Thermal Stress Field Research Articles

Establishment of Multi-Physics coupling model and analysis on thermal stress and crack risk in directional growth of TiAl alloys under electromagnetic confinement

The electromagnetic confinement directional solidification (EMCDS) technique is an optimal method for preparing large-size and non-contamination directional TiAl alloy crystals. Despite its advantages, the high temperature gradient inherent to this process induces thermal stress within the ingot, which increases the risk of cracking. To address this challenge, an innovative Integrated Multi-Physics Coupling Model was established to map and study the thermal stress field during EMCDS in this study. It synchronized the computation of the electromagnetic field, temperature field, solute field, flow field, and stress field during the crystal growth of TiAl alloy, and its high accuracy was proved by the micro-indentation experiment. Our analysis reveals that transverse temperature differences are crucial in inducing thermal stresses, and identifies that hot cracks and cold cracks are prone to occur respectively at the area of radial 23R along the sample (X = 23R) and on the sample surface, which aligns with experimental observations impressively. This model can more accurately and efficiently optimize the process parameters of the EMCDS process to avoid cracks and promote its industrial application.

Theoretical and numerical analyses of thermal stresses and temperature variations in disc cutter cutting composite strata under thermal-force multi-fields

Composite strata consisting of hard and soft rock are common during shield cutter excavation. The friction cutting process generates a large amount of cutting heat, high temperature will produce thermal stresses and thermal expansion in the disc cutter ring, resulting in wear and deformation of the cutter, reducing its rock breaking performance. From the perspective of thermal-force change in cutter, This study establishes the theory of frictional heat generation and the theory of thermal stress of elastomer to analyse the frictional heat generation and derive the thermal stress theory of elastomer model in cutter. Numerical simulations were carried out to analyse the thermal-force multi-field coupling process considering the influencing factors such as penetration, cutting time, rock strength, etc. Solve the heat conduction equation and radial temperature field distribution from the heat transfer perspective. The comparative study of theoretical analysis, numerical simulation and experimental values shows that the theoretical and numerical results of thermal stress and temperature field distributions are consistent, which verifies the reasonableness of the theoretical derivation and numerical model.

Numerical study on surface treatment of vibration-impact composite electric spark based on ABAQUS

Abstract Through numerical simulation, this study explores the effect of vibration-impact composite electric spark (VIES) surface treatment technology on the temperature and thermal stress fields of 2024-T3 aluminum alloy surfaces. The depth of the molten pool and residual stress are evaluated using orthogonal experiments to score different experimental schemes, resulting in three experimental parameters categorized as good, medium, and poor. The study then examines the temperature and thermal stress fields for these three sets of parameters during the strengthening process. The results indicate that, considering the temperature field, the distance between the heat source and the work piece directly affects the heating efficiency and temperature distribution. An appropriate distance and sufficient dwell time are essential for creating the ideal molten pool thickness. Analysis of the stress field results shows that in the early stage of strengthening, the inertia force of the small spheres is dominant, while in the later stage, the stress field created by the electric current becomes decisively dominant. This indicates that the electric current is the core of the three influencing factors in the orthogonal experiment.

Modeling and Assessment of Temperature and Thermal Stress Field of Asphalt Pavement on the Tibetan Plateau

The Qinghai–Tibet Plateau (QTP) is the highest altitude plateau in the world, characterized by strong solar radiation and large diurnal temperature differences and so on, which brings a great negative impact on the temperature and thermal stress field of asphalt pavement. The purpose of this study is to analyze the temperature field and thermal stress status of asphalt pavement in the QTP to provide a reference for pavement design and maintenance in high-altitude areas. The finite element method was applied to establish the temperature field model to study the distribution and variation of pavement temperature. On this basis, the influence of cooling amplitude on pavement thermal stress was studied during cold waves. In addition to this, the key internal factors affecting the thermal stress of pavement, such as surface thickness, surface temperature shrinkage coefficient, surface modulus, and base modulus, were analyzed by an orthogonal test. It was found that temperature and solar radiation have a significant effect on the pavement temperature field. When the cold wave came, the cooling rate had a considerable impact on the thermal stress of the pavement, that is, every 5 °C increase in cooling rate would increase the thermal stress by more than 50%. The temperature shrinkage coefficient and surface modulus of the surface layer material had the greatest influence on the pavement thermal stress. The thermal stress could be reduced by more than 0.4 Mpa for every 5 × 10−6/°C reduction in the surface temperature shrinkage coefficient or every 1000 Mpa reduction in the surface modulus. This study can provide a reference for improving the temperature field and thermal stress field of asphalt pavement in the plateau area.

