Differential Thermal Expansion Research Articles

Study of Tube Pretension Effects on the Strength of the Flat-Round Tubesheet in a Quench Boiler

A quench boiler is the key equipment in ethylene production for the rapid cooling of high-temperature cracking gas. In the boiler, heat transfer is occurs between the hot cracking gas passing through the inner heat exchange tubes with an average temperature of 385 °C and cold water (or boiler water) passing through the inner heat exchange tubes with an average temperature of 350 °C. Required for double-pipe heat transfer, special tubesheets formed by welding flat-round tubes side by side are difficult to design, as no suitable design code is available. The thermal expansion difference between the inner heat exchange tubes and the jacketed tubes could lead to high thermal stress on the tubesheet. In this study, we investigated the effects of pretension or prestretching of the heat exchange tubes on stress distribution and strength assessment of the flat-round tubesheet in a quench boiler under two dangerous load conditions. Results show that without prestretching the heat exchange tubes, the flat-round tubesheet cannot pass the strength assessment. Prestretching the heat exchange tubes is necessary, and a pretension of 9 mm is most suitable. The magnitude of the pretension of the heat exchange tubes should be determined based on the thermal expansion difference between the inner heat exchange tubes and the jacketed tubes, with consideration of the strength improvement of the flat-round tubesheet.

Lateral Selective SiGe Growth for Dislocation-Free Virtual Substrate Fabrication

Dislocation free local SiGe-on-insulator virtual substrate is fabricated using lateral selective SiGe growth by reduced pressure chemical vapor deposition. The lateral selective SiGe growth is performed around ~1.25 µm square Si (001) pillar in a cavity formed by HCl vapor phase etching of Si at 850 °C from side of SiO2 / Si mesa structure on buried oxide. Smooth root mean square roughness of SiGe surface of 0.14 nm, which is determined by interface roughness between the sacrificially etched Si and the SiO2 cap, is obtained. Uniform Ge content of ~40% in the laterally grown SiGe is observed. In the Si pillar, tensile strain of ~0.65% is found which could be due to thermal expansion difference between SiO2 and Si. In the SiGe, tensile strain of ~1.4% along <010> direction, which is higher compared to that along <110> direction, is observed. The tensile strain is induced from both [110] and [-110] directions. Threading dislocations in the SiGe are located only ~400 nm from Si pillar and stacking faults are running towards <110> directions, resulting in wide dislocation-free area formation in SiGe along <010> due to horizontal aspect ratio trapping.

Internal Thermal Stress-Driven Phase Transformation in Van der Waals Layered Materials.

High pressure or strain is an effective strategy for generating phase transformations in van der Waals (vdW) layered materials without introducing defects, but this approach remains difficult to perform consistently. We present a scalable and facile method for achieving phase transformation in vdW materials, wherein solid vdW materials are subject to internal thermal stress within a molten metal mantle as it undergoes cooling. This internal thermal stress is principally the product of differential thermal expansion between mantle and core and can be tuned by the mantle material and temperature conditions. We validated this approach by achieving phase transformation of red phosphorus to black phosphorus, and metallic 1T'- to semiconducting 2H-MoTe2 crystals. We further demonstrate quantum electronic phase transformation of suppressed charge density wave in TiSe2 by means of electron-phonon coupling using the same system.

THM Response in the Near Field of an HLW Disposal Tunnel in the Callovo-Oxfordian Clay Host Rock Caused by the Imposed Heat Flux at Different Water Drainage Conditions

