Search Results (1,221)

This study investigates steady-state heat transfer in a three-layer cylindrical system with angular non-uniformity of the temperature field. For the considered geometry, a mathematical model of heat conduction is formulated in cylindrical coordinates with piecewise constant thermophysical properties and continuity conditions at the interfaces between layers. The direct problem is solved analytically using a Fourier series expansion of the temperature field with respect to the angular coordinate. Based on experimental temperature measurements obtained for various configurations of soil layers, an inverse problem is formulated and solved to reconstruct the thermal conductivities of the individual layers and the heat transfer coefficient at the external boundary. To stabilize the solution, a regularized least-squares approach is employed. The convergence of the recovered parameters with respect to the harmonic number is analyzed, and the averaged reconstructed values are compared with the exact parameters used in the direct problem. The obtained results demonstrate the stability and accuracy of the proposed method, confirming its applicability to the identification of thermophysical parameters in multilayer soil systems based on experimental data. Full article

Concrete structures are vulnerable to fire-induced damage throughout their service life, with high-temperature exposure presenting a critical safety hazard. This study addresses the critical safety risks posed by fire-induced damage in concrete structures, particularly focusing on the distinct behavioral differences between early-age and mature concrete during both heating and cooling. To investigate these variations, concrete specimens cured for 3, 14, 28, 60, and 90 days were subjected to deformation tests and heated to target temperatures ranging from 100 to 800 °C. Key parameters, including compressive strength, mass loss, and linear expansion rate, were measured. The results show that the linear expansion rate and thermal expansion coefficient increased with temperature at all ages, with residual linear expansion rates at 800 °C ranging from 0.49% to 0.55%, decreasing slightly with age. While compressive strength was higher in older specimens at room temperature, it became similar across ages after exposure to high temperatures, especially above 500 °C. Notably, constant-temperature exposure significantly influenced the deformation behavior. These findings suggest that fire resistance assessments should account for concrete age and, more importantly, the effects of sustained high-temperature exposure, which critically alter deformation patterns and residual properties. Full article

Copper busbar inserts are critical components of high-voltage connectors in new energy vehicles. The interfacial contact stress between the insert and the polymer directly affects the sealing reliability and service life of the connector. To address the interfacial stress concentration caused by the mismatch in thermal expansion coefficients between metal and polymer, this study employs COMSOL Multiphysics 6.2 simulations to investigate the regulation laws of arc-shaped and trapezoidal microstructures on the interfacial stress of copper–polyphenylene sulfide (PPS)/polypropylene (PP). The response surface methodology (RSM) is introduced to verify simulation reliability and optimize parameters. The simulation results indicate that both structures can effectively reduce interfacial stress, and the stress exhibits a significant nonlinear relationship with the structural parameters. Due to its high temperature resistance and polar thioether bond, PPS demonstrates better interfacial compatibility than PP. Under the same structural position, the maximum stress reduction exceeds 20% (from 0.689 MPa to 0.539 MPa). Moreover, the arc-shaped structure is more effective in alleviating stress concentration than the trapezoidal structure. At the same position, compared to the trapezoidal surface, the arc-shaped surface reduces the valley contact stress of PPS from 0.527 MPa to 0.5 MPa (a decrease of 5.12%) and that of PP from 0.679 MPa to 0.605 MPa (a decrease of 10.9%). The optimal parameters are as follows: an arc-shaped radius width of 1.0 mm, a depth of 0.8 mm; a trapezoidal bottom base of 2.0 mm, a height of 1.2 mm. This study provides a basis for the interface design of metal–polymer composite components and holds significant engineering value for the reliability optimization of high-voltage connectors. Full article