Thermomechanical Response of Smart Magneto-Electro-Elastic FGM Nanosensor Beams with Intended Porosity

AbstractThis study investigates the behavior of free vibrations in a variety of porous functionally graded nanobeams composed of ferroelectric barium-titanate (BaTiO3) and magnetostrictive cobalt-ferrite (CoFe2O4). There are four different models of porous nanobeams: the uniform porosity model (UPM), the symmetric porosity model (SPM), the porosity concentrated in the bottom region model (BPM), and the porosity concentrated in the top region model (TPM). The nanobeam constitutive equation calculates strains based on various factors, including classical mechanical stress, thermal expansion, magnetostrictive and electroelastic properties, and nonlocal elasticity. The study investigated the effects of various factors on the free vibration of nanobeams, including thermal stress, thermo-magneto-electroelastic coupling, electric and magnetic field potential, nonlocal features, porosity models, and changes in porosity volume. The temperature-dependent mechanical properties of BaTiO3 and CoFe2O4 have been recently explored in the literature for the first time. The dynamics of nanosensor beams are greatly influenced by temperature-dependent characteristics. As the ratios of CoFe2O4 and BaTiO3 in the nanobeam decrease, the dimensionless frequencies decrease and increase, respectively, based on the material grading index. The dimensionless frequencies were influenced by the nonlocal parameter, external electric potential, and temperature, causing them to rise. On the other hand, the slenderness ratio and external magnetic potential caused the frequencies to drop. The porosity volume ratio has different effects on frequencies depending on the porosity model.

Mechanical properties and thermal shock resistance of TiB2‒B4C composite ceramic tool materials at microscopic scale

AbstractA finite model incorporating microstructure was developed to investigate the thermal shock resistance of TiB2‒B4C composite ceramic cutting tool materials. Numerical simulations were conducted to analyze changes in the transient temperature field and thermal stress field during the thermal shock process. TiB2‒B4C composite ceramic tool materials were fabricated using discharge plasma sintering technology. With different B4C contents, different sintering temperatures and holding times as study variables, optimization of the sintering process parameters and ceramic material components was achieved through testing the mechanical and microscopic morphology of the ceramics. Thermal shock water quenching experiments were performed, and the strength‐decay method was employed to assess the thermal shock resistance of TiB2‒B4C ceramics. The findings indicate that the optimal sintering conditions are temperature of 1700°C and holding time of 5 min. The TiB2‒B4C ceramic material containing 20 vol% B4C exhibits superior comprehensive mechanical properties and thermal shock resistance, and its relative density, fracture toughness, hardness, and flexural strength were 99.3%, 6.8 MPa m1/2, 22.8 GPa, and 598 MPa, respectively. The critical thermal shock temperature difference falls within the range of 400°C‒500°C.

Diagnosis and Prevention of Overheating Failures in Mechanical Equipment Based on Numerical Analysis of Temperature and Thermal Stress Fields

Diagnosis and Prevention of Overheating Failures in Mechanical Equipment Based on Numerical Analysis of Temperature and Thermal Stress Fields

Nanosurface-reconstructed perovskite for highly efficient and stable active-matrix light-emitting diode display.

Perovskite quantum dots (QDs) are promising for various photonic applications due to their high colour purity, tunable optoelectronic properties and excellent solution processability. Surface features impact their optoelectronic properties, and surface defects remain a major obstacle to progress. Here we develop a strategy utilizing diisooctylphosphinic acid-mediated synthesis combined with hydriodic acid-etching-driven nanosurface reconstruction to stabilize CsPbI3 QDs. Diisooctylphosphinic acid strongly adsorbs to the QDs and increases the formation energy of halide vacancies, enabling nanosurface reconstruction. The QD film with nanosurface reconstruction shows enhanced phase stability, improved photoluminescence endurance under thermal stress and electric field conditions, and a higher activation energy for ion migration. Consequently, we demonstrate perovskite light-emitting diodes (LEDs) that feature an electroluminescence peak at 644 nm. These LEDs achieve an external quantum efficiency of 28.5% and an operational half-lifetime surpassing 30 h at an initial luminance of 100 cd m-2, marking a tenfold improvement over previously published studies. The integration of these high-performance LEDs with specifically designed thin-film transistor circuits enables the demonstration of solution-processed active-matrix perovskite displays that show a peak external quantum efficiency of 23.6% at a display brightness of 300 cd m-2. This work showcases nanosurface reconstruction as a pivotal pathway towards high-performance QD-based optoelectronic devices.