Heat load from high-level radioactive waste (HLW) packages will result in elevated temperatures around the disposal tunnel. Differences in thermal expansion between rock and water will induce the redistribution of stresses. The assessment of the thermo-hydromechanical (THM) regime is necessary to evaluate the potential for fracture development. For this purpose, it is important to evaluate the nature and extent of induced strains, and their impact on rock permeability, which, subsequently, is important for radionuclide transport. This paper presents the modeling activities of the Lithuanian Energy Institute performed in the framework of the European joint program EURAD and the analysis of the influence of temperature on clay-based material behavior. Within this study, different stress conditions and material properties (isotropic, anisotropic) were analyzed with a thermo-poroelastic material model for the Callovo-Oxfordian clay host rock in the 100 m × 100 m domain. The heat load on the clay rock comes from a tunnel with a radius of 1.25 m. The overall THM response of the clay host rock system to the heat load is performed with the COMSOL Multiphysics (Burlington, MA, USA) software. The THM response near the HLW disposal tunnel was analyzed in terms of temperature, pore pressure, displacements, and stresses, and the results are presented in this work. Besides the impact of anisotropy, the effect of hydraulic conditions at the tunnel boundary was also analyzed. The modeling results revealed that anisotropy in stress and properties had an impact on the hydro-mechanical response of the material even during excavation and waiting phases. The analysis also showed that the water drainage condition on the tunnel boundary had no effect on the thermal state around the tunnel, but it had a significant impact on the hydro-mechanical response.

Non-thermal and thermal effects on mechanical strain in substrate-transferred wafer-scale hBN films

Wafer-scale thin films of hexagonal boron nitride have exceptional thermal and mechanical properties, which harness the potential use of these materials in two-dimensional electronic, device applications. Along with unavoidable defects, grains, and wrinkles, which develop during the growth process, underlying substrates influence the physical and mechanical properties of these films. Understanding the interactions of these large-scale films with different substrates is, thus, important for the implementation of this 2D system in device fabrication. MOVPE-grown 2 and 30 nm hBN/sapphire films of size 2 in. diameter are delaminated chemically and transferred on quartz, SiO2/Si, and sapphire substrates. The structural characteristics of these films are investigated by employing Raman spectroscopy. Our results suggest that not only the roughness but also the height modulation at the surface of the substrates play a pivotal role in determining substrate-mediated mechanical strain inhomogeneity in these films. The statistical analysis of the spectral parameters provides us with the overall characteristics of the films. Furthermore, a Stark difference in the thermal evolution of strain in these films depending on substrate materials is observed. It has been demonstrated that not only the differential thermal expansion coefficient of the substrates and the films, but also slippage of the latter during the thermal treatment determines the net strain in the films. The role of the slippage is significantly higher in 2 nm films than in 30 nm films. We believe that the observations provide crucial information on the structural characteristics of the substrate-coupled wafer-scale hBN films for their future use in technology.

An intelligent icephobic coating based on encapsulated phase change materials (PCM)

The phase change materials (PCMs) have attracted great interest for applications as smart icephobic coatings because of their capability to restore and release energy. PCMs release a large amount of energy as latent heat upon freezing, which is a stimuli-response behavior for anti-icing applications. Such materials embedded within coatings can be applied to exposed infrastructures to protect them against icing. Here, we encapsulated a mixture of PCMs in a urea–formaldehyde (UF) shell by in situ polymerization and then incorporated the microcapsules into a polydimethylsiloxane (PDMS) coating. Microcapsules 5–15 µm in diameter having a shell thickness of about 200 nm were fabricated. Investigating the chemical composition of the fabricated microcapsules confirmed that PCM material was successfully encapsulated within the UF shell. Moreover, the differential scanning calorimetry (DSC) analysis showed that the PCM preserved its phase-change characteristics when encapsulated and embedded within the matrix. Increasing the abundance of microcapsules within the coating lowered the ice nucleation temperature, verified by DSC, and increased the freezing-delay time because of PCM latent heat release. We utilized a custom-made apparatus, called micro-push-off set-up that allowed us to measure ice adhesion at the exact moment that the water droplet was completely frozen. Therefore, it was observed that the presence of the PCM microcapsules reduced ice adhesion strength, through either possible mechanism of the formation of quasi-liquid layer (QLL) or thermal expansion differences. Furthermore, lower ice adhesion resulted in reduced ice accumulation on the PCM-containing coatings, verified by the static accumulation test (SAT).

