Temperature Dependence Of Modulus Research Articles

Mechanical and thermal properties of potassium salts of poly(ethylene-co -ethylacrylate): Polyolefin ionomers in the absence of acid groups

The thermal and mechanical properties of ionomers prepared by partial saponification of poly(ethylene-co-ethylacrylate) (EEA) with potassium were investigated by using differential scanning calorimetry (DSC) and dynamic mechanical analysis (DMA). The Vicat softening temperature (VST) and bending modulus were also evaluated. Molecular design of the present EEA-based ionomers eliminates acid groups, which affect ionic aggregates for conventional ionomers. The DSC results showed that the melting enthalpy and main crystallization temperature decreased as the ion content increased, whereas on the other hand, the crystal melting temperature at about 360 K did not depend on the ion content, and a secondary exothermal peak was observed in the cooling process. The variance of the VST increased as the crystallinity decreased. The temperature-dependent curves of DMA data of the EEA-based potassium ionomers with a higher ion content showed elastic plateau even at temperatures above their crystal melting points. Our results indicate the existence of strong cross-linking mediated by ion aggregates. The quadratic increase of stiffness as a function of ion content, increasing VST with decreasing crystallinity, and elastic plateau of temperature-dependent moduli above crystal melting temperature are significant characteristics of the EEA-based potassium ionomers, which contain ionic aggregations without acid group presence. POLYM. ENG. SCI., 55:1843–1848, 2015. © 2014 Society of Plastics Engineers

Effect of nanofiller CeO2 on structural, conductivity, and dielectric behaviors of plasticized blend nanocomposite polymer electrolyte

A novel combination of nanoparticles of rare earth oxide ceria (CeO2) dispersed in polyethylene oxide (PEO)/polyethylene glycol (PEG) blend polymer doped with cation donor salt lithium perchlorate (LiClO4), and ethylene carbonate (EC) nanocomposite polymer electrolyte (NCPE) was prepared by standard solution casting technique. The X-ray diffraction (XRD) patterns reveal that the amorphous nature of the nanocomposite has been increased considerably on dispersion of nanofiller. The complexation was further confirmed by Fourier transform infrared (FTIR) analysis. The impedance spectroscopy technique was used to measure the ionic conductivity and activation energy of the nanocomposite electrolytes. The maximum ambient temperature conductivity of 1.18 × 10−4 Scm−1 was obtained for the nanocomposite of 68 % PEO, 16 % PEG, 11 % LiClO4, 5 % EC, and 1 % CeO2 by weight percentage. The ac conductivity follows the universal power law. The variation of dielectric permittivity, dielectric loss, and modulus spectra with frequency and temperature was consistent with conductivity. The activation energy calculated from temperature-dependent imaginary modulus well coincides with that of conductivity. The loss tangent ascertains the presence of conductivity relaxation and the minimum relaxation time for highest conducting electrolyte.

Thermomechanical properties of Y-substituted SrTiO3 used as re-oxidation stable anode substrate material

Abstract Re-oxidation robustness is important to warrant a reliable operation of anode-supported solid oxide fuel cell systems. The current work concentrates on the mechanical properties of re-oxidation stable Y-substituted SrTiO3 ceramic for the use as anode substrate material. Room temperature micro-indentation yielded Young's modulus and hardness of 160 and 7 GPa, respectively, whereas the temperature-dependent modulus was measured with a resonance-based method up to ∼950 °C. The effective Young's modulus as a function of porosity was measured at room temperature and compared with fracture strength data. The fracture toughness was assessed using a combination of pre-indentation cracks and bending test. Creep rates were measured at 800 and 900 °C in a 3-point bending configuration. Post-test fractographic analysis performed using stereo, confocal and scanning electron microscopy, revealed important information on fracture origins and critical defects in the material. A methodology to assess the mechanical properties of porous materials is suggested.

