Kerner Model Research Articles

Influence of reinforcement with multimodal distribution on thermophysical properties and fracture behavior in Al-Si/SiC composites infiltrated under super-gravity field

Super-gravity field assisted infiltration is reported as an effective method to obtain the nearly fully-dense Al-Si/SiC composites at relatively lower temperature, which inhibit the interfacial reaction and result in the enhancement of thermal conductivity (TC) and bending strength (BS). Currently, SiC reinforcement with multimodal distribution was designed to further enhance the TC and BS with lower coefficient of thermal expansion (CTE) of Al-Si/SiC composites. For the composites with monomodal SiC distribution, enlarging the size of SiC results in an enhancement of TC with the sacrifice of BS. Interestingly, for the composites with multimodal SiC distribution, the TC can be stabilized within an extended range (175-187W/m·K at 373K) with reduced CTE and higher BS. When the large to small size ratio was 1:2, the optimal comprehensive properties (CTE: 8.66×10-6K-1 ranged from 323 to 373K, TC: 179.2W/m·K at 373K, BS: 309 ± 9MPa) can be obtained. Hasselman-Johnson, Turner, and Kerner models are established to better understand the thermophysical properties, while the fracture behavior is discussed based on the track of crack propagation.

Effect of polymer infiltration and pyrolysis (PIP) on microstructure and properties of high volume fraction SiC/Al composites prepared by a novel hybrid additive manufacturing

High-volume-fraction SiC/Al (HVF-SiC/Al) composites have a wide range of applications in aerospace, optics, automotive and electronic packaging. However, because the hardness, brittleness and wear resistance increase with the increase in the volume fraction, it is difficult for traditional methods such as machining, to process HVF-SiC/Al composites to complex components. Therefore, in this paper, a novel method of the hybrid additive manufacturing is proposed to fabricate complex-structures SiC/Al composite parts. The effect of polymer infiltration and pyrolysis (PIP) on microstructure and properties of HVF-SiC/Al composites is investigated. The results show that the mechanical properties of the SiC preforms can be effctively enhanced by the PIP process, and this enhancement makes the SiC preforms meet the conditions for subsequent vacuum-pressure infiltration. The mechanical property of HVF-SiC/Al composites show a huge increase when in creasing the volume fraction of SiC. In particular, the flexural strength of HVF-SiC/Al composites increased from 202.28 MPa to 380.87 MPa, and the coefficient of thermal expansion (CTE) has also been reduced from 11.80 to 6.28 × 10−6/K, when the volume fraction of SiC increases from 42 to 80 vol%. For optimise the PIP process in the future, three theoretical models are used to predict the relationship between the CTE and the volume fraction of SiC. The results show that the experimental data are more consistent with the predicted values based on the Kerner's model, but deviate from the Rule-of-mixture (ROM) and Turner's models. Importantly, the complex-structures SiC/Al composite parts was successfully fabricated by this hybrid additive manufacturing.

Finite Element Analysis of Additively Manufactured Continuous Carbon Fiber-Reinforced Composites

AbstractThe objective of this study is to provide a numerical modeling approach for continuous carbon fiber (CCF)-reinforced fused filament fabricated composites. Although these materials have been extensively studied, an effective numerical modeling technique for their mechanical performance does not exist. To fill this technical gap, a numerical modeling approach based on finite element analysis is presented. The effective material properties of the Onyx matrix when voids are present are derived by the Kerner model. The material properties of CCF-reinforced composites are modeled by Hashin’s model. Both the flexural and tensile properties are simulated. The modeling approach is validated against various experimental results.

A Modified Kerner Model to Predict the Thermal Expansion Coefficient of Multi-Phase Reinforced Composites Al6092/SiC/LAS

A Modified Kerner Model to Predict the Thermal Expansion Coefficient of Multi-Phase Reinforced Composites Al6092/SiC/LAS

Comprehensive experimental investigations and theoretical predictions on the physical properties of natural rubber composites

AbstractConducting elastomers are highly desirable in the present world because of their major applications in the electronic industry. Conductive carbon black (CCB) is a conventional reinforcing filler commonly used in elastomers to modify the mechanical as well as electrical properties. The present study focuses on the experimental and theoretical computation of filler reinforcement, dielectric, mechanical, dynamic mechanical, and surface morphology of natural rubber (NR)/CCB composites. Two step processing method is adopted to attain homogeneous dispersion of filler in the matrix: preparation of NR/CCB masterbatch through melt mixing using internal mixer followed by compounding in a two‐ roll mill. Improved DC conductivity in the order of 10−6was obtained at higher filler loading indicating the formation of a continuous conductive network in the matrix. Percolation threshold was computed using Power law equation and obtained a value of 0.154 vol%. Theoretical predictions of mechanical modulus and tensile strength were done using rule of mixtures, Einstein, Guth and Kerner models and Nicolais‐Narkis and Kuneri‐Geil models respectively. A remarkable change in tensile strength is observed for NR as a function of the weight percentage of CCB; it is increased to 26.3 ± 0.9 MPa at 20 phr CCB from 17.1 ± 0.9 MPa for NR.

