Axial Thermal Expansion Research Articles

A non-invasive pipeline heat flux measurement method and application based on CFBG

A non-invasive, real-time monitoring, spectral analysis heat flux sensor with single measuring point based on chirp fiber Bragg grating (CFBG) has been proposed in this paper. When CFBG senses heat flux, the linear increase of axial thermal expansion leads to spectral broadening. The measurement of heat flux can be realized by the measurement of the full width at half maximum (FWHM). The theoretical model and working principle of CFBG heat flux sensor are established to determine the heat flux sensing characteristics of CFBG. The numerical analysis and theoretical calculation show that CFBG heat flux sensor can realize stable transformation of heat flux and FWHM. A heat flux calibration platform was built and its feasibility was verified by simulation. The sensitivity of CFBG sensor to monitor heat flux in a wide temperature range is 1.078 pm/(W/m2). The heat flux of the pipe wall at the outlet of the axial variable piston pump in the hydraulic system was quantitatively measured by the CFBG heat flux sensor. The sensor has a spatial resolution of 1 cm, a length of 10 mm, a diameter of 0.125 mm, and a sensitivity of 1.078 pm/(W/m2). It has the advantages of high spatial resolution, single measurement point, real-time measurement, small installation space, and non-invasiveness. The theoretical model can provide theoretical guidance for the design of fiber grating heat flux sensor, and it is convenient to design a series of sensors for specific measurement requirements.

Noncovalent Interactions and Transverse Vibration Induced Restricted Thermal Expansion of Organic Salts Derived from Imidazole and Carboxylic Acids.

Design of material showing contraction upon heating is highly challenging due to varying mechanism. However, imidazole is found to be a potential molecule that may provide low CTE materials when incorporated in the matrix. Here we have reported thermal expansion property of imidazolium salts of five aliphatic α, ω-alkane dicarboxylic acids and three aromatic acids. Either uniaxial or biaxial negative thermal expansion (NTE) has been observed in most of the salts. In some cases, axial zero thermal expansion (ZTE) has been observed. The role of imidazolium moiety for the anomalous thermal expansion behaviour of the salts has been analyzed in this study. The controlled TE behaviour of the salts is attributed to the hydrogen bonding and transverse vibration in all imidazolium salts. Owing to the high transverse vibration observed in imidazolium ion as well as the heavier oxygen atoms of acids in each case, the distance between hydrogen bonded atoms decreases-which provides either low expansion or contraction along one of the principal axes.

Compressibility, thermal expansion and Raman scattering of synthetic whitlockite Ca9Mg(PO3OH)(PO4)6 at high pressures and high temperatures

Abstract In-situ X-ray diffraction and 16 Raman scattering of synthetic whitlockite, Ca9Mg(PO3OH)(PO4)6, have been systematically measured at high pressures and high temperatures, respectively. The results show that whitlockite is stable up to ~ 15 GPa at ambient temperature and undergoes a temperature-induced dehydrogenation to merrillite above 973 K at ambient pressure. The obtained pressure-volume data were fitted using a third-order Birch-Murnaghan equation of state to yield the isothermal bulk modulus as K0 = 79(4) GPa with pressure derivative K0' = 4.3(6). When K0' was fixed at 4, the refined isothermal bulk modulus was 81(1) GPa. The volumetric thermal expansion coefficient (αV) is equal to 4.05(8) × 10-5 K-1. The axial thermal expansion coefficients (αa and αc) are 1.07(5) × 10-5 K-1 and 1.91(6) × 10-5 K-1. Both compressibility and thermal expansion show an axial anisotropy. The effects of pressure and temperature on the Raman spectra of whitlockite have been quantitatively analyzed. The isothermal and isobaric mode Grüneisen parameters, and the intrinsic anharmonic mode parameters of whitlockite were calculated. Some amounts of OH--bearing whitlockite may be preserved and could be discovered in meteorites if whitlockite undergoes a low temperature process.

Polymorphism and Phase Stability of Hydrated Magnesium Carbonate Nesquehonite MgCO3·3H2O: Negative Axial Compressibility and Thermal Expansion in a Cementitious Material.

