A new model for calculating the coefficients of thermal expansion, CTE, in all three coordinate directions is developed for composites containing aligned, axisymmetric elliptical particles, i.e., characterized by a single aspect ratio, that in the limit approximate the shapes of spheres, fibers and discs. This model is based on Elshelby's method but employs a somewhat different formulation than used in prior papers; a main advantage of the current approach is that it can be readily extended to composites based on ellipsoidal particles with no axes of symmetry, i.e., all three major axes are different, as recently demonstrated for modulus. CTE predictions for the simple case of axisymmetric particles are illustrated by calculations for glass particles in the shape of spheres, fibers and discs in an epoxy resin and are compared to those from the popular Chow theory. For spherical-shaped particles, the CTEs in all directions are the same and decrease modestly as the volume fraction of filler particles increases. As the particle aspect ratio increases from unity, the thermal expansion becomes anisotropic. The coefficient of longitudinal linear thermal expansion always decreases with increasing aspect ratio and filler loading due to the mechanical constraint of the filler. For aligned axisymmetric particles, the coefficients of linear thermal expansion are always the same in two directions. The values in the transverse direction may be higher or lower than that of the matrix depending on the values of aspect ratio and filler loading; these regions are mapped out for this particular set of matrix and filler properties. The two-dimensional constraints on matrix expansion caused by discs versus the one-dimensional effects of fibers cause quantitative differences in behavior for the two shapes.
Last. Gilles Régnier(Arts et Métiers ParisTech)H-Index: 19
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The accurate prediction of both the elastic properties and the thermal expansion coefficients is very important for the precise simulation of such processes as injection molding of short-fiber polymer-matrix composites. In this work, a two-step homogenization procedure is applied and compared with experimental values obtained on a polyarylamide/glass fiber composite for a broad range of temperatures. It is observed that the stiffness averaging version of the model surpasses the compliance averag...
Abstract Aligned nanoclay particles can be distributed randomly in a polymer matrix even at high volume fractions, but randomly oriented particles cannot be randomly distributed at high volume fractions. Instead a nanocomposite where there are clusters of nearly aligned particles is obtained. The clusters of nearly aligned particles form an effective particle with lower aspect ratio. This phenomenon which produces a nanocomposite of less stiffness than might have been expected has implications f...
Last. Donald R Paul(University of Texas at Austin)H-Index: 136
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The linear thermal expansion behavior of thermoplastic polyolefin, or TPO, nanocomposites based on a polypropylene/elastomer/masterbatch mixture was examined using a thermomechanical analyzer (TMA). For these experiments the masterbatch consisted of a mixture of organoclay and maleated polypropylene. The nanocomposites were prepared in a twin-screw extruder. The effects of both the elastomer domains and the filler particles on the thermal expansion behavior of the nanocomposites were investigate...
#2Donald R Paul(University of Texas at Austin)H-Index: 136
The rubber toughening of nylon 6 nanocomposites prepared from an organoclay was examined as a means of balancing stiffness/strength versus toughness/ductility. Nine different formulations varying in montmorillonite, or MMT, and maleated ethylene/propylene rubber or EPR-g-MA rubber content were made by mixing of nylon 6 and organoclay in a twin screw extruder and then blending the nanocomposites with the rubber in a single screw extruder. In this sequence, the MMT platelets were efficiently dispe...
#1Issam Doghri(UCL: Université catholique de Louvain)H-Index: 34
#2Laurent Tinel(UCL: Université catholique de Louvain)H-Index: 1
This paper is concerned with the micromechanics of multi-phase fiber- or inclusion-reinforced inelastic composites with a special emphasis on the numerical treatment of misaligned orientation. Mean-field homogenization of these composites involves volume and orientation averaging. The latter usually needs average orientation measures known as the second- and fourth-rank orientation tensors a and A, respectively. Usually the only orientation data available is a and a first issue is to reconstruct...
Last. Donald R Paul(University of Texas at Austin)H-Index: 136
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Abstract The relationship between morphology and the mechanical properties of thermoplastic olefin (TPO) materials that are reinforced with organoclay fillers and prepared by melt processing is reported. Nanocomposites based on blends of polypropylene and elastomer and using an organoclay masterbatch were prepared in a twin-screw extruder. Transmission electron microscopy, atomic force microscopy and wide-angle X-ray scattering were employed to carry out a detailed particle analysis of the morph...
#1K. Y. Lee(CNU: Chungnam National University)H-Index: 2
#2Donald R Paul(University of Texas at Austin)H-Index: 136
A model is developed for the mechanical properties of composites containing complex inclusions with no axes of symmetry, e.g. three dimensional ellipsoids (a1>a2>a3) characterized by two aspect ratios, α=a1/a3 and β=a1/a2, by using the Eshelby's equivalent tensor with a Mori–Tanaka type model. The influences of the primary and secondary aspect ratios on the effective elastic moduli of nanocomposites containing aligned isotropic inclusions are examined. The model is limited to unidirectionally al...
Last. Xiongjun Wang(SJTU: Shanghai Jiao Tong University)H-Index: 25
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The paper presents an analytical method to investigate thermal effects on interfacial stress transfer characteristics of single/multi-walled carbon nanotubes/polymer composites system under thermal loading by means of thermoelastic theory and conventional fiber pullout models. In example calculations, the mechanical properties and the thermal expansion coefficients of carbon nanotubes and polymer matrix are, respectively, treated as the functions of temperature change. Numerical examples show th...
