Showing papers on "Thermomechanical analysis published in 2014"

Mechanical damage assessment of Glass Fiber-Reinforced Polymer composites using passive infrared thermography

Abstract: This study deals with characterization of the damage and thermomechanical behavior of the Glass Fiber-Reinforced Polymer composite materials (GFRP), submitted to static tensile loadings, using a passive infrared thermography technique. During mechanical testing, thermal measurements are performed by means of an IR camera. The thermal data post-processing involves the analysis of both the thermal maps and the thermomechanical behavior of the material. The thermal maps analysis allows qualitative evaluation of the created material damage at high stress levels. While the thermomechanical analysis gave us a quantitative evaluation of the material damage, for both low and high stress levels, through definition of a new thermoelastic damage variable.

Polyimide nanocomposites with functionalized SiO2 nanoparticles: enhanced processability, thermal and mechanical properties

Abstract: SiO2–polyimide nanocomposites were successfully fabricated by surface modification of silica nanoparticles. In order to create structural similarity between the polymer and the SiO2 surface and to generate interfacial interaction with the polymer chain, (3-trimethoxysilylpropyl)diethylenetriamine was attached to the surface, and then, the surface amines were reacted with phthalic anhydride. The modified silica nanoparticles in polyamic acid solution were subjected to thermal imidization to obtain SiO2–polyimide (PI) nanocomposite films. Cross-sectional transmission electron microscopy results showed no significant aggregation in any of the SiO2–PI nanocomposite films having up to 20 wt% of silica nanoparticles. The effects of silica nanoparticles as a filler material on the thermal, optical, and mechanical properties of the SiO2–PI nanocomposite films were studied in comparison with those of PI by UV-vis spectrometry, thermal gravimetric analysis, thermal mechanical analysis, and nanoindentation.

Thermomechanical properties and stress analysis of 3-D textile composites by asymptotic expansion homogenization method

Abstract: This paper formulates asymptotic expansion homogenization method for the analysis of 3-D composites whereby thermomechanical effects are considered. The equivalent thermomechanical properties, viz. elastic constants and coefficient of thermal expansion, of 3-D orthogonal interlock composites are obtained based on a unit-cell derived from the optical microscopy observation. The Young’s modulus and Poisson’s ratio obtained from the analysis are compared with those obtained by experiments. The results show a good agreement especially for the Young’s modulus. Localization analysis based on the present formulation is also presented to assess the stresses within the constituents of 3-D composites (fiber tows and resin region) due to mechanical loading and temperature difference. In order to facilitate the localization analysis, the unit-cell of 3-D composites is first subjected to temperature difference in order to obtain thermal residual stresses. Subsequently, a beam model utilizing homogenized thermomechanical properties of 3-D composites is built to obtain stresses due to mechanical loading. Two loading cases are considered: beam under uniaxial tension (Case 1) and beam under bending load (Case 2). The thermal residual stresses and stresses due to mechanical loading in each case are then superposed to obtain total stresses. The total stresses are then used to understand the complete response of composite constituents under mechanical and thermal loadings.

Theoretical Study on the Mechanism of Anisotropic Thermal Properties of Ti2AlC and Cr2AlC

Abstract: Temperature dependences of thermal and elastic properties, such as the Gruneisen parameters, thermal expansion, bulk modulus, and heat capacity of Ti2AlC and Cr2AlC, are studied by combining first-principles method and lattice dynamic calculation based on the quasi-harmonic model. Experimental thermal expansion coefficient is also measured for comparison. Thermal expansion coefficients of Ti2AlC and Cr2AlC show different trends: Ti2AlC exhibits anisotropic thermal expansion while Cr2AlC shows generally isotropic character. The mechanism is explored by investigating the isotropy or anisotropy of Gruneisen parameters (phonon anharmonicity and thermal pressure) and elastic stiffness (response to thermal pressure) of Ti2AlC and Cr2AlC. In addition, the calculated bulk modulus of Cr2AlC is higher at ambient temperature but decreases faster than the value of Ti2AlC as temperature increasing.

