Calculation Of Thermal Stresses Research Articles

Improved Research on Two-Step Thermal Stress Calculation Method for Asphalt Mixture: Extended Creep Compliance Test.

The two-step thermal stress calculation method (TTSCM) is commonly used to predict the cracking temperature of asphalt mixture. The aim of this study is to improve TTSCM's mathematical model so as to enhance its prediction accuracy. First, this study evaluated the errors of predicted cracking temperatures of original TTSCM for AC-16 and AC-25 asphalt mixtures by thermal stress-restrained specimen test (TSRST). Then, an improved method called the extended creep compliance test (ECCT) was developed to modify the TTSCM. The test results show that the cracking predictions of the original TTSCM are not always accurate. Particularly for AC-16 asphalt mixture, the predicted cracking temperature is 2.9 °C (-10.6%) higher than the measured value by the TSRST. The ECCT method has been proven to be an effective way to enhance the prediction accuracy of the TTSCM. The predicted cracking temperatures modified by the ECCT method for both asphalt mixtures are relatively accurate, having an error within ±2%. The ECCT method changed the calculated thermal stress values at different temperatures of the TTSCM; however, they still conformed to a basic changing trend with respect to the initial temperature and cooling rate. Finally, a recommendation regarding the ECCT method was presented.

Calibration, testing and application of the AquaCrop model for bean crop under irrigation regimes.

Crop growth simulation models relate the soil-water-plant-atmosphere components to estimate the development and yield of plants in different scenarios, enabling the identification of efficient irrigation strategies. The aim of this study was to calibrate crop coefficients for a common bean cultivar (IAPAR 57) and assess the AquaCrop model's efficacy in simulating crop growth under different irrigation regimes (T0 - non-irrigated, T1-fully irrigated, and T2-deficit irrigated) and sowing dates (S1-March 21, S2-April 24, and S3-August 23). Successful calibration was achieved for crop seasons with suitable temperatures to crop growth (S1 and S3). However, during periods with suboptimal temperatures (April 24 season), coupled with reduced irrigation supply (T0 and T2), the AquaCrop model did not appropriately account for the combined effects of thermal and water stresses. Despite adjustments to stress coefficients, this led to an overestimation of crop growth and yield. In long-term simulations, the model successfully replicated the variability of crop water availability over cropping seasons, reflecting the impact of precipitation variations. It recommended irrigation strategies for the study region (irrigate at depletion of 120 and 170% of readily available water for sowing on March 21 and August 24, respectively) to achieve high crop yield (> 2,769kgha-1) and water productivity (1,050 to 1,445kgm-3) with minimal application depths (< 150mm). While acknowledging the need for improvements in thermal stress calculations, the AquaCrop model demonstrates promising utility in studies and applications where water availability significantly influences crop production.

Design of a multi-energy soft X-ray diagnostic for profile measurements during long-pulse operation in the WEST tokamak

The W Environment in Steady-state Tokamakwas designed and built to test ITER-like tungsten plasma facing components in a long pulse (∼1000 s) scenario. Recently, a multi-energy soft x-ray diagnostic (MESXR) was installed in the WEST (W Environment in Steady-state Tokamak), to understand the sources, transport and confinement of high-Z impurities. The purpose of this work is to describe the engineering challenges posed by the long pulse scenario for the integration of the MESXR diagnostic and how they were addressed and solved. The calculations of vacuum and thermal stress as well as heat transfer are presented and discussed.

Calculation and properties of thermal stress of monolayer film and solution of thermal stress of multilayer infrared antireflection coating by finite element analysis

