Thermal Properties Of Composite Materials Research Articles

Thermal properties of graphene-based polymer composite materials: A molecular dynamics study

Interfaces between graphene play a crucial yet poorly understood role in the transport of heat in graphene-based composite materials. The primary focus of this study was on developing a quantitative understanding of the mechanism underlying the heat flow through the structure of a graphene-based polymer matrix composite material. The macroscopic thermal properties of the composite material were studied to provide an effective way to improve thermal conductivity for polymers. Molecular dynamics simulations were performed to understand the thermal resistance of interfaces between graphene and to optimize the condition of the interface for nanoscale thermal reinforcement. A modified Maxwell Garnett effective medium theory was used to predict the thermal conductivity of the composite material. The results indicated that the thermal properties of a graphene-based polymer matrix composite material depends upon the details of the microscopic structure and atomic interactions within the composite material. Interfaces between graphene contribute significantly to the thermal conductivity of the composite material. This is even more critical for composite materials where the lateral size of graphene can affect the thermal performance of the composite material significantly. Low thermal boundary resistance and high thermal conductivity can be achieved by introducing the structure of a carbon cross-link network between graphene. The proper combination of graphene with large size and carbon cross-links with high density can lead to a fifty-fold improvement in overall thermal performance for the polymer matrix composite material. The relative position between graphene can be adjusted for the further optimization of interfacial conditions, but with little success in nanoscale thermal reinforcement. The bulk thermal conductivity of graphene nanoribbons has been found to be about 2570 W/m·K at room temperature. The results can provide a theoretical basis for understanding the applied physics of thermal transport at the nanoscale in graphene-based polymer matrix composite materials.

Mechanical and Thermal Properties of Composite Material and Insulation for a Single Walled Tank for Cryogenic Liquids

Mechanical and Thermal Properties of Composite Material and Insulation for a Single Walled Tank for Cryogenic Liquids

Thermal Properties of Composite Materials Based on the Powder Systems “Copper–CNTs”

The influence of the metal matrix filling with carbon nanotubes on the thermal properties of copper-based powder composite materials has been studied. It has been revealed that the powder systems ″copper–CNTs″ obtained according to the powder-metallurgy technology by electric-contact sintering possess anisotropic thermal conductivity under certain conditions. It has been found that during uniaxial molding, in the process of electric-contact sintering, CNTs are oriented in one direction, which leads to a rise in the values of the thermal-conductivity coefficient in this direction. It has been established that at a CNT concentration below the percolation threshold, experimental values of the thermal-conductivity coefficient of the composite materials are in good correlation with the values obtained with the Maxwell–Garnett theoretical model. It was noted for the first time that the Maxwell–Garnett theoretical model can be used to assess the distribution of a nanosize filler in a metal matrix.

Heat Transfer at the Interface of Graphene Nanoribbons with Different Relative Orientations and Gaps

Because of their high thermal conductivity, graphene nanoribbons (GNRs) can be employed as fillers to enhance the thermal transfer properties of composite materials, such as polymer-based ones. However, when the filler loading is higher than the geometric percolation threshold, the interfacial thermal resistance between adjacent GNRs may significantly limit the overall thermal transfer through a network of fillers. In this article, reverse non-equilibrium molecular dynamics is used to investigate the impact of the relative orientation (i.e., horizontal and vertical overlap, interplanar spacing and angular displacement) of couples of GNRs on their interfacial thermal resistance. Based on the simulation results, we propose an empirical correlation between the thermal resistance at the interface of adjacent GNRs and their main geometrical parameters, namely the normalized projected overlap and average interplanar spacing. The reported correlation can be beneficial for speeding up bottom-up approaches to the multiscale analysis of the thermal properties of composite materials, particularly when thermally conductive fillers create percolating pathways.

