Variation Of Thermal Stress Research Articles

Crack characteristics of pulsed laser brazed diamond grinding wheel

Experiments on pulsed laser brazing of diamond grinding wheels were carried out in this paper. The crack characteristics and residual stress of brazed layer were detected and evaluated. The influence laws of pulse width, frequency, diamond mixing ratio, number of stacked layers, powder thickness and preheating temperature on crack characteristics were investigated. The pulsed laser characteristic coefficients (peak pulse power density/pulse interval time) and the correlation law between thermal stresses and cracks are discussed. The results show that the pulse width and frequency of the pulsed laser affect the cracking rate by varying the energy input and the time between pulses. The existence of a suitable value for the pulse characteristic coefficient corresponding to pulse width and frequency corresponds to a lower cracking rate. Thermal stress variations due to changes in process conditions at different diamond percentages, number of stacked layers, and preheating temperatures are the main causes of crack rate variations. Cracking is not only affected by thermal stresses, but also by the quality of the formed surface when pulsed laser brazing diamond to nickel–chromium alloy brazing material. For example, the main reason for the variation in cracking rate is the change in the morphology of the molded surface due to the variation in the thickness of the powder spread at different variations in the thickness of the powder spread.

Multiscale Simulation of Laser-Based Direct Energy Deposition (DED-LB/M) Using Powder Feedstock for Surface Repair of Aluminum Alloy.

Laser-based direct energy deposition (DED-LB/M) has been a promising option for the surface repair of structural aluminum alloys due to the advantages it offers, including a small heat-affected zone, high forming accuracy, and adjustable deposition materials. However, the unequal powder particle size during powder-based DED-LB/M can cause unstable flow and an uneven material flow rate per unit of time, resulting in defects such as pores, uneven deposition layers, and cracks. This paper presents a multiscale, multiphysics numerical model to investigate the underlying mechanism during the powder-based DED-LB/M surface repair process. First, the worn surfaces of aluminum alloy components with different flaw shapes and sizes were characterized and modeled. The fluid flow of the molten pool during material deposition on the worn surfaces was then investigated using a model that coupled the mesoscale discrete element method (DEM) and the finite volume method (FVM). The effect of flaw size and powder supply quantity on the evolution of the molten pool temperature, morphology, and dynamics was evaluated. The rapid heat transfer and variation in thermal stress during the multilayer DED-LB/M process were further illustrated using a macroscale thermomechanical model. The maximum stress was observed and compared with the yield stress of the adopted material, and no relative sliding was observed between deposited layers and substrate components.

Barrel effect of high-rate capability determined by anode for LiNi0.5Co0.2Mn0.3O2/graphite lithium-ion battery

To date, charging time remains a critical issue that impedes the widespread application of lithium-ion batteries (LIBs). A comprehensive understanding of the attenuation mechanism of LIBs at high (dis)charging rates is essential for clarifying application strategies for extreme operating conditions and environments, thereby enhancing battery control, and guiding the design of advanced batteries with superior rate capability. In line with this focus, particular commercial NCM/graphite batteries were explored under various high-rate (dis)charging procedures, alongside the investigation of the impact of constant voltage steps on battery performance. This exploration revealed that capacity degradation occurs in three stages, and the rate of capacity decay is directly proportional to the (dis)charging rate. Furthermore, the in-situ temperature and stress of the battery during cycling, primarily caused by side reactions, were monitored to confirm the thermal effects and stress variations under high-rate conditions. By characterizing the morphology and composition of the electrode surface after post-mortem analysis, the “barrel effect” of high-rate capability determined by the anode electrode for LIBs is proposed. This research aims to establish optimal guidelines for designing batteries with excellent high-rate properties and to provide solutions for improving the safety and reliability of batteries applied in high-rate conditions.

Thermal modal analysis of hypersonic composite wing on transient aerodynamic heating

Considering the influence of thermal stress and material property variations, this study employs the Navier–Stokes equations and Fourier heat conduction law to establish a semi-implicit time-domain numerical analysis method for hypersonic aerothermal-structural coupling. Study the temporal variation pattern of different regions of the composite material wing under aerodynamic heating. Using the obtained transient temperature field of the wing, the thermal modal of the wing at different time points is calculated using the finite element method. Additionally, it conducts an analysis and discussion on the factors influencing the thermal modal. Composites can be effectively utilized as thermal protection materials for aircraft. During the aerodynamic heating process, the leading edge temperature reaches thermal equilibrium first, followed by the trailing edge, and the belly plate experiences a slower thermal response. Temperature rise significantly affects higher-order modes, with the change in material properties during the early stages of heating being the dominant factor. This leads to a faster decrease in natural frequency. As heat conduction progresses, the influencing factors of thermal stresses gradually increase, and the natural frequency decreases slowly or even rises.