Last. Donald R Paul(University of Texas at Austin)H-Index: 136
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A detailed study of the structure–property relationships for nanocomposites prepared using melt processing techniques from a sodium ionomer of poly(ethylene-co-methacrylic acid) and a series of organoclays is reported. Transmission electron microscopy, X-ray scattering, stress-strain behavior, and Izod impact analysis were used to evaluate the nanocomposite morphology and physical properties. Four distinct surfactant structural effects lead to improved levels of exfoliation and higher stiffness ...
The clay nanoparticles are readily dispersed and exfoliated in the PVC matrix with the help of Dioctyl phthalate (DOP) plasticizer. X-ray, TEM and AFM analysis of the nanocomposites indicate that there is an optimum concentration of DOP for the process. If used in high concentrations, the ability to transfer forces to the clay particles through the polymer matrix decreases due to substantial decrease in viscosity. The individual platy montmorillonite particles dispersed in PVC matrix were direct...
Abstract In order to prepare the epoxy material with high dimensional stability, alkoxysilyl-functionalized bisphenol A novolac epoxy was newly synthesized. The composite film of the new epoxy was prepared by adding polymer binder and its coefficient of thermal expansion (CTE) was measured. After alkoxysilyl-modification, the thermal expansion performance of the epoxy composite was significantly improved. At 80 wt% of silica added, the epoxy composite showed the CTE 1 (CTE at T Tg) of 9.6 ppm/°C...
This article discusses the use of biocompatible, two-part epoxies in medical devices. When used as adhesive encapsulants, these products improve the ruggedness of wire-bonded, chip-on-board microelectronic assemblies. Biocompatible products from Master Bond include EP42HT-2MED and the enhanced EP42HT-4AOMed Black product.
Epoxy resin samples were prepared using cycloaliphatic resin and anhydride curing agents. Response Surface Methodology (RSM) was applied to determine the effect of five independent variables (Silbond W12EST, MoldXA400, CSR, PC1000 and BYK3701) at 5 levels on the dependent variables thermal shock crack resistance (TSR) and track resistance. 33 experimental samples were prepared according to experimental design made by RSM. It was observed that not only an increase in the amount of MoldX A400 in t...
#2Amandine Codou(U of G: University of Guelph)H-Index: 6
Last. Manjusri Misra(U of G: University of Guelph)H-Index: 82
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Abstract Polyamide 6 (PA 6) nanobiocomposites were produced using a novel hybrid reinforcement strategy, utilizing a combination of biocarbon and nanoclay. Using melt extrusion and injection moulding, composites containing 30 wt.% filler were produced with various ratios of nanoclay to biocarbon. The morphology and crystalline structure were studied and revealed the anisotropic nature of the biocomposites. Further investigation of the polymer crystallization by differential scanning calorimetry ...
In the present investigation, a new equivalent micromechanics method is proposed, and then, an analysis model has been developed to estimate the nonlinear coefficients of thermal expansion (CTEs) of three-phase composites. As Compared with previous analytical models, the innovative point of this paper is that the influence of the debonding surface thickness is investigated. It is noted that the parameters of thickness of debonding surface have a significant effect on both the longitudinal CTEs a...
Abstract Alkoxysilyl-functionalized epoxy composites were recently reported to offer the ultra-low thermal expansion properties as low as 3–4 ppm/°C at 85 wt% of silica, not normally achievable with conventional epoxy systems . Understanding the curing mechanism of alkoxysilyl-functionalized epoxies is necessary for future applications, especially in semiconductor packaging. For this purpose, the distinctive chemistry of the alkoxysilyl-functionalized epoxy using imidazole and triphenylphosphine...
Last. Josef Breu(University of Bayreuth)H-Index: 35
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Abstract Different amounts of a low (L/h = 100) and a high aspect ratio (L/h = 22,000) synthetic clay (hectorite) have been compounded into a polyetherimide matrix by solution casting. By applying these fillers with largely different aspect ratios we were able to validate the different and partially contradicting models found in the literature to predict coefficients of thermal expansion (CTE) of nanocomposites. A comparison with experimentally observed CTEs identified Lu's model to give the bes...
In this consideration, a modified analysis model has been developed to estimate the nonlinear thermal conduction coefficients of three-phase composites through the presentation of a new equivalent micro-mechanics method. The effect of volume fractions of the fillers on the thermal conduction coefficient is studied. It is noted that the coefficients are very sensitive to the different particle volume fractions. The various thermal conductivity ratios between the fillers and matrix also have a gre...
Abstract In a micromechanics modeling of fiber reinforced composites, the thermal expansion coefficients and the elastic moduli of the composites are important physical parameters to predict the shrinkage and structure of the composites. We suggest a shrinkage inhibition concept for the composites before and after an annealing process and model the effects of the thermal expansion coefficient and the elastic modulus on the shrinkage of the composites by using the Mori-Tanaka models. The relaxati...
Abstract For the design of the semiconductor packaging material, one of the most important challenges is to overcome the higher thermal expansion property of ‘organic’ epoxy composite than that of the ‘inorganic’ IC chip. Therefore, in order to prepare the epoxy composite with the ultra-low coefficient of thermal expansion (CTE), the new material class of epoxy, i.e ., alkoxysilyl-functionalized novolac epoxy ( Si(OEt) 3 -EOCN ) was synthesized using the ortho-cresol novolac epoxy ( EOCN ) as a ...