Nanostructure characterisation of welded polyethylene using small angle X-ray scattering

Polyethylene (PE), a common thermoplastic polymer, is gaining prominence in the construction and packaging industries due to its exceptional mechanical properties, chemical resistance, safety, and integrity. However, internal defects can occur during manufacturing and throughout its service life. Neglecting this problem results in the disposal of plastic and, consequently, the accumulation of plastic waste and environmental issues, which have caused much criticism. A common method to repair the thermoplastics is welding, which introduces seams and localized thermal residual stress fields resulting in areas where damage can nucleate, potentially leading to cracks and failure over time. These cracks often start at the nanoscale and propagate to larger length scales until failure occurs. The objective of this research paper is to develop welding processes, with improved integrity and lifespan for PE. Additionally, it aims to investigate and assess the impact of PE welding on parent materials at nano- and micron-scales, to understand limitations that are challenging to overcome in such welding processes. The study involves joining PE panels together under various pre-heating and post-cooling conditions, followed by evaluating the environmental stress cracking resistance of the welds and the durability of the repaired components. The crystallinity and morphology of the PE material in the weld area and its surrounding regions were analysed using Small Angle X-ray Scattering (SAXS), and the findings were compared with results obtained from optical microscopy and Differential Scanning Calorimetry. The study concludes that SAXS results offer exceptional information about the parent PE and weld material within the welding zone.

Thermohyperelastic constitutive response for semilinear materials with application to deformation of a rotating thin disk

Constitutive modeling of soft elastomers is a well researched subject due to its numerous engineering applications. This study derives a thermodynamically consistent constitutive model for semilinear thermoelastic solids for which the strain energy density depends on the deformation gradient through the Biot stretch tensor. The Frechet derivatives, Coleman-Noll procedure, and product decomposition-based technique are employed to formulate the constitutive model. The combination of the derived model and thermomechanical field equations is specialized for application to problem of radial deformation of a rotating thin disk. The formulated model provides simple closed-form expressions for simulating thermomechanical responses of solids. Under suitable conditions, the derived three-configuration-based constitutive model reduces to the two-configuration-based constitutive equations. Finally, and among other things, the numerical solutions illustrate the effects of angular speed of rotation on thermal stress and displacement fields at points within the radially deforming rotating disk.

Effects of thermal, stress, and electric fields on microstructure and ion distribution of (Mg0.1Mn0.1Co0.1Ni0.2Ti0.1Cu0.1Zn0.2)Fe2.1O4 spinel ferrites

In this work, conventional sintering, hot-pressing sintering, and spark plasma sintering techniques were utilized to simulate the thermal field, thermal-stress field, and thermal-stress-electric field, respectively. The effects of these fields on the microstructure and cation distribution of the (Mg0.1Mn0.1Co0.1Ni0.2Ti0.1Cu0.1Zn0.2)Fe2.1O4 ferrite (HEF) material were comprehensively analyzed. The results indicate that in the temperature range of 1000–1100 °C, the thermal field provides the driving force for sintering, promotes grain growth (average particle size: 2→7 μm), and increases crystallinity degree. The stress field brings the particles into close contact with each other, facilitates diffusion, and delays grain growth (0.5→5 μm). The electric field reduces grain boundary energy, causes mass transfer, and makes the grains finer (0.5→0.7 μm) and more uniform. Mathematical model analysis reveals that the thermal field is beneficial to the random distribution of cations, which yields an inversion degree (γ) of about 2/3 and increases the configuration entropy of HEF. The stress field leads to lattice distortion, permits ions with larger radius to occupy tetrahedral positions, and changes the cell parameters and oxygen position parameter of HEF. Finally, the interaction between electric field and crystal charges increases the electrostatic field energy, which promotes the formation of positive spinel structure and maximizes the crystal field stability energy. X-ray photoelectron spectra, Raman spectra, and change in lattice constant confirm the rationality of the mathematical model, and can be used to establish the model of the crystal structure under field effects.