Thermal-force coupling simulation of carbon fibre-reinforced poly-ether-ether-ketone thermoplastic composites during the laser-assisted automated tape placement process

To reveal the thermal-force coupling characteristics of the laser in-situ consolidation (ISC) of carbon fibre-reinforced poly-ether-ether-ketone (CF/PEEK) composites, a two-dimensional transient thermal-force model of CF/PEEK composites was constructed using COMSOL Multiphysics finite element simulation software to calculate the temperature history and the thermal stress variation of CF/PEEK composites during the laser-assisted automated tape placement (LATP) process. The results show that the temperature field formed on the surface of each layer by the laser spot during LATP is stable, and the temperature gradient at the front of the spot movement direction is higher than that at the back edge. The maximum stresses in the laminate occur on both sides of the first CF/PEEK layer and the stresses are unevenly distributed along the length and thickness directions of the lay-up. The composite material on both sides of the laminate tends to ‘shrink’ compared to its original position.

Research on lightweight design method of diesel engine steel piston based on heat transfer characteristics

Steel pistons are gradually replacing traditional aluminum–silicon alloy pistons as the preferred choice for high-power density engines. However, there is still a lack of systematic research on the heat transfer characteristics of steel pistons in the field of small bore diesel engines. For this reason, this paper was based on the storage temperature testing system to study the variation of temperature field and thermal stress in steel pistons of the small-bore diesel engine under the maximum torque conditions. The results show that there are significant temperature variations in the circumferential path of the steel piston head, indicating that the temperature distribution of the steel piston is highly uneven. The highest temperatures and maximum thermal stresses were found in the rim. To further achieve the lightweighting of the steel piston, a lightweight design method based on heat transfer characteristics was proposed. A multi-objective optimization algorithm was used to optimize the top land height and the position and shape of the cooling gallery. The structural design solutions with volume and thermal stress control were finally obtained. The optimized design solution can reduce the mass by a maximum of 10.01 %, the maximum temperature by a maximum of 35.04 °C and the maximum thermal stress by a maximum of 18.38 % compared to the original design.

Thermal stress estimation of a constrained metallic plate using symmetric and antisymmetric Lamb wave group velocities

This paper presents a technique for estimating thermal-induced stress in constrained metallic plates using the group velocity of Lamb waves, the accuracy of which is crucial for assessing the structural integrity and serviceability of metallic structures. However, without the ability to gauge the current stress levels, obtaining such measurements is technically challenging. To overcome this, we propose a thermal stress estimation technique that uses changes in the group velocities of the fundamental symmetric (S0) and antisymmetric (A0) Lamb wave modes caused by thermal and stress variations. First, this study introduces a theoretical-based zero-crossing algorithm to measure the group velocities of S0 and A0 Lamb wave modes. Next, leveraging the acoustoelastic coefficients corresponding to the S0 and A0 modes, which are determined before the plate’s installation, this study generates the lines depicting the changes in group velocity induced by temperature variations (CT) for both the S0 and A0 modes. These CT lines are derived from the lines illustrating changes in group velocity due to thermal stress variations (CTS), which are obtained after plate installation. Ultimately, the generated CT lines can be used to estimate thermal stress throughout the entirety of the plate’s operational life span by isolating the distinct stress variation effects from the CTS lines. The numerical validation results show favorable accuracy in thermal stress estimation in a constrained plate subjected to temperature variation using both S0 and A0 Lamb wave modes, with average errors of 0.63 % and 0.91 %, respectively.

