Internal Thermal Stresses Research Articles

Initial temperature conduction process and fracture response of rock impacted by ultra-low-temperature fluid: A case study of polymethyl methacrylate

Injecting ultra-low-temperature fluids, such as liquid carbon dioxide (CO2) and liquid nitrogen (LN2), into deep, low-permeability reservoirs for fracturing is an emerging waterless fracturing technology. When these fluids enter the reservoir, they rapidly exchange heat with the fracture walls, triggering intense cold shock, which influences fracture development. Although many scholars have studied the effects of nitrogen freezing and thawing on coal seams, the initial thermal exchange and cold shock process when LN2 first enters the rock mass remains unclear. This paper uses the visualizable material polymethyl methacrylate (PMMA) as the research object, conducting low-temperature impact experiments under different preset temperatures (20 °C, 40 °C, 60 °C, and 80 °C) to investigate the impact of thermal exchange during cold shock on PMMA fracturing. The results show: (1) During LN2 impact, PMMA's temperature changes in three stages: slow cooling (micro-cracks initiation), rapid cooling (formation of long fractures), and temperature recovery (crack formation completion). (2) In prolonged impacts, PMMA temperature decreases linearly, while in short-term cyclic impacts, temperature decreases exponentially with faster recovery, increasing the likelihood of micro-cracks formation. (3) Temperature differences have a dual effect on crack formation and propagation: they significantly enhance internal thermal stress, leading to rapid micro-cracks initiation and expansion, while also causing uneven temperature gradients in the crack propagation region, shifting fracture modes from tensile to complex composite failures and promoting secondary crack formation. However, a significant temperature differential may result in the development of a singular crack propagation path, hindering the formation of complex fracture networks. These findings offer theoretical insights into fracture network formation in waterless fracturing of low-permeability reservoirs.

Microstructural and Oxidation Effects of Nb Additions to U3Si2

U3Si2 is a long term, accident-tolerant nuclear fuel candidate for light-water reactors because of its superior thermal conductivity and increased uranium density when compared to traditional uranium dioxide (UO2). While reducing internal thermal stresses and increasing efficiency, U3Si2 exhibits energetic oxidation during certain off-normal and accident scenarios, which include coolant or steam exposure. To mitigate this, Nb is investigated as an alloy constituent to enhance corrosion resistance and increase mechanical strength. The work presented investigates the response of Nb-alloyed U3Si2 to steam atmospheres. A thermogravimetric analysis is conducted in flowing steam to T > 1000 °C to assess oxidation resistance. The phase characterization of as-melted, thermally annealed and post-oxidation compositions with up to 12 vol% Nb by powder X-ray diffraction, scanning electron microscopy, and energy dispersive spectroscopy is reported.

Glass-based encapsulant enabling SiC power devices to long-term operate at 300 °C

The high-temperature applications of Silicon Carbide (SiC) power devices are constrained by traditional epoxy molding compound (EMC). A significant challenge arises from the mismatch between the thermal expansion coefficients (CTE) of the encapsulant and the SiC chip, generating thermal and mechanical stresses during prolonged high-temperature operation. While glass encapsulants offer stability above 300 °C, these stresses can lead to mechanical degradation and eventual failure of SiC power devices. We design a glass-based encapsulation material to adjust the CTE of the glass to match that of the SiC chip (3–9 ppm/℃), enabling encapsulation of the device for long-term operation at 300 °C. Finite element analysis (FEA) confirms that the CTE adjustment effectively reducs internal thermal stresses. The glass composite with 10 wt% PbTiO3demonstrates a Tg of 310 °C and a CTE of 8.48 ppm/℃, successfully encapsulating a SiC schottky barrier diode in TO-247 package form. The encapsulated device exhibits low leakage current, a reverse breakdown voltage of 1,700 V, and a thermal resistance of 0.45 °C/W. Notably, the device maintains excellent performance even after 1,176 h of high-temperature aging, including 336 h at 300 °C and exhibits minimal change during thermal cycling between −50 and 150 °C for 100 cycles. Long-term performance analysis demonstrates superior stability compared to EMC encapsulation. These results highlight the potential of glass-based encapsulants for wide band gap power devices, offering reliability and performance under extreme conditions.