Experimental Thermomechanical Analysis of Elastomers Under Uni- and Biaxial Tensile Stress State

Abstract: The objective of the present work is to demonstrate an experimental methodology to determine the viscoelastic material behavior of elastomers independent of the mechanical loading conditions. For this purpose two model materials (elastic and damper formulation) were investigated. The experimental effort ranged from classical uniaxial dynamic thermomechanical analysis (DTMA) and monotonic loading to monotonic biaxial testing. The performed monotonic experiments were loading rate and temperature dependent. Before applying the experimental methodology, some fundamental presumptions had to be verified. First, the applicability of the well-known time-temperature superposition principle to the elastomers, and second the separation of thermomechanical loadings, in which the temperature effects on the mechanical behavior of the materials could be characterized by an appropriate shift factor function; if this function is fundamental, then it should be independent of the mechanical loading condition. The shift factor functions were determined for the investigated elastomers from the DTMA results and were applied for the monotonic uni- and biaxial loading. Two biaxial tests (bulge test and planar biaxial tension test) were performed to show a direct calculation method for the stresses from planar biaxial tests by utilizing FEA with a material model, whose parameters were defined by the bulge test results.

Thermal Expansion, Electrical Resistivity, and Spreading Area of Sn-Zn-In Alloys

Abstract: Thermal expansion and electrical resistivity of alloys based on Sn-Zn eutectic with 0.5, 1.0, 1.5, and 4.0 wt.% additions of In were studied. Thermal expansion measurements were performed using thermomechanical analysis tester over 223-373 K temperature range. Electrical resistivity measurements were performed with four-probe method over 298-423 K temperature range. The electrical resistivity of alloys increases linearly with temperature and concentration of In; also coefficient of thermal expansion of the studied alloys increases with In concentration. Scanning electron microscopy revealed simple eutectic microstructure with In dissolved in Sn-rich matrix. The results obtained were compared with the available literature data. Spreading tests on Cu of Sn-8.8Zn alloys with 0.5, 1.0, and 1.5 at.% of In were performed. Wetting tests were performed at 250 °C, by sessile drop method, by means of flux, and wetting times were 3, 8, 15, 30, and 60 min. In general, no clear effect of wetting time on spreading was observed.

Effect of nano/micro-mixed ceramic fillers on the dielectric and thermal properties of epoxy polymer composites

Abstract: Nano/micro ceramic-filled epoxy composite materials have been processed with various percentage additions of SiO2, Al2O3 ceramic fillers as reinforcements selected from the nano and micro origin sources. Different types of filler combinations, viz. only nano, only micro, nano/micro, and micro/micro particles, were designed to investigate their influence on the thermal expansion, thermal conductivity, and dielectric properties of epoxy polymers. Thermal expansion studies were conducted using thermomechanical analysis that revealed a two-step expansion pattern consecutively before and after vitreous transition temperatures. The presence of micro fillers have shown vitreous transition temperature in the range 70–80°C compared with that of nano structured composites in which the same was observed as ~90°C. Similarly, the bulk thermal conductivity is found to increase with increasing percentage of micron-size Al2O3. It was established that the addition of micro fillers lead to epoxy composite materials that exhibited lower thermal expansion and higher thermal conductivity compared with nano fillers. Moreover, nano fillers have a significantly decisive role in having low bulk dielectric permittivity. In this study, epoxy composites with a thermal expansion coefficient of 2.5 × 10−5/K, thermal conductivity of 1.18 W/m · K and dielectric permittivity in the range 4–5 at 1 kHz have been obtained. The study confirms that although the micro fillers seem to exhibit good thermal conductivity and low expansion coefficient, the nano-size ceramic fillers are candidate as cofillers for low dielectric permittivity. However, a suitable proportion of nano/micro-mixed fillers is necessary for achieving epoxy composites with promising thermal conductivity, controlled coefficient of thermal expansion and dielectric permittivity. Copyright © 2013 John Wiley & Sons, Ltd.

Thermal properties and the structure of amorphous Sb 2 Se 3 thin film

Abstract: The amorphous Sb2Se3 film with a thickness ~0.9 µm was prepared by thermal evaporation and its composition was confirmed using an energy-dispersive X-ray analysis. The amorphous state was checked by an X-ray diffraction analysis. The optical gap E g opt was determined to be 1.32 eV. The glass transition temperature could not be found by either a differential scanning calorimetry or a thermomechanical analysis. The film was crystallized and characterized using the quasi-isothermal method. The temperature dependence of the isobaric heat capacity was raised monotonously and no drop over the course of the crystallization was observed. The temperature-modulated thermomechanical analysis determined a temperature T = 133 °C which can be assumed to be the temperature of the structural reorganization beginning. Raman spectra of amorphous Sb2Se3 revealed that the vibrations of both the amorphous and crystalline phase are close to one other. Raman scattering revealed that both the short and the medium-range order of amorphous and crystalline phases are similar.