Thermal properties of diamond/Cu composites enhanced by TiC plating with molten salts containing fluoride and electroless-plated Cu on diamond particles

To improve the thermal properties of diamond/Cu composites for thermal management applications, we designed dual-coated diamond particles for preparing composites. A thin TiC coating is formed on diamonds using molten salt with NaCl-KCl-NaF, then electroless plating of Cu is applied. The effects of salt bath temperature on the formation of TiC coating and the percentage of modified diamonds on the thermal performance of the composites were investigated. At temperature as low as 700 °C, Ti and diamond particles forms a TiC coating with a thickness of 1 μm in molten salt containing fluoride. In response to an increase in temperature, the thickness of the formed TiC coating increases and is prone to cracking and flaking. Cu coating well coats the TiC/diamond by electroless plating. The hot-pressing diamond/Cu composite with 60 vol% modified diamonds exhibits the best thermal conductivity of 495.5 W·m−1·K−1, slightly below the values predicted by the model H-J and DEM, and lower thermal expansion coefficient of 5.86 × 10−6 K−1, corresponding to the Kerner model.

Design of ultrastretchable and super-elastic tailorable hydrophilic thermoplastic elastomeric materials

In this work, new ultrastretchable and super-elastic hydrophilic thermoplastic elastomeric (TPEs) materials were developed for the first time from the thermoplastic polyurethane (TPU) and epichlorohydrin-ethylene oxide-allyl glycidyl ether (GECO) rubber using straightforward melt-blending and dynamic vulcanization approaches, which allows the creation of tailorable hydrophilic TPE materials. The resulting materials can absorb up to ∼80% water within 4 h. The absorbed water convert itself into hexagonal ice crystals in the TPE matrix which was directly evident from differential scanning calorimetry and cryo-transmittance electron microscopy. The phase components of developed TPE were found to be interactive which was analysed from the torque and loss tangent values. Interaction was further enhanced after dynamic vulcanization which was predicted from the rheological Palierne model. Interestingly, interfacial tension between the TPU and GECO was significantly reduced after dynamic vulcanization which suggested stronger inter-domain interaction between the phase components. It was revealed that the resulting TPE possess droplet-matrix phase morphological structure which was supported from the theoretical Kerner model prediction. Surprisingly, resulting materials showed extraordinary elastomeric properties than that of TPEs reported earlier, such as very high strain at break (∼800–1000%) and lowest tension set (∼2–6%) which enables the creation of ultrastretchable and super-elastic materials. • A new kind of ultra-stretchable, superelastic and tailorable hydrophilic TPE was developed. • The developed TPE showed extraordinary elastic properties having high strain at failure (1000%) and low-tension set (∼2%). • The hexagonal ice crystals were formed in the TPE matrix by absorbed water.

Preparation and characterization of innovative poly(butylene adipate terephthalate)‐based biocomposites for agri‐food packaging application

AbstractThe present work reports on the preparation and subsequent mechanical, morphological and thermal characterization of composites based on poly(butylene adipate terephthalate) (PBAT), reinforced with micro‐particles of inorganic bioabsorbable calcium‐phosphate glass (CPG) at different contents up to 40 wt%. The PBAT‐CPG composites were prepared by solvent casting. The resulting composite pellets were used for the injection molding of model 1BA specimens, according to standard UNI EN ISO 527. PBAT‐CPG composites displayed an effective increase of the Young's modulus (E) up to 82% compared to the pristine polymer, while showing a reduction of the yield stress (σy) up to 20%, of the stress at break (σB) up to 46%, of the strain at break (εB) up to 57% and of the toughness (T) up to 72%. The values of E, σy and σB were also compared and validated with theoretical values calculated using Kerner's and Pukanszky's models. Scanning electron microscopy (SEM) images display homogeneous dispersion and distribution of the filler particles in the polymer matrix with no aggregates or phase separation that would cause a deterioration of the material properties. Infrared (IR) spectroscopy did not show structural variations of the polymer matrix due to the CPG presence. The oxygen permeability in PBAT‐based samples assumes significantly lower values when benchmarked with the permeability of low‐density polyethylene (LDPE). Among the different composites, a decrease in oxygen permeability is observed as the CPG concentration increases. Regarding water vapor permeability, PBAT‐based samples show a lower barrier effect than polyethylene (PE): in particular, permeability to water vapor assumes an increasing trend as the quantity of filler increases. The tuneable degradation of the final composite materials was defined by the disintegration degree (DD) determination under composting conditions in a laboratory‐scale reactor. The developed materials prove to be valid biodegradable and eco‐friendly alternatives to traditional thermoplastic polymers, such as LDPE, and can be applied in many fields, especially in package and mulch film applications.