The deposition of infrared antireflection coatings on silicon lenses is a widely practiced technique that has been extensively investigated by researchers over an extended period. Thermal stress is essential to the adhesion between the film and the substrate. To measure the magnitude of thermal stresses, we use the mechanical analysis method to convert thermal stresses into shearing and peeling stresses. Expressions for these two stresses are then derived. Then, we analyzed the effect of the monolayer film's properties on the silicon substrate's stress. The results indicate that peeling stress is the main factor affecting the adhesion between the film and the substrate, and various approaches can be employed to successfully mitigate the peeling stress exerted on the substrate. The influence of the multilayer film's structure on the peeling stress experienced by the silicon substrate was investigated through the utilization of finite element analysis. In this study, three distinct infrared antireflection coatings were deposited on silicon substrates individually. Subsequently, these coated substrates underwent rigorous environmental testing. The findings from this testing confirmed the accuracy of the stress analysis results obtained by finite element analysis for the multilayer film. Our research has resulted in solutions for determining the magnitude of shearing and peeling stress. We have employed finite element analysis to identify a suitable structure for an antireflection coating that exhibits minimal peeling stress. This advancement has the potential to improve the effectiveness of design processes and the adaptability of infrared antireflection coatings in various environmental conditions.

Calculation and Analysis of Motor Thermal Stress With or Without Eccentricity for In-Wheel Electric Vehicle Applications

The requirement of high-power density and the problems of high temperature and uneven air gap caused by environmental constraints make the alternating effect of internal temperature and related constraints between components during the operation of the motor for in-wheel electric vehicle. These effects and constraints will lead to thermal stress and concomitant deformation, and seriously affect the safe operation of in-wheel motors (IWMs) and vehicles. Aiming at the above problems, this paper takes a 15kW IWM as the research object. Based on the analysis of the mutual coupling relationship between the multi-physics field, such as the electromagnetic field, the temperature field, the flow field and the structural field, a thermal stress analysis model of the IWM is established and verified firstly. Then, quantitative calculation of the thermal stress/strain state of the IWM with or without eccentricity is carried out under different working conditions. The analytical results show that the thermal load generated internally leads to the generation of uneven thermal stress and accompanying thermal deformation, and the maximum thermal stress (MTS) and maximum thermal deformation (MTD) do not appear on the same component. Although eccentricity does not affect the position of the MTS and the MTD, it has an important effect on the maximum value of the stress and deformation, especially the eccentricity exceeds 30%. The results also demonstrate that the permanent magnet (PM) is most significantly affected by the eccentricity.

CALCULATION OF NORMAL TEMPERATURE DIFFERENCE ON MAIN GAS PIPELINES WITH LONG SERVICE LIFE

In the global pipeline transport, including main pipelines (MР) with a long service life (40 years or more), the reliability of operation is ensured by compliance with regulatory requirements. Calculations of the stress-strain state of gas pipelines, in particular, longitudinal stresses, are carried out in accordance with Standart SP 36.13330.2012 «Main pipelines», which does not take into account the life of the facilities.&#x0D; The analysis of SP 36.13330.2012 «Main pipelines» for the effect of the temperature factor on the magnitude of the longitudinal stresses of the gas pipeline section showed that the calculation of longitudinal stresses from the temperature difference ∆Т provides for taking into account four values: Тс – maximum and minimum temperatures during construction; Tр – the highest and lowest temperatures during operation.&#x0D; When considering the stages of construction of gas pipelines, it was established that during this period the pipeline experiences the action of four temperature regimes, and when put into operation, the fifth complex one: from the temperature and pressure of the gas, at which the consolidation of the main pipeline with the surrounding soil occurs predominantly in during which the linear-altitude position of the MР section with a minimum of stresses is predominantly formed.&#x0D; It has been proved that, in relation to the calculations of longitudinal stresses of gas pipelines with a long service life, it is necessary and sufficient to limit the calculated temperature difference by Tр.&#x0D; SP 36.13330.2012 is intended for calculations during the construction of new pipelines, and its use for long-term operated gas pipelines, taking into account the standard value of ∆Т, mainly leads to rejection, and, therefore, to repair.&#x0D; We believe that for the operation of MР with a long service life, for the calculation of thermal stresses, it is necessary to develop a standard that allows the calculation of the temperature difference ∆Т by the value of the operating temperature Tр.

