Thermal Expansion Displacement Research Articles

High-temperature electrical breakdown and energy storage performance of ladderphane copolymer enhanced by molecular bondage and deep trapping

The advancement of renewable energy urgently needs dielectric capacitors with high energy storage performance at elevated temperatures. The energy loss and energy storage density are the core performance of these capacitors, which are determined by the conductivity and breakdown characteristics that are significantly influenced by the parameters such as trap characteristics, free volume, thermal expansion, and polymer chains displacement. Therefore, it is imperative to establish a quantitative correlation between microscopic parameters and energy storage performance of the ladderphanes for their substantial enhancement in energy storage density presently to elucidate this mechanism and further improve the performance. In this paper, the criterion of breakdown caused by the long displacement of polymer chains under the action of electric and thermal fields was proposed. Combining charge transport, heat transfer, and polymer chains motion, a joint simulation model of conductivity-breakdown-energy storage was established. The simulation results were consistent with the experimental results of high-temperature breakdown and energy storage. It was unveiled that the aggregate structure enhances the high-temperature breakdown and energy storage capabilities of ladderphane copolymer by restraining polymer chains motion and impeding charge transitions.

Kinetic- and Strain-Energy Approaches in the Thermal Analysis of Constrained Mechanical Systems: A Comparative Study

Abstract Despite the unconstrained thermal expansion is assumed stress-free, the conventional FE approach requires formulating elastic forces, and this in turn leads to elastic stresses. A displacement-based formulation, on the other hand, can be used to address this limitation by converting the thermal energy to kinetic energy instead of strain energy. The fundamental differences between the strain- and kinetic-energy approaches are discussed. It is shown that the unconstrained thermal expansion predicted using the kinetic-energy approach is independent of the continuum constitutive model, and consequently, such a formulation can be used for both solids and fluids. The displacement (kinetic) and strain (stress) formulations are discussed to shed light on the mechanism of thermal expansion at the macroscopic level. The thermal-expansion displacement formulation (TEDF) and position-gradient multiplicative decomposition into thermal and mechanical parts are used to compute the thermal stresses due to boundary and motion constraints (BMC). TEDF implementation issues are discussed and constant matrices evaluated at a preprocessing stage after applying sweeping matrix technique to eliminate rigid-body thermal-displacement translational modes are identified. Furthermore, the softening effect due to the constitutive-model dependence on the temperature is investigated at high temperatures. Numerical results are presented to show fundamental differences between the TEDF approach that converts heat energy to kinetic energy and conventional FE approach that converts heat energy to strain energy that produces elastic stresses.

Simulation analysis of thermal shock response of piezoelectric shock wave pressure sensor

Under the influence of transient high temperatures, piezoelectric shock wave pressure sensors produce a thermal shock response that affects the accurate acquisition of the pressure signal. In order to analyse the effect of thermal shock on the measurement of piezoelectric pressure sensors, a rectangular pulse temperature of 1800 ℃ with a duration of 30 ms was applied to the surface of the sensor diaphragm by the method of thermal coupling, and the temperature distribution inside the sensor under transient thermal excitation was explored, and the thermal expansion displacement and preload change of the sensor were analysed. The results show that: the temperature rise of the piezoelectric crystal is small and does not reach the Curie point temperature, which has less influence on the material properties of the piezoelectric crystal; the thermal shock response of the piezoelectric pressure sensor is mainly caused by the thermal deformation of the pressure-sensing diaphragm, which affects the stability of the preload inside the sensor and leads to a negative signal output from the sensor. This study provides a reference for the research of thermal shock suppression methods for piezoelectric pressure sensors.

Silicon-nitride-based entrance slit design for the high-power-density monochromator in TPS 45A.

Details of the design and operational status of the silicon-nitride-based entrance slit installed in the Taiwan Photon Source (TPS) 45A beamline are given. The slit is a diamond blade edge etched onto a copper slit part, which is in thermal contact with the silicon nitride base. A stable slit opening smaller than 4 µm is achieved in TPS 45A. The beam size at the slit has a full width at half-maximum of 3 µm in the vertical direction with a power of 20 W. Additionally, a hard stop made of invar is incorporated to control the thermal expansion displacement. The slit reduces the size and increases the stability of the source of the monochromator. Consequently, a higher energy resolution and excellent beamline stability are achieved.