Non-axisymmetric Modeling of a Moving Heat Source for Thermal Stress and Fatigue Analysis of Railway Vehicle Disc Brakes

Railroad vehicles require the use of disc brakes for safety purposes, however, the brakes are susceptible to thermal stress, which ultimately shortens their lifespan. Hence, to accurately predict the life of railway disc brakes in thermal load simulations, the availability of a model that considers spatial and temporal variations of temperature and thermal stress is essential. A non-axisymmetric moving heat source model was successfully developed to address spatial temperature variations (Deressa and Ambie in Urban Rail Transit 8(3–4):198–216, 2022. 10.1007/s40864-022-00176-9), and this study aims to extend this model to predict thermal stress and fatigue life, and assess its effectiveness. The analysis includes braking time thermal analysis, cooling time thermal analysis, and structural analysis. Spatially varying temperature is incorporated into the structural analysis to calculate thermal stress and strain. A fracture mechanics-based fatigue life estimation method is applied to critical areas of the friction surface. The model is implemented on two braking conditions (service and emergency) and two disc geometries (actual and modified). The model successfully resolves spatial heat considerations by estimating maximum stress variations of up to 46 MPa along the disc circumference. Stress differences of 3 MPa and 6 MPa are observed between the leading and trailing edges of the pad trace during late and mid-braking times, respectively. Fatigue life results identify critical positions and directions for fatigue life initiation. Additionally, these results are in accord with previous observations available in the literature. The proposed model can be easily implemented in various sliding friction applications such as drum brakes, engine pistons/cylinders, and camshafts.

Innovative liquid metal strategy for real-time thermal control in additive manufacturing

Metal additive manufacturing (AM) involves rapid cycles of melting and solidification, often resulting in significant thermal stress variations, microcrack formation, and compromised structural integrity, especially for complex structures. Effective strategies are crucial for regulating temperature and stress distribution during laser-based metal AM processes; however, traditional thermal management approaches suffer from limitations in action area and response speed. In this study, the novel Liquid Metal-Assisted Additive Manufacturing (LMAAM) process is developed to enhance real-time temperature and stress control during deposition. This is the first known attempt to utilize liquid tin as an auxiliary thermal management material for AM. Numerical simulations and experimental analysis are performed to determine the relationship between LMAAM process conditions and resultant material microstructural properties. The results show that compared to AM without active thermal management, the incorporation of liquid tin yields an approximate 20 % increase in the cooling rate, a roughly 30 % reduction in residual tensile stress, a decrease in part grain size, and a roughly 30 % enhancement in microhardness. LMAAM technology opens up new possibilities for metal AM of highly reliable and intricate structures like multi-chambers, multi-channels, and deep blind holes.

A two-step in situ measurement method for temperature and thermal stress of power device based on a single Raman peak

Temperature and thermal stress are primary factors leading to the performance failure of power devices. Thus, simultaneously determining the temperature and stress variation of the working devices has become the premise of revealing the failure mechanism. However, the existing methods are still unsatisfactory for in-situ temperature-stress decoupling measurement. To solve this problem, a two-step decoupling method based on a single Raman peak is proposed. In the calibration step, the effective temperature - Raman shift coefficients at different positions of the power devices were measured in the OFF state, and the contribution ratio of temperature and thermal stress to the single peak shift can be determined by analyzing the difference of effective temperature - Raman shift coefficients with intrinsic temperature - Raman shift coefficient. In the in-situ measurement step, the temperature rise and thermal stress variation can be calculated based on the Raman peak shift of the target semiconductor layer and the calibrated contribution ratio. A measurement of the GaN high electron mobility transistor was used to further illustrate the advantages of the proposed method. Compared with the previous multi-peak decoupling method, the temperature and thermal stress distributions of the working device obtained by the two-step decoupling method make more physical sense, and the measurement uncertainty of temperature and stress can be reduced to 1/4 and 1/3 of the previous method respectively. The consistency with the thermo-stress simulation further verifies the reliability and accuracy of the proposed method.

Evaluation of heat transfer in porous scaffolds under cryogenic treatment: a numerical study.