The P-T phase diagram of the hydrated magnesium carbonate nesquehonite (MgCO3·3H2O) has not been reported in the literature. In this paper, we present a joint experimental and computational study of the phase stability and structural behavior of this cementitious material at high-pressure and high-temperature conditions using in situ single-crystal and synchrotron powder X-ray diffraction measurements in resistive-heated diamond anvil cells plus density functional theory calculations. Our results show that nesquehonite undergoes two pressure-induced phase transitions at 2.4 (HP1) and 4.0 GPa (HP2) at ambient temperature. We have found negative axial compressibility and thermal expansivity values, likely related to the directionality of the hydrogen bonds. The equations of state of the different phases have been determined. All the room-temperature compression effects were reversible. Heating experiments at 0.7 GPa show a first temperature-induced decomposition at 115 °C, probably into magnesite and a MgCO3·4H2O phase.

Negative to positive axial thermal expansion switching of an organic crystal: contribution to multistep photoactuation.

Materials displaying negative thermal expansion (NTE), in contrast to typical materials with positive thermal expansion (PTE), are attractive for both fundamental research and practical applications, including the development of composites with near-zero thermal expansion. A recent data mining study revealed that approximately 34% of organic crystals may present NTE, indicating that NTE in organic crystals is much more common than generally believed. However, organic crystals that switch from NTE to PTE or vice versa have rarely been reported. Here, we report the crystal of N-3,5-di-tert-butylsalicylide-3-nitroaniline in the enol form (enol-1) as the first organic crystal in which the axial thermal expansion changes from negative to positive at around room temperature. When heated, the crystal shrinks along the a-axis below 30 °C and then it expands above 30 °C. Geometric calculations revealed that below 30 °C, the decrease in the tilt angle of the molecule exceeds the increase in the interplanar distance, causing NTE, whereas above 30 °C, the increase in the interplanar distance outweighs the decrease in the tilt angle, resulting in PTE. By combining photoisomerisation and the NTE-PTE switching induced by the photothermal effect, multistep crystal photoactuation was achieved. Moreover, actuation switching of the same crystal sample by changing atmosphere temperature was realised by utilising the NTE-PTE change. Such NTE-PTE switching without a thermal phase transition provides not only new insight into organic crystals but also a new strategy for designing crystal actuators.

Experimental Study on Axial Thermal Expansion of Composite Thin-walled Tube

Carbon fiber reinforced composite thin-walled tubes have the characteristics of light weight, high strength and small deformation, and are widely used in aviation, aerospace and other fields. Under the working conditions of high and low temperature, the thermal deformation of tube will directly determine the service reliability of their constituent structures. It is necessary to accurately measure the thermal expansion performance of composite thin-walled tube and reasonably evaluate the stability of their constituent structures. When the existing thermal expansion performance measurement system measures the thermal expansion of tube, there are problems of sampling damage to the structural state and failure to effectively contact the end face of tube in real time. For the above situations, A method for measuring the axial thermal expansion performance of composite thin-walled tube is proposed, and the measurement system is built. The thermal expansion performance of thin-walled tube is successfully and effectively evaluated, and the error of the measurement system is reasonably evaluated using the standard parts with known thermal expansion coefficient.

Thermal expansion behavior of vanadium pernitride, CuAl2-type VN2, synthesized under high pressures

CuAl2-type VN2, which is synthesized under high pressure, is a recoverable material at ambient conditions and has a high bulk modulus. In this study, we investigated the thermal expansion behavior of CuAl2-type VN2 by low-temperature X-ray diffraction measurements between 109.3(5) K and 298.3(8) K. The axial thermal expansion coefficient of VN2 was determined to be αa = 2.7(9) × 10−6 K−1 and αc = 17.8(12) × 10−6 K−1 at 298.3(8) K, which has large anisotropy similar to that of compression behavior. It is found that the small coefficient of thermal expansion of the a-axis is due to the negative and positive effects on the a-axis length with increasing temperature of the bond angles and bond lengths of VN2, respectively. As a result, VN2 exhibits very large anisotropic thermal expansion behavior.