A coupled thermomechanical beam finite element for the simulation of shape memory alloy actuators

Abstract: The proposed article describes the development of a new beam finite element for the coupled thermomechanical analysis of shape memory alloy actuators. The element is formulated, assuming coupled equilibrium equations for the thermoelastic stresses and thermal loads. Displacements and temperature are treated as internal degrees of freedom giving the ability to predict the coupled thermal–displacement response of a shape memory alloy beam. The constitutive shape memory alloy model of Lagoudas and coworkers is implemented in the formulation. A generalized beam theory is formulated assuming shear deformation with a cubic temperature field through the thickness. The new element is capable to simulate heat transfer phenomena, electric Joule heating as direct input, and heat convection effects. The coupling between mechanical and thermal equilibrium equations due to endothermic/exothermic martensitic transformation procedures is also included. Numerical results and evaluations of the developed beam element are p...

Thermomagnetic processing of liquid-crystalline epoxy resins and their mechanical characterization using nanoindentation.

Abstract: A thermomagnetic processing method was used to produce a biphenyl-based liquid-crystalline epoxy resin (LCER) with oriented liquid-crystalline (LC) domains. The orientation of the LCER was confirmed and quantified using two-dimensional X-ray diffraction. The effect of molecular alignment on the mechanical and thermomechanical properties of the LCER was investigated using nanoindentation and thermomechanical analysis, respectively. The effect of the orientation on the fracture behavior was also examined. The results showed that macroscopic orientation of the LC domains was achieved, resulting in an epoxy network with an anisotropic modulus, hardness, creep behavior, and thermal expansion.

Effect of reinforcement of sustainable β‐CaSiO3 nanoparticles in bio‐based epoxy resin system

Abstract: The β-CaSiO3 nanoparticles (NPs) were prepared using calcium carbonate from egg shells and silica as precursors. These NPs were incorporated (1–4 wt %) into bio-based epoxy resin to fabricate nanocomposites. Thermal and mechanical tests were carried out on these composites. The results of dynamic mechanical analysis showed significant improvement in the storage modulus of 1 and 2 wt % composites. The thermomechanical analysis data revealed ∼19 and 20% of reduction in coefficient of thermal expansion for 1 wt % of CaSiO3 before and after glass transition as compared to the neat epoxy system. Thermogravimetric analysis results also showed delayed thermal degradation of the composites by significant amounts (17–35°C) for 5% of decomposition, a proportional increase in residues corresponding to the loading concentrations. The flexure tests showed significant improvements in strength (17–36%), modulus (5–33%), and toughness for 1–4 wt % of reinforcement of β-CaSiO3 NPs. Theoretical calculations of the reinforcement effect on the flexure modulus of the composites agree well with the experimental values. The scanning electron micrograph of the fractured surfaces revealed better interfacial interactions in the composites and enhancements in crack path deflections over the neat specimen. © 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014, 131, 40867.

Thermal analysis of phase transitions in perovskite electroceramics

Abstract: Perovskite oxide ceramics have found wide applications in energy storage capacitors, electromechanical transducers, and infrared imaging devices due to their unique dielectric, piezoelectric, pyroelectric, and ferroelectric properties. These functional properties are intimately related to the complex displacive phase transitions that readily occur. In this study, these solid–solid phase transitions are characterized with dielectric measurements, dynamic mechanical analysis, thermomechanical analysis, and differential scanning calorimetry in an antiferroelectric lead-containing composition, Pb0.99Nb0.02[(Zr0.57Sn0.43)0.92Ti0.08]0.98O3, and in a relaxor ferrielectric lead-free composition, (Bi1/2Na1/2)0.93Ba0.07TiO3. The (Bi1/2Na1/2)0.93Ba0.07TiO3 ceramic develops strong piezoelectricity through electric field-induced phase transitions during the poling process. The combined thermal analysis techniques clearly reveal the differences in unpoled and poled ceramics.

