Thermal Expansion Effects Research Articles

Influence of swift heavy ion irradiations on temperature dependent phononic behavior of epitaxial LaNiO3 thin film

The effects of Ag15+ (200 MeV) swift heavy ion irradiations on the structural and phononic properties of epitaxial LaNiO3 (LNO) thin film have been investigated using high resolution x-ray diffraction and Raman spectroscopy. After irradiation, the decrease in the out-of-plane lattice parameter of LNO toward its bulk value indicates the relaxation of epitaxial strain. The temperature dependency of phononic response for different ion irradiation doses was studied by performing the Raman measurements in a temperature range of 80−300 K. For pristine as well as irradiated samples of LNO, the observed phononic modes A1g and Eg shows softening with an increment in the temperature. The temperature coefficient of both modes varies with ion fluence. For the A1g mode, temperature coefficient increases from −0.087 cm−1 K−1 for pristine to −0.092 cm−1 K−1 for a maximum ion fluence of 1012 ions/cm2, while for the Eg mode, it decreases from −0.022 cm−1 K−1 for pristine to −0.015 cm−1 K−1 for 1012 ions/cm2. Raman frequency shift for both the modes shows non-linear behavior with temperature. This temperature dependent behavior was quantitatively analyzed by using a model which suggests that Raman shifts of the A1g mode emerged predominantly due to four phonon processes whereas, for the Eg mode, major contribution came from the thermal expansion effect. Ion irradiation did not change the dominating mechanism resulting in these temperature dependent Raman shifts, although the relative contribution of different processes was altered with ion fluence.

Spatial and temporal changes in physical properties of epoxy during curing and their effects on the residual stresses and properties of cured epoxy and composites

This study presents modeling and analyses of epoxy curing incorporating gradual changes in the thermal and mechanical properties of epoxy due to the cross-linking process. The model includes an exothermic process from the cross-linking, heat conduction across the specimen, and deformations of the specimen during curing. The study examines the influence of volumetric changes from the thermal expansion and shrinkage effects and gradual changes in the thermal and viscoelastic properties of epoxy on the deformation of the epoxy and the formation of stresses. The effects of curing temperatures and pressure on the formation of stress during curing and residual stress after complete curing are also investigated. The temporal and spatial changes in the physical properties of epoxy during curing affect the elastic modulus of the cured epoxy specimens. Furthermore, this study also investigates the existence of fiber reinforcements on the curing process of unidirectional fiber composites comprising carbon fibers in an epoxy matrix. A unit-cell model is generated and used to examine the formation of residual stresses in the composites and their influences on the mechanical properties of the composites.

Stress fields around magma chambers influenced by elastic thermo-mechanical deformation: implications for forecasting chamber failure

Defining the conditions that lead to the rupture of a magma chamber is essential to forecast eruptions. So far, models simulating magma chamber dynamics have neglected the effects of elastic thermal expansion in the host rocks surrounding a new injection of magma, focusing instead primarily on elastic-plastic deformation and more recently, on visco-elastic deformation. Here we fill this gap by building a suite of elastic thermo-mechanical models to determine the stress field around a variably heated crustal magma chamber. We first consider linear elastic mechanical models with only the effect of magma pressure. We then present purely thermal models simulating heat distribution around a heated chamber. Finally, we present coupled linear elastic thermo-mechanical models that highlight the influence of temperature on the distribution of crustal stresses. Results show that thermal expansion–induced stresses generate two competing consequences: (1) they increase the level of shear stress around the magma chamber and (2) they partially suppress the level of tensile stress generated by the magmatic pressure. These competing effects influence the short-timescale conditions required for the failure of immature magmatic systems and hence the nucleation of dikes which may ultimately feed eruptions during unrest. Therefore, soon after a new magmatic recharge event, the contribution of temperature increase in the host rocks, following the new influx of magma into a crustal magma chamber, should be considered.