Temperature-dependent Raman spectra and thermal expansion of MgP2O6

The Raman spectra and thermal expansion of MgP2O6 metaphosphate were investigated at various temperatures up to 1073 K at ambient pressure. No temperature-induced phase transition was observed in this study. The effect of temperature on the Raman active vibrations and unit cell parameters was determined. All the observed Raman active bands of MgP2O6 showed linear temperature dependences in the range of −2.61 × 10−2 ∼ −0.49 × 10−2 cm−1 K−1. The thermal expansion coefficient of MgP2O6 was estimated to be 3.21(2) × 10−5 K−1. An axial anisotropic thermal expansion exists and the c-axis shows the smallest thermal expansion. The isobaric mode Grüneisen parameters of MgP2O6 were calculated. The obtained results were compared with other compounds in the MgO-P2O5 system.

Fire performance of gypsum-sheathed cold-formed steel walls with rectangular section studs

This study conducted axial compression experiment of one full-scale CFS wall at ambient temperature and four full-scale fire experiments of CFS walls with two initial load ratios of 0.27 and 0.85. Specimens were sheathed with double layers of gypsum plasterboard, rock wool was the cavity insulation and the wall studs had rectangular cross sections. A finite element model was used to optimize the arrangement of rock wool cavity insulation for the CFS walls. The results showed that the failure mode changed from local buckling of the hot flange under a load ratio of 0.27 to local buckling of the whole stud section under a load ratio of 0.85. The fire resistance time of the specimen without rock wool insulation in the stud cavity was 7 min longer than that of the specimen with rock wool insulation. This was attributed to the thermal radiation effect of the stud cavities, which delayed the increase in hot flange temperature and improved the fire resistance time of the CFS walls. Thus, for CFS walls with rock wool-insulated cavities, the stud cavity configuration was more reasonable without than with rock wool insulation. When the axial thermal expansion load was considered, the load on the wall studs increased by a maximum of 43.3 kN per stud. In addition, for CFS walls with low load ratios of 0.27, the wall studs near the face-layer board joints tended to buckle first.

Temperature Dependent Crystal Structure of Nd2CuTiO6: An In Situ Low Temperature Powder Neutron Diffraction Study

Herein we reported the crystal structure and crystal chemistry of orthorhombic perovskite type Nd2CuTiO6 in between 2 K and 290 K as observed from the in situ temperature-dependent powder neutron diffraction (PND) studies. It is observed that the cations in octahedral sites are statistically occupied, and the ambient temperature orthorhombic structure is retained throughout the temperature range of the study. Absence of any long-range magnetic ordering down to 2 K is confirmed by both low-temperature PND and magnetization studies. The lattice shows strong anisotropic thermal expansion with increasing temperature, viz. almost no or feeble negative expansion along the a-axis while appreciably larger expansion along the other two axes (αb = 10.6 × 10−6 K−1 and αc = 9.8 × 10−6 K−1). A systematic change in the rotation of octahedral units with temperature was observed in the studied temperature range, while the expansion of unit cells is predominantly associated with the polyhedral units around the Nd3Ions. The temperature-dependent relative change in unit cell parameters as well as coefficients of axial thermal expansion show anomalous behavior at lower temperatures, and that seems to be related to the electronic contributions to lattice expansion.

Thermal expansion behavior of Li-bearing tourmalines investigated by high-temperature synchrotron-based X-ray diffraction

The high-temperature unit-cell parameters and volumes of three Li-bearing tourmalines (elbaite (CC05), elbaite (CC11) and schorl (D54)) have been determined through in situ synchrotron radiation angle-dispersive X-ray diffraction experiments. No phase transition of these tourmalines has been observed up to the maximum temperature in this study. The volumetric thermal expansion coefficients of the three Li-bearing tourmalines are determined from the measured unit-cell volumes at high temperatures with Berman's equations. And the elbaite (CC05) has the least volumetric thermal expansion coefficients among the three Li-bearing tourmalines in this study. Furthermore, the axial thermal expansion behavior of these Li-bearing tourmalines is also fitted with “linearized” Berman's equation. The results show that Li-bearing tourmalines has an intense anisotropic axial thermal expansivity, where the c-axis has a larger axial thermal expansion coefficient than a-axis. The potential factors influencing on the thermal expansivity and the anisotropic axial thermal expansivities of Li-bearing tourmalines are further discussed.

