Temperature Behavior Research Articles

Effectiveness of thermoviscoplastic material models in predicting the thermomechanical behavior of rolled homogenous armor steel

This paper studies the dynamic and elevated temperature behavior of rolled homogeneous armor steel, which is crucial for applications such as blast, impact, crash, and ballistic resistance. The deformation behavior is analyzed through tensile tests. The tensile tests of RHA steel are conducted at quasi-static 10−4s−1≤εṗ≤10−1s−1 to dynamic 10−1s−1≤εṗ≤36.439s−1 strain-rates and at high temperatures ranging from room temperature (RT,27°C) to 500°C. Phenomenological Johnson-Cook (JC) models and semi-physical Rusinek-Klepaczko (RK) material models are employed in finite element (FE) simulations of tensile tests. The JC failure model, with a small modification, is used along with the material models to simulate the loss of load-bearing capacity of the component. All necessary material parameters are extracted from the test data. The material models and the damage model are integrated into ABAQUS CAE FE software through a user-defined material subroutine (UMAT). The simulated outcomes acquired from diverse material models are validated with relevant experimental findings, and the effectiveness of each material model is evaluated through qualitative and quantitative assessments. Observations reveal limitations in the existing models to accurately replicate material behavior under tension, particularly in the dynamic strain rate, and elevated temperature range. Consequently, a modified version of the JC model (MJC) is explored to better account for the impact of temperature on strain hardening and strain rate hardening. The proposed modification in the material model significantly enhances the predictive accuracy of FE simulations of tensile deformation across the entire spectrum of studied strain rates and temperatures compared to the original JC and RK models.

Revisiting the averaged annihilation rate of thermal relics at low temperature

We derive a low-temperature expansion of the formula to compute the average annihilation rate ⟨σv⟩\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$${\\langle {\\sigma v}\\rangle }$$\\end{document} for dark matter in Z2\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$${\\mathbb {Z}}_2$$\\end{document}-symmetric models, both in the absence and the presence of mass degeneracy in the spectrum near the dark matter candidate. We show that the result obtained in the absence of mass degeneracy is compatible with the analytic formulae in the literature, and that it has a better numerical behaviour for low temperatures. We also provide as ancillary files two Wolfram Mathematica notebooks, which perform the two expansions at any order.

Assessing the Performance of a Dual-Speed Tool When Friction Stir Welding Cast Mg AZ91 with Wrought Al 6082.

A novel dual-speed tool for which the shoulder and pin rotation speeds are separately established was utilized to friction stir weld cast magnesium AZ91 with wrought aluminum 6082-T6. To assess the performance and efficacy of the dual-speed tool, baseline dissimilar welds were also fabricated using a conventional FSW tool. Optical microscopy characterized the weld microstructures, and a numerical simulation enhanced the understanding of the temperature and material flow behaviors. For both tool types, regions of the welds contained significant amounts of the AZ91 primary eutectic phase, Al12Mg17, indicating that weld zone temperatures exceeded the solidus temperature of α-Mg (470 °C). Liquation, therefore, occurred during processing with subsequent eutectic formation upon cooling below the primary eutectic temperature (437 °C). The brittle character of the eutectic phase promoted cracking in the fusion zone, and the "process window" for quality welds was narrow. For the conventional tool, offsetting to the aluminum side (advancing side) mitigated eutectic formation and improved weld quality. For the dual-speed tool, experimental trials demonstrated that separate rotation speeds for the shoulder and pin could mitigate eutectic formation and produce quality welds without an offset at relatively higher weld speeds than the conventional tool. Exploration of various weld parameters coupled with the simulation identified the bounds of a process window based on the percentage of weld cross-section exceeding the eutectic temperature and on the material flow rate at the tool trailing edge. For the dual-speed tool, a minimum flow rate of 26.0 cm3/s and a maximum percentage of the weld cross-section above the eutectic temperature of 35% produced a defect-free weld.