Investigation on Anomalous Thermal Quenching of Mn4+ Luminescence in A2XF6:Mn4+

Studying luminescence properties of phosphor materials is not only of scientific interest, but also technological importance. Here, we investigate luminescence intensity as a function of temperature for Mn4+-activated fluoride and oxide phosphors. A recent study suggested that an anomalous increase in Mn4+ luminescence intensity (I PL) with increasing lattice temperature (T) in various fluoride phosphors is likely a pitfall caused by a diminishment in the optical path lengths of the spectrofluorometer stemming from lattice thermal expansion. We show that such anomalous enhancement of I PL is due to the increased phonon number that makes it possible to gain the parity and spin-forbidden 2 E g → 4 A 2g transitions rather than an extrinsic effect of lattice thermal expansion. The temperature dependence of the zero-phonon line emission intensity I ZPL may be a good indicator for deciding whether an observed anomaly of I PL is due to an intrinsic or an extrinsic effect because its intensity should in principle not be dependent on T. The experimental data on the Rb2GeF6:Mn4+ fluoride and Cs2WO2F4:Mn4+ oxyfluoride phosphors are presented as a direct verification of this. A discussion is also given on the 2 E g → 4 A 2g transition properties in connection with the inelastic light scattering spectroscopy.

In-situ TEM Investigation of Solid Phase Transformations and Reactions

In this paper, an example of phase analysis during annealing is presented using in-situ TEM. The example is demonstrated on amorphous Cu-Mn/C thin films focusing on phase identification in a multicomponent system. The transient states following the crystallization of the amorphous Cu-Mn alloy and the reaction with the C substrate were analyzed by evaluating the diffraction patterns recorded at different temperatures. The camera constant was calibrated using the internal standard method. The change in composition of the Cu(Mn) solid solution was calculated by separating the effect of thermal expansion and solute concentration. Identification of the forming phases was aided by analyzing and comparing the probability of formation of all phases in the Cu-Mn-C-O system. After the crystallization of amorphous Cu-Mn alloy into Cu(Mn) and α-Mn-based solid solutions, the formation of the following carbide phases was observed: Mn23C6, Mn5C2 and Mn7C3.

Precise numerical study on the behaviour of gassy marine soils subjected to thermal and mechanical loadings

Gassy soils are widely distributed in river deltas, coastal and marine sediments. The discrete bubbles, commonly formed in gassy soil, are sensitive to temperature and pressure variations and contribute to the changes in soil properties, e.g. compressibility and permeability. This paper develops a precise model, considering the effects of gas bubble thermal expansion, saturation degree (S) and distance from the soil to water surface (H), to investigate the behaviour of gassy marine soils. The expansion and compression of bubbles are introduced into a new derived non-isothermal seepage equation. With the aid of Taylor series expansion and integral transform, such problems are solved by a recently developed precise integration method (PIM), which proves to be remarkably efficient and several orders more precise for quasi-static problem of porous media than conventional numerical approaches. Typical examples are performed to examine the effects of bubble expansion, S and H on the gassy soils behaviour. The bubble thermal expansion induces remarkable excess pore pressure and increase the displacement amplitude, which is enhanced by larger H or lower S. Under mechanical loading, instantaneous displacement decreases with S and H, and a S-H critical line is proposed to assess this effect, which is conducive to engineering design.

Quantification of Performance Variation and Crack Evolution of Bond-Wire Interconnects Under Harsh Temperature Environments by S-Parameter Analysis