316LN stainless steel is widely used in critical nuclear fusion structural components due to its excellent mechanical properties and machinability. However, its high thermal expansion coefficient and low thermal conductivity promote welding distortion, while work hardening causes residual stress accumulation. Thermo-elastic–plastic finite element modeling (FEM) is the primary numerical method for predicting these effects. Yet, despite hardware advances, full-scale simulations—especially for thick plates with multi-pass welds—remain computationally expensive, hindering the balance between efficiency and accuracy. To address the inherent trade-off between welding efficiency and dimensional accuracy in multi-pass, multi-layer welding of thick-section components, this study employs MSC. Marc to develop a finite element model of a 15 mm thick butt-welded joint fabricated from 316LN stainless steel. Three distinct heat source models—instantaneous, enhanced moving, and moving element-set—are systematically implemented to simulate transient temperature fields, residual stress distributions, and welding deformation. All numerical predictions are rigorously validated against experimental measurements to comprehensively assess both accuracy and computational efficiency. Results indicate that: (i) the predicted molten pool geometries and characteristic thermal cycle profiles from all three models exhibit strong agreement with experimental observations; (ii) longitudinal residual stress distributions predicted by all models align closely with measured values; (iii) transverse residual stresses predicted by the moving element-set and enhanced moving heat sources agree well with experiments, whereas those from the instantaneous heat source show marked deviation; (iv) angular distortion predictions from the moving element-set heat source achieve over 90% conformity with experimental data, while the instantaneous heat source substantially underestimates angular distortion, and the enhanced moving heat source yields approximately 65% agreement; and (v) in terms of computational efficiency, the instantaneous heat source requires only ~40% of the computation time needed by the moving heat source. Full article

The key to metallic fuel development is the fabrication of uranium metal and alloys into fuel forms. U-Nb alloys are one of the best candidates for a metallic fuel alloy with high-temperature strength sufficient to support the core, acceptable nuclear properties, good fabricability, and compatibility with usable coolant media. Melt processing has been a key component of the metallic fuel cycle, and process models require thermophysical parameters at elevated temperatures, particularly above the melting temperatures, regarding which experimental data are scarce, for accurate simulations and process development. By means of ab initio density-functional theory (DFT) quantum molecular dynamics (QMD), we have calculated the main thermophysical parameters—the density, thermal expansion coefficient, specific heat, thermal conductivity, melting temperature, latent heat of fusion, and viscosity—used in the modeling of the U-6 wt.% Nb alloy casting. The melting temperature of the U-6 wt.% Nb alloy at ambient pressure is obtained by means of QMD simulations using the Z-method. The ambient volume change and latent heat of melting of U-6 wt.% Nb are also derived from QMD simulations in conjunction with analytical fitting for the energy and pressure. The thermal conductivity for the solid U-Nb alloy is calculated from the semi-classical Boltzmann transport equation combined with an estimate of the electron relaxation time obtained from DFT simulations. Full article

Functionally graded materials (FGMs) effectively alleviate residual stress induced by physical property mismatch at dissimilar material interfaces through a graded transition in composition or structure. Among these, the matching of the coefficient of thermal expansion (CTE) is a core indicator for ensuring the service reliability of the joint. Traditional composition design relies on empirical trial-and-error, which makes it difficult to efficiently identify the optimal path in a high-dimensional composition space. This study proposes a data-driven, machine learning-assisted composition design method. Based on a high-precision dataset covering 15 elements and 747 CTE data points, six typical regression models were systematically evaluated. The results show that the random forest (RF) model achieves the best performance, with a coefficient of determination (R²) of 0.929 and a root mean square error (RMSE) of 0.658 on the test set. Using the SHapley Additive exPlanations (SHAP) method, the lattice constant (c), Young’s modulus (YM), and temperature (T) were identified as the key physical descriptors governing the thermal expansion behavior. Experimental validation shows that the CTE prediction deviation of the model for the high-performance Fe-based alloy Norem02 in the range of 20–300 °C is only 0.89%. Based on this framework, the composition of the 316L/Norem02 transition layer was successfully designed in this study. This effectively reduced the interfacial thermal expansion mismatch. Consequently, it provides a reliable theoretical basis for the rational design of dissimilar material interfaces under extreme service conditions. Full article

Thermal barrier coatings (TBCs) require materials with intrinsically low thermal conductivity and high grain-boundary thermal resistance to maximize the temperature gradient across the top coat. In this work, the effective thermal conductivity of more than 40 prospective TBC oxides belonging to seven structural families (YSZ/YSH, pyrochlores/fluorites A₂B₂O₇, defective fluorites A₃BO₇, fergusonite/monazite ABO₄, and perovskites ABO₃) was systematically deconvoluted into intrinsic grain thermal conductivity (k_grain) and grain-boundary (R_gb) contributions. It is shown that grain-boundary Kapitza resistance dominates heat transport in virtually all advanced oxides, contributing 60–90% to the total thermal resistance of polycrystalline samples. The lowest k_grain values (4–12 W m⁻¹ K⁻¹) are found for cerates and certain tantalates, while the highest R_gb (up to 7.2 × 10⁻⁶ m² K W⁻¹) are characteristic of high-entropy and heavily doped perovskites. Orthorhombically distorted SrCeO₃-based and high-entropy perovskites combine moderate k_grain (4.7–27.9 W m⁻¹ K⁻¹), high R_gb, and tunable thermal-expansion coefficients (10–13 × 10⁻⁶ K⁻¹), making them the most promising candidates for next-generation TBCs. These findings provide a rational basis for microstructure engineering and composition design aimed at maximizing the temperature drop across TBC layers while maintaining phase stability and CMAS resistance. Full article