A hybrid shape functions based temporal finite element method to solve transient heat conduction problems

A novel temporal finite element method is presented to solve Fourier and non-Fourier heat conduction problems. Two kinds of temporal finite element models are developed using Gurtin variational principle and weighted residual technique, respectively. A kind of hybrid shape function with polynomial and trigonometric basis is stressed to give more flexible and appropriate description of temporal behavior of temperature. A recursive algorithm is developed by which the temperature solution at a specific time can be obtained only via a matrix power product with the initial condition, and a criterion of stability analysis is derived, which is can numerically be conducted when the constitution of shape function and time step size are prescribed. The proposed approach is available for Fourier and non-Fourier heat transfer problems, and can conveniently be combined with well-developed numerical algorithms for the boundary value problem, such as FE, SBFEM, etc. Various numerical examples, including those with the nonlinear thermal conductivity, radiative boundary condition, etc. are provided to illustrate the efficiency of proposed approaches, and impacts of the temporal FE model, constitution of shape functions, and step size, etc. are taken into account. Satisfactory results are achieved in comparison with the analytical and the ABAQUS based numerical solutions.

Improved Operating Behavior of Self-Lubricating Rolling-Sliding Contacts under High Load with Oil-Impregnated Porous Sinter Material

Resource and energy efficiency are of high importance in gearbox applications. To reduce friction and wear, an external lubricant supply like dip or injection lubrication is used to lubricate tribosystems in machine elements. This leads to the need for large lubricant volumes and elaborate sealing requirements. One potential method of minimizing the amount of lubricant and simplifying sealing in gearboxes is the self-lubrication of tribosystems using oil-impregnation of porous materials. Although well established in low-loaded journal bearings, self-lubrication of rolling-sliding contacts in gears is poorly understood. This study presents the self-lubrication method using oil-impregnated porous sinter material variants. For this, the tribosystem of gear contacts is transferred to model contacts, which are analyzed for friction and temperature behavior using a twin-disk tribometer. High-resolution surface images are used to record the surface changes. The test results show a significant increase in self-lubrication functionality of tribosystems by oil-impregnated porous sinter material and a tribo-performance comparable to injection-lubricated tribosystems of a sinter material with additionally solid lubricant added to the sinter material powder before sintering. Furthermore, the analyses highlight a significant influence of the surface finish, and in particular the surface porosity, on the overall tribosystem behavior through significantly improved friction and wear behavior transferable to gear applications.

The scandium effect in Gd-rich BMGs: How and why does this ingredient work better than others?

Scandium is commonly known as a superior modifier for most alloys and compounds, substantially improving their phase stability and physical properties, as well as glass-forming ability. A special case is rare-earth based magnetic metallic glasses, which are an unique platform for intra-elemental substitution due to the chemical affinity of the lanthanides, yttrium and scandium. The latter, used as an alloying additive and being the smallest atom among the entire family, can drastically affect structure formation and magnetism in these metallic glasses. The main issue is that its modifying role is not well understood due to scarce information on the scandium effects in such rare-earth systems. This study is focused on thermal and magnetic analysis of some popular Gd-based BMGs redesigned with minor Sc additives. Here, we consider temperature behavior of specific heat capacity and entropy functions for both amorphous and crystalline phases to estimate the scandium effect on GFA and thermal stability of the glasses. As well, we inspect magnetic and magnetocaloric properties of these BMGs to understand whether this very expensive metal can radically improve the alloy magnetism and make these materials suitable for potential applications.

Investigation of the Temperature Coefficients of Perovskite Solar Cells for Application in High-Temperature Environments.

Perovskite solar cells are actively investigated for their potential as highly efficient and cost-effective photovoltaic devices. However, a significant challenge in their practical application is enhancing their durability. Particularly, these cells are expected to be subjected to heating by sunlight in real-world operating environments. Therefore, high-temperature durability and device operation under such conditions are critical. Our study aims to improve the durability of perovskite solar cells for practical applications by examining their temperature coefficients at elevated temperatures using MA-free compositions. We assessed these coefficients and investigated their correlation with the ideality factor, revealing that carrier recombination markedly affects the temperature behavior of these cells. Our methodology involves simple J-V measurements to evaluate device degradation at high temperatures, paving the way for further research to enhance device performance in such environments.