Temperature Field Distribution and Thermal Stress Analysis of Pumped Storage Electric Motors

Abstract With the increasingly important role of pumped storage in energy systems, new and higher requirements have been put forward for the operation, safety, and economy of pumped storage power plants. The article takes a three-phase salient pole synchronous pumped storage motor as the research object, by using ANSYS finite element analysis software, a finite element model of a three-phase synchronous generator motor was established to analyze the internal temperature field distribution and thermal stress distribution of the motor. The results show that the higher temperature region of the entire system was concentrated at the winding, followed by the stator and rotor. Therefore, when optimizing the design of the motor in the future, the first step should be to start from the winding. The analysis of the thermal stress situation of the stator shows that the thermal stress and strain were mainly distributed at the inner diameter of the stator core, which was consistent with the distribution of the temperature field at the stator. The results of this study can provide theoretical guidance for the key maintenance areas and maintenance time of pumped storage power generation motors.

Impact of annealing on the characteristics of 3D-printed graphene-reinforced PLA composite

Manufacturing through additive techniques, especially utilizing the fused filament fabrication (FFF) method, is a transformative technology revolutionizing design and manufacturing. FFF builds parts layer by layer using thermoplastic polymer and polymer composite filaments. However, weak interlayer connections often lead to low interlaminar resistance in printed structures. Recent studies suggest that post-deposition heat treatments can mitigate this issue by reducing internal thermal stresses and enhancing layer adhesion, thereby improving part properties. This research delves into the impact of annealing heat treatment on a composite of Polylactic Acid (PLA) reinforced with graphene. The annealing process was conducted at temperatures of 90, 100, and 120 °C for durations of 60, 120, and 240 min. The annealing response of the graphene-reinforced PLA composite is compared to that of natural PLA for reference, analyzing its effects on electrical, thermal, chemical, and mechanical properties. Chemical characterization was performed using X-ray diffraction (XRD), Raman spectroscopy, and Fourier-transform infrared spectroscopy (FTIR). Thermal properties were analyzed via thermogravimetric analysis (TGA) and differential scanning calorimetry (DSC). Electrical properties were assessed by measuring resistance, resistivity, and conductivity. Mechanical properties were evaluated through tensile, flexural, notch sensitivity, impact tests, and hardness measurements. The results demonstrated that annealing of graphene-reinforced PLA and natural PLA did not alter their functional groups but increased their crystallinity. This treatment improved thermal stability, electrical conductivity, and mechanical properties, including tensile strength, flexural strength, and Shore D hardness. However, it reduced impact and notch sensitivity resistances. The increased crystallinity had a greater beneficial impact on some properties than the graphene reinforcement. These findings have potential applications in the automotive, aerospace, electronics, and medical sectors, given the increasing use of PLA in these industries.

In-situ thermal Raman mapping and stress analysis of CNT/CF/epoxy interfaces

A study of the interfacial behavior and internal thermal stress distribution in fiber-reinforced composites is essential to assess their performance and reliability. CNT/carbon fiber (CF) hybrid fibers were constructed using electrophoretic deposition. The interfacial properties of CF/epoxy and CNT/CF/epoxy composites were statistically investigated and compared using in-situ thermal Raman mapping by dispersing CNTs as a Raman sensing medium (CNTR) in a resin. The associated local thermal stress changes can be simulated by capturing the G‘ band position distribution of CNTR in the epoxy at different temperatures. It was found that the G‘ band shifted to lower positions with increasing temperature, reaching a maximum difference of 2.43 cm−1 at 100 °C. The interfacial bonding between CNT/CF and the matrix and the stress distribution and changes during heat treatment (20–100 °C) were investigated in detail. This work is important for studying thermal stress in fiber-reinforced composites by in-situ thermal Raman mapping technology.