Standard versus natural fire resistance for partially restrained composite floor beams: 2-Analysis

A thermo-structural reduced-order finite element modeling approach is used to evaluate the results of two fire tests (presented in Part 1 of this study) on identically designed, highly composite floor beam specimens with SFRM protection, shear tab connections at each end, a lightweight concrete slab on a corrugated metal deck, and partial restraint of both axial thermal expansion and connection rotation. Model validation is performed for both an ASTM E119 standard fire and a parametric natural fire, with a constant load applied to the specimens via four-point bending to a maximum service condition. Predictions of temperature increase in the protected steel beam and the composite slab show good agreement with experimental measurements by implementing a series of weighted averaging strategies on thermal FE results for 2D cross-sections at the thick and thin portions of the composite slab. Predictions of temperature-induced deflections, which used the results of thermal FE analysis as input, also show good agreement with experimental results when little-to-no rotational stiffness is applied to the connections. The numerical models are then re-analyzed at a reduced loading level (representing a middling service condition) and with varying rotational stiffness in the shear tab connections. The results of parametric analysis are used to draw correlations between standard fire resistance and natural fire robustness as a function of applied loading and temperature increase in the steel beam. Simplified modeling strategies and recommendations for performance-based structural-fire design are discussed, and opportunities for future research are highlighted.

On red tin (II) oxide: temperature‐dependent structural, spectroscopic, and thermogravimetric properties

AbstractPolycrystalline red tin(II)oxide (RSO) has been synthesized by a fast reflux method. X‐ray powder diffraction (XRPD) data Rietveld refinement confirms the orthorhombic space group Cmc21 (Z=8). The presence of 5 s2 lone electron pair (LEP) of the Sn2+ cation results in layers of highly distorted SnO4 tetrahedra with an averaged Wang‐Liebau eccentricity (WLE) parameter of 4.3(1) x10−5 as a measure of the stereochemical activity. The significantly different Sn−O bond distances demonstrate the under‐bonding nature of both the tin and the oxygen atoms in the SnO4 coordination. The band gap of red tin(II)oxide is found to be 1.75(1) eV which is compared with those of blue‐black tin(II) (BSO) and white tin(IV) oxide (WSO) based on the UV‐Vis diffuse reflectance spectral data. Temperature‐dependent XRPD reveals the phase transitions, which is complemented by thermogravimetric and differential scanning calorimetry (TG/DSC) investigations. Moreover, in‐situ Raman spectroscopy additionally hints to an intermediate phase either of Sn2O3 or Sn3O4 appears within a short temperature range before the RSO to BSO transition occurs. Due to axial negative thermal expansion for the b‐lattice parameter RSO exhibits nearly a zero thermal expansion coefficient for a given temperature range above room temperature.

High temperature structure and vibrational properties of GdVO4

In this manuscript the temperature evolution of crystal structure and vibrational properties of tetragonal GdVO4 as observed from in situ high temperature powder XRD and Raman spectroscopic studies are reported. The material shows anisotropic expansion with a larger coefficient of thermal expansion along c-axis (αc) compared to that along the a-axis (αa). The average axial thermal expansion coefficients in the temperature range of 298–1373 K are: αa = 3.75 × 10−6 K−1 and αc = 11.1 × 10−6 K−1. The degree of anisotropy in thermal expansion decreases with increasing temperature. The thermal expansion behavior of GdVO4 was mainly contributed by the orientation and expansion of Gd–O bonds in the structure. The temperature dependent Raman spectroscopic investigations indicate decreasing trend of all the observed phonon mode frequencies. All the low energy modes show larger anharmonicity compared to the high energy stretching modes and they contribute significantly to the expansion of GdVO4.