Evaporation of Primordial Charged Black Holes: Timescale and Evolution of Thermodynamic Parameters

The evolution of primordial black holes formed during the reheating phase is revisited. For reheating temperatures in the range of 1012–1013 GeV, the initial masses are respectively of the order of 1010–108MP, where MP is the Planck mass. These newborn black holes have a small charge-to-mass ratio of the order of 10−3, a consequence of statistical fluctuations present in the plasma constituting the collapsing matter. Charged black holes can be rapidly discharged by the Schwinger mechanism, but one expects that, for very light black holes satisfying the condition M/MP<<MP/mW (mW is the mass of the heaviest standard model charged W-boson), the pair production process is probably strongly quenched. Under these conditions, these black holes evaporate until attaining extremality with final masses of about 107–105MP. Timescales to reach extremality as a function of the initial charge excess were computed, as well as the evolution of the horizon temperature and the charge-to-mass ratio. The behavior of the horizon temperature can be understood in terms of the well-known discontinuity present in the heat capacity for a critical charge-to-mass ratio Q/GM=3/2.

Residual strength and time to failure of bonded wooden lap joints at high temperatures and superimposed constant loading

ABSTRACT The study focused on the effect of high temperatures on wooden bond lines of single lap tensile shear specimens according to EN 302-1 made from beech wood at superimposed sustained mechanical loading. The quasi-duration of load (DOL) tests encompassed temperature levels of 160–232°C with specimens loaded at 30% of their mean shear strength at ambient temperature for 40 min. The investigations comprised one phenol resorcinol formaldehyde (PRF), two melamine urea formaldehyde (MUF) and three one-component polyurethane (1C-PUR) adhesives as well as solid wood reference specimens. Complementary ramp load tests were performed with specimens heated in unloaded state up to 250°C. The investigations revealed three highly differentiated adhesive DOL behaviours although showing a well comparable pure temperature-bound strength reduction effect at 200°C. PRF and one MUF showed little to no additional influence of applied load, while for two 1C-PUR brands a drastic impact on survival times and residual strength was revealed. One MUF and a special 1C-PUR forwarded results between both extremes. The investigations provide evidence that the assessment of the temperature behaviour of structural adhesives can be biased when relying exclusively on ramp load tests with specimens heated in unloaded state, and thus necessitates a superimposed load as present in realistic fire scenarios.

Droplet temperature measurement using a fiber Bragg grating

The need to measure droplets temperature with high precision in moderate or extreme environments has driven the development of advanced methods. Here, we report, for the first time, the measurement of droplet temperature using optical fiber-based temperature sensors. Specifically, a fiber Bragg grating sensor was used as a non-invasive technique to determine the temperature behavior of single micro-volumetric pendant droplets. The fiber sensor method, which provides indirect measurements, was validated by experimental and simulation data from the literature, showing good agreement. The temperature measurements rely on monitoring the vapor layer temperature near the droplet at sub-millimeter fiber-to-droplet distances and on determining a coefficient that characterizes the temperature difference between the droplet and the surrounding vapor layer at the liquid–gas interface. We calibrated the method by conducting measurements under various relative humidities and fiber-droplet contact conditions. We found that the coefficient remains constant for a specific distance regardless of the relative humidity or the droplet volume. Furthermore, we observed the minor influences that the environmental relative humidity and droplet content has on the behavior of the recorded temperatures during the short period after droplet generation.

Temperature distribution in the PGAA system: Collimator, shutter, and filter in TRIGA Mark II reactor

This article examines the impact of temperature on the steel collimator cap and the primary beam shutter. These components will be used to implement the Prompt Gamma Activation Analysis (PGAA) technique in the Moroccan TRIGA Mark-II research reactor. The steel collimator plug is essential for forming the neutron beam, while the main role of the shutter is to stop the beam when the channel is inactive. This study analyzes the effect of temperature on the collimator and shutter system, particularly focusing on the variation in maximum temperature over a month of operation with 8-h cycles per day, the behavior of temperature over 24 h, the total heat flux as a function of the length of the experimental device, the temperature distribution in mild steel (E235) and 304L stainless steel materials, and the total displacement and strain gradient as a function of temperature. All calculations were performed using COMSOL Multiphysics simulation software, based on the finite element method.