The present work had evaluated the effect of cryogenic treatment (233K) on the degradation of polymeric biomaterial using a numerical model. The study on effect of cryogenic temperature on mechanical properties of cell-seeded biomaterials is very limited. However, no study had reported material degradation evaluation. Different structures of silk-fibroin-poly-electrolyte complex (SFPEC) scaffolds had been designed by varying hole distance and hole diameter, with reference to existing literature. The size of scaffolds were maintained at 5 [Formula: see text] 5 mm2. Current study evaluates the effect of cryogenic temperature on mechanical properties (corelated to degradation) of scaffold. Six parameters related to scaffold degradation: heat transfer, deformation gradient, stress, strain, strain tensor, and displacement gradient were analyzed for three different cooling rates (- 5K/min, - 2K/min, and - 1K/min). Scaffold degradation had been evaluated in the presence of water and four different concentrations of cryoprotectant solution. Heat distribution at various points (points_base, point_wall and point_core) on the region of interest (ROI) was found similar for different cooling rates of the system. Thermal stress was found developing proportional to cooling rate, which leads to minimal variation in thermal stress over time. Strain tensor was found gradually decreasing due to attenuating response of deformation gradient. In addition to that, dipping down of cryogenic temperature had prohibited the movement of molecules in the crystalline structure which had restricting the displacement gradient. It was found that uniform distribution of desired heat at different cooling rates has the ability to minimize the responses of other scaffold degradation parameters. It was found that the rates of change in stress, strain, and strain tensor were minimal at different concentrations of cryoprotectant. The present study had predicted the degradation behavior of PEC scaffold under cryogenic temperature on the basis of explicit mechanical properties.

Thermal performance investigation of the newly shaped vacuum tubes of parabolic trough collector system

The parabolic trough collector (PTC) system is currently the most mature technology for concentrator solar power (CSP) plants. However, the huge radiative heat loss under high temperatures is one of the major obstacles restricting its thermal efficiency and development to the higher temperature. To reduce the radiative heat loss, this study proposes a newly shaped tube (NS-tube) with flatted upper and lower surfaces based on the Negative thermal-flux region theory. By considering different opening angles and tracking errors of the shaped tubes, an optical simulation is developed to analyze the heat flux distribution, and a heat transfer model is established to investigate the heat loss and thermal efficiency. Results show that the thermal efficiency of the NS-tube with optimum opening angles can be improved by 0.62%–4.64% compared to the original tube. The improvement effect is more obvious at high operating temperatures and low Direct Normal Irradiance. Additionally, the thermal stress variation is also analyzed by Ansys fluent. The result shows that the thermal stress of the NS-tube is even smaller than that of the original tube due to the uniform thermal flow effect caused by the flattened lower surface.

Numerical thermo-mechanical analysis of a railway train wheel

Abstract In this paper, the variation of thermal stresses, strains and deformations created by combined thermal and mechanical loads is investigated in block braked railway wheels. Thermo-mechanical analyses of the railway wheel were performed by using finite element (FE) for the numerical analysis. Before performing FE analyses, input parameters, e.g. heat flow, heat conduction, heat convection, applied loads and boundary conditions were transferred from railway wheel conditions in reality. The thermal analysis of wheel structure in the analysis calculation was evaluated experimentally, and validated with numerical result used in current model. In this purpose, ANSYS Workbench module package was used to simulate the distribution of stress and temperature field over the wheel. Combined thermal and mechanically induced damage surfaces of the railway wheel in reality were compared with numerical results in ANSYS. It was concluded from the results that 3D simulations in this wheel model showed a significant effect of thermal loading rather than mechanical loading on wheel braking tread, and combination of thermal and mechanical loading caused the detrimental effect on railway wheel structures those used in this model.

Analytical Computation of Thermal and Electrical Issues in E-Mobility Cabling Network

The demand for pollution-free transportation is increasing daily worldwide due to increasing concerns about global warming, greenhouse gas emissions, and the depletion of fossil fuels. In e-mobility, electric vehicles (EVs) have received massive popularity due to their performances and efficiencies compared with IC engine vehicles in recent decades. Cables play an essential role in delivering electric power to the different electrical components system from the battery source of vehicles. Electrical insulation is the backbone of the power cable, and its state is usually used to reflect the healthy condition of this cable and any electrical networks. Deterioration of the cable during normal operation is a major concern. Usually, electric cables receive less maintenance as compared to other electrical components in EVs. Due to the many stresses, the cable insulation must constantly withstand better connectivity between different parts in e-mobility. In the analytical method, the solution obtains known elementary functions by integrating a partial differential equation better to understand the variation of thermal and electrical stresses. This paper studied the high voltage cabling network of electric vehicles and the analytical method used for computing conductivity, temperature, and electrical stress distribution in electric vehicle cabling networks by including the higher vehicle ambient temperatures. The thermal and electrical stress maximizes at the conductors' surface and gradually reduces the function of the radial distance.