Mechanism of ultrasonic effects on thermal-stress field in Cu/Al-FSW process

This paper examined the mechanism of ultrasonic depressive effects on Al/Cu intermetallic compounds (IMCs) during friction stir welding (FSW) process by combining numerical simulations and macro/microstructural evolution analyses. The coupling process of ultrasonic field and the multienergy field for Al/Cu-FSW was simulated for the first time. The ultrasonic mechanisms of the acoustic thermal effect, acoustic anti-friction effect and acoustic softening were considered in the constitutive model and thermal-stress boundary conditions. Based on our research, ultrasonic vibration (UV) could homogenize the Al/Cu plastic difference and the Al/Cu rheological properties in the mixed zone. The modeling results showed that the difference in flow stress between Al and Cu was reduced on the two sides of the weld. The gradient of the phase-volume fraction in the weld cross section was reduced under UV, which reduced the power of Al/Cu interdiffusion and inhibited the generation of IMCs via diffusion. In addition, the acoustic softening and antifriction effects reduced the contact interfacial heat flux and the peak temperature. The heat generation within the nugget zone decreased by approximately 12.8 %. The UV reduced the absolute value of the effective heat of formation (EHF) for Al2Cu and Al4Cu9, which indicated that ultrasound could inhibit the generation of IMCs to some extent. The decrease of heat and concentration gradient weakened the atomic diffusion and growth rate of IMCs. Therefore, the SEM images of the Al/Cu interfaces showed that the total thickness of the Al/Cu-IMCs decreased by approximately 30.5 %, the distribution of IMCs was more uniform, and the boundaries were straighter under ultrasonic effects. Under ultrasonic action, more fine Cu particles entered the Al side, and the Cu particles were scattered, showing a dispersed distribution. Furthermore, acoustic softening enhanced the plastic flow and increased the number of layered staggered structures at the Al/Cu interface, which enhanced the mechanical interlocking of the Al/Cu composite. The tensile strength improved 21.3 % under the ultrasonic treatment.

The shape function method of nonlinear thermal stress of granite fracture tips in a high-temperature environment

Exposed rock masses in tunnel portals are susceptible to thermal deterioration in southern China, where temperatures are relatively high. The thermal stress field of rock masses is affected by fracture shape and distribution as fractures near the surface are channels for solar radiation energy to be converted into rock thermal energy. In this study, a function expression is developed for triangular heat sources of fractured rock masses in a tunnel portal in a high-temperature environment. By the function expression, the temperature field and thermal stress field are calculated, and the influence of fracture shape parameters and multi-fracture interaction is analyzed. The results are as follows: (1) the temperature field and thermal stress field of exposed rocks are redistributed by fractures. The internal temperature of the fractured rocks is higher than that of non-fractured rocks, and thermal stress near the fracture tip increases. (2) For triangular fractures of the same length, thermal stress increases as the apex angle increases. (3) When the spacing between parallel fractures or coplanar fractures is close, the superposition effect of thermal stress becomes significant. (4) In a high-temperature environment, temperature field and thermal stress field of a fractured rock are both nonlinear as temperature and thermal stress around fractures increase significantly. The results provide effective reference for stability evaluation of fractured rock masses in tunnel portals and offer theoretical foundation for thermal diseases analysis and protection measures of tunnel engineering in high-temperature environments of southern China.

Effect of Forge-Time on Electrode Indentation, Thermal and Residual Stress Fields in Resistance Spot Weld Joints of AISI 1008 Steel Sheets

Effect of Forge-Time on Electrode Indentation, Thermal and Residual Stress Fields in Resistance Spot Weld Joints of AISI 1008 Steel Sheets