Corrosion and oxidation behaviors of CoAlTiWTa RHEA coating on Inconel 718 superalloy prepared by laser cladding

CoAlTiWTa refractory high-entropy alloy (RHEA) coating was prepared on Inconel 718 superalloy by pulsed laser cladding. Corrosion behavior in 3.5 wt% NaCl solution at room temperature and oxidation behavior at 600 ℃ of the coating were systematically investigated. The electrochemical performance, surface morphology, and corrosion and oxidation products were carefully characterized. The results show that the RHEA coating has a higher corrosion potential, smaller corrosion current, higher resistance value, and a more obvious passivation effect. Duplex-layer oxide film composed of an internal Al2O3-TiO2 layer and an external Co oxide layer is formed on the RHEA coating, improving high-temperature oxidation resistance.

Comparison of the thermofluidic behaviors of 2-m nitrogen-charged cryogenic loop heat pipe under anti-gravity and horizontal conditions

One of the main advantages of a cryogenic loop heat pipe (CLHP) is its heat transfer capability over long distances and operability under anti-gravity conditions. However, there are only a few studies on the thermal characteristics of long-distance CLHPs. It is essential to investigate the effect of a hydraulic head on CLHP performance to enhance the utilization of CLHPs in various applications. This study investigated the thermofluidic behaviors of a 2-m nitrogen CLHP with a capillary starter pump (CSP) under horizontal and anti-gravity conditions where the evaporator was 350 mm higher than the condenser. The novelty of the study is to reveal the heat transfer characteristics and operating mechanisms under anti-gravity conditions based on comparisons with experimental results under horizontal conditions. In the CLHP, a fine stainless-steel porous wick with a pore radius of 1.0 μm and permeability of 1.3 × 10−13 m2 was used for an evaporator and the CSP. The lengths of the vapor line, condenser, and liquid line were 2000, 1500, and 2000 mm, respectively. When a heat load of 4 W was applied to the CSP and evaporator, the CLHP successfully started with an initial cooling condition called a supercritical startup under anti-gravity conditions. The startup temperature behaviors were compared under horizontal and anti-gravity conditions. The thermal resistance of the CLHP with a stepped-up evaporator heat load and various CSP heat loads was evaluated for two CLHP orientations. The CLHP stably operated under evaporator heat loads of 4–24 W (horizontal) and 4–20 W (anti-gravity) for three CSP heat loads of 0, 2, and 4 W. The effect of the CLHP orientation on the thermal resistance with various CSP heat loads is discussed. This study enhances the applicability of the long-distance CLHP to various applications with a high degree of postural freedom by revealing the operating mechanism and thermal characteristics of the long-distance CLHP under anti-gravity and horizontal conditions.

Acetamide-based deep eutectic solvents as efficient electrolytes for K–MnHCFe//Zn dual-ion batteries

In this study, a cost-effective, eco-friendly deep eutectic solvent (DES), comprising acetamide, sodium perchlorate, and zinc chloride serves as an innovative electrolyte for dual ion batteries. Notably, the DES exhibits a broad electrochemical stability window, self-extinguishing behavior, and great resilience in low temperatures. The interplay between the electrolyte components is being thoroughly scrutinized, with a particular focus on the benefits of adding a co-solvent to the DES. This addition prevents unwanted reactions and zinc dendrite growth through the formation of a solid electrolyte interphase (SEI) layer, ultimately leading to enhanced coulombic efficiency and cyclic stability. The electrochemical performance of zinc ion batteries (ZIBs) using a Prussian blue analog (K–MnHCFe) as cathode is being examined in the dual-ion DES electrolyte. The device displays a discharge capacity of 76.4 mAh g−1 at 0.3 A g−1 and a maximum energy density of 111.7 Wh kg−1 at a power density of 437.5 W kg−1. Furthermore, it retains 65 % of its initial specific capacity even after 3000 cycles at 0.5 A g−1. It is noteworthy that the ZIB device with dual-ion DES operates normally in temperatures as low as −20 °C, outperforming traditional cells with aqueous electrolytes.