High-accuracy transmission and fluorescence XAFS of zinc at 10 K, 50 K, 100 K and 150 K using the hybrid technique.

The most accurate measurements of the mass attenuation coefficient for metals at low temperature for the zinc K-edge from 9.5 keV to 11.5 keV at temperatures of 10 K, 50 K, 100 K and 150 K using the hybrid technique are reported. This is the first time transition metal X-ray absorption fine structure (XAFS) has been studied using the hybrid technique and at low temperatures. This is also the first hybrid-like experiment at the Australian Synchrotron. The measured transmission and fluorescence XAFS spectra are compared and benchmarked against each other with detailed systematic analyses. A recent method for modelling self-absorption in fluorescence has been adapted and applied to a solid sample. The XAFS spectra are analysed using eFEFFIT to provide a robust measurement of the evolution of nanostructure, including such properties as net thermal expansion and mean-square relative displacement. This work investigates crystal dynamics, nanostructural evolution and the results of using the Debye and Einstein models to determine atomic positions. Accuracies achieved, when compared with the literature, exceed those achieved by both relative and differential XAFS, and represent a state-of-the-art for future structural investigations. Bond length uncertainties are of the order of 20-40 fm.

Mechanical behavior and fatigue failure analysis of standing seam aluminum alloy roof system under temperature effect

Standing seam metal roof systems with universal high-strength, lightweight, and thin-walled characteristics have been applied worldwide in massive large-span landmark buildings, such as gymnasiums, airports, and railway stations. The existing research focuses on the wind uplift design, but there are few studies on the mechanical properties under the temperature effect. In this paper, the temperature effect of the standing seam aluminum alloy roof (SSAAR) system was studied. To be familiar with the mechanical and deformation characteristics of the SSAAR system, the static loading tests under different temperatures and boundary constraints were carried out. Two specimens, one with anti-wind clips and the other without anti-wind clips, were further tested under cyclic loading to evaluate and quantify the fatigue failure characteristics of the roof system. The testing results indicate that the stress concentration, thermal expansion displacement, and wear of the SSAAR system are significant. The slab rib stress is the largest, accounting for about 83.7% of the yield strength, followed by the slab surface stress, and the slab bottom stress is the smallest. The horizontal displacement is greater than the vertical displacement, and the maximum is about 20.42 mm. The boundary constraint mainly affects the support stress and vertical displacement to increase by 47.2% and 79.3% respectively. The anti-wind clips mainly increase the wear thickness of the roof slab, which is increased by 67.5%.

Thermal properties of TiNiSn and VFeSb half-Heusler thermoelectrics from synchrotron x-ray powder diffraction

Half-Heusler (HH) alloys are an important class of thermoelectric materials that combine promising performance with good engineering properties. This manuscript reports a variable temperature synchrotron x-ray diffraction study of several TiNiSn- and VFeSb-based HH alloys. A Debye model was found to capture the main trends in thermal expansion and atomic displacement parameters. The linear thermal expansion coefficient α(T) of the TiNiSn-based samples was found to be independent of alloying or presence of Cu interstitials with α av = 10.1 × 10−6 K−1 between 400 and 848 K. The α(T) of VFeSb and TiNiSn are well-matched, but NbFeSb has a reduced α av = 8.9 × 10−6 K−1, caused by a stiffer lattice structure. This is confirmed by analysis of the Debye temperatures, which indicate significantly larger bond force constants for all atomic sites in NbFeSb. This work also reveals substantial amounts of Fe interstitials in VFeSb, whilst these are absent for NbFeSb. The Fe interstitials are linked to low thermal conductivities, but also reduce the bandgap and lower the onset of thermal bipolar transport.