Electrical interconnects play important roles in both the performance and reliability of integrated circuits. As the operating frequency has increased and products have been exposed to harsh environments such as temperature extremes and thermal cycling, it has become essential to quantify the thermal effects on the reliability of such circuits. In particular, the effects on the signal transmission performance of the interconnects and the evolution of cracks caused by thermo-mechanical stresses need to be investigated. This study proposes that both research goals can be accomplished by S-parameter analysis alone. First, the performance variation was experimentally quantified by in situ measurements of S21 (an indicator of signal transmission performance) on bond-wire test vehicles at static temperatures between -60 °C and 120 °C. An impedance model of the interconnect was developed focusing on thermal expansion effects and it predicted the performance variation of the interconnect successfully at the given temperatures. Second, the results of ex situ measurements of S11 (an indicator of return signal) obtained using a test vehicle under thermal cycling were compared with scanning electron microscopy images of crack propagation in the interconnect. In the crack initiation phase, a resonance peak occurred on the S-parameter pattern and the peak moved toward lower frequencies as the crack propagated until failure. SPICE simulations using a suggested impedance model of the cracked interconnect confirmed the experimental results. In addition, this study demonstrates that monitoring the resonant frequency in the S-parameter pattern as a prognostic factor can predict the initiation and evolution of cracks earlier and is more sensitive than the conventional dc resistance measurement method.

Dynamic length metrology (DLM) for accurate dimensional measurements in a production environment by continuous determination and compensation of thermal expansion effects in turning steel

This work concerns the accurate dimensional measurement of metal parts directly in a production environment. Applying an approach with the simultaneous measurement of part dimension and temperature over time (dynamically) followed by modeling of the thermo-mechanical effects, the corrected length at 20 °C and its measurement uncertainty can be predicted. This paper describes a test campaign where the local diameter of a 40 mm cylindrical steel workpiece cooling down from an initial surface temperature after turning of 27 °C to an ambient temperature of 21 °C was predicted after 10 min with a systematic error of 0.5 µm and an expanded uncertainty (k = 2) of 0.9 µm.

Strong anharmonicity in tin monosulfide evidenced by local distortion, high-energy optical phonons, and anharmonic potential

Recently, SnSe has been found to possess a remarkable thermoelectric performance. As an isostructural compound to SnSe, SnS contains a more environmentally compatible and earth abundant element, which enables SnS a promising thermoelectric material for commercial application. In this work, we have performed systematic studies of the crystal structures and the lattice vibrations by means of neutron total scattering, Raman scattering measurements, and first-principle calculations. A structural transition has been observed by both temperature dependent neutron diffraction and pressure dependent Raman scattering. The lattice anharmonicity has been revealed by the local distortion induced by the Sn $5{s}^{2}$ lone pair and is also evidenced from the temperature dependent atomic displacement parameter of the Sn atom. By separating the intrinsic anharmonicity and lattice thermal expansion effects, we found that the former plays the primary role in the softening of the Raman active modes. Such anharmonicity has also been observed experimentally by the linewidth broadening of the high-energy optical modes and confirmed by frozen phonon calculations. Furthermore, our frozen phonon calculation reveals the presence of the quartic anharmonicity potential of those high-energy optical modes vibrating along the $b$ axis. Our data will contribute to a better understanding of the thermal conduction in SnS, which will be beneficial for the enhancement of the thermoelectric performance of this material.

Development of a membrane reactor with a closed-end silica membrane for nuclear-heated hydrogen production

Hydrogen production from nuclear energy has attracted considerable interest as a clean energy solution to address the challenges of climate change and environmental sustainability. With respect to the large-scale and economical production of hydrogen using nuclear energy, the thermochemical water-splitting iodine-sulfur (IS) process is a promising method. The IS process uses sulfur and iodine compounds to decompose water into its elemental constituents, hydrogen and oxygen, by using three coupled chemical reactions: the Bunsen reaction; sulfuric acid decomposition; and hydrogen iodide (HI) decomposition. The decomposition of HI is the efficiency-determining step of the process. In this work, a membrane reactor with a silica membrane closed on one end was designed, and its potential for hydrogen production from HI decomposition was explored. In the reactor-module design, only one end of the membrane tube was fixed, while the closed-end of the tube was freely suspended to avoid thermal expansion effects. The closed-end silica membranes were prepared for the first time by a counter-diffusion chemical vapor deposition of hexyltrimethoxysilane. In application, HI conversion of greater than 0.60 was achieved at a decomposition temperature of 400 °C, which is three times greater than the equilibrium conversion (0.20). Thus, the membrane reactor with closed-end silica membrane was shown to produce a successful equilibrium shift in the production of hydrogen via HI decomposition in the thermochemical IS process.