A review of thermal shock behavior of ceramics: Fundamental theory, experimental methods, and outlooks

AbstractThe thermal shock resistance of ceramics is a key factor for determining the durability of ceramic components under transient thermal conditions and is also one of the key factors for evaluating the stability of ceramics under extreme thermal conditions. After rapid heating or cooling, the surface and internal thermal stress mismatches of ceramics can cause severe thermal damage. Two main types of ceramic thermal shock exist: rapid cooling and rapid heating thermal shock. This article presents a broad understanding and insight into fundamental theory and experimental methods for ceramic thermal shock testing. The experimental equipment and procedures, test result evaluation, and material characterization of ceramic thermal shock are summarized. Moreover, outlooks and perspectives are discussed for testing and characterizing ceramic thermal shock resistance. This review will be helpful to researchers performing studies in the relevant fields of ceramics.

Long-term oxidation of Ti3Al0.8Sn0.2C2 in air at 1200 °C

The addition of Sn into the raw materials is currently one of the most widely used methods to improve the purity and mechanical properties of Ti3AlC2. It follows in this work to investigate the oxidation behavior of the resulting Ti3Al0.8Sn0.2C2 at 1200 °C with the oxidation time up to 500 h. The oxidation kinetics shows that its oxidation resistance is much worse than that of common MAX phases including Ti3AlC2, Ti2AlC, and Cr2AlC. The oxide layer mainly consists of TiO2 and Al2O3, with only a small amount of SnO2 at the beginning of the oxidation stage. Cracks induced by the internal thermal stress penetrate through the entire oxide layer after only 1 h, which is an important reason for the rapid oxidation of the internal substrate layer. This work is expected to provide some inspiration and reference for Ti3Al0.8Sn0.2C2 used as the potential high-temperature structural material.

Localized Phonon Transport Study of GaN/SiO2 Core/shell Nanowires under Thermal-Stress Coupling.

In order to comprehensively explore the intricate mechanisms of thermo-mechanical interactions, this study employs the molecular dynamics method to investigate the influence of heat flux density, shell thickness and length, as well as stress on the radial interface phonon transport in GaN/SiO2 core/shell nanowire. Additionally, the surface eigenmode decomposition method is employed to analyze the interface phonon dispersion curves. The investigation reveals that with increasing heat flux density, internal thermal stresses intensify, leading to a complex distribution of thermal stresses within the system. Under the influence of thermal stress, the nonlinear acoustic properties interact with phonon scattering, resulting in the pronounced localization of interface phonons. Compressive stress causes an upshift in low-frequency phonons, while tensile stress induces a downward shift in the high-frequency optical branches at the interface. The localized phonon vibrations at the SiO2/GaN interface under nonuniform stress are identified as the primary cause for the abundant presence of nondispersive phonon modes at the radial interface. By elucidating the subtle interplay between lattice vibrations and stress fields, this study offers a novel and profound understanding of thermo-mechanical coupling effects, thereby providing innovative theoretical foundations for the design and performance management of thermoelectric devices.

Temperature Control and Crack Prevention Measures for Concrete Ship Locks Subjected to Prolonged Casting Interruptions

During the construction of concrete ship locks, prolonged interruptions between the casting of the floor and lock wall are inevitable. In terms of mass concrete, long placement delays are one of the major reasons for the presence of cracks in newly placed concrete. Therefore, this study examines both the placement and structural characteristics of ship locks after long casting interruptions based on the mass concrete thermal stress theory to determine the major causal factors for cracks in newly poured concrete. Specifically, a block placement method is proposed to reduce thermal stress in newly placed concrete, and the temperature control and crack prevention capacities of the proposed method are verified using the finite element method. The development of the structure’s thermal stress under different temperature control measures is analyzed, finding that thermal stress in the lock walls can be effectively reduced by 50% through low-temperature block casting. The results demonstrate that the proposed method can significantly reduce the internal thermal stress of newly placed concrete after prolonged casting interruptions, thereby highlighting its applicability for achieving effective temperature control and crack prevention in concrete ship locks.

