Volume Fraction Of Filler Particles Research Articles

Heat conduction model based on percolation theory for thermal conductivity of composites with high volume fraction of filler in base matrix

In this article, we propose a computational heat conduction model to estimate the thermal conductivity of composites with high volume fraction of filler particles distributed randomly in the base matrix. Most of the presently available models used for estimating the thermal conductivity of the composite materials fail after a certain volume fraction of the filler due to the effect of percolation i.e. the formation of ‘heat transfer paths’ formed by the filler particles within the composite. The proposed model accounts for this percolation effect and estimates the thermal conductivity of a composite material with Aluminium as the filler in the Epoxy matrix. The algorithm for the proposed model is developed using MATLAB program and is used to obtain the thermal conductivity of the composite by entering the specifications of the parent components of the composite. The proposed model is able to predict the thermal conductivity of composites of high volume fraction of filler over the temperature range of 50 K–300 K and the results obtained are in good agreement with the experimental data.

Sandwich-Structured PVDF-Based Composite Incorporated with Hybrid Fe3O4@BN Nanosheets for Excellent Dielectric Properties and Energy Storage Performance

High-performance energy storage materials are of essential importance in advanced electronics and pulsed power systems, and the polymer dielectrics have been considered as a promising energy storage material, because of its higher dielectric strength and more excellent flexibility compared with that of inorganic ceramic dielectrics. However, the energy storage capability of pristine polymer has been limited by its low intrinsic dielectric permittivity and ordinary ferroelectric performance. Herein, this work demonstrates a favorable method to achieve a sandwich-structured poly(vinylidene fluoride) (PVDF)-based composite by the electrospinning, solution casting, thermal quenching, and hot-pressing process. This innovative method combines with the 0.5Ba(Zr0.2Ti0.8)O3-0.5(Ba0.7Ca0.3)TiO3 nanofibers (BZT-BCT NFs), which possesses good ferroelectric hysteresis, and the hybrid particles of hexagonal boron nitride nanosheets (BNNSs) coated by ferroferric oxide (Fe3O4@BNNSs), which hold high breakdown strength (Eb). It is worth mentioning that the Fe3O4 particles disperse well on the surface of BNNSs to form the dipoles with the BNNSs at the interfacial region, resulting in an enhancement of the electric displacement and the dielectric permittivity of the composite. Furthermore, the influence of the volume fraction of filler particles on the electrical performance of composite was systematically investigated. Notably, the enhanced performance in terms of electric displacement (D), Eb, and discharged energy density (Ue) was achieved in the sandwiched BZT-BCT NFs-PVDF/Fe3O4@BNNSs-PVDF/BZT-BCT NFs-PVDF composite. The Ue of ∼8.9 J/cm3 was achieved at 350 kV/mm, which was 740% higher than the Ue of biaxially oriented polypropylene (BOPP, Ue ≈ 1.2 J/cm3 at 640 kV/mm). Of particular note is that the hybrids Fe3O4@BNNSs play a critical role to enhance the D and Eb and suppress the remnant displacement (Dr) of sandwiched composite. This contribution proposes an efficient and scalable method to prepare polymer-based dielectric composite for the demanded applications.

The Young's Modulus, Fracture Stress, and Fracture Strain of Gellan Hydrogels Filled with Whey Protein Microparticles.

Texture modifying abilities of whey protein microparticles are expected to be dependent on pH during heat-induced aggregation of whey protein in the microparticulation process. Therefore, whey protein microparticles were prepared at either pH 5.5 or 6.8 and their effects on small and large deformation properties of gellan gels containing whey protein microparticles as fillers were investigated. The majority of whey protein microparticles had diameters around 2 μm. Atomic force microscopy images showed that whey protein microparticles prepared at pH 6.8 partially collapsed and flatted by air-drying, while those prepared at pH 5.5 did not. The Young's modulus of filled gels adjusted to pH 5.5 decreased by the addition of whey protein microparticles, while those of filled gels adjusted to pH 6.8 increased with increasing volume fraction of filler particles. These results suggest that filler particles were weakly bonded to gel matrices at pH 5.5 but strongly at pH 6.8. Whey protein microparticles prepared at pH 5.5 showed more enhanced increases in the Young's modulus than those prepared at pH 6.8 at volume fractions between 0.2 and 0.4, indicating that microparticles prepared at pH 5.5 were mechanically stronger. The fracture stress of filled gels showed trends somewhat similar to those of the Young's modulus, while their fracture strains decreased by the addition of whey protein microparticles in all examined conditions, indicating that the primary effect of these filler particles was to enhance the brittleness of filled gels.