Analysis of tissue displacement induced by high-intensity focused ultrasound exposure for coagulation monitoring

Decorrelation between two ultrasound images has been investigated for real-time monitoring of lesion formation caused by high-intensity focused ultrasound (HIFU) exposure. However, the origin of the decorrelation remains unclear. In this study, the distributions of tissue displacement were obtained from numerical simulation and experimental data, and the latter was compared to the decorrelation map. The results show the possibility that decorrelation of ultrasonic signals can be explained by thermal expansion and apparent displacement caused by the temperature dependence of the speed of sound.

Neutronics analysis for MSR cell with different fuel salt channel geometries

The neutronic properties of molten salt reactors (MSRs) differ from those of traditional solid fuel reactors owing to their nuclear fuel particularity. Based on the Monte-Carlo N particle transport code, the effects of the size and shape of the fuel salt channel on the neutron physics of an MSR cell are investigated systematically in this study. The results show that the infinite multiplication factor (k∞) first increases and then decreases with the change in the graphite cell size under certain fuel volume fraction (FVF) conditions. For the same FVF and average chord length, when the average chord length is relatively small, the k∞ values for different fuel salt channel shapes agree well. When the average chord length is relatively large, the k∞ values for different fuel salt channel shapes differ significantly. In addition, some examples of practical applications of this study are presented, including cell selection for the core and thermal expansion displacement analysis of the cell.

An Analysis on the Thermal Expansion Displacement of Concrete Bridge by 3D Laser Scanning Technology

Bridges are one of the most critical transportation structures related to a country’s national life, and usually main arteries of national economic development. In the past, the bridge construction only pursues the speed, along with the time passage, the bridge collapse accident often can causes the human life casualties. The concrete bridge materials behavior and the thermal expansion can cause the deformation. Therefore, in this paper, as temperature differences, analysis of the concrete bridge deformation by the 3D laser scanning Technology.

Study on heat transfer characteristics and thermal error suppression method of cylindrical giant magnetostrictive actuator for ball screw preload

Based on the structure analysis and the working principle of cylindrical giant magnetostricve actuator (CGMA) for ball screw preload, a thermal error suppression method using oil cooling system to control the temperature is proposed. Firstly, the heat transfer model and thermal circuit model of CGMA are established; next, the steady-state temperature model and the thermal expansion displacement model of cylindrical giant magnetostrictive material (CGMM) are obtained according to the heat-transfer rules and loop analysis method in circuit analysis; finally, the design parameters of the oil-cooling temperature control system are determined by combining thermal circuit model analysis with finite element simulation analysis. Such optimization method saves a lot of computation and provides a simple way for the design of oil cooling structure. In addition, a test platform for the CGMA is established. The experimental results indicate that the measured temperatures are in good agreement with the simulation results under forced oil cooling, and the relative error is less than 5%, which proves the rationality of the temperature control system. Moreover, the output accuracy and stability of the CGMA is significantly improved with proposed oil cooling method, which further confirms the thermal error suppression method is effective. As a result, this study provides a basis for the application of CGMA in the precise adjustment of double-nut ball screw preload.

A Full‐Spectrum Bedrock Thermal Expansion Model and Its Impact on the Global Positioning System Height Time Series

AbstractBedrock thermal expansion includes prominent seasonal (annual and semiannual) terms and intricate nonseasonal variations (high‐frequency change and transient signals). However, the nonseasonal variations are usually ignored in geodetic studies due to defects in analytical solutions. In this study, we calculate the full‐spectrum bedrock thermal expansion displacement using the skin temperature from the ERA5 reanalysis data set. The results show that the nonseasonal variations of bedrock thermal expansion, with a range (maximum minus minimum) reaching 3 mm in some regions, can be observed by geodetic instruments and thus cannot be ignored. Moreover, the mean power of the nonseasonal variations accounts for 20% of the entire thermal expansion. Without considering the influence of the nonseasonal variations, this “noise” would remain in the original observations and contaminate related geophysical inversions.