Model for calculation of thermal stresses in concrete pavement slabs with refined non-linear deformation constraints

Few investigations have considered comprehensive deformation constraints when calculating thermal stress of concrete slab. In this paper, the comprehensive and refined non-linear deformation constraints model of concrete slab is firstly proposed by setting non-linear spring elements at bottom and side of the slab and the capacity of shear load transfer across joints is considered as well. The results show that thermal stresses calculated by refined non-linear deformation constraints model are in good consistent with experimental results. The foundation reaction modulus has little effect on thermal stresses, but has a significant effect on gap between slab and its foundation. The stiffer base results in higher curling stresses at bottom of slab, and the types of base have an important effect on frictional resistance in horizontal direction at bottom of slab. The larger shear stiffness of joints will increase thermal stresses and shear force along joints but decrease deflections of slab.

Energy load of metal brake frictions elements

Problem. The mathematical description of the temperature field of the rim of the brake pulley can have both an independent value and be the goal of solving a problem (for example, when calculating the time of heating or forced cooling), and also be used as an auxiliary result for solving another, more complex problem (for example, calculating thermoelastic stresses in brake pulley rim). Goal. The purpose of the work is to assess the energy load of metal friction brake elements during the braking process. Methodology. Solving the tasks involved taking into account the fact that the surface-volume temperatures of the polished working surface of the pulley rim are local when assessing the energy load of the belt pulley rim; surface-volume temperatures are always higher than the "pure" volume temperatures of the pulley rim; polished and matte surfaces of the pulley rim are considered. Results. It is proposed that a new approach to the calculation of local thermal stresses, which is implemented for the first time in the theory of friction and wear. The reliability of the obtained results was confirmed experimentally. Originality. The need to find the non-stationary field in the investigated single- ("pad-pulley") and in multi-pair ("tape-pad" and "pad-pulley") friction nodes is proposed. In the last friction nodes, the friction pads act as insulation between the tape, which is freed from the pads, and the working surface of the brake pulley rim. Practical value. The proposed approach made it possible to establish that the magnitude of stresses on the surface of heat release is almost 5 times greater than in the volume of the pulley rim. At the same time, the nature of the influence of the intensity of heat exchange on the magnitude of stresses is the same as during heating, which leads to a decrease in the formation of cracks on the surface of the pulley rim.

Volumetric Dilatometer Study of Thermoreversible Aging Properties in Crumb Rubber–Modified Asphalt Binders

Abstract The primary objective of this paper is to investigate the thermoreversible aging mechanism of crumb rubber–modified asphalt binders (CRMAs). In order to achieve this goal, an extended bending beam rheometer (Ex-BBR) test and volumetric dilatometer test were conducted. Additionally, isothermal crystallization kinetics (Avrami theory) and thermal stress calculation using the Hopkins and Hamming algorithm were employed to process the test data. The low-temperature properties of the asphalt specimens were characterized through calculations of creep stiffness (S), creep rate (m-value), grade loss (GL), thermal stress, and Avrami index (n). The experimental results indicate that thermoreversible aging is present in all asphalt samples during the long-term isothermal hardening process. This aging is characterized by continuous macroscopic volume shrinkage, accumulation of thermal stress, a crystallization process, and a process akin to crystallization (i.e., crumb rubber adsorbed oil at low temperatures). It was observed that CRMAs exhibit more severe thermoreversible aging and faster physical hardening rates due to their unique properties at a constant low temperature when compared with base asphalts. However, it was also observed that CRMAs can reduce the thermal stress by reducing the volumetric shrinkage coefficients and S. It is important to note that the volumetric shrinkage coefficients are not constant, which are related to the base asphalts, crumb rubber, and conditioning time. Therefore, it is not appropriate to use a single empirical constant to calculate thermal stress. Instead, multiple coefficients may need to be incorporated to account for the variability in shrinkage behavior.

