Generation Of Thermal Stresses Research Articles

Multiphysics Study of Thermal Profiles and Residual Stress in Welding.

One of the effects of welding is residual stress. Welding involves complex tests concerning differences in values of the mechanical parameters of its regions as an effect of residual stress. Such multiphysics characteristics of welding pose a challenge in predicting residual stress. In the present study, a thermo-mechanical constitutive model considering phase transformation and transformation plasticity is implemented in the numerical model in ABAQUS user subroutines. In order to consider phase evolution in welding, the metallurgical parameters for Leblond's phase equation were obtained from the calibration of DH36 steel with a CCT diagram. In addition, the effects of welding speed on thermal profiles and residual stress generation were investigated. Analysis has suggested that the width of the heat-affected zone (HAZ) decreases with an increase in welding speed, and the phase fraction is significantly affected by this kind of parameter. Such phase transformation has led to the generation of a compressive stress in the fusion zone (FZ) and HAZ. The volume difference between coexisting phases produces a compressive stress in cooling, and its magnitude was increased with martensite increasing.

Numerical and experimental study of residual stress in multi-pass laser welded 5A06 alloy ultra-thick plate

The laser welding technology of ultra-thick plates has been widely applied in many crucial engineering structures, where its safety and stability still suffer from the residual stress brought by the welding temperature. In this work, experimental and numerical studies are carried out to reveal the evolution and distribution of the residual stress. A 5A06 aluminum alloy plate with 30 mm thickness is used to conduct the laser welding experiment, and the short-wavelength X-ray diffractometer (SWXRD) is employed to measure the residual stress. Furthermore, a multi-pass laser welding numerical model is developed to predict the residual stress during the welding process. The simulation results of the weld pool geometry and residual stress agree well with the experimental data, which gives a good validation of the numerical model. Based on the proposed numerical model, the influence of the welding parameters, including inter-pass cooling time and welding rate are also investigated. It is discovered that the reduction of the inter-pass cooling time results in weakness effect of the temperature gradient, which hinders the generation of plastic deformation and leads to a lower residual stress value. Meanwhile, the simulation results also show that the increase in welding rate promotes the generation of thermal stress, which brings a higher residual stress value appeared in the structure.

Effects of partial shading on thermal stress and exergetic efficiency for a high concentrator photovoltaic

Highly concentrated photovoltaic systems can produce higher energy yields than conventional photovoltaic panels but have yet to reach widespread deployment, partly because of lower lifetime and hence cost effectiveness. One limiting factor in the lifetime is the excessive generation of thermal stress. This study takes a multi-objective approach to the calibration of a highly concentrated photovoltaic thermal hybrid system. Novelty is found by exploring the relationship and trade-off between thermal stress and exergetic efficiency. A variety of optical configurations are compared by partially shading the input aperture of the primary optics. Similarly, adjustments to the receiver are made by changing the angle of the solar cell by 45°. To minimise light spillage. The primary and secondary optic positions stay the same throughout all calibrations.By experimentally validating a COMSOL model of the concentrator photovoltaic system (including irradiance distribution) a thorough analysis is conducted. It was found that the maximum thermal stress within the solar cell in this study could drop by almost 10 % with small losses (<3.5 %) to total exergetic efficiency after only small changes to receiver position. Further investigations into other specialised concentrator photovoltaics are required to understand the range of impact on thermal stress.

Wire Arc Additive Manufacturing: A Study of Process Parameters Using Multiphysics Simulations

In this work, analyses focus on understanding the effects of the scanning pattern and speed on the thermal profile, phase transformation, and residual stress generation in the WAAM deposition. An FE numerical model is constructed that takes into account the phase evolution and transformation plasticity using the ABAQUS user subroutine, UMAT. The results show that the scanning pattern significantly affects the heat accumulation and the cooling rate during the AM deposition, and, eventually, the generation of residual stresses. According to the simulation results, the highest residual stress is generated in the case of the out–in scanning, while the alternate pattern leads to the lowest residual stress. The influence of the scanning speed on the thermal profiles and residual stress are also examined. The analyses show that an increase in the scan speed leads to a decrease in the peak temperature and an increase in the cooling rate, which result in an increase in the martensite volume fraction of the deposition.