Temperature sensing and energy harvesting with A MEMS parametric coupling device under low frequency vibrations

The frequency-based self-powered sensor has an important place in the era of the Internet of Things. In existing reports, the resonator is used either as an energy harvester or a sensor, yet it cannot undertake both demands simultaneously in a single structure. A parametric coupling device (abbreviated as PCD), capable of both temperature sensing and energy harvesting, is proposed with a common wings-inspired structure. Under one low frequency vibration excitation, the vibration energy can be potentially converted to electric energy, while the output frequency is observed to have a linear relationship with the temperature. The wings-inspired structure is comprised of three parts bonded in series, two side beams for collecting vibration energy one of them synchronously for temperature sensing, and a middle flexible beam for achieving parametric coupling. Once the heat is applied to the sensing one, the internal thermal stress is generated in the beam, while the reaction force acts on the anchor end of the beam to create compressive stress, for which the stiffness is decreased to cause frequency shifts and turn the working frequency domain. The parametric coupling is designed to improve the PCD performance, which is supported by theoretical analysis and experimental verification. With a manufactured MEMS PCD prototype, under a harmonic vibration excitation, when the temperature varies from 35.85 °C to 48.35 °C, both frequency shifts for sensing and working frequency domain for harvesting are 13.7 Hz which is 3.5 times larger than those of a non-parametric coupling device (abbreviated as NPCD). The sensing sensitivity of PCD is measured as 2.91 times higher than that of NPCD under a harmonic vibration excitation, while that of PCD is analyzed as 1.69 times higher than that of NPCD under a random one. Theoretical analysis shows the maximum temperature detection range is from 33.32 °C to 84.07 °C and can be further enlarged from 33.32 °C to 108.54 °C by adjusting the length of the sensing beam. The proposed PCD has the potential to be applied to temperature compensation systems or to maintain the operating environments of sensing nodes in self-powered wireless sensing networks (WSN).

Improving mechanical properties of an additively manufactured high-entropy alloy via post thermomechanical treatment

Thermomechanical treatment is applied to a CrMnFeCoNi high-entropy alloy fabricated via laser melting deposition (LMD) with 5 wt% WC addition to improve its mechanical properties. After the thermomechanical treatment, the yield strength of the LMD-fabricated alloy increases by 323 MPa, while the elongation remains nearly unchanged. Microstructures of the alloy before and after the thermomechanical treatment are thoroughly characterized. The LMD-fabricated alloy consists of the face-centered cubic matrix and M23C6 precipitates distributed both at grain boundaries and within matrix grains. The thermomechanical treatment leads to a significant refinement of the matrix grains and a more uniform distribution of the M23C6 precipitates, and largely these two factors give rise to the increase in yield strength. Numerous dislocations induced by internal thermal stress due to LMD are effectively eliminated through the thermomechanical treatment, contributing to the preservation of the ductility. The M23C6 carbide precipitates are characterized regarding their spatial distribution, chemical composition, and stacking faults, along with the orientation relationship and the interfaces between the matrix and the precipitates.

Concrete corrosion in nuclear power plants and other nuclear installations and its mitigation techniques: a review

Abstract Nuclear power plants (NPPs) have been affected by various failures through corrosion which causes economic losses, increased chance of the radiation exposure and environmental risk. One of the major durability issues in reinforced concrete is the corrosion of reinforcement which significantly reduces the life of reinforced concrete. Considering the increasing demand for longer service lives of NPPs, and the high cost involved in building and maintaining it, adequate preventive measures should be followed to minimize the corrosion. This review majorly discusses about the mechanism of corrosion of steel in NPP structures with emphasis on the mechanisms relevant to NPPs, possible reasons for the concrete corrosion as well as potential failure happening in NPPs. The majors reason for the concrete corrosion in nuclear power plants are mainly corrosive external and internal environment, thermal and mechanical stress, moisture content, microorganisms and stray electrical currents. The corrosion of NPPs may result in loss of structural integrity and leakage of radioactive material. The review also discusses about various corrosion prevention and protection techniques against concrete corrosion and concludes with an overview of present methods and possible future perspectives used to enhance the efficiency of concrete corrosion mitigation methods with focus of NPPs.