Concurrent design error, poor welding, and code inadequacy cause jet‐FIRE on a topping column

AbstractThe paper reports the analysis of an accident that occurred in a petroleum refinery. During the start‐up maneuver of the topping column, the anchoring of the riser pipe to metal guide support on the topping column suddenly failed. This caused a rip in the riser pipe, and gasoline squirted out, followed by the ignition of a jet fire. The investigations showed an unusual differential thermal expansion between the topping column and riser. The riser guide to the column was wrongly installed, preventing adequate relative displacements when thermal expansion occurred. Metallographic and fractographic analyses did not discover any inadequacy in the steel of the failed parts. But the lack of penetration of the welding seam resulted in a weak bond between the support and the riser. The high stress induced by the badly installed guide and the weakness of the welding was the cause of the failure and the jet fire. The paper also analyses the application of existing codes to the riser support installation and shows that the code recommendations do not satisfactorily cover the case of topping column risers. The issue is raised to alert operators in the plant, stimulate the improvement of the codes and standards, and avoid future accidents.

Thermo-mechanical analysis of laminated cylindrical shell with viscoelastic bonding interlayers

This work proposes analytical solutions to present coupling thermo-mechanical analysis of laminated cylindrical shells bonded by viscoelastic interlayers, considering the temperature effects on both thermal expansion difference of adjacent layers and temperature-dependent viscoelastic property of bonding interlayer. In the analytical model, according to the heat transport theory, the solutions of non-uniform temperature fields in the laminated cylindrical shells are solved by means of the transfer matrix method. Then, based on the thermo-elasticity theory as well as the viscoelasticity theory, the governing equations for the laminated cylindrical shell are established. The standard linear solid model is employed to simulate the temperature-dependent viscoelastic property of the interlayer, in which the viscoelastic constants are determined according to the time–temperature equivalence principle. At last, the analytical solutions of time-dependent stresses and displacements are determined by the Laplace transform and the Fourier series expansion. The results indicate the present solutions are consistent with the finite element solutions. The influences of temperature, material and geometric parameters on the long-term bending behavior of the laminated cylindrical shell are studied.

Enhanced Phase Stability of Compressive Strain-Induced Perovskite Crystals.

Control of strain in perovskite crystals has been considered as an effective strategy to ensure the phase stability of perovskite films where a compressive strain is particularly preferred over a tensile strain due to a lowered Gibbs free energy by the unit cell contraction effect. Here we adapt the strategy of strain control into perovskite solar cells in which the compressive strain is applied by utilizing a thermal expansion difference between the perovskite film and an adjacent layer. Poly(4-butylphenyldiphenylamine), with a higher thermal expansion coefficient compared to that of perovskite, is employed as a substrate for perovskite crystal growth at 100 °C, followed by cooling to room temperature. The applied compressive strain at the interface, as a result of a greater contraction of the polymer compared to the perovskite film, is confirmed by grazing incidence X-ray diffraction showing a red peak shift with increasing secondary angle. The compressive strain-induced perovskite film shows relatively constant absorbance spectra as a function of time. In the meantime, the absorbance spectra of a film without strain control exhibit a gradual decay with developing an Urbach tail. Importantly, the effect of strain engineering is remarkably prominent in the long-term photovoltaic performance. The photocurrent drops by 41% over 911 h without controlling strain, which is significantly improved by employing compressive strain, showing only a 6% drop in photocurrent from a shelf-stability test without encapsulation. It is also noted that an S-shaped kink appears in the current-voltage curves since 579-h-long storage for the device without strain control, leading to unreliable and overestimated fill factor and conversion efficiency. On the other hand, a 16% increase in fill factor with a stable performance is derived over 911 h from the compressive strain-induced device.