HiTIC-Monthly: a monthly high spatial resolution (1 km) human thermal index collection over China during 2003–2020

Abstract. Human-perceived thermal comfort (known as human-perceived temperature) measures the combined effects of multiple meteorological factors (e.g., temperature, humidity, and wind speed) and can be aggravated under the influences of global warming and local human activities. With the most rapid urbanization and the largest population, China is being severely threatened by aggravating human thermal stress. However, the variations of thermal stress in China at a fine scale have not been fully understood. This gap is mainly due to the lack of a high-resolution gridded dataset of human thermal indices. Here, we generated the first high spatial resolution (1 km) dataset of monthly human thermal index collection (HiTIC-Monthly) over China during 2003–2020. In this collection, 12 commonly used thermal indices were generated by the Light Gradient Boosting Machine (LightGBM) learning algorithm from multi-source data, including land surface temperature, topography, land cover, population density, and impervious surface fraction. Their accuracies were comprehensively assessed based on the observations at 2419 weather stations across the mainland of China. The results show that our dataset has desirable accuracies, with the mean R2, root mean square error, and mean absolute error of 0.996, 0.693 ∘C, and 0.512 ∘C, respectively, by averaging the 12 indices. Moreover, the data exhibit high agreements with the observations across spatial and temporal dimensions, demonstrating the broad applicability of our dataset. A comparison with two existing datasets also suggests that our high-resolution dataset can describe a more explicit spatial distribution of the thermal information, showing great potentials in fine-scale (e.g., intra-urban) studies. Further investigation reveals that nearly all thermal indices exhibit increasing trends in most parts of China during 2003–2020. The increase is especially significant in North China, Southwest China, the Tibetan Plateau, and parts of Northwest China, during spring and summer. The HiTIC-Monthly dataset is publicly available from Zenodo at https://doi.org/10.5281/zenodo.6895533 (Zhang et al., 2022a).

Nanoscale pulverization effect in double-layered MOF-derived hierarchical G/Co@C composites for boosting electromagnetic wave dissipation.

Metal-organic frameworks (MOFs) have drawn a lot of interest as prospective starting points for highly effective electromagnetic wave (EMW) absorbers. However, the inevitable shrinkage and probable densification that occur during pyrolysis significantly reduce the microwave-loss capacity. A dual-layer MOF, ZIF-8@ZIF-67, is created and effectively decorated on graphene sheets as a solution to this problem. The shrinkage and densification were then suppressed by the subsequent pulverization effect between the two MOFs. Due to suitable compositions and specialized microstructures, G/Co@C exhibits excellent impedance matching and dissipates EMW by combining magnetic and dielectric loss. The maximum reflection loss of G/Co@C-7/paraffin is -55.0 dB at 5.8 GHz with just 7% filler. Therefore, the preparation of high-efficiency MOF-derived microwave absorbers by the pulverization effect is demonstrated to be an efficient strategy.

Basin-scale estimates of thermal stress and expelled petroleum from Mesozoic-Cenozoic potential source rocks, southern Gulf of Mexico

The Campeche and Yucatan salt basins remain two of the least explored areas of the Gulf of Mexico basin. This study uses a grid of 23,600 line-km pre-stack depth migrated (PSDM) 2D seismic reflection profiles, shipborne gravity data, and open-source geologic information to model the thermal stress of four potential source intervals (Oxfordian, Tithonian-centered, Cenomanian-Turonian, lower Miocene). We performed map-based, and 1D thermal modeling along two margin-perpendicular transects, each consisting of five pseudo-wells tied to the regional grid of seismic reflection data. Our modeling takes into account thermal stress variations related to the depth of base lithosphere, crustal type and thickness, paleo-water depth, Jurassic salt thickness, and the transient heat flow effects related to recent clastic sedimentation. We predict that deeply-buried, salt-related minibasins along the outer marginal trough are mature for petroleum expulsion with deeply-buried Mesozoic source rocks within the oil window from late Paleogene to early Neogene time. The ‘lag time’ required for vertical oil migration explains why oil maturation occurred during the late Paleogene to early Neogene but active oil seeps are observed today at the sea surface. We predict that oil is present in subsurface traps in the deepest part of the outer marginal trough and we calculate that the Oxfordian source interval has expelled a cumulative 20 million bbl of oil equivalent [BOE]/km2 and that the Tithonian-centered source interval has expelled 67 million bbl of oil equivalent [BOE]/km2.