Effects of Phase Lags on Three-Dimensional Wave Propagation with Temperature-Dependent Properties

A three-dimensional model of equations for a homogeneous and isotropic medium with temperature-dependent mechanical properties is established under the purview of two-phase-lag thermoelasticity theory. The modulus of elasticity is taken as a linear function of the reference temperature. The resulting non-dimensional coupled equations are applied to a specific problem of a half-space whose surface is traction-free and is subjected to a time-dependent thermal shock. The analytical expressions for the displacement component, stress, temperature field, and strain are obtained in the physical domain by employing normal mode analysis. These expressions are also calculated numerically for a copper-like material and depicted graphically. Discussions have been made to highlight the joint effects of the temperature-dependent modulus of elasticity and time on these physical fields. The phenomenon of a finite speed of propagation is observed graphically for each field.

The influence of various kinds of PA12 interlayer on the interlaminar toughness of carbon fiber-reinforced epoxy composites

Modifying the impact toughness of carbon fiber-reinforced epoxy composites by introducing thermoplastic inserts in the interlaminar layer is state-of-the-art. This article compares the introduction of thermoplastics in continuous and discontinuous form. Test plate samples were produced using unidirectional noncrimp carbon fabrics with two different aircraft resin systems: HEXFLOW RTM6 (Hexcel) and Cycom 890 RTM (Cytec). In addition, Polyamide 12 (PA12) was laid in the interlaminar layer in the forms of two different laid scrims, as powder or as nonwoven fabric (NWF). The performance of the resulting combinations was assessed by testing the samples in Mode I and II interlaminar fracture toughness (GIc and GIIc), interlaminar shear strength (ILSS), and compression strength after impact (CAI). The results show that in nearly all the tests a fine-mesh laid scrim performs similarly to a NWF with twice the weight per surface area. They show furthermore that the curing dynamics of the resin systems together with the melting characteristics of the thermoplastic during processing have an important effect on the performance of the test samples. Hardening of the resin before the PA12 reaches its melting point hinders the compacting of the thermoplastic. This limits the reduction in the original thickness of the insert, leading to an increase in the sample thickness and, thus, reducing the fiber volume content. Otherwise, the discrete arrangement of the laid scrim has positive effects on the material properties of the composite at elevated temperatures, considerably reducing the falloff in ILSS resulting from the temperature-dependent Young's modulus of PA12. POLYM. COMPOS., 36:1249–1257, 2015. © 2014 Society of Plastics Engineers

Local structure change evidenced by temperature-dependent elastic measurements: Case study on Bi1/2Na1/2TiO3-based lead-free relaxor piezoceramics

The temperature-dependent Young's modulus Y(T) of the lead-free piezoceramics of 0.8Bi1/2Na1/2TiO3-0.2Bi1/2K1/2TiO3 (20BKT) and 0.96(0.8Bi1/2Na1/2TiO3-0.2Bi1/2K1/2TiO3)-0.04BiZn1/2Ti1/2O3 (4BZT) is measured with the impulse excitation technique and contrasted with corresponding dielectric and structural data. While the dielectric properties suggest a phase transition, the high resolution XRD patterns remain virtually unchanged from room temperature up to high temperatures, confirming no change in their long-range order. In contrast, the elastic properties indicate a broad and diffuse ferroelastic transition denoted by a minimum in Y(T). By analogy to the elastic and dielectric data of PbZrxTi1−xO3 and PLZT, it is concluded that 20BKT and 4BZT are relaxors with polar nanoregions embedded in a metrically cubic matrix. Interestingly, no indication for the freezing temperature was reflected in any of the employed measurement techniques. From the saturation of Y(T), it is suggested that the Burns temperature may be approximated as 700 °C. Moreover, it is found that the modification with the ternary end-member BiZn1/2Ti1/2O3 results in an increase in Young's modulus. A comparison with the Bi1/2Na1/2TiO3-BaTiO3-K0.5Na0.5NbO3 yields the same results.