Ultra-broad-spectrum laser-pulse damage of low-dispersion mirrors

The broadband optical parametric chirped-pulse amplification scheme is considered as a promising approach for developing the 100 PW or even exawatt laser facilities. Based on a quarter-wavelength optical-thickness mirror with a reverse-chirped structure, a Nb2O5/SiO2 low-dispersion mirror (LDM) and a Nb2O5–Al2O3/SiO2 composite LDM (CLDM) for a 910 (±100 nm) laser system are designed and experimentally evaluated. The laser damage properties of the mirrors were investigated in an uncompressed nanosecond laser pulse with a spectrum bandwidth of 200 nm for the first time. From the aspects of both broad-spectrum electric field and thermal stress, the damage behavior is elucidated. The results show that the protective layer has both positive and negative effects in the broad spectrum and the competing results of the two effects determine whether the protective layer can play a protective role. Damage morphology and thermal stress calculations show that the laser introduced thermal stress mismatch will lead to the peeling damage of CLDM. This study shows that broad-spectrum optics should be designed and fabricated by considering the electric field of all spectrum components and thermodynamic properties of layer materials; this provides insight into the development of high-performance broad-spectrum optics.

Design-oriented study on target station for spallation neutron source at KOMAC

A neutron-production target system, composed of targets, moderators, reflectors, and shielding, has been conceptually designed for the future MW-class spallation neutron source based on a high-intensity proton accelerator at KOMAC. For targetry, we tentatively adopted a fixed-metal target concept; tantalum-clad tungsten plates in a water-cooled target shroud made of stainless steel. In the thermal analysis and stress calculations using ANSYS, the von Mises stress was found to exceed the yield stress of SS316L at the edges of the structure for a 500-kW proton beam on target. Relatively high stress at edges seems to be a stress concentration that could be reduced by minor design modifications. Preliminary calculation results for a conservative design of target shielding show that radiation dose after the outermost shielding could be lower than 10 upmuSv/h in a 500-kW operation condition, implying that the design could be optimized to reduce construction costs without loss of shielding performance.

High velocity impact response of carbon/epoxy composite laminates at cryogenic temperatures

Composite laminates are subjected to cryogenic temperatures in exposed aircraft structures during flight or in cryogenic tanks. The combination of cryogenic temperatures and high velocity impacts represents a threat to their integrity. This work investigates the behaviour of carbon-epoxy laminates under high velocity impacts (from 70 to 500 m/s) at room and cryogenic (-150 °C) temperatures and under two different plate orientations with respect to the projectile direction. The damage pattern of impacted specimens at low temperature, revealed by C-scan and X-ray tomography, exhibits a higher density of fiber breaks and shear matrix cracks which do not translate to a larger projected damaged area. The experimental analysis through interlaminar shear strength tests and the calculation of ply thermal stresses exclude the association of this particular pattern to damage mechanisms induced during the temperature decrease.

Understanding the performance of profiled composite walls in fire

To understand the performance of structural elements subject to one-side heating, the combined effects of temperature and temperature gradient (or the non-uniform temperature increase) must be accurately considered in developing structural performance models. However, due to insufficient consideration of such effects, the direct application of current understanding of general structural performance at high temperature on structural elements like profiled composite walls (PCWs) seems insufficient because of the complex role that the different materials can have in the presence of significant temperature gradients. Therefore, more research is needed to understand the performance of these structural elements when subjected to temperature increase and temperature gradients. Only then, the performance of PCWs at high temperature can be appropriately addressed. This paper presents and verifies a structural performance model that can be used to analyse the performance of PCWs subjected to combined thermal and mechanical loadings. First, details of an analytical study are presented, including thermal stress calculation within inhomogeneous and composite cross-section by fully considering the effects of non-uniform stiffness, non-linear temperature gradient, shifting of the neutral axis, and the coupling effects between stress and thermal expansion. Second, previously published experimental results into the performance of PCWs subjected to combined mechanical loading and one-side heating are then used to verify the newly-developed analytical model. It is also argued that the methodology for stress and curvature calculation developed in this study can be used to assess the performance of any structural elements (PCWs included) subjected to one-side heating. (244 words).