Influence of different thermoplastic polymer/wood ratios on the mechanical and thermal properties of composite materials

This work compares the influence of different thermoplastic polymer/wood powder ratios on the mechanical and thermal properties of composite materials. These mass ratios were varied between 70:30 and 50:50, respectively. Moreover, the effect of a coupling agent incorporation, namely maleic anhydride polypropylene (MAPP), to promote better adhesion between both components, on these properties was evaluated. The composite materials were obtained by compression moulding process. The mechanical tests were subsequently performed to evaluate the tensile, flexural and impact properties. Besides that, the thermal properties were obtained using an Alambeta testing device. The experimental results show that the wood powder has the capacity to reinforce the thermoplastic polymer used, polypropylene (PP). The increase of mass fraction of wood powder on the final composite materials allows better mechanical properties, such as Young’s and flexural modulus. Comparing the composite materials with 70:30 and 50:50 ratios, it was verified the improvement of Young’s modulus by 1773 MPa to 2808 MPa, and flexural modulus by 1569 MPa to 1739 MPa. In the other hand, it was also verified that this trend contributes to the slight decrease on the thermal conductivity, namely from 0.145 W m-1 K-1 to 0.141 W m-1 K-1, respectively. The 2% MAPP incorporation leads to an even higher increase of the mechanical properties, namely in the Young’s modulus to 3320MPa, with 50:50 ratio. However, despite this trend, the same was not verified on the thermal conductivity, which increases to 0.145 W m-1 K-1. These results allow to conclude that the increase of wood powder can increase the mechanical properties of the PP composites, and the MAPP incorporation contributes to the better compatibility between both materials, increasing also these properties.

Transient Thermal Multiscale Analysis for Rocket Motor Case: Mechanical Homogenization Approach

This paper describes a mechanical homogenization approach to the application of a multiscale formulation for a transient heat transfer problem. The presented formulation evaluates the effective macroscopic thermal properties of composite materials and, by scaling down to the microscale level, provides the microscopic heat flux field by solving elastic problems at the microscopic scale (unit cell). This novel method has the advantage of applying periodic boundary conditions and a uniform macroscopic temperature gradient over the unit cell, which is not easy and often not practical to achieve with heat transfer computation software. The proposed multiscale analysis is verified by various examples of composite materials, and its efficiency is demonstrated on a large-scale problem involving a solid rocket motor.

Evaluation of effective thermal diffusivity and conductivity of fibrous materials through computational micromechanics

The aim of present study is to investigate the effective thermal properties of composite material via micromechanical modeling of the composite material as a heterogeneous material. These properties mainly include the thermal diffusivity and the thermal conductivity of composites. For this purpose, a definition is presented for effective thermal diffusivity for heterogeneous materials based on heat diffusion rate into the material in a transient heat transfer. A micromechanical model based on the Representative Volume Element (RVE) is presented for modeling the heat conduction in the fibrous composite materials. An appropriate heat transfer problem for the RVE is defined so that by the analogy of the numerical results the effective properties of the RVE can be estimated. A numerical method is employed to analyze the steady-state and transient heat flux and temperature in the RVE. To validate the model, the predictions of present model are compared with results of analytical method, FEM and some available experimental data in the open literature. The effective thermal conductivity and thermal diffusivity are then obtained for fibrous composites via the present micromechanical model. The SiC/Ti, SiC/Ti6%Al4%V and Glass/Epoxy composites with various fiber volume fractions are considered in this study.

Thermal properties of composite materials with a complex fractal structure

In this work, we report the thermal characterization of platelike composite samples made of polyester resin and magnetite inclusions. By means of photoacoustic spectroscopy and thermal relaxation, the thermal diffusivity, conductivity and volumetric heat capacity of the samples were experimentally measured. The volume fraction of the inclusions was systematically varied in order to study the changes in the effective thermal conductivity of the composites. For some samples, a static magnetic field was applied during the polymerization process, resulting in anisotropic inclusion distributions. Our results show a decrease in the thermal conductivity of some of the anisotropic samples, compared to the isotropic randomly distributed ones. Our analysis indicates that the development of elongated inclusion structures leads to the formation of magnetite and resin domains, causing this effect. We correlate the complexity of the inclusion structure with the observed thermal response through a multifractal and lacunarity analysis. All the experimental data are contrasted with the well known Maxwell–Garnett effective media approximation for composite materials.