Electronic structure and thermodynamic properties of millerite NiS from first principles: Complex fermi surface and large thermal expansion coefficient

The electronic structure, Fermi surface, phonon dispersion, and thermodynamic properties of millerite nickel sulfide (NiS) have been investigated systemically from first principles. The calculations suggest that there are two bands across the Fermi level, and the corresponding Fermi surfaces are very complex, which implies the rich physical and chemical properties of this material. The predicted phonon frequencies of millerite are in good agreement with recent Raman spectroscopy experiment. In addition, the temperature-dependent equilibrium volumes, bulk moduli, and thermodynamic properties including heat capacities, entropies and thermal expansion coefficient are also determined by quasi harmonic approximation (QHA), which are found to agree with available experiment. Most importantly, we also found that the predicted thermal expansion coefficients of millerite NiS are larger than glass. This suggested that thermal expansion may contribute an additional enhancement to the volume expansion induced by α-β phase transformation of NiS and thus increase the risks of the spontaneous failure of thermally toughened glass. The various properties present here will be useful for understanding the underlying mechanism of performance degradation and failure related to NiS under working conditions.

Frequency- and temperature-dependent storage and loss moduli of microfibrous thin films of Parylene C

Elastic cyclic loading of ~110µm-thick Parylene C thin films comprising parallel slanted microfibers was performed in the frequency range 5–200Hz, to determine the dependences of their storage and loss moduli on the temperature and the frequency. The glass-transition temperature was identified as about 65°C from the temperature-maximum of the loss modulus. A low-frequency peak (at 115–135Hz) in the variation of the loss modulus is due to the resonance of an individual microfiber loaded by the remaining microfibers in the film.

Viscoelasticity of Ells River bitumen sand and 4D monitoring of thermal enhanced oil recovery processes

Samples of Ells River bitumen sand from Alberta, Canada were measured at low frequencies (0.2–205 Hz) to determine the temperature and frequency dependence of velocities and attenuations. The samples were first measured “as received” where the pore space is mostly filled with bitumen but also contains small amounts of air and water. With residual air in the pores, at 5°C, there is strong dispersion in the P-wave modulus and a peak in attenuation at seismic frequencies. The frequency-dependent moduli and attenuations shift by three orders of magnitude in frequency as temperature is increased from 5°C to 48°C, consistent with the bitumen viscosity. Samples were then saturated so any empty pore space is filled with water. After saturation, at 1 Hz, increasing temperature from 5°C to 49°C causes a 30% reduction in the saturated P-wave modulus, a 34% reduction in the saturated bulk modulus, and a 6% reduction in the shear modulus. This behavior can only be explained by the temperature-dependent bulk modulus of bitumen. The results enable predictions regarding the P-velocities that can be expected during seismic monitoring of thermal enhanced oil recovery processes. Velocities for cold bitumen sand are near [Formula: see text] at reservoir pressure and temperature. Following steam injection, velocities should be very low (near [Formula: see text]) in heated zones more than 50°C with a free gas phase, which could be steam or gas. There will be a progressive reduction in velocities, i.e., [Formula: see text] at 25°C and [Formula: see text] at 49°C, in areas of formation heating, but without steam or gas in the pores. Albeit smaller than the effect of steam, the effect of formation heating alone is large enough to be easily detected by today’s 4D surveys. With local rock physics calibration, it should be possible to map the areal extent of formation heating using 4D seismic data.

Temperature-Dependent Modulus of Metals Based on Lattice Vibration Theory

Fundamentally understanding the temperature-dependent modulus is the key issue for materials serving in high temperature environments. This paper proposes a model based on lattice vibration theory to predict the temperature-dependent modulus with respect to isothermal and isentropic assumption. The thermal vibration free energy is expressed as a function of the two independent scalars from the strain tensor and temperature. By using the Einstein theory, we present the analytical expression for the temperature-dependent Young's modulus, bulk modulus, shear modulus, and Poisson's ratio. The theoretical prediction agrees well with the experimental data. The proposed model is further degenerated to Wachtman's empirical equation and provides the physical meaning to the parameters in Wachtman's equation.