This paper probes into the propagation characteristics of Rayleigh waves in a partially saturated, porous, thermo-viscoelastic half-space, with full consideration of the fractional viscoelastic effect and thermal coupling effect. A fractional Zener model is introduced to depict the thermo-viscoelastic mechanical behavior of the solid skeleton by constructing a complete set of governing equations that include mass balance, generalized Darcy’s law, momentum balance, and generalized heat conduction. Field equations are derived by means of Helmholtz vector decomposition, and the dispersion equation, and the phase velocity expression of Rayleigh waves are obtained by combining the traction-free and adiabatic boundary conditions of the medium. The impacts of key material properties, such as medium saturation, intrinsic permeability, medium viscoelasticity, and thermal expansion coefficient, on the dispersion feature of Rayleigh waves are discussed in detail. Numerical analysis results show that an increase in the thermal expansion coefficient will lead to a rise in Rayleigh wave phase velocity, in which the increase in P1 compressional wave velocity plays a dominant role among the velocities of various types of waves. Meanwhile, the attenuation coefficient of Rayleigh waves presents a decreasing trend and gradually tends to be stable with the growth of the thermal expansion coefficient. Similarly, the phase velocity of Rayleigh waves also increases with the rise in fractional order index, which is jointly dominated by the velocity enhancement of P1 waves and S waves. In addition, the attenuation coefficient of Rayleigh waves increases first and then decreases with the increase in fractional order index and reaches the peak value when the fractional order index is about 0.4. The research results reveal the influence of laws of thermal expansion characteristics and viscoelasticity on Rayleigh wave propagation and provide theoretical support for the analysis of wave propagation characteristics in porous media in relevant engineering applications. Full article

The rapid advancement of high-performance computing has spurred growing demand for miniaturized, high-density, high-power, and highly reliable electronic packaging. Through-silicon via (TSV), as a pivotal technology enabling high-density integrated packaging, achieves vertical interconnection that reduces signal latency and power consumption while substantially improving system integration. However, inherent challenges persist due to coefficient of thermal expansion mismatches among heterogeneous materials in TSV and parasitic effects introduced by high-density TSV arrays, leading to critical concerns regarding thermomechanical reliability and signal integrity. This study focuses on TSV structures, investigating their thermomechanical reliability and electrical performance. First, the macro–micro model of 2.5D package structure was established to address cross-scale challenges based on Representative Volume Element (RVE) homogenization and sub-model technique. Then, an equivalent circuit model integrating transmission line network theory was developed and validated through full-wave electromagnetic simulations using S-parameter analysis to analyze signal transmission characteristics. Finally, by introducing an improved multi-objective grasshopper algorithm, the structural parameters of TSV are co-optimized using a genetic algorithm back propagation network (GA-BP) and an improved multi-objective grasshopper algorithm (IMOGOA) to enhance both thermomechanical reliability and electrical characteristics simultaneously. The proposed approach offers a practical and effective solution for improving the reliability and performance of high-density integrated packaging, providing valuable insights for future packaging design and optimization. Full article

The alloy with a chemical composition of 64 at. % Fe and 36 at. % Ni is known as Invar36 and is characterized by a coefficient of thermal expansion (CTE) less than 2 × 10⁻⁶ °C⁻¹ below Curie temperature (about 250 °C). The conventional method of obtaining Invar36 alloys consists of melting and casting, followed by a series of heat treatments. In recent years, research has focused on unconventional technologies for Invar36 preparation such as the sintering of Fe and Ni elemental powders. Also, Invar36 in powder form can be synthesized by mechanical alloying (MA). The aim of this paper is the characterization of Invar36 compacts obtained by conventional sintering of mechanically alloyed Fe and Ni elemental powders. MA was performed in a high-energy planetary ball mill (Ar atmosphere). Mechanically alloyed powders were densified by conventional sintering (simple and double). The sintering parameters used are those specific to the sintering of ferrous parts. After simple sintering, the relative density was 74%. Re-pressing and double sintering lead to an increase in the relative density to 78.6%. The microstructure of Invar36 compacts consists of two phases. The coefficient of thermal expansion (CTE) was determined for Invar36 compacts obtained by both simple and double sintering at 1120 °C in endogas. The CTE values of Invar36 simple sintered (α = 0.6 × 10⁻⁶ °C⁻¹) and double sintered (α = 0.5 × 10⁻⁶ °C⁻¹) are very low, up to 195 and 225 °C, respectively. HV_0.05 values of the Invar-ss sample are lower than the values of the Invar-ds sample. Thus, the HV_0.05 value in areas where the γ phase predominates increases from 203 to 218, while in areas where the α phase is predominant it increases from 257 to 271. The results of this study have potential applicability in obtaining Invar parts by sintering under the specific conditions used for ferrous parts, without requiring any modification of the production flow. Full article