A study of physical effects in magnetic-phase-transition materials

<p indent=0mm>Magnetic-phase-transition materials possess abundant physical properties and exhibit magnetocaloric, magnetostrictive, elastocaloric, and negative thermal expansion effects under magnetic, stress or temperature fields. They show promising applications in many fields, including refrigeration, sensor, and energy conversion. As a new class of functional magnetic materials, research fields and contents based on the magnetic-phase-transition materials are becoming enriched. In this paper, we first introduce the phase transition types of magnetic materials and present some emphatic descriptions of the first-order magnetic-phase-transition materials. Thereafter, we review recent research progress on the related effects of the first-order magnetic-phase-transition materials driven by magnetic, stress, and temperature fields.

Modeling and characterization for straight twisted polymer fiber actuators in blocked torsion: effect of radial thermal expansion

This paper discusses a new model and experimental characterization for thermal responses of straight twisted polymer fiber (TPF) actuators in blocked torsion. The proposed model is derived from combining the fiber stiffness matrix with Shafer’s model of free torsion. The derived model predicts that the blocking torque increases as the initial twist increases. Although it is not widely recognized, the tension of a straight TPF decreases as the initial torsion increases, and this paper explains this fact. The proposed model predicts the decrease in tension by using Shafer’s kinematic model that considers the effect of radial thermal expansion. Experimental characterization and model verification are performed using nylon 6 (polyamide 6) fiber samples with ten different initial twists, ranging from weak to strong. The results indicate that as the initial twist increases, the torque increases and the tension decreases. The tension fluctuates with respect to time. The experimental results show that the shear modulus increases as the initial twist increases. The predictions of the proposed model are reasonably consistent with the experimental thermal responses of straight TPFs in blocked torsion when the constants obtained by experimental characterization are used.

Dual‐Stimuli‐Responsive Photoluminescence of Enantiomeric Two‐Dimensional Lead Halide Perovskites

Abstract2D hybrid organic–inorganic perovskites (HOIPs) are highly responsive to external stimuli and therefore have application potential as sensing materials. Though their optical properties upon singular thermal or pressure stimulation have been recently investigated, their dual‐stimuli‐responsive behaviors have not yet been explored. Here, the dual‐stimuli‐responsive luminescence of a pair of new enantiomeric 2D Dion–Jacobson HOIPs, R+[(4‐aminophenyl)ethylamine]PbI4 and S‐[(4‐aminophenyl)ethylamine]PbI4, is reported. The photoluminescence results show that their 485 nm emissions can be red‐shifted by ≈6 nm upon heating, and further increased to 529 nm under pressure. Such dual‐stimuli‐responsive emissions expand their Commission Internationale de L'Eclairage coordinates successively from (0.140, 0.272) to (0.283, 0.473). Detailed structural analysis and first principles calculations reveal that the temperature‐ and pressure‐responsive behaviors arise from the predominant electron–phonon interactions over thermal expansion effect and pressure‐induced in‐plane PbI bond contraction, respectively. The findings open up a new pathway to successively tune the optical emission of 2D HOIPs via a dual‐stimuli‐responsive approach.