Thermal stress calculation of wax-based warm mix asphalt considering thermorheologically complex behavior

The warm mix asphalts which reduce the environmental pollution always show thermorheologically complex behavior under the realistic working conditions (the long-term loading at the low temperature) in the cold region. However, many scholars ignore the thermorheologically complex behavior when calculating thermal stresses. In this paper, the new thermal stresses calculation method considering thermorheological complexity of four wax-based warm mix additives (Fischer-Tropsch (F-T) based wax, fatty acid amides (FAA) based wax, polyethylene (PE)-based wax, and linear aliphatic hydrocarbon (LAH)-based wax) modified asphalt binders were proposed, which was the process of incremental iterative (Named as ‘the incremental method’). The results show that the warm mix asphalt exhibits the thermorheologically complex behavior under long-term loading condition at the low temperature through the tail of the master curve of stiffness modulus, and the thermal stresses considering thermorheologically complex characteristics calculated by the incremental method are greater than that calculated by the traditional Monismith method. Therefore, the incremental method should be used to calculate the thermal stress of asphalt binders under the long-term loading condition instead of the Monismith method, otherwise the cracking risk of the asphalt binder will be underestimated. The wax-based warm mix additives with longer chain molecules and cold storage time can increase the thermorheological complexity more evidently, and the thermal stresses of asphalts with thermorheologically complex characteristics are more sensitive to cooling rate. All in all, the proposed incremental method will provide a supplement to the calculation method of the thermal stresses in the asphalt binder.

Calculation of thermal state stress of the wind turbine’s foundation slab for the improvement of the quality and crack resistance

The thermal stress state of massive concrete and reinforced concrete structures during the construction period is characterized by the risk of large tensile stresses and, as a result, temperature cracks that violate the integrity of the structure. These defects are unacceptable for crack-resistant structures. The process of concrete hardening is accompanied by the release of a large amount of heat as a result of the hydration reaction of cement. The most dangerous cases are with uneven temperature distribution within the block body. Significant gradients can lead to stresses that exceed the stresses from operational loads. The thermal stress state is also influenced by temperature fluctuations of the surrounding environment, solar radiation, cooling rate of the block, initial and boundary conditions, and the possible cutting of a massive structure into separate concrete blocks. The latter factor is the subject of the research reflected in this study. The article establishes that, despite the possible increase in the construction time cutting the foundation plates into separate blocks by height can make the thermal stress state of the plate significantly more favorable in terms of ensuring crack resistance. In some cases, cutting can be such a successful method of combating temperature cracks that it will allow for the abandonment of special thermal insulation on the surface of the structure. The study shows the effectiveness of the cutting method depending on the number of blocks for the improvement of foundation slab quality.

Low-temperature heat transfer and stress analysis of LNG loading arm pipeline supports

The pipeline support is a complex component structure in liquefied natural gas (LNG) loading arm. In order to study the impact of ultra-low temperature conditions on the mechanical performance of pipeline brackets, the heat transfer analysis and thermal stress calculation of the pipeline support of the LNG loading arm are carried out under low-temperature conditions in this paper. Based on the principle of steady-state heat transfer, the finite element method is used to study the sensitivity of ambient temperature to heat transfer results of pipe support, the results show that the heat dissipated by the duct support is proportional to the temperature difference. The temperature field distribution of the pipe-bundle rib on the duct support under ice-free and ice-covered conditions is analyzed, and two different paths are selected to study the temperature distribution law of the structure, and the conclusion that the ice has the effect of cooling is drawn. Finally, based on the temperature field distribution results obtained by the heat transfer analysis, the low-temperature stress analysis of the pipe support is carried out. According to the thermal stress results, the corresponding improvement measures are proposed. It provides some guidance for the structural design of the loading arm.

Hollow Cylinder with Thermoelastic Modelling by Reduced Differential Transform

The term thermal stresses are related to mechanics of materials. The thermal stress is formed due to any changes in temperature of a material. The large change in temperature concludes to higher the thermal stresses. Also, there is an effect of thermal expansion coefficient on thermal stresses. The thermal expansion coefficient is different for different materials. In the present paper, the design of a mathematical model concerning the thermal stresses in hollow cylinder subject to the heat conduction with initial and boundary conditions have developed. The basic aim of this work is related to calculations of thermal stresses and thermoelastic displacement in the hollow cylinder by using the reduced differential transform method. The analytical solution is satisfied with the aim of special cases for the copper material properties. The numerical results are illustrated graphically by using mathematical software SCILAB.