Simulating Multiphysics of Discrete Fracture Path Development in Fibrous Composites

The long-term properties of continuous fiber reinforced composite materials are increasingly important as applications in airplanes, cars, and other safety critical structures are growing rapidly. The mechanical, electrical, and thermal properties of composite materials are altered by the initiation and accumulation of discrete fracture events whose distribution and eventual interaction defines the limits of design, such as strength and life. While a strong foundation of understanding has been established for damage initiation and accumulation during the life, an understanding of the nature and details that define fracture path development at the end of life has not been established. The present paper reports a multiphysics study of that progression, which is focused on measured and predicted changes in through-thickness electric/dielectric response of polymer based composites. Experimental data are compared to simulations of microdefect interactions and changes in electrical and mechanical properties. Applications of the concepts to prognosis of behavior are discussed. doi:10.12783/issn. 2168-4286/2.3/Reifsnider

Palm fibre-reinforced hybrid composites of poly(butylene succinate): characterisation and assessment of mechanical and thermal properties

The biodegradability and mechanical and thermal properties of composite materials made from glycidyl methacrylate-grafted poly(butylene succinate) (PBS-g-GMA) and palm fibre (PF) were evaluated. Composites of PBS-g-GMA and PF (PBS-g-GMA/PF) exhibited noticeably superior mechanical properties compared with those of PBS/PF, due to greater compatibility of PBS-g-GMA with PF. The dispersion of PF in the PBS-g-GMA matrix was highly homogeneous as a result of condensation reactions. In addition, the PBS-g-GMA/PF composites were more easily processed due to their lower melt torque. The water resistance of PBS-g-GMA/PF was higher than that of PBS/PF, although the weight loss of composites buried in soil compost indicated that both were biodegradable, especially at high levels of PF substitution. The PBS/PF and PBS-g-GMA/PF composites were more biodegradable than pure PBS, which implies a strong connection between PF content and biodegradability.

Dependence of SLS Parameters on Thermal Properties of Composite Material of Cement with Polyamide 12

SLS employs powder-processing in the construction of parts and SLS parameters depending on the thermal properties of the powder. An average of 80% to 90% of the powder in the build chamber is not sintered during the SLS process and could be reused in relation to its properties. However, the properties of un-sintered powder deterioratedue to exposure to a various temperature for extended periods of time during the SLS system material build-processin three stages, starting from warm up stage, the build stage, where the powder is exposed to just below the melting point of the material, and the cool-down stage. An experimental study of the thermal properties of composite material of cement and PA12 to determine the optimum parameters of SLS process are being investigated. The investigationuses the thermal properties of different proportions of composite material of cement and PA12. In addition, an experimental study of the thermal properties and physical properties of used or un-sintering powder to expand a methodology of controlling the SLS parameters, in turn to obtain consistent, good quality fabricated SLS specimens. ``

Thermal properties of composite materials : effective conductivity tensor and edge effects

The homogenization theory is a powerful approach to determine the effective thermal conductivity tensor of heterogeneous materials such as composites, including thermoset matrix and fibres. Once the effective properties are calculated, they can be used to solve a heat conduction problem on the composite structure at the macroscopic scale. This approach leads to good approximations of both the heat flux and temperature in the interior zone of the structure, however edge effects occur in the vicinity of the domain boundaries. In this paper, following the approach proposed in [10] for elasticity, it is shown how these edge effects can be corrected. Thus an additional asymptotic expansion is introduced, which plays the role of a edge effect term. This expansion tends to zero far from the boundary, and is assumed to decrease exponentially. Moreover, the length of the edge effect region can be determined from the solution of an eigenvalue problem. Numerical examples are considered for a standard multilayered material. The homogenized solutions computed with a finite element software, and corrected with the edge effect terms, are compared to a heterogeneous finite element solution at the microscopic scale. The influences of the thermal contrast and scale factor are illustrated for different kind of boundary conditions.

A technique for spatially-resolved contact resistance-free electrical conductivity measurements of aligned-carbon nanotube/polymer nanocomposites