Effect of thermal expansion on thermal contact resistance prediction based on the dual-iterative thermal–mechanical coupling method

This study investigates the effect of thermal expansion on thermal contact resistance prediction, proposing a dual-iterative coupling method (DICM). The contact surfaces in the simulation model are reconstructed based on either the actual measured topography or the hypothetical topography, and a mathematical formulation for numerically predicting the thermal contact resistance (TCR) is established. The DICM includes four steps: first, mechanical analysis is conducted based on the ideal single point contact condition, according to the elastic–plastic constitutive equations. Second, heat transfer analysis is carried out based on the deformed geometry originating from the prior mechanical analysis. Third, another step of mechanical analysis is implemented to consider the effect of thermal expansion with the temperature distribution determined in the second step. Fourth, another step of heat transfer analysis is carried out based on the deformed geometry originating from the second-step mechanical analysis. The conventional prediction method only contains the first and second steps, and is known as the single sequential coupling method (SSCM). The TCRs of two engineering examples are predicted using both DICM and SSIM. The results show that the mechanical–thermal-mechanical–thermal dual-iterative coupling method, i.e., DICM, should be recommended for simulating contact pairs with axisymmetric geometries, while SSCM is suggested for contact pairs with non-axisymmetric geometry.

Effects of thermal expansion and degeneracy on ambipolar carrier mobility of non-peripherally hexyl-substituted phthalocyanine

The origin of the negative temperature dependence of carrier mobility in a crystal phase of 1,4,8,11,15,18,22,25-octahexylphthalocyanine was studied by utilizing a charge transport simulation based on Marcus theory and density functional theory. In order to understand the unique negative temperature dependence of carrier mobility, the theoretical calculation was carried out by taking the thermal expansion of the lattice parameters into consideration. The calculated hole mobility exhibited the similar temperature dependence as the experimental results. In the electron mobility calculation, the negative temperature dependence could be simulated by considering the degeneracy of lowest unoccupied molecular orbitals as well as the thermal expansion.

Cold compression deformation method for reducing residual stress and uniformizing micro-property in ferrite steel

To reduce internal residual stress and homogenize micro-property of hot-rolled ferrite steel, the cold compression deformation method with small reduction rate has been performed in the hot-rolled samples, and X-ray diffraction and nanoindentation test have been used to detect the residual stress and micro-property. The samples with deformation rate of 0–5.59% or annealing at 550 °C are analyzed. The results show that, due to the coupling effect of thermal expansion and cold contraction and the volume expansion of microstructural transformation from austenite to ferrite, compressive residual stress was found inside the hot-rolled samples. With the increase in cold compression deformation, the dislocation density increased and the microhardness increased gradually, and there is no obvious rule for the change of mean nano-hardness in micro-zone for the center of samples. However, the uniformity of nano-hardness in the micro-zone increased first and then decreased, and the value of residual stress has obvious corresponding relationship with the uniformity of micro-zone property. The cold compression deformation with appropriate reduction rate can reduce residual stress and improve nano-hardness uniformity of the hot-rolled samples, but more deformation (such as reduction rate e = 5.59%) makes residual stress increase and makes uniformity of nano-hardness deteriorate.

Turbulence topology evolution in weakly turbulent premixed flames

In turbulent premixed flames, not only the isotropy of velocity fluctuations is altered by the thermal expansion effect but also the dissipative structure of the turbulent flow field and the flow topology are also deeply influenced by the flame. Considering the joint probability density function of the second and third invariants of the velocity gradient tensor (VGT)—or its traceless counterpart—is a classical way to deduce the topology of turbulent flows at these smallest scales. These quantities are analyzed by considering direct numerical simulation databases of premixed flame kernel growth in homogeneous isotropic turbulence. Two conditions of turbulence–combustion interaction are considered, which correspond to two distinct values of the Bray number. The analysis of the VGT shows that the propagating premixed flame and its associated density variations significantly modify the turbulence structure and flow topology. To understand this behavior as the flow interacts with the flame front, Lagrangian dynamics of the VGT and its invariants are studied by considering the conditional mean rate of change vectors. Special emphasis is thus placed on the Lagrangian evolution equations of these invariants. To the best of authors' knowledge, this is first time that such budgets are scrutinized under premixed combustion conditions. The pressure Hessian contribution to the VGT invariant transport equations is shown to be one of the leading-order terms in this evolution, making it critically important to the flow dynamics and turbulence structure.