Multi-Physical Coupling Field Study of 500 kV GIL: Simulation, Characteristics, and Analysis

With the construction of a large number of hydropower stations, transmission lines crossing a river and urban utility tunnels, gas insulated transmission line (GIL) has been applied widely due to its large transmission capacity, low environmental impact and high reliability. Accurate modelling of physical quantities and their characteristics of GIL provides a theoretical basis for its design and operation, which is of great significance to ensure the safety and reliability of GIL operation. The mathematical model and their relationship of GIL multi-physical fields are analyzed at first, upon which simulation model of GIL is built. Secondly, multi-physical coupling field model of electric, magnetic, thermal, fluid and stress field for GIL is studied, while simulation results are basically in consistent with experimental data to verify effectiveness of the model. Thirdly, distribution of multi-physical fields and their relationship are simulated and analyzed, while proximity effect, edge effect and compression factor of GIL multi-physical field are discussed. The results show that the radial temperature inside GIL is higher at the top, lower at the bottom, leading to uneven distribution of thermal expansion displacement, while the axial temperature distribution is basically uniform, which falls firstly and then rises near basin insulator thus results in edge effect. Proximity effect leads to asymmetric distribution and a slight increase of temperature inside GIL as well as a dramatic increase of air velocity around GIL. In addition, when ambient temperature is lower than -5 °C, the compression factor is much lower than 1 and the effect of compression factor should be considered in simulation.

Significant differences in NaNbO3 ceramics fabricated using Nb2O5 precursors with various crystal structures

NaNbO3 (NN)-based solid solutions show potential applications in energy storage capacitors, strain actuators, and electrocaloric cooling devices. However, NN ceramics with distinct structures, which are prepared using various Nb2O5 precursors, have not been studied. In this work, two types of Nb2O5 precursors were used, including coexisting orthorhombic and monoclinic phases (denoted as OM), and single orthorhombic phase (denoted as O). Phase structure, grain morphology, sintering characteristics, ferroelectric performance, dielectric properties, and thermal-expansion properties were systematically investigated. Rietveld refinement of XRD data revealed that synthesized and sintered samples showed different phase structures. The content of ferroelectric phase (Q phase, space group P21ma) was 82.7% in synthesized NN-OM, whereas it was only 73.2% in synthesized NN-O; it was 33.8% in sintered NN-OM, while it was 18.6% in sintered NN-O. Raman spectra verified that the Q phase in NN-OM was more than that in NN-O. Curie temperature (Tc) of NN-OM was 363 °C, whereas Tc of NN-O was only 352 °C. Furthermore, compared with NN-O, NN-OM showed an inhomogeneous grain size distribution, lower optimum sintering temperature, higher phase transition temperature, stronger ferroelectric performance, and larger thermal-expansion displacement. Therefore, crystal structure of Nb2O5 has a great influence on the structure and performances of NN ceramics.

On thermal expansion behavior of invar alloy fabricated by modulated laser powder bed fusion

In the present research, structural analyses are conducted on Invar (64% Fe-36% Ni) samples manufactured by modulated laser powder bed fusion (LPBF) under different laser power regimes. Within the selected process window, the results obtained from X-ray computed tomography analysis indicate that the relative density of as-built samples increases with an increase in laser power. In addition, it is observed that irregular-shaped pores with the longest axis normal to the building direction are significantly reduced with increasing the laser power. Microstructural investigation suggests that with increasing the laser power, a transformation from conduction to transition and keyhole modes occurs. In X-ray diffraction patterns of the as-built samples, only fcc γ-phase is detected and no reflection of bcc α-phase is found. Texture measurements show that the intensity of 〈110〉 crystallographic orientation along the building direction of the as-built samples increases with increasing laser power. Coefficient of thermal expansion of the as-built samples is very low and comparable to that of conventionally manufactured Invar alloy. Furthermore, as-built samples fabricated at lowest (250 W) and highest (400 W) laser powers exhibit the lowest and highest thermal expansion displacement, respectively. Finally, the thermal expansion behavior and its correlation with structural integrity and texture are discussed.