Precessed electron diffraction study of defects and strain in GaN nanowires fabricated by top-down etching

Gallium nitride (GaN) nanowires (NWs) have been fabricated by top-down etching from GaN heteroepitaxial films, which provides an accurate control of their position and dimensions. However, these NWs contain, similar to the initial GaN films, high density of structural defects such as threading dislocations (TDs). In this work, different strategies to reduce the density of defects along the NWs have been compared based on two different wet etching approaches followed by a rapid thermal annealing (RTA) at 750 °C. The addition of a 30 nm SiNx coating is also explored. The defects and strain/stress along the NWs have been studied by high resolution transmission electron microscopy, diffraction contrast imaging in two-beam conditions and 4D STEM, as well as strain maps calculated from scanning precession electron diffraction measurements. RTA reduced the density of TDs at the middle of GaN NWs with bare surfaces by approximately 25%. The reduction increased to approximately 70% by RTA of GaN NWs with surfaces coated by amorphous SiNx, which is attributed to enhancement of dislocation movements by stresses induced from differential thermal expansion of GaN and SiNx. These results suggest a process route that, if optimized and combined with reduction of NW diameter, could establish etching as an efficient fabrication method for high crystal quality GaN NWs.

Electro-thermally driven biaxial bending artificial muscle based on oriented graphite nanoplate nanocomposite/polyimide complex structure

In recent years, artificial muscle is of great research interest due to its promising application. However, low deformation, complicated fabrication process, and high cost hinder their development. Herein, electro-thermally driven biaxial bending artificial muscle based on oriented graphite nanoplate nanocomposite (GN)/polyimide (PI) complex structure is successfully fabricated by cost-effective process utilizing coefficient of thermal expansion difference between them. GN/PI bi-layer films were further assembled and packaged into multi-unit biaxial bending actuator, which could extend and contract like artificial muscle. The unique characteristics of large deformation, easy control, low cost and simple fabrication process distinguish the GN/PI bi-layer based artificial muscle from others. Driven by the voltage of 10 V, the artificial muscle could reversibly reach a shrinkage rate of 11% and a maximum lifting height of 2.5 cm with the object weight of 5.0 g. Moreover, a walking robot has also been designed to achieve a large displacement.

Analysis of Annual Deformation Characteristics of Xilongchi Dam Using Historical GPS Observations

Global Positioning System (GPS) has been confirmed to be a feasible tool to measure displacement of civil engineering structures. In this paper, we report on an analysis of annual deformations of a pumped-storage power station dam using historical GPS observations. Data spanning more than nine years are resolved using the GAMIT (GPS at MIT) software, and a GPS time-series method is employed to extract linear trends and annual cycle signals. It is evident that the monument located on the main dam has a linear trend, with rates of 1.0 mm/yr and 1.8 mm/yr in east and up directions, respectively. Annual cycles with amplitudes larger than 0.5 mm are shown in coordinate components at all monitoring stations. However, the annual amplitude can be 30–84% lower when a monitoring station whose monument materials and height are similar to other monitoring stations is chosen as the reference station. This suggests that differential thermal expansion of monuments could be 30% to 80% and even higher in baseline time series. A spurious offset style annual signal with 5 mm amplitude that is highly correlated with annual temperature variance is observed in the east–west direction of the monitoring station located at the east side of the reservoir. This suggests that upper ground layer movement correlated with temperature could be responsible for these annual cycles. Meanwhile, no periodic correlations are observed between the water level data and the baseline time series.

Structural and thermal properties of Yb:CaBTeX glasses as a function of TeO2 content

Yb3+-doped Calcium Borotelurite glasses were synthesized. The structural and thermal properties were investigated by X-ray diffraction, density, Fourier-transform infrared, Raman, Vickers microhardness, differential thermal analysis, specific heat, and thermal expansion. The thermal mirror was used to determine thermal diffusivity and thermal conductivity. The results were discussed as a function of tellurium oxide content. There were an increase in density and a decrease in Vickers microhardness due to the substitution of CaO, and B2O3 for TeO2. By Fourier-transform infrared spectra, the fraction of tetrahedral borons increase up to 31% mol of TeO2, however, for 54% there was a decrease, indicating a reduction of BO4 and the formation of BO3 units. The thermal expansion coefficient and thermal stability increased with TeO2 content, while there was a reduction for specific heat and thermal diffusivity. The results indicated that Yb:CaBTeX glasses have good thermal and structural properties with potential for applications in optical devices.