Effects of Methane Pre-Reforming Percentage and Flow Arrangement on the Distribution of Temperature and Thermal Stress in Solid Oxide Fuel Cell

To obtain detailed information on the temperature field and thermal stress field inside the solid oxide fuel cell (SOFC) fueled with partially pre-reformed methane. A three-dimensional geometric and mathematical model of the SOFC is implemented by using the finite element method in the commercial software COMSOL Multiphysics®. The coupling characteristics were analyzed for electrode chemical reaction, multi-component mass transfer, and heat transfer process under typical operating conditions, which was further applied for predicting and analyzing the thermal stress distribution. After model validation, parametric simulations are conducted to investigate how the methane pre-reforming percentage and flow arrangement affect the temperature and the thermal stress of SOFC. The simulated results show that reducing the methane pre-reforming percentages can decrease the temperature maximum and the variation range of the first principal stress, but will increase the possibility of carbon deposition. The maximum temperature of the counter-flow is about 20 K lower than that of the co-flow, and the first principal stress variation range of the counter-flow is 8.6 Mpa lower than that of the co-flow. The methane pre-reforming percentages have a significant effect on the heat transfer and the thermal stress, and the counter-flow can improve the temperature uniformity and reduce the thermal stress variation range.

Interactive Effects of Thermal and Salinity Stress Cause Cell Cycle Arrest in the Nile Tilapia

The goal of this study was to test the interactive effects of sub‐lethal thermal stress and environmental salinity variation on a tropical freshwater species, the Nile tilapia, Oreochromis niloticus. This economically important species is vulnerable to increased morbidity at low temperatures, a condition sometimes termed “Winter Stress Syndrome”. It is possible that in addition to extreme weather events, saltwater intrusion into freshwater systems presents physiological challenges to this species. To test this hypothesis, Nile tilapia were exposed to a variety of treatments (two temperatures: 21°C & 14°C, three salinities: 0ppt, 16ppt, 34ppt) for 1‐h. Following exposures, flow cytometry was used to assess cell cycle staging in the spleen and liver. Specifically, we were testing the synergistic effects of temperature and salinity stress on cell cycle arrest and apoptosis, both metrics of sub‐lethal stress and a switch away from growth and towards stress responses. Both liver and spleen responded to temperature and salinity stress by inducing cell cycle arrest in a tissue‐specific manner. Apoptosis was also detected in the spleen. These findings support our hypothesis that the combination of thermal and salinity stress have deleterious impacts on the health of this important global source of protein.

Why are 'suboptimal' temperatures preferred in a tropical intertidal ectotherm?

In thermally extreme environments, it is challenging for organisms to maximize performance due to risks associated with stochastic variation in temperature and, subsequently, over evolutionary time minimizing the exposure to risk can serve as one of the mechanisms that result in organisms preferring suboptimal temperatures. We tested this hypothesis in a slow-moving intertidal snail on tropical rocky shores, where temperature variability increases with time from 30min to 20hr when recorded at 30min intervals (due to short-term environmental autocorrelation where temperatures closer in time are more similar as compared to temperatures over a long period of time). Failure to accommodate temporal variation in thermal stress by selecting cool habitats can result in mortality. Thermal performance curves for different traits (heart rate and locomotion) were measured and compared to the snail's thermal preferences in both the field and laboratory. Predicted performances of the snails were simulated based on thermal performance curves for different traits over multiple time-scales and simulated carryover effects. A strong mismatch was found between physiological and behavioural thermal maxima of the snails (physiological thermal maximum being higher by ~7°C), but the snails avoided these maxima and sought temperatures 7-14°C cooler. Such a risk-averse strategy can be explained by their predicted performances where the snails should make decisions about preferred temperatures based on time periods ≥5hr to avoid underestimating the temporal variation in body temperature. In extreme and stochastic environments, where the temporal variation in environmental conditions can lead to substantial divergence between instantaneous and time-averaged thermal performances, 'cooler is better' and 'suboptimal' body temperatures are preferred as they provide sufficient buffer to reduce mortality risk from heat stress.