A study on the impact of using a subchannel resolution for modeling of large break loss of coolant accidents

The nuclear industry is investigating the feasibility of transitioning from 18- to 24-month fuel cycles because of the positive impact it would have on the operational costs for the current fleet of light-water reactors. A challenge to making this change is the increased risk of fuel fragmentation, relocation, and dispersal (FFRD) due to the known potential for ceramic fuel to pulverize into fine particles at the higher discharge burnups. Previous work has been performed by the Nuclear Energy Advanced Modeling and Simulation program to assess FFRD risk in high-burnup cores using the BISON fuel performance code and a coarse mesh thermal hydraulics (T/H) solution for a loss-of-coolant accident (LOCA) using the TRACE system T/H code. Because of the importance of the T/H solution for FFRD assessment, this study seeks to investigate the impact of using higher-fidelity subchannel techniques for modeling of the LOCA transient. CTF was used to model a subregion of a high-burnup core that was depleted by the Virtual Environment for Reactor Applications (VERA) multiphysics core simulator. Both coarse-mesh and pin-resolved models were created in CTF, and a consistent coarse-mesh TRACE model was also developed to allow for benchmarking the code results. A large-break loss-of-coolant accident (LBLOCA) reflood transient was simulated using these three models, and results were compared. Results showed some consistent differences between the CTF and TRACE coarse models, including a higher peak cladding temperature (PCT) prediction in CTF and later quenching in CTF; however, the transient clad temperature behavior was similar, and these differences are likely due to post-critical heat flux heat transfer modeling differences and minimum film boiling temperature model differences. The pin-resolved results indicate that the PCT in the lumped model is often under-predicted by as much as 70 °C and that PCT occurs at a different location than the high-power pin in the assembly. The lumped model predicts a difference of 10 °C or less between the average and hot pins in the assembly, whereas the pin-resolved model predicts a range of over 100 °C. These results indicate that higher-fidelity T/H results may have an impact on predicted core behavior during LOCA, which may be important to consider when assessing FFRD risk.

Characterisation Techniques for Bituminous Binder

Bituminous binders, often referred to as asphalt, play a pivotal role in the construction and maintenance of flexible pavements. As the demand for durable and sustainable infrastructure continues to rise, a thorough understanding of the physical and rheological properties of bituminous binders becomes imperative. This manuscript presents a comprehensive review of various mechanical tests used to assess bituminous binder properties, including penetration (Pen), softening point (SP), penetration ratio (PR), penetration index (PI), ductility tests and absolute and kinematic viscosities. These mechanical tests serve as fundamental tools for evaluating binder consistency, hardness, ductility and flow behaviour. SP and Pen measurements are employed to grade bituminous binders based on their response to temperature. Additionally, PR and PI provide valuable insights into binder performance under varying environmental conditions. Ductility tests offer critical information about a binder’s ability to elongate without breaking, a crucial factor in withstanding the stresses imposed by traffic. In parallel, the manuscript underscores the significance of understanding the rheological properties of bituminous binders. Dynamic shear rheometry (DSR) is introduced as a method for characterising complex modulus (G*), fail temperature and phase angle (δ) behaviour under different temperature and loading conditions. These tests are well established in the USA based on Strategic Highway Research Program (SHRP) specifications. Their relevance in the Indian context is discussed, with recent inclusion of rheological parameters in the Bureau of Indian Standards (BIS) specification. The manuscript highlights the role of instrumental analysis techniques, including Fourier transform infrared spectroscopy (FTIR), nuclear magnetic resonance (NMR) and scanning electron microscopy (SEM), in uncovering the molecular and microstructural aspects of bituminous binders. FTIR aids in identifying functional groups within the binder, elucidating chemical composition and aging effects, while NMR provides insights into molecular mobility and heterogeneity. SEM is instrumental in revealing the binder’s microstructure and its interaction with aggregates. In conclusion, this manuscript offers a comprehensive analysis of both mechanical and rheological testing, emphasising their significance in evaluating bituminous binder properties. It also stresses the growing importance of instrumental analysis techniques, particularly for chemically modified bitumen. The primary aim is to provide a valuable resource for researchers, engineers and practitioners in the field of civil engineering and infrastructure development.