Simulation of thermal expansion mismatch at high temperature

The thermal expansion mismatch between cement mortar and aggregate at high temperature is one of the main reasons causing the deterioration of concrete at high temperature. In this study, the thermal damage of concrete caused by the thermal expansion mismatch between aggregate and cement mortar was investigated using a meso-scale concrete model. The meso-scale concrete model is composed of mortar, aggregate and the interfacial transition zone (ITZ). Laboratory tests on the mechanical properties of cement mortar at high temperature were conducted to provide the necessary mechanical parameter for the meso-scale concrete model. The simulation results show that the particle size, content, distribution and mechanical properties of the aggregate have an effect on the thermal damage of concrete at high temperature. The smaller the particle size of concrete aggregate and the higher the elastic modulus of aggregate, the greater the damage of concrete under high temperature. Due to the increasing thermal expansion difference between aggregate and cement mortar, and the deterioration of the cement mortar with the increasing temperature, the damage of concrete increased sharply after 500 °C.

Influences of the substrate strain on microstructures of L10 FePt-X thin films by using phase field simulation

The microstructure evolution of the FePt-X (segregant) thin films is studied by employing a two-dimensional phase field model based on the elastic effect. Simulated results show that the lattice mismatch between the FePt-X thin film and substrate leads to slight rafting (preferential coarsening) of columnar FePt grains along the direction of the misfit strain, and produces more rounded grains, while an amorphous segregant is doped. The elastic energy primarily affects the areas between the FePt grains, where more than 90% of the elastic energy is concentrated. Moreover, the elastic energy is relaxed gradually with the formation of columnar periodic arrays of FePt grains. To generate columnar FePt grains microstructure in the FePt-X thin films, the lattice mismatch between the thin film and substrate should be controlled within 3% when the thermal expansion difference between the thin film and substrate is ignored.

Resonant-Opto-Thermomechanical Oscillator (ROTMO): A Low-Power, Large Displacement, High-Frequency Optically Driven Microactuator.

A light-driven micromechanical oscillator is presented, which can be operated by a low optical power (in the mW, or even the µW range), can produce large mechanical displacements (>5-100µm), and can be designed to operate at frequencies from sub-kHz up to more than 200kHz. The actuation of the oscillator is achieved by an asymmetrically metal-coated optical microwire configured into a silica micromechanical oscillator. The metalized optical microwire confines and absorbs the light strongly over a short distance, which results in a controlled optical power conversion into heat, and, consequently, into mechanical actuation through the temperature rise and the difference in thermal expansions of the silica microwire and the asymmetrically applied metal layer. Mechanical displacements are amplified further by the resonance operation of the oscillator, which is driven by a low-power, harmonic optical excitation signal generated by a current-modulated laser diode. Proper selection of the micromechanical oscillator's geometrical configuration and materials allows for a high-frequency operation at large mechanical displacements of the oscillator, while relying on low excitation optical power. The presented concept of a fully optically driven micromechanical oscillator may, thus, present a basis for realization of new classes of actuated micro-opto-mechanical Systems and similar photonics microdevices.

Creep of an FRP-strengthened metallic beam under cyclic temperature and cyclic load

Metallic beams can be strengthened using fibre reinforced polymer (FRP) plates that are adhesively bonded to their soffit. This relies critically upon the bonded adhesive joint, and because the adhesives are viscoelastic it is known that creep at warm services temperatures can potentially result in large slips that can reduce the effectiveness of the strengthening. This paper examines the impact of adhesive creep upon the performance of an FRP-strengthened metallic beam when subjected to daily temperature cycles and daily load cycles. A finite element (FE) study was conducted that incorporates a linear viscoelastic constitutive model for the adhesive, temperature and load cycles of up to 50 years were considered, and the behaviour of the strengthened beam was examined. Differential thermal expansion between the FRP plate and metallic beam is shown to be significant because it results in both (a) additional instantaneous shear stress across the adhesive joint and (b) the shear stress due to sustained differential thermal expansion results in additional creep of the adhesive that can further reduce the effectiveness of the strengthening. An equivalent cumulative time approach is demonstrated to predict the creep response of the strengthened metallic beam without the need for a complex cyclic analysis.