English

This paper reports on the application of a special purpose finite element analysis tool that combines augmented finite element methodologies (AFEM) and cohesive zone model (CZM) methods to simulate initiation and propagation of both cohesive and adhesive cracks. The constitutive behaviour of an aluminium/silicon carbide metal matrix composite was predicted and compared with experimental data as an example of a material system controlled by cohesive cracks. The simulation allowed to determine the strain level, at which particle fracture was initiated and illustrates how the overall material response is dominated by particle fracture beyond that strain level. The effects of silica filler particles on the lifetime of polyurethane matrix aircraft coating systems were investigated in a second example in which adhesive cracks at the filler/matrix interface are a dominant failure mechanism. The influence of particle volume fraction and particle/matrix interface adhesion strength on coating lifetime predictions were investigated and the results show that low filler particle volume fraction and high interface adhesion strength improve coating durability. In general, the paper demonstrates the potential of combined AFEM and CZM micromechanical damage simulation to gain improved understanding of damage mechanisms in heterogeneous materials and to support analysis and design of advanced material systems. Key words: Augmented finite element method, phantom node method, cohesive zone modelling, metal matrix composite, aircraft coatings.

Mechanical properties of a diamond–copper composite with high thermal conductivity

Abstract Using pressureless infiltration of copper into a bed of coarse (180 μm) diamond particles pre-coated with tungsten, a composite with a thermal conductivity of 720 W/(m K) was prepared. The bending strength and compression strength of the composite were measured as 380 MPa. As measured by sound velocity, the Young's modulus of the composite was 310 GPa. Model calculations of the thermal conductivity, the strength and elastic constants of the copper–diamond composite were carried out, depending on the size and volume fraction of filler particles. The coincidence of the values of bending strength and compressive strength and the relatively high deformation at failure (a few percent) characterize the fabricated diamond–copper composite as ductile. The properties of the composite are compared to the known analogues — metal matrix composites with a high thermal conductivity having a high content of filler particles (~ 60 vol.%). In strength and ductility our composite is superior to diamond–metal composites with a coarse filler; in thermal conductivity it surpasses composites of SiC–Al, W–Cu and WC–Cu, and dispersion-strengthened copper.

Physical and Thermal Characterization of Red Mud Reinforced Epoxy Composites: An Experimental Investigation

The present paper deals with the effect of volume fraction of filler particles on the effective thermal conductivity (keff) of particulate filled polymer composites. A new class of epoxy based composites reinforced with an industrial waste i.e. red mud, with filler content ranging from 0 to 25 vol % has been prepared by conventional hand lay-up technique. keff of these fabricated samples are measured and then compared with the values obtained from themathematical model proposed by the authors in their earlier investigation and also with some existing models. A significantenhancement of about 135% in the value of keff is observedfor maximum filler loading. This comparison tells that,among all the models,the results obtained from the proposed model are in closest approximationwith the measured values. Some physical properties like density and void fraction together with morphological behavior of the entire fabricated specimens are also reported.

Pengaruh partikel filler terhadap modulus elastisitas resin komposit Effect of filler particles on the elastic moduli of resin composites

Modulus of elasticity is one of the mechanical properties of composite resins affects the resistance to deformation,the strength of bonding with tooth structure and wear resistance. Modulus of elasticity is determined by the volumefraction of filler particles as the inorganic phase composite resin. This literature study aims to evaluate the size,shape and type of filler particles that affect the modulus of elasticity for composite resin. In a constant volumefraction, the larger size of filler material tends to make more rigid while irregular shape of particles produceshigher modulus of elasticity than spherical form of particles. In addition, the type of filler particles also determinesthe modulus of elasticity for resin composite, such as silica as the main type of filler particles will enhance themodulus of elasticity whereas zirconium can result in a higher stiffness. In order to get composite resin restorationwith appropriate modulus of elasticity the necessary knowledge about the effect of different filler particle isrequired.