The improvement of temperature sensitivity by controlling the thermal expansion coefficient of no-core fiber

In this paper, a liquid sealed temperature sensor is assembled based on single-mode-no-core-single-mode (SNCS) optical fiber structure. Theoretical calculations and experiments verify the sensing characteristics of this structure. The structure improves the temperature sensitivity to −355 pm/°C by encapsulating an organic solvent with large thermal optical coefficient and using packaging material with large thermal expansion coefficient. The theoretical results are in good agreement with the experimental results. Theoretical simulations are completed on MATLAB using far from the cut-off condition. The SNCS structure is encapsulated in a microfluidic chamber by applying microfluidic processing technology. The axial thermal expansion coefficient of the no-core fiber (NCF) is increased and radial thermal expansion coefficient is suppressed by the polydimethylsiloxane (PDMS) mold stretching NCF to improve the temperature sensitivity. The enhancement effect of PDMS stretching NCF on temperature sensitivity is verified by contrast experiment. Due to the wrapping of PDMS, the sensor has strong resistance to mechanical damage and external interference.

Preparation, uniaxial negative thermal expansion and Raman study in semiconductor oxide Nb2WO8 ceramic

Negative thermal expansion materials exhibit important promising to tailor thermal expansion due to their abnormal thermal shrinkage characteristics. Here, the Nb2WO8 ceramic has been synthesized, which exhibits axial negative thermal expansion (αa = −2.05 × 10−6 K−1) from 300 to 1000 K without water absorption or phase transformation. Along a axis, the one O atom is located between two identical Nb atoms and the Nb–O–Nb atomic linkages are formed, in which the Nb2–O2–Nb2 bond angle decreases upon heating, resulting in the negative thermal expansion of a axis. Although the b axis and c axis show positive thermal expansion, the low thermal expansion (αl = 2.30 × 10−6 K−1, 173–1073 K) occurs in unit cell volume due to the negative thermal expansion of a axis. The variable pressure Raman shows that the translational and rotational modes of the polyhedron play a key role in axial negative thermal expansion. This work shows potential application prospects of Nb2WO8 as a low thermal expansion semiconductor ceramic.

Thermal expansion of minerals in the tourmaline supergroup

Abstract The thermal behavior of 15 natural tourmaline samples has been measured by X-ray powder diffraction from room temperature to ~930 °C. Axial thermal expansion is generally greater along the c crystallographic axis (αc 0.90–1.05 × 10–5/K) than along the a crystallographic axis and the symmetrically equivalent b axis (αa 0.47–0.60 × 10–5/K). Ferro-bearing samples show lower expansion along a than in other tourmalines. In povondraite the thermal expansion along the c axis is higher than in other tourmalines, whereas along a it is lower [αa = 0.31(2) and αc = 1.49(3) × 10–5/K]. Volume expansion in the tourmaline-supergroup minerals is relatively low compared with other silicates such as pyroxenes and amphiboles. Volume also exhibits a relatively narrow range of thermal expansion coefficients (1.90–2.05 × 10–5/K) among the supergroup members. An interpretation for the small changes in thermal expansion in a compositionally heterogeneous group like tourmaline is that all members, except povondraite, share a framework of dominantly ZAlO6 polyhedra that limit thermal expansion. Povondraite, with a framework dominated by ZFe3+O6 polyhedra, displays thermal expansion that is different from other members of the group. Unit-cell dimensions of tourmalines having significant Fe2+ deviate from linearity above 400 °C on plots against temperature (T); along with the resulting substantial reduction in unit-cell volume, these effects are likely the result of deprotonation/oxidation processes. Lithium-rich and Fe2+-free tourmalines deviate similarly at T > 600 °C. In Li- and Fe2+-free tourmalines, no such deviation is observed up to the highest temperatures of our experiments. It is not clear whether this is due to cation order-disorder over Y and Z sites that occurs during the highest temperature measurements, a phenomenon that is apparently inhibited (at least in the short term) in Li-free/Mg-rich samples. If so, this must occur at a relatively rapid rate, as no difference in unit-cell values was detected at 800 °C after heating in both one- and 12-h experiments on Na-rich rossmanite.