Sequentially Coupled Thermal-Hydraulic-Mechanical Simulation for Geomechanical Assessments of Caprock Integrity in SAGD

Oil sand reservoirs and caprock undergo deformations triggered by pore pressure increases and thermal induced stresses during the steam-assisted-gravity-drainage (SAGD) processes. Geomechanical assessments are mandated by energy regulators to evaluate the caprock integrity and ensure the safe SAGD operations. Commercial reservoir simulation packages started to incorporate geomechanical effects when predicting flow response; however, these geomechanical modules are not able to correctly model the plastic deformations caused by thermal-hydraulic-mechanical (THM) interactions, which has a first order effect on predicting steam chamber propagation and evaluating caprock integrity.&#x0D; An integrated coupled THM modeling methodology is proposed here to improve the modeling of reservoir deformations and caprock integrity in a heterogeneous oil sand reservoir with interbedded shale barriers. The pressure and temperature front are found to propagate at different speed and that dominate the elastic and plastic deformations caused by changes of shear and mean effective stress. Therefore, four stages are divided in the SAGD process that can be interpretations of changes in stress paths including buildup of pore pressure, generation and dissipation of thermal induced stresses. The response surfaces of minimum factor of safety (FOS) are introduced and computed to provide a conservative estimate for caprock integrity during SAGD of a heterogeneous reservoir with multiple layers of caprocks in Athabasca oil sands. &#x0D;

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.

Effects of Cooling Conditions and &lt;i&gt;γ&lt;/i&gt; Grain Size on Each Behavior of Transformations, 3-Dimensional Thermal Deformation and Stress Generation during Immersion Cooling of Steel Bloom

Effects of Cooling Conditions and &lt;i&gt;γ&lt;/i&gt; Grain Size on Each Behavior of Transformations, 3-Dimensional Thermal Deformation and Stress Generation during Immersion Cooling of Steel Bloom

Parametric sensitivity analysis to investigate the effects of operating and design parameters on single direct methane steam reforming solid oxide fuel cell performance and thermal impacts generation

Solid oxide fuel cells (SOFCs) with high operational temperature provide direct methane steam reforming (MSR) but at the same time results in high thermal impacts (thermal stresses and strains) generation. In the present work, parametric and sensitivity analysis have been presented to understand the effects of different operational (operating temperature, air–fuel ratio) and geometrical parameters (porosity, flow configurations and electrolyte thickness) on cell performance and thermal impacts generation in porous electrodes and solid electrolyte. Simulation results show that 25 % increase in operating temperature (800° to 1000 °C) causes an increase of 85.85 % in current density (2146.37 A/m2 to 3989.06 A/m2) and 10.5 % larger thermal stress generation (1673.18 MPa to 1849.69 MPa). The sensitivity analysis has been performed by implementing Taguchi Method. Analysis of variance (ANOVA) indicates that operating temperature substantially affects the overall cell performance with a significant contribution of 61.81 %, followed by electrolyte thickness 22.42 %, material porosity 13.90 %, air–fuel ratio 0.56 %, and flow configuration 0.40 %, respectively.

Surface characteristics optimization of biocompatible Ti6Al4V with RCCD and NSGA II using die sinking EDM

Machining of titanium alloy grade V (Ti6Al4V) is very difficult by conventional metal cutting process due to low thermal conductivity, ability to retain strength at elevated temperature, tendency to work harden. This may result in high heat at the cutting zone and the generation of thermal stresses. Therefore, in the present research die-sinking electrical discharge machining is used to machine Ti6Al4v alloy. A non-dominated sorting genetic algorithm (NSGA II) coupled with rotary central composite design (RCCD) based on response surface methodology (RSM) is employed to optimize machining parameters in die-sinking electrical discharge (EDM) machining of Ti6Al4V. A quadratic mathematical model has been developed for material removal rate (MRR) and surface roughness (Ra) in terms of peak current (I), pulse on time (Ton) and pulse off time (Toff) as independent input parameters. Die-sinking EDM experiments are planned using RCCD based on response surface methodology. Results revealed that peak current is the most influencing EDM parameter on both MRR and Ra with PC of 35.86% and 57.10% respectively. MRR continuously increases with peak current. MRR firstly decreases and then increases with an increase in Ton. Ra continuously increases with peak current and starts decreasing after a coded value of 1.5. The Optimization result obtained by NSGA II is validated through confirmation experiments which are in good agreement with the experimental value with an absolute error of 6% and 4.8% in MRR and Ra respectively.