Structural fire design of square tubed-reinforced-concrete columns with connection to RC beams in composite frames

The tubed-reinforced-concrete (TRC) column is an innovative type of steel-concrete composite column that is gaining increasing engineering usage, and structural fire performance should be an important consideration of its design. As affected by the adjacent members and beam-to-column joints, the fire behaviour of TRC columns integrated into a frame may largely differ from that of isolated columns with idealised end conditions. However, the fire performance of TRC columns in composite frames has not been studied, except for some work done on the fire performance of isolated TRC columns with certain end restraints. This paper presents finite element analysis on single-storey and single-span non-sway frames with square TRC columns, employing the software package ABAQUS. The thermal and deformation behaviour, development of axial stress, axial force and bending moment during heating, working mechanism and failure mode of the frame exposed to fire are numerically investigated. The difference between the fire performance of TRC columns in a frame and those of equivalent isolated columns is quantified. The fire resistance of the framed column is found to lie between those of the columns with rotational end restraints and columns with idealised pinned ends. The complex effects of the connected RC beam on the fire behaviour of TRC columns, e.g. the beneficial restraining effect and the negative effect due to restrained differential thermal expansion, are clarified. Finally, a practical fire resistance design approach is proposed for TRC columns considering the continuity and interactions between structural elements within a composite frame.

Influence of ceramic particles additions on the properties of Ca3Co4O9

Ca3Co4O9 + x wt% B4C, AlN, TiC, TiB2, or TiN (x = 0.0, 0.25, 0.50, and 0.75) samples were prepared by the conventional solid-state route. In all samples, only the Ca3Co4O9 phase was identified by powder XRD. Nevertheless, microstructural studies have shown that most of the additives have reacted with air and Ca3Co4O9 phase on their surfaces, producing new phases. Moreover, it seemed that grain sizes were, at least, slightly reduced. On the other hand, while nearly no modification of the Seebeck coefficient has been observed, independently of the added compound and proportion, electrical resistivity decreased in all cases, when compared to the pristine sample. Consequently, the power factor of samples with additions was higher than the one determined for the pure sample. Linear thermal expansion also decreased with these additives, pointing out to the formation of relatively strong grain boundaries which can improve the carrier mobility and decrease the thermal expansion. The lowest thermal expansion value has been measured in 0.25 wt% B4C samples, being only around 20% higher than that of Al2O3, which can help to reduce the differential thermal expansion in thermoelectric modules working at high temperatures; these results may be very interesting for applications prospects.Article highlightsAddition of different ceramic additives to Ca3Co4O9 phase increases electrical conductivity, and power factor.All additive ceramics react with oxygen and the Ca3Co4O9 phase modifying the properties of pristine compound.The decrease of thermal expansion coefficient will allow reducing the differential thermal expansion in modules.

Thermo-mechanical optimization of ceramic substrate with through ceramic vias by Taguchi-Grey method

Through ceramic via (TCV) interconnection technology has emerged as a promising technology applied to high-density three-dimensional (3D) packaging. However, due to the large coefficient of thermal expansion (CTE) difference between the copper-filled TCV and the ceramic substrate, the reliability of TCV is always a problem of ceramic substrate cracks under thermal cycling. In this paper, finite element simulations combined with Taguchi-Grey method are used to optimize the thermo-mechanical behaviors of the ceramic substrate with in-line copper-filled TCVs. An L27 (36) orthogonal array integrated with Grey relational analysis (GRA) are employed to assess the influences of TCV diameter, TCV height, pitch, substrate material, metal layer thickness and substrate cross-sectional area on the thermal deformation, thermal stress and plastic strain. The results indicate that the substrate material and the metal layer thickness are the most important parameters that affect thermal deformation, with the contribution ratios of 40.82% and 31.44%, respectively. For thermal stress, the effects of substrate material, TCV diameter and pitch are account for 46.7%, 26.49%, and 9.38%, respectively. For plastic strain, the TCV diameter has the largest effect, reaching 69.43%. The optimal design parameters are also derived by using GRA and weighting method to compromise each response.