Buckling enhancement of tubular metamaterial with axial zero thermal expansion by integrating two adjustment mechanisms

Artificially designed mechanical metamaterials with desired property of zero thermal expansion (ZTE) have already made great progress motived by the urgent needs of high-end equipment and instruments served in large fluctuating temperature environment. Various thermal expansion adjustment mechanisms are developed to achieve controllable thermal deformation. However, only designing ZTE is not normally sufficient, but must be combined with enough mechanical performances for carrying mechanical loads. Hence in this study, a method of bucking enhancement for designing tubular metamaterials with axial ZTE is firstly proposed by integrating two existing adjustment mechanisms. Compared with the previous design under the single Poisson contraction mechanism, the present axial ZTE property is mainly achieved through thermally bending-adjustment mechanism, and therefore avoid the unfeasibility of requiring too large thermal expansion coefficient difference for constituent materials. Meanwhile, the significant buckling capacity loss caused by the introduced initial curvature used for triggering thermally bending-adjustment mechanism is prominently improved by taking the advantage of Poisson contraction mechanism. The results obtained from detailed numerical simulations verify the design targets of simultaneous axial ZTE and buckling enhancement. The proposed design strategy of mechanism combination is also proved effective to enhance the buckling capacity of present dual-mechanism metamaterial without obvious increase of structural mass.

Investigation on the free expansive deformation of concrete during the heating process

Concrete experiences expansive deformation at high temperatures. The thermal stress resulted in the development of cracks inside the concrete members. To investigate the free expansive deformation of concrete during the heating process, the concrete specimens were heated from room temperature to different target temperatures with an electric furnace. The temperature in the furnace was maintained at the target temperature to provide a thermostatic condition until the center of the specimen also reached the target temperature. The deformation values of the concrete specimens in both of the temperature rising stage and temperature holding stage were measured and analyzed. The experimental results show that the concrete began to deform at 40–60 °C. The thermal-induced axial strain and thermal expansion coefficient of concrete gradually increased with a rise in temperature. After being heated to 800 °C, thermal-induced axial strain and thermal expansion coefficient of concrete M35 reached 1.018% and 13.135 × 10−6 °C, respectively. The thermal-induced axial strain of concrete continued to increase during the temperature holding stage and gradually stabilized after 60–65 min. After the temperature in the center of the specimen reached 800 °C, the thermal-induced axial strain and thermal expansion coefficient of concrete M35 reached 1.252% and 16.155 × 10−6 °C, respectively. For concrete M45 with higher compressive strength than M35, the thermal-induced axial strain and thermal expansion coefficient of concrete M45 show a variation law similar to concrete M35.

Influence of cover thickness in structural frames exposed to fire and service loads.

This paper deals with the effect of cover thickness in a reinforced concrete columns of 3-D (three dimensional) frame structures under progressive collapse assessment. The concrete cover protects the reinforcements of structural elements from corrosion and other environmental effects. Even under thermal effects, the concrete cover plays a vital role by preventing the temperature to reach the reinforcements which are present inside. An optimum amount of cover thickness must be provided to the structural elements to withstand sufficient loads and sustain environmental conditions. To study the influence of cover thickness in frame structures, a single-bay single-story 3-D reinforced concrete frame was analyzed under fire scenarios using ABAQUS (FEA). Two nominal cover thicknesses were adopted likely 40 mm and 45 mm for the columns in the frame structure as they are the main load-carrying element. The important structural aspects such as axial load-carrying capacity, thermal expansion, deformation, stiffness, bending moment, and shear force were studied under the considerations of frames with slab and masonry infill wall. It was observed that the nominal cover thickness of 45 mm increases the structural performance and thermal resistance, and can sustain other environmental conditions in a better way.