The temperature sensitivity coefficient greatly affects the interior ballistic performance of propellant charges. Even under consistent loading conditions, variations in environmental temperature can lead to maximum chamber pressure fluctuations of 40–80 MPa, thereby compromising weapon efficiency and operational safety. In order to obtain a single-base propellant with a higher energy and lower temperature sensitivity coefficient, ultra-fine RDX particles were added into the single-base propellant. The difference in thermal expansion coefficients between RDX and the single-base propellant matrix leads to temperature-dependent microcracking. These microcracks increase the burning surface area at low temperatures, compensating for the reduced chemical reaction rate and thereby lowering the temperature sensitivity coefficient. A scanning electron microscope (SEM) was used to observe the inner structure of the single-base propellant with and without RDX particles. The thermal mechanical analysis (TMA) results, together with SEM observations, reveal that the interfaces between the propellant matrix and the RDX particles are temperature-dependent. As a result, the burning surface area of the modified single-base propellant varies with temperature, contributing to a reduced temperature sensitivity coefficient. Closed bomb tests were conducted to verify this inference, and the obtained curves and relevant quickness (RQ) values showed that the modified single-base propellant had stable burning behavior and lower temperature sensitivity. This study leverages the structural interactions between high-energy fillers and polymer matrices to provide a potential strategy for designing climate-resilient ammunition. Full article

Distributed fiber optic temperature sensing (DTS) monitoring technology is increasingly widely applied in oil reservoir water injection development. However, existing DTS interpretation methods for layered water injection processes have insufficiently considered the effects of multilayer injection and reservoir damage. To address this issue, this paper takes into account interlayer heterogeneity and reservoir damage and, based on the laws of conservation of mass and energy, comprehensively incorporates the effects of friction, the Joule–Thomson effect, thermal convection, and thermal expansion. By coupling wellbore pipe flow with formation seepage, a temperature profile prediction model for multilayer water absorption under steady-state water injection conditions is established. Comparative validation against classical models such as those by Babak and Nowak demonstrates that the proposed model achieves high computational accuracy. Using this model, the influence patterns of injection rate, tubing diameter, formation coefficient, and skin factor on wellbore temperature distribution are systematically analyzed: a higher injection rate leads to a smaller temperature rise in the injected water; a larger tubing diameter results in a greater temperature rise; the formation coefficient affects the temperature profile by regulating interlayer water absorption distribution, while reservoir damage (skin factor) has a relatively limited direct impact on the temperature profile. The model is applied to interpret DTS field data from Well A, and the water absorption rate of each sublayer is quantitatively obtained: the main water absorbing intervals are 1878.7–1897.5 m and 1919.5–1950.6 m, with water absorption accounting for 30.57% and 24.28% of the total injection rate, respectively, while the remaining intervals exhibit secondary water absorption. These interpretation results are in good agreement with earlier oxygen activation tests. This study provides a theoretical basis and analytical method for applying distributed fiber optic temperature measurement technology to monitor water absorption profiles in multilayer injection wells. Full article