Prognosis of Li-ion Batteries Under Large Load Variations Using Hybrid Physics-Informed Neural Networks

The development of new modes of transportation such as electric vertical takeoff and landing aircraft and the use of drones for package and medical delivery have increased the demand for reliable and powerful electric batteries. Therefore, accurately predicting the degradation of a battery’s state-ofhealth (SOH) and state-of-charge (SOC) is a crucial albeit still challenging task. There is a need for models that can accurately predict the SOH and SOC while taking into account the specific characteristics of a battery cell and its usage profile. While traditional physics-based and data-driven approaches are used to monitor the SOH and SOC, they both have limitations related to computational costs or that require engineers to continually update their prediction models as new battery cells are developed and put into use in battery-powered vehiclefleets.Battery capacity degradation can vary from battery to battery and can also be influenced by changes in load due to internal thermal stress. While sophisticated electrochemistry-based models can provide precise predictions of the SOC during adischarge cycle when parameters are well-tuned, using highfidelity models for prognostics purposes can be computationally expensive. Those models also require tuning to specific battery types and at times to specific specimens, thus hindering generalization. In contrast, purely data-driven approaches can learn the relationship between input and output for SOC prediction based on load input, but they require a large and diverse training dataset and lack any physical or electrochemical understanding, making far-ahead predictions challenging if test loading conditions fall outside the training distribution. To address some of the drawbacks of the aforementioned modeling approaches, in this paper, we enhance a hybrid physics-informed machine learning version of a battery SOC model we presented in previous work to predict voltage dropduring discharge. The enhanced model captures the effect of wide variation of load levels, in the form of input current,which causes large thermal stress cycles. The cell temperature build-up during a discharge cycle is used to identify temperature-sensitive model parameters. Additionally, we enhance an existing aging model built upon cumulative energy drawn by introducing the effect of the load level. We then map cumulative energy and load level to battery capacity with a Gaussian process model. To validate our approach we use a battery aging dataset collected on a self-developed testbed, where we used a wide current level range to age battery packs in accelerated fashion. Prediction results show that our model can be successfully calibrated and generalizes across all applied load levels.

ВНУСТРІШНЬОСТРУКТУРНІ ТЕРМОНАПРУЖЕННЯ В АСФАЛЬТОБЕТОННИХ І ЦЕМЕНТОБЕТОННИХ МАТЕРІАЛАХ, ПІДСИЛЕНИХ ФІБЕРГЛАСОВОЮ, ФІБЕРКАРБОНОВОЮ, ФІБЕРБАЗАЛЬТОВОЮ ТА ФІБЕРАРАМІДНОЮ АРМАТУРОЮ

By the methods of mathematical modeling, the internal structural thermomechanical effects that are blamed on asphalt concrete and cement concrete materials, reinforced with the fiberglass, fibercarbon, fiberbasalt and fiberara-mide strands, are investigated under conditions of change the temperature of the system. The analysis of the thermome-chanical incompatibility of the phases of the composites with the aim of establishing its influence on the values of the internal structural thermal stresses, which are attributable to these changes, is performed. It is shown that for the as-phalt concrete material the incompatibility is small and so the system internal structural thermal stresses are also small and do not exceed the values of the limit strength of the fractions of the composite material. For composites with a cement concrete matrix, the thermomechanical incompatibility of their fractions is essential and for this reason the ther-mal stresses, which are due to the temperature change, significantly exceed the values of the limit strength of the cement concrete. The established features may be used during the design of reinforced road pavements and cement concrete structures, which work under conditions of changing temperatures. Keywords: composite materials, reinforced concrete, epoxy coating, corrosion damage, thermomechanical incompati-bility, thermal stress.

Effect of Final Electromagnetic Stirring on Internal Thermal Stress, Strain and Cracking of Continuous Casting Bloom

Effect of Final Electromagnetic Stirring on Internal Thermal Stress, Strain and Cracking of Continuous Casting Bloom

Thermal Stress Analysis of a Solid Oxide Fuel Cell Considering Interconnect Deformation

Deformation of the interconnect in a solid oxide fuel cell (SOFC) stack affects the internal thermal stresses of the cell at high temperatures. In this study, the effect of the interconnect deformation on the cell temperature and thermal stress at different operating voltages was simulated based on the thermal-chemical-electrical-mechanical multiphysics coupling theory. The results show that when the operating voltage of the cell is above 0.85 V, the interconnect mainly generates a compressive strain. When the operating voltage is below 0.85 V, the interconnect produces tensile strain, which increases with decreasing voltage. Interconnect deformation significantly increases the thermal stress of the cells within the stack, but effectively improves the uniform distribution of thermal stress. The coupling effect of interconnect deformation on cell thermal stress within the stack varies at different operating voltages.