Effects of Nd content on thermal expansion behavior of Mg-Nd alloys

The effects of annealing temperature, thermal cycle times, precipitates, and Nd content on the thermal expansion behavior of as-extruded Mg-xNd (x=2, 4) binary alloys were investigated. It demonstrated that the coefficient of thermal expansion (CTE) of alloys decreased with the increasing of Nd content. The annealing treatment eliminated partial residual stress inside the alloy, which led to the CTEs of annealed samples higher than that of the unannealed samples at low temperature. However, it was opposite at high temperature after multiple thermal cycles due to the amount of Mg41Nd5 phase increased after annealing treatment. The results of the calculated cumulative residual strain of the Mg-Nd alloys with thermal cycling indicated that the alloys annealed at 325 ℃ has the best thermal stability. The rule of mixtures (ROM) and Kerner model were proposed to predict the CTEs of Mg-Nd alloys. It was found that the prediction of the Kerner model was agrees well with the experimental data of 1st thermal cycle of samples without internal stress.

Microstructure, Dislocation Density and Thermal Expansion Behavior Using Thermo Elastic Models of Zircon Sand Reinforced as Cast ZA-27 Composites

In the present work stir casting route is used to fabricate the ZA27 Metal matrix composites containing 3 wt%, 6 wt%, 9 wt%, and 12 wt%. Zircon sand particulates of size 100 mesh. Microstructure studies using Optical Microscopy, SEM-EDAX are carried out to ascertain the distribution and morphology of particulates in the composites. Effect of zircon sand as reinforcement on bulk density, porosity, of the fabricated composites is studied. SEM studies are carried out to understand the behavior of as-cast ZA27 alloy reinforced with zircon sand. The dislocation density of the fabricated composite affects the strength of the composites and depends on the strain due to thermal mismatch and is found to increase with increase in weight% of zircon sand. However, it does not consider casting defects of voids/clustering observed in micrographs of the fabricated composite. Porosity in composites does not have influence on Coefficient of thermal expansion (CTE) of the ZA27 composites studied using thermoelastic models like Kerner and turner model and rule of mixtures of composite.

Theoretical Investigation of Thermal Expansion Coefficients of SiC Reinforced Copper Matrix Composites

The thermal expansion coefficient (CTE) of the copper element, which is widely used in the electronics industry, is quite high. It is of great importance to decrease the CTE value in order not to deform against the heat it is exposed to. In this study, it is aimed to theoretically examine the changes in CTE value when SiC supplement is applied to pure copper. For this purpose, CTE value calculations were made according to Kerner and Turner's models for composites that were reinforced at different rates by volume. Sample studies in the literature have been utilized for percent component ratios. In this context, the amount of reinforcement was adjusted to be 5, 10, 15, and 20vol.% by volume. According to the findings, it was observed that there was ̴ %4-17 decrease in CTE value based on the Kerner model and ̴ %7-26 decrease based on the Turner model.

Improvement of thermal properties of Al/Cu/SiC composites by tailoring the reinforcement microstructure and comparison to thermoelastic models

In the current investigation, Al/Cu/SiC composites with different reinforcement contents were prepared for thermal applications via powder metallurgy and hot pressing technique to study the effects of reinforcement content and structure on the thermal behavior of the samples. Microstructural characterizations showed that SiC and Cu particles were uniformly distributed, and a continuous Cu network structure was formed in the Al matrix. Density measurements revealed that the samples Al/15Cu/10SiC and Al/45Cu/20SiC had the highest and lowest relative density (97% and 90%), respectively. Microhardness evaluations displayed that the composite hardness improved as the Cu and/or SiC contents increased. Besides, the coefficient of thermal expansion of the composites increased nonlinearly by elevating the temperature and it reduced with increasing the SiC content. A comparison of thermal expansion coefficient values to the Turner and Kerner models showed a slight difference (lower that 8%) only for Al/15Cu/10SiC and Al/45Cu/20SiC samples. Thermal cycles examination exhibited that as the number of cycles increased, the thermal strain of the composites increased. Furthermore, the thermal expansion coefficient of Al/45Cu/20SiC reduced to values lower than 7 ppm that indicates the significance of Cu network structure.