Deep potential generation scheme and simulation protocol for the Li10GeP2S12-type superionic conductors.

Solid-state electrolyte materials with superior lithium ionic conductivities are vital to the next-generation Li-ion batteries. Molecular dynamics could provide atomic scale information to understand the diffusion process of Li-ion in these superionic conductor materials. Here, we implement the deep potential generator to set up an efficient protocol to automatically generate interatomic potentials for Li10GeP2S12-type solid-state electrolyte materials (Li10GeP2S12, Li10SiP2S12, and Li10SnP2S12). The reliability and accuracy of the fast interatomic potentials are validated. With the potentials, we extend the simulation of the diffusion process to a wide temperature range (300 K-1000 K) and systems with large size (∼1000 atoms). Important technical aspects such as the statistical error and size effect are carefully investigated, and benchmark tests including the effect of density functional, thermal expansion, and configurational disorder are performed. The computed data that consider these factors agree well with the experimental results, and we find that the three structures show different behaviors with respect to configurational disorder. Our work paves the way for further research on computation screening of solid-state electrolyte materials.

Optimization of 25-bar truss structure with the consideration of thermal expansion

This paper presents the change in the optimal cross-sectional areas of 25-bar truss structure due to thermal expansion. The 25-bar spatial truss is commonly used in structural engineering as a benchmark for structural optimization. Previous studies used different optimization methods to compute the optimal cross-sectional areas of the truss structures related to the minimal weight of each bar element. However, most of the previous studies conducted the optimization under mechanical load only and reported almost the same optimal areas and minimum weight with slight variations depending on the method used. However, very little has been done on the structural optimization with the consideration of thermal expansion. This study aimed to investigate the effect of thermal expansion in structural optimization and conducted optimization of this structure under the thermal load and the same mechanical load case with the previous studies. The difference in the optimal areas between with and without thermal expansion is analysed through optimization of both cases using MATLAB Optimization Toolbox. The optimization method used is fmincon with Sequential Quadratic Programming (SQP) . The result shows both an increase and decrease in optimal cross-sectional areas. The optimal weight of the structure increases by 12.26% at the surrounding temperature of 30°C. Therefore, this study highlights the needs of consideration of thermal load in optimizing the cross-sectional areas of the structure for minimum weight and this is particularly of important consideration in designing the truss structures in tropical climate. One of the limitations of this study that the SQP may not be appropriate for large structure and hence the robustness of the method should be tested with more variable.

Linear creep of bonded FRP-strengthened metallic structures at warm service temperatures

Ambient cured epoxy adhesive is widely used for bonding fibre reinforced polymer (FRP) plates to metallic structures. The present paper examines a typical strengthening adhesive to investigate the effect of adhesive thermo-viscoelasticity. The response of the adhesive was determined using a series of tests using the multi-frequency scanning mode of a dynamic mechanical analyser (DMA). The thermo-mechanical properties of the adhesive were then characterised using time–temperature superposition parameters and a Prony series representation for generalised Maxwell creep. The adhesive response was in turn used within two finite element (FE) models to examine the effect of creep in the adhesive at warm temperatures (<100 °C) on the performance of a lab-scale carbon fibre-reinforced polymer (CFRP) plate strengthened steel beam and a real-scale CFRP plate strengthened cast-iron beam respectively. The study found that thermo-viscoelastic creep of the adhesive bonding layer causes an increase in the slip between the FRP and the structure, which could induce damage in the bonded joint and make the CFRP becomes less effective, potentially resulting in failure of the strengthening system during the long-term service. Differential thermal expansion effects can enhance the joint bonding stress and allow the plate to maintain its contribution to the moment capacity of the beam; however, this benefit could be lost when temperature decrease, and the additional irreversible damage caused by the increased joint stress could reduce the effectiveness of strengthening further..