Performance of Two-Dimensional Functionally Graded Anode Supported Solid-Oxide Fuel Cells

Abstract Ceramic materials used in solid-oxide fuel cells (SOFCs) are subjected to high thermal stresses which is a result of the unequal thermal expansion coefficient of different layers. As a result, SOFCs are susceptible to failure at elevated temperatures, and therefore the maximum operating temperature is limited. Consequently, the power density is limited as well. Fuel cells with electrodes that have graded compositions in the thickness direction have been investigated to control the thermal expansion. In this study, two-dimensional grading is proposed for the electrodes and compared with the one-dimensional grading in terms of thermal stress and performance. A comprehensive model is developed for high-temperature SOFCs that include the momentum, species, energy, and charge transport equations. Furthermore, the bilinear elastoplastic model is used for the calculation of thermal stresses and failure of solids. Two-dimensional functionally graded electrodes are studied in which the grading is implemented in the thickness and length directions. Results indicate that continuous one-dimensional grading functions reduced thermal stresses by 40% for m = 0.8 compared with conventional electrodes. It also improved the electrochemical performance, as the maximum power density increased by 15%. For the 2D piecewise linear grading function, a further improvement of reducing thermal stresses by an extra 16.5% is obtained. Two-dimensional graded SOFCs can therefore operate at higher temperatures safely in terms of thermal stresses. This creates an opportunity to fabricate high-temperature, compact SOFCs for high-power applications.

Effect of Accelerated Cooling on Linepipe Steel Mill Scale and Resulting Localized Corrosion Susceptibility

The structure and composition of mill scale on linepipe steel formed with and without accelerated cooling conditions (ACC) was investigated and correlated to localized corrosion susceptibility. The mill scale structure/composition was investigated using scanning electron microscopy equipped with x-ray energy dispersive spectroscopy and electron backscatter diffraction, as well as x-ray diffraction. Localized dissolution of the mill scale was investigated using electrochemical techniques including open-circuit potential measurements, electrochemical impedance spectroscopy, and electrochemical noise measurements in a corrosive phase solution. The various surface analytical and electrochemical techniques indicated that the mill scale formed without ACC consists of a relatively crack-free, thick inner wüstite layer with a thinner magnetite outer layer. However, the mill scale formed with ACC comprised a magnetite layer containing islands of retained wüstite, with some evidence of magnetite/iron eutectoid formation and which exhibited a relatively high density of through-scale cracks. These cracks can provide direct paths that connect the corrosive solution to the steel substrate, leading to a more rapid breakdown of the mill scale. Additionally, the cracks can form a crevice between the mill scale and the steel surface, providing sites for pit initiation and growth. Coefficient of thermal expansion mismatch thermal stress calculations indicate that a magnetite-based scale is more susceptible to cracking/spalling than a wüstite-based scale, resulting in the ACC plate being more susceptible to localized corrosion.

Design and engineering challenges of a multi-energy hard x-ray camera for long-pulse profile measurements at WEST tokamak

The WEST tokamak has recently been prepared for long pulse operation with a water-cooled full first wall. Heating is provided by radiofrequency systems, including Lower Hybrid Current Drive (LHCD). The Princeton Plasma Physics Laboratory has developed a multi-energy hard x-ray camera for profile measurements at WEST. The camera is based on a new generation of 2D pixel array detectors that allow the energy threshold to be independently set for each pixel. The diagnostic will provide spatial, temporal and energy resolved measurements of the hard x-ray emission from the full plasma cross-section, investigating several physical quantities such as the electron temperature from continuum emission, the fast electron tail density produced by radiofrequency current drive and runaway electrons, as well as characteristic tungsten x-rays due to beam-target emission at the edge. This work describes the engineering challenges that the WEST long pulse scenario poses for this diagnostic and how the design addresses and solves them. Vacuum, thermal stress and heat transfer calculations are presented and discussed.