Influence of partial substitution of carbon black with silica on mechanical, thermal, and aging properties of super specialty elastomer based composites

AbstractThe reduction of the carbon black quantity in elastomeric composites is a massive requirement from environmental perspective and a huge challenge for industrial implementation. The present work consists of the replacement of half amount of carbon black with silica without compromising the basic properties along with ushering of superior characteristics of fluoroelastomer and silicone rubber blends. The comparative study of carbon black‐silica hybrid filler (1:1 ratio) with carbon black and silica at different loadings shows much superior aging behavior and thermal stability compared with the other composites with unforeseen increment of tensile strength (56%). The fundamentals of rubber‐filler interaction and reinforcement phenomenon of the hybrid filler composites have been determined by the correlation of the experimental findings with different models like Nicolais‐Narkis, Nielsen, Guth, and Kerner model. Furthermore, enhanced compatibility between the two rubber phases has been observed in terms of Tg shifting (3.8°C) and reduced FKM domain size (from 450 to 300 nm) in the silicone rubber matrix for hybrid filler composites. Morphological studies reflect the selected homogeneous dispersion of the carbon black in fluoroelastomer domain and silica in silicone rubber phase. These super specialty elastomeric composites can be used as oil and fuel resistant gaskets and O‐rings for wide temperature range.

Microstructure and thermal properties of Cr7C3 coated graphite flakes/Al composites

Graphite flakes (Gf) were coated with Cr7C3 by salt bathing coating, and the Cr7C3 coated Gf reinforced Al matrix composites were prepared by gas pressure infiltration. Surface morphology of uncoated and Cr7C3 coated Gf, the interfacial characteristics of Cr7C3 coated Gf/Al composites were observed by SEM. Surface of Cr7C3 coated Gf is smooth without defects, the Cr7C3 coating effectively improved the wettability. When volume fraction of Gf is below 50%, the experimental value of thermal conductivity (TC) is basically consistent with the calculated value of the EMA model. When volume fraction of Gf is over 50%, the growth of deviates from the EMA model curve. Coefficient of thermal expansion (CTE) of composite was predicted by Kerner model and Orientation Disc model, because Kerner model does not consider the anisotropy of Gf and inaccurately predict the change of CTE. However, the Orientation Disc model can predict the change of CTE better, but there is certainly deviation.

The evolution on the microstructure and thermal expansion behavior of Al–50Si alloy with different P contents

In the previous work, the Al–50Si alloy with fine primary Si is prepared by a low-cost technology. In addition, the morphology of primary Si and the metamorphic mechanism as well as the thermal expansibility of alloy are also investigated in this work. The mean size of primary Si can obtain the min value of 33.82 µm when the content of modifier is 3%. The thermal expansibility of alloy decreases with the increasing of modifier. The influence of microstructure, solid solubility as well as porosity on the thermal expansibility are also studied in this research. Moreover, several theoretical models such as ROM model, Turner model, Kerner model and Schapery model are also used to predict the coefficient of thermal expansion (CTE) of alloy.

Friction and Mechanical Properties of Highly Filled Polybenzoxazine Composites: Nanosilica Particle Size and Surface Treatment

AbstractFrictional and mechanical properties of highly filled polybenzoxazine [poly(BA‐a)] composites which are influenced by nanosilica contents, particle sizes, and surface treatments are investigated. The coefficient of friction and wear resistance, storage moduli, and microhardness of the nanosilica‐filled poly(BA‐a) composites systematically increase with an increase of nanosilica content, while those values of the nanocomposites are improved with decreasing particle sizes at the equivalent nanosilica content. The modulus can be predicted by the Kerner model with the maximum packing fraction, while the microhardness of the nanocomposites is in agreement with the Halpin–Tsai model. The nanocomposites fabricated with untreated nanosilica particles exhibit higher frictional and mechanical properties when compared with the surface‐treated nanocomposites at the equivalent particle sizes. The interfacial interactions via covalent bond formation between the nanosilica and the poly(BA‐a) are determinative factors for the nanocomposite properties. Highly filled nanosilica‐poly(BA‐a) composites can be employed in various applications where wear‐resistance plays an important role.