Numerical investigation of thermal stress in the fuel element of high-temperature air-cooled nuclear reactor

The direct-cycle nuclear reactor cooled by the air can be adopted in the aircraft of near space. The operation conditions are with high temperature and heat flux which can lead to the generation of thermal stress and result in the crack of the fuel element. To confirm the effect of air parameters and heating conditions caused by nuclear reactor on the thermal stress of the new type of reactor, the numerical investigation based on the multi-physics coupling method is conducted. Firstly, the boundaries and main physical properties of the fuel element are determined. Subsequently, the coupled methods of Computational Fluid Dynamics and Computational Structural Mechanics are adopted after being validated. Afterwards, the effects of cosine heating, heat flux, inlet temperature and pressure on thermal stress of the fuel element are investigated. The results reveal that the position with maximum thermal stress is close to the position with maximum heat flux. The condition with low heat flux can be adopted to obtain the sketchy thermal stress under high heat flux conditions ranging from 221 kW/m2 to 1.013 MW/m2 before the crack of the fuel element. The effect of the inlet temperature on thermal stress can be ignored compared with the heat flux. The effect of pressure on thermal stress is limited, but higher pressure is recommended. The research can lay the basis for the design of the reactor cooled by air.

鋳片浸漬冷却時の変態，3次元熱処理変形および応力発生の各挙動に及ぼす冷却条件およびγ粒サイズの影響

To optimize reverse transformation treatment, which is effective in preventing hot rolling cracking in the CC-HCR (Continuous Casting - Hot Charge Rolling) process, three-dimensional metallo-thermo-mechanical analyses were performed. The metallo-thermo-mechanics and a CCT (Continuous Cooling Transformation) diagram estimation method using JMatPro were used to obtain the required cooling time for reverse transformation in immersion cooling with water jet and to elucidate the effects of nonuniform cooling and γ grain size on thermal deformation and stress generation behaviors during cooling and the mechanisms of these events.

Atomistic simulation on the generation of defects in Cu/SiC composites during cooling

The coefficient of thermal expansion (CTE) mismatch between the reinforcement and the matrix results in thermal residual stresses and defects within metal-matrix composites (MMCs) upon cooling from the processing temperature to ambient temperature. The residual stresses and thermally induced defects play an important role in the mechanical properties of MMCs, it is critical to understand the mechanism of defect formation and evolution. This study provides atomistic simulations to reveal the generation of thermal residual stresses, dislocation and incomplete stacking fault tetrahedron (ISFT) during cooling in the idealized Cu/SiC composites. We found that dislocations are generated explosively in a certain temperature range during cooling, which results in a non-linear relationship between dislocation density and temperature. The combined effect of the stresses induced by CTE mismatch and the thermodynamic state of the metal leads to the rapid generation of dislocations. The Shockley partial and the highly stable stair rod are the two dominant dislocation structures. The immobile stair-rod dislocations and the highly stable ISFTs formed in the initial high temperature stage inhibit further development of plastic deformation. The present results provide new insights into the defect formation mechanism and the dislocation strengthening mechanism of MMCs caused by thermal mismatch between constituents.