Relationship between interfacial stress and thermal expansion coefficient of copper–matrix composites with different reinforced phases

Abstract: Copper–matrix composites reinforced with Al2O3, SiO2, SiC and MgO nanoparticles were fabricated using powder metallurgy. The effects of the different nanoparticles on the thermal expansion behaviour of the composites were examined. The thermal expansion properties of the composites were evaluated using the coefficient of thermal expansion from 50 to 500°C. The relationship between interface stress and coefficient of thermal expansion of the copper–matrix composites with various reinforced phases was determined using theoretical models and experimental data. The results show that introducing dispersed nanoparticles into the copper matrix can significantly reduce the coefficient of thermal expansion. By contrast, increasing the temperature increases the thermal expansion coefficient of the copper–matrix composites and the interfacial pressure between the reinforcements and the copper matrix. The calculated pressure values at the nanoparticle–copper matrix interface suggest that plastic deformation o...

New epoxy thermosets modified with amphiphilic multiarm star polymers as toughness enhancer

Abstract: The synthesis and characterization of two novel amphiphilic multiarm star polymers with linear polyethylene glycol (PEG) and poly(e-caprolactone) (PCL) arms and their use as toughening modifiers of epoxy anhydride thermosets are reported. The new star polymers were obtained by partial pegylation of a hyperbranched polyester and subsequent growth of PCL arms. The curing process was studied by calorimetry and thermomechanical analysis, demonstrating the accelerating effect and the influence on gelation of the hydroxyl terminal groups. The curing kinetics was analyzed by model-free and model-fitting methods. The final properties of the resulting materials were determined by thermal and mechanical tests. The addition of the star-like modifiers led only to notable improvement on impact strength in the material containing a 10% of the star with PCL and PEG arms, without compromising glass transition temperature and thermal stability. The morphology of the resulting materials depended on the structure of the toughness modifier used, as demonstrated by electron microscopy, but all modified thermosets obtained showed phase-separated morphologies with nanosized particles.

Thermal properties of concrete with different Swedish aggregate materials

Abstract: Earlier studies show that different concrete aggregates have different thermal properties, and from this an idea to optimize thermal properties of concrete was developed. The purpose of this master thesis is to investigate thermal properties of concrete so additional costs and negative environmental impacts can be minimized. Measurements of thermal properties of different Swedish aggregates from existing quarries were investigated. It will also study if the thermal properties affect ther thermal expansion of concrete. The experimental study in this work was done in laboratory conditions. Preparation studies that were made before casting concrete were sieving aggregates, density of aggregates and moisture content. While the concrete was fresh standard tests such as slump, air-content and density of fresh concrete were made. When the concrete was 28 days old compressive cube strength and thermal expansion measurement were executed. The thermal properties (thermal conductivity, volumetric heat capacity and thermal diffusivity) were measured on aggregates and concrete cubes with the instrument Hot Disk 2500-S. The results show that the minerals quartz and magnetite have significantly different thermal properties than the other studied aggregates/concretes. The aggregate/concrete with high amount quartz mineral has high thermal conductivity and diffusivity. The aggregates/concrete with magnetite has high thermal conductivity and volumetric heat capacity. The other aggregates and concretes have similar thermal properties. The thermal expansion coefficients have similar values (12.6-15.5∙ 1 /⁰C) for different aggregates, and it was not possible to see if there was a correlation between them and the thermal properties. Thus was the value of thermal expansion coefficient in a range that is normal for concrete. The thermal shock resistance is dependent of the thermal conductivity, thermal expansion coefficient, fracture strength and elastic modulus. The concretes with high thermal conductivity also had high thermal shock resistance whereas so such concrete should better resist rapid temperature changes. The conclusions that can be drawn from this work are that the thermal properties of the aggregates will be reflected in the properties of the concrete. For both thermal conductivity and heat capacity the values for the dry concretes (RH 10-30%) were about 40-70% of the values of the aggregates. Note that this conclusion only applies for thermal conductivity and heat capacity and does not apply on thermal diffusivity, since diffusivity is the ratio of conductivity and capacity it will be similar in the concrete. In this study only two aggregates significantly affected the thermal properties: quartz has high thermal conductivity and diffusivity and magnetite rock has high thermal conductivity and heat capacity. Another conclusion from this study was high thermal conductivity also give high thermal shock resistance, where the concrete resist rapid temperature changes better.