The use of carbon nanotubes (CNTs) as an additive in polymer nanocomposites (PNCs) is being driven by a need to improve the mechanical, electrical, and thermal properties of composite materials for a variety of applications including advanced aerospace vehicles. The magnitude of electrical conductivity in CNT-containing PNCs is primarily influenced by the volume fraction, dispersion, interconnectivity and alignment of CNTs as well as the individual CNT properties, which are a function of diameter, chirality, and defects. Measurement techniques used to quantify the electrical conductivity of composites containing CNTs suffer from a host of issues including the influence of contact resistance, poor sample preparation leading to inadequate electrical contact of all concentric shells in aligned multi-walled CNT PNCs, and poor spatial resolution, which can obscure the micrometer- to millimeter-scale effects of inhomogeneities. In this study we demonstrate a new technique for measuring the local (∼100 μm resolution) conductivity of PNCs fabricated by infusing aligned CNT arrays with a non-conductive polymer, where the CNTs are continuous through the thickness of the composite. The technique involves the use of improved surface preparation processes, prior to the formation of electrical contacts, to ensure good electrical engagement of the CNTs. Furthermore, this technique provides a systematic process to remove the contribution of contact resistance and therefore measure the conductivity of the polymer nanocomposite alone. Using this technique we have measured a conductivity of 2.2 × 104 S/m for aligned CNTs (20% volume fraction) in RTM-6 aerospace epoxy.

Modeling and Simulation in Composite Materials: Integration from Nanostructure to Component-Level Design

The current special issue topic ‘‘modeling and simulation in composite materials’’ is intended to capture the recent advancements in the area of modeling and simulation in composite materials. The articles that appear under this topic describe theoretical models, molecular mechanics methods, finite-element methods, and multiscale methods for mechanical and thermal properties of composite materials. Review articles on the use of multiscale methods for composite materials, properties of metallic nanowires, and thermal conductivity of hollow particle filled syntactic foams have been included. The rapid growth in the usage of composite materials has made it necessary to summarize the progress made in the modeling and simulation fields and thus determine future perspectives.

Polyester/cellulose acetate composites: Preparation, characterization and biocompatible

AbstractThe biocompatibility, morphology, and mechanical thermal properties of composite materials composed of maleic anhydride‐grafted polylactide (PLA‐g‐MA) and cellulose acetate (CA) were evaluated. Composites containing maleic anhydride‐grafted PLA (PLA‐g‐MA/CA) exhibited noticeably superior mechanical properties due to greater compatibility between the two components. The dispersion of CA in the PLA‐g‐MA matrix was highly homogeneous as a result of ester formation, and the consequent creation of branched and cross‐linked macromolecules, between the carboxyl groups of PLA‐g‐MA and hydroxyl groups in CA. The human skin dermal fibroblasts (FBs) seeded on these two novel series membranes to verify the wound dressing characterization properties. With time‐dependent course, the FBs proliferation demonstrated a better increasing performance on the series membranes of PLA/CA than PLA‐g‐MA/CA. The immunofluorescent staining illustrated FBs with normal morphological features. The collagen amount from FBs on the PLA/CA series was 25% higher than that seeded on regular culture‐plates after 7 days incubation. With CA content from 0 to 20%, the collagen amount increased apparently and up to the position of CA20%. Otherwise, with PLA‐g‐MA membranes, the collagen amount showed moderate stimulations. The SEM image presented secreted collagen from FBs on the PLA/CA membrane, indicating the bio‐functional properties of these membranes. The above result analysis, this PLA‐g‐MA/CA composites has good mechanical properties and biocompatible, in the future when use adjusts the formula according to the functionality, may increase the product utility. © 2012 Wiley Periodicals, Inc. J Appl Polym Sci, 2012

Polycaprolactone-Based Green Renewable Ecocomposites Made from Rice Straw Fiber: Characterization and Assessment of Mechanical and Thermal Properties

The biodegradability and mechanical and thermal properties of composite materials made from maleic anhydride-grafted polycaprolactone (PCL-g-MA) and agricultural residues (rice straw fiber, RSF) were evaluated. Composites of PCL-g-MA and RSF (PCL-g-MA/RSF) exhibited noticeably superior mechanical properties compared to those of PCL/RSF due to greater compatibility of PCL-g-MA with RSF. The dispersion of RSF in the PCL-g-MA matrix was highly homogeneous due to ester formation between the anhydride groups of PCL-g-MA and the hydroxyl groups of RSF that resulted in the formation of branched and cross-linked macromolecules. In addition, the PLA-g-MA/RSF composites were more easily processed due to their lower melt viscosity. Water resistance of PCL-g-MA/RSF was higher than that of PCL/RSF, although weight loss of composites buried in soil compost indicated that both were biodegradable, especially at high levels of RSF substitution. The PCL/RSF and PCL-g-MA/RSF composites were more biodegradable than pure PCL,...