Fluctuation of Magnetic Field in Magnetic Nano-Particles Thermometer

In this study, some important factors have been identified for the fluctuation of the magnetic field over time, which provides a basis for improving the temperature measurement accuracy and long-term stability of the magnetic nanoparticles thermometer (MNPT). We improved the mathematical model between the relative error of the magnetic induction intensity and the temperature measurement error of MNPT. The simulation founded that when the relative error of the magnetic induction intensity is kept within the range of <0.01%, the temperature measurement error is less than 0.1 K. Then, the multi-physics (magnetic field, temperature field, and thermal stress field) coupling relationship in the Helmholtz coil is established. During the coupling process, the temperature field of the Helmholtz coil affects the resistance of coil wire, and its thermal stress field is affected by the temperature field, which also changes the coil radius. After the temperature field and thermal stress field change, the magnetic field fluctuates immediately. Further simulation found that the problem of coil temperature rise becomes more serious as the size of the Helmholtz coil increases. The method of forced air cooling can make the fluctuation of the large Helmholtz coil magnetic field < 0.01%, and improve the measurement accuracy of MNPT.

Deep Learning-Based Cooperative Modelling of Thermal Flow and Stress Fields in Laser Powder Bed Fusion

Deep Learning-Based Cooperative Modelling of Thermal Flow and Stress Fields in Laser Powder Bed Fusion

Discretized and experimental investigation of thermo-hydraulic behavior in a compact heat exchanger manufactured via SLM process

The demand for a better understanding of the fluid thermal and hydrodynamic behavior along the heat exchanger makes it necessary to develop a discretized analysis. The temperature and pressure distributions from the local analysis allow the obtaining of mechanical and thermal stress fields, making the method advantageous in comparison to the conventional global analysis. This work developed a local thermo-hydraulic model for a compact heat exchanger manufactured via Selective Laser Melting (SLM) process. The cross-flow heat exchanger core, produced with American Iron and Steel Institute (AISI) 316L, has 100 mm height, 100 mm width, 100 mm length, and a 2 mm channel diameter. The local steady-state models were compared with experimental data. The experiments were performed with water on both sides, using different temperatures for the hot side, and Reynolds numbers ranging from 1748 to 12247. The local analytical models have a good agreement, with 14% average errors for the thermal and hydrodynamic models. Besides, the impacts of channel diameter and surface roughness in the pressure drop were studied.

Determining thermomechanical response of thin disk lasers with physics-informed neural networks

Acquiring structural behavior related to thermal effects is essential to the design of high-power thin disk lasers. However, quantifying the thermomechanical response of a thin disk laser crystal (TDLC) is challenging since these variables of interest are always highly tensorial. Herein, we developed a method to directly quantify the thermo-induced structural behavior of a TDLC from scalar temperature by a physics-informed neural network (PINN). The PINN is established to approximate the unknown states (thermal displacement, strain, and stress fields) using the loss functions encoded with sparse temperature and thermal mechanics equations. Steady-state and transient results of thermo-induced structural responses are precisely obtained from the temperature field by training PINN. In addition, transfer learning is demonstrated to enhance the computation efficiency of PINN for TDLCs with various materials and geometric properties. Implanting PINNs into thin disk lasers paves the way for precise quantification of highly tensorial thermal effects of lasers in-situ using easily accessible scalars.

Role of interface tension in the thermoelastic analysis of inclusions: Unified formulation and closed-form results

We study the thermoelastic problem of an inclusion of general shape surrounded by a foreign elastic matrix under plane deformation and the influence of an in-plane far-field heat flux. The small-scale interface effects, related to not only interface conductivity, interface stretching rigidity and interface thermal expansion but also (residual) interface tension, are incorporated in the corresponding analysis. We establish general boundary value formulations in both heat conduction and thermoelasticity for an arbitrary inclusion shape, allowing for analytic or at least semi-analytic treatment of the problem. Specially, we derive closed-form solutions for the case of circular inclusion and obtain concise expressions for describing the remote heat flux-induced thermal stress near the interface (at both the inclusion side and matrix side). Surprisingly, it is shown that for the case of circular inclusion, interface tension plays the same role as interface stretching rigidity in determining the full thermal stress field, or in other words, the full thermal stress field depends on only the sum of interface tension and interface stretching rigidity but not on the specific value of either of them. Numerical examples are also given to illustrate the influence of interface tension on the von Mises stress distribution in the vicinity of the interface.

Thermal Stress Field and Microstructure Evolution of Ti-6Al-4V Fabricated by Laser Engineered Net Shaping

Thermal Stress Field and Microstructure Evolution of Ti-6Al-4V Fabricated by Laser Engineered Net Shaping