6.11-1 and provide boundary conditions for the thermal fatigue analysis. To predict the thermal fatigue life of the internal combustion engine exhaust manifold effectively, the transient heat-transfer process between exhaust gases and exhaust manifolds should be reflected accurately. The transient fluid-solid-thermal coupling simulation on the exhaust manifold is carried out by using serial coupling method. The research of dealing with the problems of transient temperature loading, the mesh generating and the interface temperature interpolation of fluid and solid are conducted in the process of numerical simulation. The goal of bidirectional fluid and solid coupling simulation between the CFD software STAR-CCM+ and the FEA software ABAQUS is achieved and the transient temperature and thermal stress distribution are obtained. Comparison with the steady analysis results shows that it's a necessary and effective way of conducting transient analysis.

Transient thermal stress distribution in a circular pipe heated externally with a periodically moving heat source

This study presents the effects of periodically moving heat source on a circular steel pipe heated partly from its outer surface under stagnant ambient conditions. While the pipe is heated with this heat source applied on a certain section having a thickness of heat flux, the water flows through it to transfer heat. It is assumed that the flow is a fully-developed laminar flow. The heat source moves along from one end of the outer to the other end with a constant speed and then returns to the first end with the same speed. It is assumed that the heat transfer rate has a constant value, and that the thermo-physical properties of the steel do not change with temperature (elastic analysis). The numerical calculations have been performed individually for a wide range of thermal conductivity of steel and for different thicknesses of heat flux. The moving heat source produces the non-uniform temperature gradient and the non-uniform effective thermal stress, and when it arrives at the ends of the pipe, the temperature and effective thermal stress ratio profiles rise more excessively. The tangential component is more dominant in the effective thermal stress than the radial component.

Temperature and Thermal Stress Simulation of Window Glass Exposed to Fire

In a compartment fire environment, the high temperature encountered could induce important stresses in glass panes, resulting into cracks and possible fallout of the glazing. The aim of the present work is to investigate thermal stress distributions in a glazing system for fire scenarios. A two dimensional glass thermal stress model to calculate the transient temperature and thermal stress distributions in a typical window glass under fire conditions was developed based on the Kong's work. The basic thermal conduction equation and thermal stress equation for glass were discretized by using the Galerkin method. A computer program based on the model was also developed. For validation purposes, simulations have been carried out using literature experimental data on glazing behavior in an enclosure fire. The glass surface temperature (exposed side) and thermal stress distributions in the glass pane were calculated. The simulation results of the transient temperature and thermal stress are overall in line with the experimental data reported in literature. The major principal thermal stress distribution in the glass at the time of first crack is consistent with the experimental crack patterns. The calculated maximum stress is located at the top edge of the glass pane, as the first crack recorded by experiments. The model does not predict second or later cracks. These results illustrate the relatively good predictions and usefulness of the developed simulation code.

Analysis of Transient Temperature and Thermal Stress Distribution on the High-speed Strain Brake Disk by Simulation

At present the thermal fatigue damage of brake disks is the main threaten of train brake safety.The transient temperature and thermal stress distribution on the disk during the braking are the basis for research on the thermal fatigue damage.In order to simulate the temperature field and thermal stress distribution from the thermal load caused by the friction during braking under different conditions,the math model of 3D temperature field without inside thermal source of the brake disc is built and the thermal elastic-plastic finite element method is used.At the same time,the temperature field load is calculated with fiction power method and the brake cases are one time usual brake,one time emergent brake,three times emergent brake and one time ramp brake respectively.It is shown that the temperature change rules on the brake disk surfaces are similar under different cases.At the beginning of brake the temperature rises fast with the strong thermal flow inputting and reaches peak value.Then the temperature decreases slowly through radiation and convection.The temperature during the ramp brake rises slower than the other cases.The temperature and thermal stress distributions of the brake disk can give the basis for the thermal fatigue properties study of the composite material used in high-speed train brake disc.

Stress Evolution and Thermal Shock Computation Using the Finite Volume Method

This work presents a novel numerical approach to thermal shock and transient thermal stress distribution based on the Finite Volume method. A unified approach was developed based upon the coupling between a three-dimension thermal solution and a linear thermo-elastic, multi-layered plane stress approximation. Temperature distributions were compared to analytical solutions for a flat plate and to experimental results using a temperature-dependent heat transfer coefficient. The numerical results were assessed against three analytical methods: Timoshenko and Goodier, Lu and Fleck, and Collin and Rowcliffe. This work demonstrates that the FVM provides also accurate results for thermal stress distributions in solids.

Transient Temperature and Thermal Stress Distributions in a Hollow Disk Subjected to a Moving Uniform Heat Source

This study presents numerical analyses of transient temperature and thermally induced stress distributions in a stationary hollow steel disk partially heated by a moving uniform heat source from its outer surface under stagnant ambient conditions. The moving heat source applied on a certain angular segment of the processed surface rotates with a constant angular speed (ω). The peak levels of the temperature gradients and the thermal stress ratios at the heated segments do not rise very much after 2–3 cycles. When the value of ω is increased, the maximum effective thermal stress ratio can be decreased in a considerable amount.

Transient Thermoelectromechanical Response of a Functionally Graded Piezoelectric Material Strip with a Normal Crack

Considered in this paper is a functionally graded piezoelectric material (FGPM) strip containing an embedded crack or an edge crack perpendicular to its boundaries. The problem is solved for an FGPM strip that is suddenly heated or cooled from the bottom surface. The top surface is maintained at the initial temperature. The crack faces are supposed to be completely insulated. Material properties are assumed to be exponentially dependent on the distance from the bottom surface. First, the transient temperature and thermal stress distributions in an uncracked strip are calculated by using the Laplace transform. Then, the thermal stress is used as the crack surface traction with opposite sign to formulate the mixed boundary value problem. By using the Fourier transform, the electromechanical problem is reduced to a singular integral equation which is solved numerically. The numerical results for the thermal stress intensity factors are computed as a function of the normalized time for various values of the nonhomogeneous and geometric parameters. The temperature and thermal stress distributions for the uncracked problem and the results for the crack contact problem are also included.