CMOS-compatible ruggedized high-temperature Lamb wave pressure sensor

This paper describes the development of a novel ruggedized high-temperature pressure sensor operating in lateral field exited (LFE) Lamb wave mode. The comb-like structure electrodes on top of aluminum nitride (AlN) were used to generate the wave. A membrane was fabricated on SOI wafer with a 10 µm thick device layer. The sensor chip was mounted on a pressure test package and pressure was applied to the backside of the membrane, with a range of 20–100 psi. The temperature coefficient of frequency (TCF) was experimentally measured in the temperature range of −50 °C to 300 °C. By using the modified Butterworth–van Dyke model, coupling coefficients and quality factor were extracted. Temperature-dependent Young's modulus of composite structure was determined using resonance frequency and sensor interdigital transducer (IDT) wavelength which is mainly dominated by an AlN layer. Absolute sensor phase noise was measured at resonance to estimate the sensor pressure and temperature sensitivity. This paper demonstrates an AlN-based pressure sensor which can operate in harsh environment such as oil and gas exploration, automobile and aeronautic applications.

Smart material (sma)-based actively tuned dynamic vibration absorber for vibration control in real time applications

Dynamic Vibration Absorber (DVA) can be used as an effective vibration control device. A (DVA) is essentially a secondary mass, attached to an original system via spring and damper. The natural frequency of the DVA is tuned such that it coincides with the frequency of unwanted vibration in the original system. This result in absorbing the inertial energy transferred from the primary structure. This current study aims at developing an actively tuned dynamic vibration absorber with the help of shape memory alloy (SMA) springs in order to attenuate the vibration for a range of excitation frequencies. In this study, the unique property of SMAs temperature-dependent Young's modulus has been used to change the stiffness of the spring actively to control the vibration. Experiments were carried out with SMA-based dynamic vibration absorber to study the effect of reduction in amplitude of vibration of a cantilever structure. A micro controller-based proportionate control system has been developed for timely actuation of SMA and to supply optimum current to the SMA springs, which are connected in parallel. The experimental results show that the SMA-based dynamic vibration absorber is more effective in reducing the amplitude of vibration for a wider frequency range. The effectiveness of the developed SMA-based DVA was checked in real time-piping application, and the results demonstrate that the SMA springs has good potential to be used as vibration control device.

Effect of Temperature-Dependent Properties on Cyclic Plasticity of Bond Coat in Thermal Barrier Systems

The accumulation of cyclic plasticity in bond coat (BC) is a key factor controlling the displacement instability of the thermally grown oxide (TGO) in thermal barrier systems. The cyclic plasticity is affected by the component material properties, which vary observably with the service temperature. A numerical model with the behavior of creep and thermal growth in TGO under thermal cycling is used to explore the effect of temperature-dependent properties on cyclic plasticity in BC. The influence of temperature-dependent Young's modulus of thermal barrier coating (TBC), TGO, BC and substrate, thermal expansion coefficient of TBC, BC and substrate, and the yield strength of BC on cyclic plasticity in BC is discussed respectively.

Low-frequency noise in gallium nitride nanowire mechanical resonators

We report on the low-frequency 1/f (flicker) parameter noise displayed by the resonance frequency of doubly clamped c-axis gallium nitride nanowire (NW) mechanical resonators. The resonators are electrostatically driven and their mechanical response is electronically detected via NW piezoresistance. With an applied dc voltage bias, a NW driven near its mechanical resonance generates a dc and Lorentzian rf current that both display 1/f noise. The rf current noise is proportional to the square of the derivative of the Lorentzian lineshape with a magnitude highly dependent on NW dc bias voltage conditions, consistent with a model wherein noise in the NW's electrical impedance leads to temperature noise from local Joule heating, which in turn generates resonance frequency noise via thermal expansion and the temperature-dependent Young's modulus. An example device with a 27.8 MHz resonance frequency experiences an approximate resonance frequency shift of −1.4 Hz/nW. The resonance frequency noise increases as the square of the bias voltage, indicating specific operating conditions that optimize the signal-to-noise ratio in proposed NW sensors.