Effect of the Core–Shell Exchange Coupling on the Approach to Magnetic Saturation in a Ferrimagnetic Nanoparticle

The generally accepted model of the magnetic structure of an iron oxide core‒shell nanoparticle includes a single-domain magnetically ordered core surrounded by a layer with a frozen spin disorder. Due to the exchange coupling between the shell and core, the spin disorder should lead to nonuniform magnetization in the core. Suppression of this inhomogeneity by an external magnetic field causes the nonlinear behavior of the magnetization as a function of the field in the region of the approach to magnetic saturation. The equation proposed to describe this effect is tested using a micromagnetic simulation. Analysis of the approach to magnetic saturation of iron oxide nanoparticles at different temperatures using this equation can be used to estimate the temperature evolution of the core‒shell coupling energy and the size of the uniformly magnetized nanoparticle core and the temperature behavior of this size.

Double honeycomb symmetry: Effective-field theory study

The double hexagonal lattice model is a new statistical model constructed by connecting two-dimensional hexagonal structured materials such as Graphene and Lie symmetries. The double hexagonal structure of this model appears in the G2 symmetry of Lie algebras. To investigate the magnetic properties of this new lattice model, an Ising-1/2 model was constructed with spin values σ = ±1. An effective-field theory (EFT) method was used with the differential operator technique to formulate the identity of the spin system, based on Callen's work. Different phase diagrams were established by varying the double-exchange interaction couplings and the super-exchange interaction coupling present in the model. The accurate results obtained by the EFT method were compared with those found by the mean-field approximation (MFA) method. The symmetry of the MFA diagrams was broken in the EFT diagrams. The critical temperature behavior was found to depend on the type of super-exchange ferromagnetism.

Temperature behavior of long-span cable-stayed bridges by using unified analysis

Varying temperatures significantly affect long-span cable-stayed bridges. However, previous studies on the temperature behavior of bridges were either limited by finite sensors, failing to capture the accurate relation between the temperature and responses, or constrained to a “divide-and-conquer” strategy, requiring considerable manual intervention. This study develops a unified approach to the investigation of thermal behaviors of cable-stayed bridges by integrating heat-transfer analysis and structural analysis based on the same refined global 3D finite element model. A navigation channel bridge of Hong Kong‒Zhuhai‒Macao Bridge is used as the testbed. First, the heat-transfer analysis is conducted based on thermal boundary conditions carefully determined from real-time ambient temperature, wind, and solar radiation, which are tailored for each surface to reflect the influence of the geometric configuration and temperature difference. Then, the detailed temperature distribution results are automatically converted to thermal loads, and thermal elements are changed to structural elements to calculate the temperature-induced responses. Results show that temperature has a significant effect on the structural responses of the bridge. The calculated temperatures and temperature-induced responses are in good agreement with their measured counterparts, verifying the effectiveness of the proposed unified approach to investigating the temperature behavior of cable-stayed bridges.

A multifunctional memristor with coexistence of NDR and RS behaviors for logic operation and somatosensory temperature sensing applications

The negative differential resistance (NDR) effect has been widely applied in logic circuits, wireless communications, and neural networks, but the study for the coexistence of NDR and resistance switching (RS) behaviors is still in the initial stage. In this work, a memristive device with an Ag/ZnOx/TiOy/indium tin oxide (ITO) structure was fabricated, and the device exhibits coexistence of RS and NDR behaviors with the change of applied voltages at air environment. Further, the stable and controllable coexistence of RS and NDR behaviors can be achieved in the memristive device under extreme environments. In addition, the multifunctional applications of the as-prepared memristor based on the coexistence of RS and NDR behaviors in logic operation and somatosensory temperature sensing were also demonstrated. Finally, based on the in-depth analysis of the experimental data and the energy band theory, the physical models of water molecule (H2O) decomposition, oxygen vacancy (Vo2+), Ag ions (Ag+), and hydroxide ions (OH–) migration were proposed, which reasonably explained the working mechanism of the coexistence of RS and NDR behaviors. Therefore, this work proves that the coexistence behavior of NDR and RS behaviors controlled by multiple factors in memristor has great application prospects for logic operation and somatosensory temperature sensing.