Using the Unit Force Method to Analyze Thrust Acting on Anchor Blocks Caused by Thermal Expansion Displacement of X80 Tunnel Pipelines

To restrict the thermal expansion displacement of X80 tunnel pipelines, anchor blocks are commonly designed and installed at entrances and exits of tunnels, which makes the anchor block design one of the most important issues. As well known, the key step for anchor block design is to calculate the thrust acting on the anchor block caused by the thermal expansion displacement. In this paper, an analysis method of the thrust is proposed, considering the effects of the vertical earth pressure, transverse horizontal earth pressure, internal pressure, temperature variation, and pipeline–soil friction. Using the condition of deformation compatibility and the hypothesis of stagnation point, the axial force of tunnel pipelines is derived by the unit force method. By combining the compatibility condition between the transition segment length of anchored side pipelines and the displacement of anchor blocks, the thrust acting on anchor block is derived. Using the analytical method and finite-element software, the results of thrust acting on anchor block of the X80 tunnel pipeline for a specific gas pipeline project are calculated and compared. The results show that the analytical results agree well with those determined by finite-element software, and the maximum relative error is only 2.9%. The parameter analysis of the thrust and displacement of anchor blocks is investigated, including the buried depth for anchored pipeline side, the pipeline–soil friction coefficient, the volume of anchor block, the block–soil friction coefficient, the soil reaction coefficient, and the buried depth of anchor block.

Study on the Thermal Expansion Displacement during Spot Welding Depending on the Multi-Physical Coupling Finite Element Model

An incremental and thermal electro-mechanical coupled finite element model has been presented in this study for predicting spot nugget size, gap between workpieces, and thermal expansion displacement during spot welding process. Approximate temperature dependent material properties, including physical and mechanical properties, have been considered. The spot nugget shape and the thermal expansion displacement were obtained by simulation. The solutions showed that the displacement of workpieces was directly related to the quality of solder joints and can be as a monitoring parameter of spot weld quality. These calculations provide a theoretical reference for nugget quality monitoring and forecasting by electrode expansion displacements.

초고속기용 열박음 로터 제작을 위한 로터의 치수에 따른 가열온도의 해석적 예측

This paper deals with shrink fit analysis of rotor by 2D cross-section, 2D axis-symmetry, and 3D FEM model. And this paper presents 2nd order approximation function of thermal expansion displacement by design variables (shape dimension, heating temperature, sleeve length, interference etc.), table of orthogonal array and RSM(response surface methodology). The possibility of the rotor with shrink fit is evaluated by thermal expansion displacement. If thermal expansion displacement is larger than interference, shrink fit enable to make the rotor. 2D axis-symmetry model and 3D model are more reasonable than 2D cross-section model, because stress and strain is different along length of shaft.

Negative thermal expansion ofReO3: Neutron diffraction experiments and dynamical lattice calculations

We have investigated the temperature variation of the unit-cell volume of ${\text{ReO}}_{3}$ by neutron diffraction. The lattice parameter and the unit-cell volume decrease continuously as the temperature is increased from $T=2\text{ }\text{K}$ to about $T=200\text{ }\text{K}$. After exhibiting minima at about 200 K they increase with increasing temperature linearly up to about 305 K, the maximum temperature investigated during the present experiment. We attribute the negative thermal expansion of ${\text{ReO}}_{3}$ to be the results of rigid antiphase rotations of the neighboring ${\text{ReO}}_{6}$ octahedra. We have done model lattice dynamical calculation of phonon dispersions, thermal expansion, and atomic displacement parameters in ${\text{ReO}}_{3}$. The results of these calculations are in agreement with the experimental results.

Molecular Dynamics Simulations of Graphite at High Temperatures

Graphite, a key structural and moderator material in the proposed Generation IV roadmap, is expected to experience irradiation at temperatures up to 1800 K. In this study, a molecular dynamics (MD) code is developed for the purpose of performing atomistic simulations of high-temperature graphite. The MD computations are benchmarked against thermal expansion and mean-squared displacement data, and modifications to the potential energy function are devised as needed to fit experimental measurements. Graphite-specific alterations include a plane-by-plane center-of-mass velocity correction, anisotropy in the potential energy cutoff function, and temperature-dependent parameterization of the interatomic potential. The refined MD model is then employed to investigate the threshold displacement energy at temperatures of 300 and 1800 K. It was found that the threshold displacement energy depends strongly on the knock-on direction, yet the angle-averaged threshold energy exhibits relatively little variation with temperature.