Comparative Study on Experimental and Kerner Model Predictions of Viscoelastic Properties of Polyamide 6/ Polyvinyl Alcohol Blends

The Polyamide 6 (PA6) / Polyvinyl alcohol (PVOH) blends of different compositions (80/20, 60/40 and 50/50) were prepared by melt mixing in a Haake Rheomixer. The selected blend systems (80/20 and 60/40) were modified with dicumyl peroxide (DCP) and tertiary butyl cumyl peroxide (TBCP). The dynamic mechanical properties of blends were systematically investigated with special reference to the effect of blend ratio and effect of presence of peroxide over a temperature range -20°C to 110°C. The effect of change in the composition of the polymer blends on tan δ was studied to understand the damping characteristics. The mean field theory developed by Kerner has been used to estimate the dynamic properties and the estimated values are compared with the experimental values. The loss tangent curve of the blend exhibited single transition peak corresponding to the glass transition temperature (Tg) of Polyamide 6. Kerner model was found to satisfactorily predict the viscoelastic properties of the blends with polyamide content in the range 50 to 80 wt% assuming PA6 as matrix and for all compositions except 80/20 assuming PVOH as matrix. The Kerner model predictions for the selected blend systems with peroxides are not satisfactory and the co-continuous morphology of the peroxide treated blends were revealed by SEM observations.

Tunable Dielectric Properties of Poly(vinylidenefluoride-co-hexafluoropropylene) Films with Embedded Fluorinated Barium Strontium Titanate Nanoparticles

Fluoropolymer nanocomposites of poly(vinylidene fluoride-co-hexafluoropropylene) (PVdF-HFP) were prepared using fluorinated barium strontium titanate (Ba1−xSrxTiO3, BSTO) nanoparticles (NPs) by low-temperature synthesis using a modified liquid–solid solution process. The exact stoichiometry of as-synthesized BSTO NPs was confirmed by X-ray diffraction analysis along with lattice parameter calculations. The synthesized BSTO NPs were fluorinated using 2,2,2-trifluoroacetic acid as a fluorous ligand. The BSTO NPs showed high solubility in the fluorous system (polymer and solvent) on account of their modified surface. The root-mean-square roughness of the fluorinated BSTO/PVdF-HFP nanocomposite was 76 times lower than that of the nonfluorinated BSTO/PVdF-HFP nanocomposite. The dielectric constant of the fluorinated BSTO/PVdF-HFP nanocomposite exhibited Curie temperature behavior. The dielectric constant of the nanocomposite predicted using the modified Kerner model at room temperature agreed well with the experimental values.

Frequency-dependent dielectric properties of BTO/parylene nanocomposites with layered structure

First the frequency-dependent dielectric spectrum of a self-assembled pure $$\hbox {BaTiO}_{3}$$ (BTO) nanocrystalline thin film with consideration of the packing density is studied using the Lichtenecker logarithmic rule and the modified Kerner model. Then the Wiener lower bound is modified to evaluate the overall effective dielectric properties for 2–2 type of layered nanocomposites within a large frequency range, and a simple rule of mixture is found to be suitable for predicting the dielectric permittivity of multi-layered composites. The calculated dielectric properties of the BTO/parylene nanocomposites agree reasonably well with the experimental data, whereas a little discrepancy in the dielectric loss tangent is shown in the frequency range beyond $$10^{5 }\hbox {Hz}$$ .

Temperature dependence of the mechanical and thermal expansion behaviors of MoSi2-RSiC composites with a three-dimensionally (3D) interpenetrated network structure

In this paper, microstructure and temperature dependence of mechanical properties and thermal expansion coefficient (TEC) of the MoSi2–RSiC composites was investigated via XRD, SEM, mechanical and thermal behaviors test, etc. three-dimensionally fracture photographs confirm the 3D interpenetrating network structure of the composites, main compositions of the composites are 6H-SiC and tetragonal-MoSi2, a small amount of Mo4.8Si3C0.6 mainly exists on the interface between RSiC and MoSi2; With the increase of tested temperatures, flexural strength and fracture toughness of the composites both increase, fracture toughness of M-S-2.30 reaches 2.05 MPa m1/2 (1400 °C), showing the highest improvement of 57.69% as compared to that of RT value, the interface cracks self-healing behavior occurred at higher temperatures helps to improve the interface compressive stresses and increase the fracture toughness of the composites; With the increase of volume fraction of MoSi2, TEC values of the composites increase, mainly being due to the bond energy difference between Mo-Si (76.020 kJ mol−1) and Si-C(285.0 kJ mol−1) bonds. Theoretical analysis exhibits that modified Kerner model is fitter to express the temperature dependence of thermal expansion behavior of 3D interpenetrated network structure composites than that of modified Kerner and Schapery bound model.