Thermal expansion behavior of composites based on axisymmetric ellipsoidal particles

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.

Optimization of Thermal Interface Materials for Electronics Cooling Applications

Thermal interface materials (TIMs) are used in electronics cooling applications to decrease the thermal contact resistance between surfaces in contact. A methodology to determine the optimal volume fraction of filler particles in TIMs for minimizing the thermal contact resistance is presented. The method uses finite element analysis to solve the coupled thermo-mechanical problem. It is shown that there exists an optimal filler volume fraction which depends not only on the distribution of the filler particles in a TIM but also on the thickness of the TIM layer, the contact pressure and the shape and the size of the filler particles. A contact resistance alleviation factor is defined to quantify the effect of these parameters on the contact conductance with the use of TIMs. For the filler and matrix materials considered-platelet-shaped boron nitride filler particles in a silicone matrix-the maximum observed enhancement in contact conductance with the use of TIMs was by a factor of as much as nine.

Micromechanics of deformation in particle-toughened polyamides

It is now well appreciated that a number of semicrystalline polymers can be effectively toughened by the addition of a well-dispersed secondary phase, when the average interparticle matrix ligament thickness, Λ, of the blend is reduced below a critical length parameter, Λ c. This critical parameter is a specific material characteristic of the base polymer and can be achieved by various combinations of filler particle volume fraction and particle size. Recently, the significant improvements in toughness achieved when Λ≤ Λ c were attributed to a morphological transition taking place when interface-induced crystallization of characteristic thickness Λ c/2 successfully percolates through the primary phase. These transcrystallized layers are highly anisotropic in their mechanical response and, as a result, change the preferred modes of plastic deformation in the material, enabling the large plastic strains, which provide the high toughness. This study aims to elucidate the micromechanics and micromechanisms responsible for the high toughness exhibited by these morphologically altered heterogeneous systems via a series of micromechanical models. The case of polyamide-6 modified with cavitating spherical elastomeric particles treated as voids is modeled. It is found that the mechanical response and local modes of plastic deformation of these systems depend strongly on the morphology of the primary phase, the volume fraction of filler particles and the level of applied stress triaxiality. In particular, when Λ< Λ c and highly textured material percolates through the matrix, the material is found to deform by multiple shear banding along crystallographic planes of low shear resistance in the matrix ligaments diagonally bridging particles. This mode of plastic deformation is found to be robust to increases in triaxiality and, indeed, the textured material acts to resist void growth while promoting shear along the preferentially oriented crystallographic planes.

Onset of electrical conduction in isotropic conductive adhesives: a general theory

A new theory is introduced for the onset of electrical conduction in isotropic conductive adhesives, based on the observation that conduction is a result of the creation of conducting contacts in metal–insulator composite adhesives. The present theory resolves several prevalently contradicting issues including the onset dependency of electrical conduction on the volume fraction of filler particles, the particle size, the pressure effect, and the type of insulator matrix of an adhesive. The theory also predicts the condition for the occurrence of two percolation thresholds.

Effects of temperature on mechanical properties of composite dental restorative materials

In the oral environment, dental restorative materials are exposed to temperatures ranging from 10 degrees to 50 degrees C. Since the properties of many polymeric materials are sensitive to temperature of this magnitude, it is important to define the effects of service temperature on the mechanical properties of polymer matrix dental composites. Six commercial composites were tested in compression at 11 temperatures, ranging from 2 degrees to 80 degrees C. The volume fraction of filler particles in the materials is either 0.45 or 0.55, and they contain a range of particle sizes and particle compositions. The tests show that ultimate strength decreases linearly with increasing temperature. Strength is higher for the lower volume fraction material and is decreased by the presence of a small percentage of very large particles. Elastic modulus and yield strength decrease sigmoidally with increasing temperature and depend only on particle volume fraction. In the clinically significant temperature range, ultimate strength decreases 14%, the decrease in elastic modulus is either 6 or 11%, and the yield strength decreases 45%. The data show that the temperature conditions of the oral environment can significantly affect the mechanical properties of composite dental restorative materials.