Crack-free 60 wt% WC reinforced FeCoNiCr high-entropy alloy composite coating fabricated by laser cladding

• Crack-free 60 wt% WC reinforced HEA composite coating was successfully prepared. • The obtained composite coating shows good wear resistance. • No obvious texture and residual stress in composite coating. Crack control of metal-ceramic composite coatings with high content of ceramic particles remains a challenge due to their intrinsic brittleness and the generation of huge thermal stress during the laser cladding process. In this paper, the crack-free 60 wt% of tungsten carbide (WC) particles reinforced FeCoNiCr high-entropy alloy composite coating was successfully prepared by laser cladding technology. The composite coating is composed of face centered cubic (FCC) solid-solution phase, WC, W 2 C and Co 4 W 2 C. The composite coating consists of dendrite grains, massive precipitates and fishbone precipitates distributed around WC particles. No obvious texture observed in composite coating. The average microhardness of the composite coating is 506 HV 0.05 . The average friction coefficient and wear volume loss are 0.474 and 0.041 mm 3 , respectively.

Three-dimensional fluid-structural interaction and thermal analysis of a large diameter horizontal cryogenic transfer line

This paper focuses on the thermal stress analysis and the thermal bowing phenomenon in a large 12-inch diameter cryogenic transfer line during chill-down with liquid oxygen. To investigate the chill-down characteristics and corresponding thermal stress generation, a threedimensional fluid-structural numerical model has been adopted in this work. The numerical simulation is performed on a 2 m long transfer line having an internal diameter of 30.48 cm (12 inch). Three dimensional modelling has been performed to numerate the channel wall temperature distribution along with the flow, at the top and the bottom portions. Based on the temperature data from CFD calculations, transient structural analysis and deformation of the transfer line are studied using a finite element model. Results show that the bowing in the transfer line occurs when there is a strong circumferential variation in temperature. Furthermore, this study provides a numerical simulation that predicts the chill-down time and the time when a stratified flow occurs in the line. This numerical method has been found to be a useful tool for the evaluation, design, and development of a large diameter cryogenic transfer line for transportation of large quantity of cryogenic fluid.

Negative Thermomechanical Effects in Granular Composites with Incompatible Thermomechanical Parameters of Their Components

Within the framework of the theory of thermoelasticity, the problem of the generation of additional internal thermal stresses in a composite material with granular fillers under the influence of temperature is posed. Using the spherical inclusion model applied in the theory of composites, constitutive equations are formulated, and their analytical closed-form solutions are constructed. It is shown that the internal thermal stresses initiated in the system have a localized character, are proportional to the values of the elastic moduli of the materials of each phase and the difference between their coefficients of linear thermal expansion, and decrease in inverse proportion to the cube of the radial coordinate. With the help of specific applied examples, it has been established that even at relatively moderate values of temperature changes, these stresses can reach limit values that contribute to the initiation of internal latent localized defects and cracks in the system. The cases of thermally stressed states of a spherical inclusion coated with a layer of another material, an inclusion with a cavity, and a spherical pore are also considered.

Effect of in-situ temperature and loading rate on the out-of-plane performance of carbon nanofiber embedded glass fiber / epoxy composite

This article studies the influence of in-situ temperatures (30 °C, 60 °C, 90 °C, and 120 °C) and loading rates (1 mm/min and 100 mm/min) on the out-of-plane flexural performance of Glass fiber reinforced epoxy composite with and without carbon nanofiber (CNF) (GE and CNF-GE). Improved stress transfer in CNF-GE composites than GE composite resulted in enhanced flexural properties at 30 °C. The crack propagation time is reduced as the loading rate increases. Due to the substantial obstruction of CNF against crack propagation, CNF-GE composites displayed higher flexural properties than GE composites. However, with the rise in temperature over 60 °C, CNF-GE composites showed a severe decrement in flexural properties than GE composites due to the generation of thermal stresses at the CNF/epoxy interface. The evidence of interfacial debonding at the fiber/epoxy and CNF/epoxy was obtained through fractography, satisfying the explanation provided during flexural analysis.