Thermophysical properties of Ti-5Al-5V-5Mo-3Cr-1Zr titanium alloy

Abstract: The thermophysical properties of the Ti-5Al-5V-5Mo-3Cr-1Zr titanium alloy in a wide range of temperatures from room temperature to 1000°C have been studied by the methods of differential scanning calorimetry, the laser flash method, and dilatometry. The obtained data on heat capacity, thermal diffusivity, and thermal expansion have been used for calculating coefficient of thermal conductivity. The sequence and temperatures of structural transformations during heating of the alloy have been established. It has been shown that the studied alloy possesses a coefficient of thermal conductivity that is 3.5–4 times smaller than that of pure titanium.

An optimized preparation of bismaleimide–diamine co-polymer matrices

Abstract: The main aim of this study was to develop an improved method for the preparation of a bismaleimide-diamine (BMI/DDM) polymer matrix, achieving shorter curing time, longer processing time (pot life), and good thermal mechanical properties. A matrix of BMI/DDM thermoset was prepared at optimal conditions and formulation, containing BMI and DDM in a 2:1mol ratio with 0.1wt% of dicumyl peroxide (DCP) as the curing accelerator. An optimal temperature of 150°C was selected for both melt-mixing and curing processes. The mechanism of matrix preparation was also investigated using differential scanning calorimetry and quantitative Fourier transformed infrared analysis. DCP at the optimal concentration was found to accelerate cross-linking reactions between BMI and DDM without inhibiting the chain-extension reaction of BMI. The specified formulation exhibited longer gel time (208s/g) and shorter post-curing time (2h) compared to other formulations. In addition, thermomechanical behavior and thermal stability were analyzed by dynamic mechanical analysis and thermomechanical analysis, and thermogravimetric analysis, respectively. The storage modulus (E'), glass transition temperature (Tg), and decomposition temperature (Td) of the BMI/DDM thermosets increased with the BMI content of the formulations, while the coefficient of thermal expansion and damping behavior (tan I´) decreased in a similar manner, primarily because of an increase in the degree of cross-linking.

Coefficient of thermal expansion and mechanical properties at cryogenic temperature of core-shell rubber particle modified epoxy

Abstract: In order to obtain epoxy based composite with low coefficient of thermal expansion (CTE) and good mechanical properties at cryogenic temperature (77 K), core–shell rubber (CSR) particles were integrated into epoxy. Fourier transform infrared spectroscopy results showed the occurrence of intermolecular hydrogen bond between the CSR particles and the epoxy matrix. The results of thermomechanical analysis indicate that the CTE of CSR–epoxy composites below Tg reached the minimum of the CSR content of 0·5 wt-%, then followed by an increase when the CSR content was higher than 0·5 wt-%. The CTE value under Tg was decreased 18·89% with 0·5 wt-% CSR content. The tensile strength, Young’s modulus and impact strength of CSR–epoxy composites at 77 K all reached a maximum with the CSR content of 0·5 wt-%, followed by a decrease when the CSR content was higher than 0·5 wt-%. The storage modulus of CSR modified epoxy resin in glassy region was higher than that of the neat epoxy resin.

Structural and Contact Analysis of a 3-Dimensional Disc-Pad Model with and without Thermal Effects

Abstract: A B S T R A C T The motivation of this work is to identify thermal effects on the structural and contact behaviour of a disc-pad assembly using a finite element approach. The first analysis is performed on the disc-pad model without the presence of thermal properties. Structural performance of the disc-pad model such as deformation and Von Mises stress is predicted. Next, thermomechanical analysis is performed on the same disc-pad model with the inclusion of convection, adiabatic and heat flux elements. The prediction results of temperature distribution, deformation, stress and contact pressure are presented. Comparison of the structural performance between the two analyses (mechanical and thermomechanical) is also made. From this study, it can assist brake engineers to choose a suitable analysis in order to critically evaluate structural and contact behaviour of the disc brake assembly. © 2014 Published by Faculty of Engineering