Effects of glass-to-rubber transition on the temperature, load and speed sensitivities of nano-ZrO2 reinforced polybenzoxazine

In the present work, nano ZrO2 reinforced polybenzoxazine composites were produced. The friction behaviors of ZrO2–polybenzoxazine nanocomposites were evaluated on a chase friction material test machine. An attempt was made to examine the variation of storage modulus, loss modulus and glass-to-rubber transition on the effect of the temperature, load and speed sensitivity of ZrO2–polybenzoxazine nanocomposites. The results revealed that the temperature and load sensitivity of nanocomposites increased with the increasing of load and temperature. This behavior was speculated to be due to the effect of the temperature dependence of modulus in the surface topography and strength. But speed sensitivity varies with the temperature, due to the effect of temperature dependence of viscoelastic response in the energy dissipation.

A new temperature-dependent modulus model of glass/epoxy composite at elevated temperatures

Temperature-dependent modulus of glass fiber/epoxy composite laminates was studied at temperatures ranging from room temperature up to 120℃. The storage modulus, loss modulus, loss factor, and glass transition temperature of two layer-up composite laminates were investigated by dynamic mechanic analysis. Static flexural modulus was also measured by control force mode in dynamic mechanic analysis. A new and simple temperature-dependent model both for the dynamic storage modulus and static flexural modulus was developed. This model depends only on one parameter which has specific physical meaning. The model prediction showed excellent agreement with our own experimental results over the full range of transition region. Furthermore, comparing our model’s prediction and other experimental data of many types of composites, which were studied by other researchers, we point to the fact that our model can be applied to many different polymer matrix composites.

Predicting failure within TBC system: Finite element simulation of stress within TBC system as affected by sintering of APS TBC, geometry of substrate and creep of TGO

Demand for economically efficient and environmental friendly gas turbine engines leads to the usage of a thermal barrier coating (TBC) system, which is usually sprayed on the top of a superalloy substrate. The system includes a ceramic TBC, a bond coat (BC) and a thermally grown oxide (TGO) layer. Thermo-mechanical mismatch stresses created within the coating at the end of a thermal cycle lead to spallation of the ceramic coating and a rapid increase in the temperature of the substrate. The thickness of the oxide layer and the amount of aluminium depleted during high temperature operation also affect the lifetime of the TBC. As a first step to the prediction of the failure mechanisms and the lifetimes of TBCs, a preliminary study of how the stress distribution within the TBC system is affected by different factors is required. This paper investigates the effects of the sintering of the ceramic layer, of the geometry of the substrate and of the creep of the TGO, on the stresses built up in the TBC system. Three different TBC system geometries were modelled using plane strain FE models with three different sets of TGO creep properties. An Arrhenius equation was fitted to the temperature dependent modulus of the sintered TBC using results published in the open literature. The equation was later implemented within the FE model. It is concluded that the TBC on the top of flatter regions of substrate produces smaller tensile residual stresses compared to sharp corners of the substrate. It was also found that the initiation and propagation of cracks within a TBC, during steady state operation depends on the choice of the creep parameters of the TGO. At the cooling stage, increase in the modulus of the TBC, due to sintering, has been shown to produce stresses within the TBC near the TGO interface that are as large as twice the value that is predicted using a model without sintering.