A Study of Thermal Stress Generation During The Rewarming Process of Cryopreserved Large Biomaterials

A Study of Thermal Stress Generation During The Rewarming Process of Cryopreserved Large Biomaterials

Microchanneling on bio-inert dental ceramic using dry pulsed laser ablation and liquid supported pulsed laser ablation approach

As the rate of heat energy transferred in yttria-partially stabilized zirconia (Y-PSZ) is very slow, it entraps the high temperature at localised region in laser microchanneling process eventually causes thermic damages which results in geometrical howlers and poor channel quality. Present work justifies, experimental inquisitions and microstructural with an aid of EDS analysis to determine the potentiality of laser ablation processes under D-PLA and LS-PLA approach. However, microchannels processed by D-PLA approach exhibit critical issues like, generation of thermal stress, frequent formation of cracks, re-deposition of eroded material and HAZ; to address these issues, a novel technique of underwater nanosecond laser micro machining was adopted. The phenomena behind the formation of channels in LS-PLA are unalike to that in D-PLA. The objective of this research is to discuss those phenomena during the study of influencing parameters over dimensional veracity of microchannels with an aid of surface integrity. In accession to that, multi-objective desirability based optimization using PSO algorithm (MOPSO) was applied to obtain the desired values of microchannel characteristics.

Numerical prediction of machining-induced surface residual stress for TC4 cryogenic turning

Liquid nitrogen(LN2) cryogenic machining is a green, sustainable, and high-performance machining technology. LN2 cryogenic machining of TC4 can significantly strengthen the local cooling environment of cutting, accelerate the heat dissipation, thus effectively reduce the cutting temperature, and suppress the generation of thermal stress, reduce the residual tensile stress on the workpiece surface. In this paper, a finite element model(FEM) of numerical prediction is established to analyze the effect of LN2 cryogenic machining on residual stress distribution. Firstly, mechanism analysis of surface residual stress is carried out to explore the source of residual stress during TC4 cryogenic turning. Next, to observe residual stress distribution clearly, the cutting zone separation model is designed, and then, the material model is built to reflect the change of material properties. Then, a FEM of the numerical prediction made up of explicit dynamic solution module and standard static solution module is established to simulate residual stress distribution; after that, residual stress can be ultimately acquired by linear superposing the above two module simulation results. Based on FEM proposed in this paper, the effect of LN2 cryogenic machining on surface residual stress distribution of TC4 is analyzed, and it is indicated that LN2 cryogenic machining can reduce the residual tensile stress effectively. Finally, the experiment is carried out, and the results show that the general trend of the prediction model is the same as that of the experimental results, which greatly verify the availability of the prediction model. Research provides some reference for the numerical prediction and suppression of residual stress in the future.

Assessing the hydraulic and mechanical impacts of heat generating radioactive waste at the whole repository scale

Radioactive waste disposal facilities for heat generating waste are designed to maintain a compressive stress regime in the host rock. Field-scale tests have been undertaken to study how heating of the host rock can reduce the effective stress on the rock. However, it is not possible to carry out experiments at the scale of a whole repository (km-scale), so variation of host rock properties that might be encountered at this scale is not captured by the experiments.Previous numerical modelling of field scale experiments has demonstrated that the physical processes leading to changes in the stress regime are well understood. Here those models are applied at the km-scale, considering approaches to representing a whole repository and the effect of variability in the properties of the host rock. A dataset from the Callovo-Oxfordian Claystone at the Meuse/Heute-Marne Underground Rock Laboratory is used to characterise the natural variability of a potential host rock at the scale of a disposal facility.The modelling demonstrates that for understanding the generation of thermal stresses, considerable learning can be gained from models that employ symmetry conditions and represent a small part of the repository, hence reducing the size of the computational problem. The host rock at the mid-point between waste cells remained in vertical compression for all the parameter combinations used, which builds confidence that horizontal fracturing of the host rock between waste cells due to thermal pressurisation is unlikely for the disposal concept discussed here. Ground surface uplift was also considered and is in the range of 9–13 cm for disposal system studied.Spatial variability in the properties of the host rock has the potential to lead to significant variability in temperature, pressure, effective stress and displacement around the facility. In particular, thermal conductivity, permeability, Young’s modulus and coefficient of thermal expansion need to be well characterised.