Characterization of cellulose acetate-reinforced aliphatic–aromatic copolyester composites

Abstract The biodegradability, morphology, mechanical, and thermal properties of composite materials composed of maleic anhydride-grafted poly(butylene adipate-co-terephthalate) (PBAT) and cellulose acetate (CA) were evaluated. Composites containing maleic anhydride-grafted PBAT (PBAT-g-MA/CA) exhibited noticeably superior mechanical properties due to greater compatibility between the two components. The dispersion of CA in the PBAT-g-MA matrix was highly homogeneous as a result of ester formation, and the consequent creation of branched and cross-linked macromolecules between the anhydride carboxyl groups of PBAT-g-MA and hydroxyl groups in CA. Each composite was buried in soil and monitored to assess biodegradability. Both the PBAT and the PBAT-g-MA/CA composite films were eventually completely degraded, and severe disruption of film structure was observed after 60–100 days of incubation. Although the degree of weight loss after burial indicated that both materials were biodegradable, even with high levels of CA, the higher water resistance of PBAT-g-MA/CA films indicated that they were more biodegradable than those made of PBAT.

Studies on the Composite Thermochomic Energy-Storage Materials Prepared by Sol-Gel Method

Composite thermochromic energy-storage materials (CTEM)were prepared by sol-gel method, Factors exerting influence on thermochomic and thermal properties of composite materials were discussed, such as the molar ratio of ester to water, the dosage of thermochomic materials, pH value were optimized via 3 factors and 3 levels of L9 (33) orthogonal design. Based on the research，when the molar ratio of ester to water was 1:7, dosage of thermochomic materials was 14g, pH value was 3, the optimal chromatic aberration and cooling time of the composite thermochromic energy-storage materials was successfully acquired. Results showed that the thermochomic materials were firmly enwrapped in silica of three-dimensional network structure, solving the problem of liquid release in the process of phase change and increasing its applications in textile, meanwhile it also had excellent thermochomic and thermal performance.

Preparation, characterization, and biodegradability of renewable resource‐based composites from recycled polylactide bioplastic and sisal fibers

AbstractThe biodegradability, morphology, and mechanical thermal properties of composite materials composed of polylactide (PLA) and sisal fibers (SFs) were evaluated. Composites containing acrylic acid‐grafted PLA (PLA‐g‐AA/SF) exhibited noticeably superior mechanical properties because of greater compatibility between the two components. The dispersion of SF in the PLA‐g‐AA matrix was highly homogeneous as a result of ester formation and the consequent creation of branched and crosslinked macromolecules between the carboxyl groups of PLA‐g‐AA and hydroxyl groups in SF. Furthermore, with a lower melt temperature, the PLA‐g‐AA/SF composite is more readily processed than PLA/SF. Both composites were buried in soil to assess biodegradability. Both the PLA and the PLA‐g‐AA/SF composite films were eventually completely degraded, and severe disruption of film structure was observed after 6–10 weeks of incubation. Although the degree of weight loss after burial indicated that both materials were biodegradable even with high levels of SF, the higher water resistance of PLA‐g‐AA/SF films indicates that they were more biodegradable than those made of PLA. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2011

Polyester/natural fiber biocomposites: preparation, characterization, and biodegradability

In this study, the biodegradability, morphology, mechanical, and thermal properties of composite materials composed of polybutyleneterephthalate (PBT), acrylic acid-grafted PBT (PBT-g-AA), and sisal fibers (SFs) were evaluated. Composites containing acrylic acid-grafted PBT (PBT-g-AA/SF) exhibited superior mechanical properties because of their greater compatibility with SF than PBT/SF. The dispersion of SF in the PBT-g-AA matrix was highly homogeneous due to ester formation and the creation of branched and cross-linked macromolecules between the carboxyl groups of PBT-g-AA and the hydroxyl groups of SF. Furthermore, due to its lower melting temperature (Tm), the PBT-g-AA/SF composite was more readily synthesized. Each composite was subjected to biodegradation tests in a soil environment. Both the PBT and PBT-g-AA/SF composite films were completely degraded, with severe disruption of the film structures observed after 60–100 days of incubation. Although the degree of weight loss following burial indicated that both materials were biodegradable, even with high levels of SF loading, the higher water resistance of PBT-g-AA/SF films indicated their higher biodegradability than the PBT films.