Designing stable and multifunctional perovskite materials with tunable electronic and optical properties is crucial for advancing next-generation optoelectronic and high-temperature applications. In this study, the structural, electronic, optical, mechanical, and thermal properties of XYO₃ (X = Nb, Ta; Y = Ag, Au) cubic perovskites were systematically investigated using density functional theory (DFT). Each compound crystallized into a cubic perovskite structure and was found to be both thermodynamically and dynamically stable. Hybrid functional (HSE06) calculations indicate semiconducting behavior with band gaps of 1.885 eV (NbAgO₃), 1.298 eV (NbAuO₃), 3.074 eV (TaAgO₃), and 1.801 eV (TaAuO₃). The density-of-state analysis reveals strong hybridization between the O-2p and Nb/Ta-d orbitals, which hints at mixed ionic/covalent bonding. Optical properties exhibit large absorption coefficients (about 10⁶ cm⁻¹) in the ultraviolet range and at lower reflectivity, especially of NbAgO₃ and TaAgO₃, indicating efficient light absorption. NbAgO₃ and NbAuO₃ possess moderate direct band gaps, making them suitable for optoelectronic and photovoltaic applications, whereas the wide bandgap of TaAgO₃ is beneficial in ultraviolet optoelectronic devices. Mechanical analysis confirms the ductile nature of all compounds, with TaAuO₃ exhibiting the highest ductility. Thermal analysis indicates that NbAgO₃ and TaAgO₃ exhibit higher lattice rigidity and thermal conductivity, but NbAuO₃ and TaAuO₃ are more anharmonic and have higher thermal expansion. Overall, these results demonstrate the multifunctional potential of XYO₃ perovskites for applications in optoelectronics, photovoltaics, ultraviolet devices, flexible electronics, and high-temperature environments. Full article

This study presents unique polymeric materials applicable to plastic substrates for use in flexible-display devices that overcome the trade-off between low linear coefficients of thermal expansion (CTE) and low thickness-direction birefringence (Δn_th) while combining a very high T_g, sufficiently high thermal stability, excellent optical transparency, good solubility, and minimum-required ductility. Polyimide (PI) films obtained from 1,2,3,4-cyclobutanetetracarboxylic dianhydride (CBDA) with 2,2′-bis(trifluoromethyl)benzidine (TFMB) under different conditions resulted in widely varying CTE values and provided a clear CTE–Δn_th correlation, which can be regarded as a virtual lower boundary in the CTE–Δn_th relationship for various PI systems. The pristine CBDA/TFMB and CpODA/TFMB (CpODA = norbornane-2-spiro-α-cyclopentanone-α′-spiro-2″-norbornane-5,5″,6,6″-tetracarboxylic dianhydride) systems were modified using numerous specifically designed monomers, i.e., a vertical-alignment-type liquid-crystalline diamine and cardo-type and spiro-type monomers. However, it was very challenging to overcome the trade-off between low CTE and low Δn_th, that is, to significantly exceed this lower boundary by modifying the pristine systems, while ensuring other target properties. One of the keys to achieving the present goal was compatibility with chemical imidization or one-pot polymerization processes (i.e., high solubility of the PIs), because these processes were more advantageous in reducing CTE and enhancing film transparency than the conventional two-step process. The modifications using phenyl-substituted xanthene-pendant 2,7-diaminofluorene and fluorene-pendant 2,3,6,7-xanthenetetracarboxylic dianhydride exhibited a prominent effect on overcoming the trade-off without the help of any fillers, while combining other excellent target properties. Polarized FT-IR difference spectra measured at varying incidence angles suggested that these side groups, which are connected perpendicularly to the PI main chains, align in the Z-direction, rationalizing the observed prominent effect. Thus, unique high-temperature transparent materials applicable to plastic substrates were successfully obtained in this study. Full article

High-entropy perovskite oxides attract considerable attention due to their outstanding properties and extensive applications. In this work, the lattice distortion and the mechanical, thermal and electronic structure properties of high-entropy (Ca_0.2Sr_0.2Ba_0.2La_0.2Pb_0.2)TiO₃ (CSBLPT) are investigated through first-principles calculations. The results suggest that the influence of O atoms on lattice distortion is predominant, and the effect of overall A-site atoms plays a distinctly greater role than that of the B-site atoms. The mechanical results show that the high-entropy CSBLPT has a lower Young’s modulus and higher fracture toughness than ternary SrTiO₃. The Debye temperature also indirectly indicates that the thermal expansion coefficient of the studied high-entropy perovskite is greater than that of SrTiO₃. As for thermal conductivity, the obtained result of CSBLPT is also appreciably lower than that of SrTiO₃, and the lowest thermal conductivity is along the [100] direction. The Fermi level of high-entropy CSBLPT is transferred to the conduction band, exhibiting a degenerate n-type semiconductor behavior with metallic-like characteristics, and the Bader charge values are also related to the local lattice distortion, which may cause differences in thermomechanical properties between high-entropy CSBLPT and SrTiO₃. Above all, high-entropy CSBLPT is a preferable TBC material with excellent performance under working conditions compared to SrTiO₃. Full article