A coupling strategy for excellent mechanical properties and enhanced interfacial performance of polyimide/carbon fiber composite with metal-free catalyzed-curing route

The structure and properties of carbon fiber reinforced composites (CFRC) depend on main factors, especially the unpredictable interface. In this work, a kind of thiocarbonyl disulfide compound is introduced to achieve the catalyzed-cure of phenylethynyl terminated polyimide (PI) and plays the role of coupling medium to constitute covalent-bonded structure at the PI/CF interface. The organocatalyzed cure not only follows the free radical mechanism with an initial curing temperature down to 260.4 °C, but also endows the composite with reduced internal thermal stress and enhanced interface structure. Due to both CF surface-initiated free radical curing reaction and coupling reaction between thiocarbonyl-containing PI matrix and hydroxyl-rich sizing layer, the composite performs an improved interfacial shear strength (IFSS) of 123.9 MPa, being 2.47 times as the thermally cured ones, plus the anti-bacterial reinforcement of the PI matrix. Besides, the interface enhancement brings the CFRC specimen improved electrical properties, performing a 92.6% increase of transverse electrical conductivity to 367.6 S/m. This study gives perspective for improving the interfacial performance of high-temperature processed CFRC with “as-received” fiber reinforcers, plus a clear outlook to future research directions and open challenges to prepare high-performance CFRC.

Comparative study of thermal breakage of annealed and tempered glazing with different thicknesses under uniform radiation conditions

Glass façades are extensively used in high-rise buildings; however, glass panes may break and fall out when subjected to transient heating from a fire, likely altering the fire dynamics both within and outside the building. This work tested annealed glass (non-tempered) and fully tempered glazing with different thicknesses of 6, 10, 12, 15 and 19 mm under uniform incident radiation of 50 kW/m2. Parameters measured included glass surface temperature, breakage time, fracture behaviour, and incident heat flux to study the different phenomena between annealed and tempered glass. A finite element method (FEM) thermal and mechanical model of annealed and tempered glass considering the glass prestress field was developed to deepen the understanding of the coupling between the internal prestress and thermal stresses under uniform radiation conditions. The simulated glass surface temperature distributions are in reasonable agreement with the measured values, with relative errors of 1.8% (annealed glass) and 2.2% (tempered glass) in terms of breakage times, thus partially validating the glazing heat transfer model. A sequential thermal-mechanical method was then used to predict the glass breakage times, with average relative errors of 10.5% and 12.2% between the predicted and measured results for the annealed and tempered glasses, respectively, regardless of glazing thicknesses. It was established that maximum tensile stresses were located at the edge's centre on the radiation-exposed-side surface for annealed glass; for tempered glass, the maximum stresses were in a region approximately 0.3 of the thickness from the heated side surface, where the cracks are prone to initiating. The time needed to overcome the compressive prestress with thermal tensile stress resulting from transient heating is considered the primary reason for the enhanced ability of tempered glazing to resist fracture, which was approximately double that of annealed glass under the conditions studied in this work.

Inverted metamorphic photovoltaics for space applications utilizing a distributed Bragg reflector compatible with epitaxial lift-off

MicroLink Devices manufactures triple-junction inverted metamorphic solar cells on GaAs wafers with a selectively etched release layer in an epitaxial lift-off (ELO) process to create ultra-thin foils of semiconductor with a metal backing. To improve radiation tolerance, each absorber layer is thinned and doping levels are reduced. The bottom subcell employs a mirror structure to maintain current, while the middle subcell requires a distributed Bragg reflector (DBR) to increase the absorption path length and maintain current. MicroLink utilizes a non-conventional In x (Al y Ga1−y )1−x P/GaAs DBR that is compatible with ELO. The DBR has a bandwidth of ∼110 nm and a peak reflectance in air near 95%. Average cell efficiencies of 28% (1-Sun AM0) are achieved with a power retention of 84% after 1E15 cm−2 electron dosing (1 MeV energy). Large-area cells and coupons underwent internal thermal stress testing and showed no degradation. Clear pathways to achieve >29% efficient cells with >85% power retention are discussed.