유기화 처리된 층상 실리케이트가 보강된 폴리락티드 나노복합체의 구조, 열안정성 및 기계적 탄성률

We have manufactured polylactide (PLA) nanocomposites reinforced with layered silicates by the melt compounding method and have investigated their structure, thermal stability under oxygen or nitrogen atmosphere, and temperature-dependent mechanical modulus by adopting XRD, SEM, TGA, and DMA. Octadecylammonium-modified montmorillonite (organo-MMT) is used as an organically modified layered silicate and, for comparison, sodium montmorillonite (Na-MMT) is adopted as a purely inorganic layered silicate. X-ray diffraction patterns and SEM images confirm that the organo-MMT is intercalated and dispersed homogenously in the PLA matrix, whereas Na-MMT remains unchanged by forming agglomerated domains in the matrix. Unlike the PLA/Na-MMT nanocomposites, the thermal stability of PLA/organo-MMT nanocomposites is found to be substantially improved with the increment of organo-MMT content, especially under oxygen gas atmosphere. In addition, the mechanical modulus of PLA/organo-MMT nanocomposites in the glassy state are highly improved.

Influence of the third monomer component on the temperature-dependent crystallite modulus and tie chain fraction evaluated for ethylene-tetrafluoroethylene copolymers

Temperature dependence of apparent crystallite modulus along the chain axis Ecapp has been measured on the basis of X-ray diffraction measurement under the assumption of homogeneous tensile stress distribution for the uniaxially-oriented ethylene-tetrafluoroethylene (ETFE) alternating copolymers with and without the third monomer component of short or long side groups. The Ecapp of the 2-components alternating ETFE copolymer was found to decrease remarkably in the phase transition temperature region between the low- and high-temperature phases at around 80 °C. For the ETFE copolymer sample with the third comonomer component of long C4F9 side groups the Ecapp was found to show the similar temperature dependence to that of the pure alternating copolymer although the Ecapp value itself was slightly lower than the latter. The ETFE copolymer with short CF3 side groups was found to show remarkably low Ecapp value in the temperature region from −50 to 50 °C since the crystal structure transferred already to the high-temperature disordered phase in this temperature region. The bulk Young’s moduli of these copolymer samples, estimated by the dynamic viscoelastic measurements, were analyzed on the basis of a complex mechanical model consisting of parallel and series sequences of Ectrue and Ea, where Ectrue and Ea were the true moduli of the crystalline and amorphous regions, respectively. The temperature dependences of the bulk moduli observed for these three samples were successfully reproduced by estimating the Ectrue as a function of temperature. The Ectrue estimated at a low-temperature, was 215 GPa for ETFE 2-components sample, which was consistent with the value 230 GPa calculated theoretically for the planar-zigzag chain conformation. The parallel crystalline component, which was assumed to be a kind of taut tie chain to support the mechanical toughness of the bulk sample, was found to be lower in population for ETFE 2-components sample and higher for the copolymer samples containing the third monomer component. This tendency is consistent with that of the actually-observed stress crack resistance or the mechanical toughness in a high-temperature region near the melting point: ETFE < ETFE-CF3 < ETFE-C4F9. In this way, the terpolymer sample has an important role to create the higher content of taut tie chains, resulting in the higher stress crack resistance.

Enzyme-modified guar gum/xanthan gelation: An analysis based on cascade model

The gel properties of a mixture of enzymatically-modified guar gum (EMG) and xanthan (XG) were investigated. The guar gum sample treated with α-galactosidase to remove galactose residues had a mannose/galactose ratio of 3.02, and was capable of forming a synergistic gel with xanthan. The concentration-dependent and temperature-dependent modulus data for the EMG/XG gel were analyzed by the two-component cascade model which assumed a heterotypic association between segments of EMG and XG. The optimal functionalities (number of cross-linking sites per chain), f EMG and f XG, were found to be 300 and 30, respectively. The former is equal to the number of segment size with more than six unsubstituted mannose residues in a galactomannan backbone, while the latter corresponds to a cross-link density of one per 37 repeating units in a xanthan molecule. The cascade analysis of the composition dependence of critical gelling concentration was performed by introducing the effect of the homotypic association of XG or EMG, which became significant in the gel point measurement. The enthalpy change per cross-link for the heterotypic association was found to be two times higher than that for the homotypic association.