Thermal Expansion Coefficient Of Composite Research Articles

Effects of cryo-thermal cycling on interlaminar shear strength and thermal expansion coefficient of carbon fiber/graphene oxide-modified epoxy composites

Carbon fiber reinforced polymer (CFRP) composites used in cryogenic environments have to bear cryo-thermal cycling but the effects of cryo-thermal cycling on the mechanical and physical properties of the CFRP composites have been rarely reported. Interlaminar shear strength (ILSS) and coefficient of thermal expansion (CTE) are two critical parameters for the successful applications of CFRP composites used in cryogenic environments. In this work, graphene oxide (GO) with a content range of 0.0-0.5 wt% was first introduced to modify epoxy resins in order to improve the ILSS and reduce the CTE of CF/epoxy composites. The GO-modified epoxy resins were then used as matrices to manufacture CFRP composites by a hot-press molding process. The effect of cryo-thermal cycling on the ILSS and CTE of CF/GO-modified epoxy composites were systematically investigated. It was displayed that the ILSS was enhanced by the addition of GO to epoxy resins and reached the maximum value at 0.2 wt% GO before and after cryo-thermal cycling; the CTE was also lowered to some degree by the addition of GO. Moreover, the results showed that the ILSS of the CF/modified epoxy composites was slightly increased after 50 cryo-thermal cycles while slightly decreased after 100 cryo-thermal cycles. Particularly, it was exhibited that the composite CTE was obviously influenced by the cryo-thermal cycling treatment. These results were properly interpreted in terms of fracture surfaces and interfacial thermal stresses. This work provides some valuable knowledge for guiding the usage of CFRP composites in cryogenic environments.

Thermal, mechanical, and electrical properties of LSCo/mullite composite contact materials for solid oxide fuel cells

AbstractLanthanum strontium cobaltite (LSCo) is considered as a good candidate cathode contact material for solid oxide fuel cells, due to high electrical conductivity. However, LSCo has a very large coefficient of thermal expansion (CTE) than the cells and metallic interconnects. As a result, poor mechanical stability is expected during thermal cycling. To minimize the CTE mismatch, we investigate a composite approach involving mixing LSCo with an inert material of low CTE, such as mullite at volume fractions from 0.1 to 0.4. Composite's CTE shows a decreasing trend with increasing mullite volume fractions and is consistent with model predictions. X‐ray powder diffraction analysis of sintered LSCo/mullite composites exhibits no presence of other phases for samples aged for 500 hours at 800°C, indicating chemical compatibility. Electrical conductivity by a 4‐pt method shows a decreasing trend with increasing mullite content. Contact strength of as‐sintered and thermally cycled samples show that only the composite with 0.4 volume fraction has a measurable strength; the other composites have no strength. Overall, the composite approach is demonstrated in the LSCo/mullite system to lower the CTE and hence achieve thermal cycle stability. The addition of the inert phase to the LSCo matrix, however, also reduces the electrical conductivity.

Effect of tensile rates on thermal and mechanical properties of porous PTFE composites

ABSTRACTTo achieve polymer‐matrix composites for sealing materials with thermostability and toughness, PTFE composites filled with short glass fibers (SGFs) were hyperthermal stretched to prepare a substrate material with high thermal stability and porosity. The effects of various tensile rates on the thermal and mechanical properties and morphologies were investigated. The results revealed that the thermal stability could be improved slightly and the thermal expansion coefficient of composites increased by the tensile rate. Through observing the morphologies, tensile process produced cavities and the increased tensile rate had negligible effects on porosity, which also could be proved by density test. From mechanical properties analysis, stretched composites exhibited that the tensile strength increases first and then decreases with the increased tensile rate. Although the variation tendency of Young's modulus is similar to that of tensile strength, which is smaller than that of unstretched composite. When the tensile rate reached 50 mm·min−1, the tensile strength and Young's modulus of the stretched composites increased by 65 and 9% to maximum, respectively. Meanwhile, elongation at break and shore hardness decreased. The thermal and mechanical properties improvement could be ascribed to the strain‐induced crystallization and crystal alignment. In addition, the interplanar spacing and grain size were inversely proportional to the tensile rate. © 2019 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2019, 136, 48175.

Coefficients of Thermal Expansion for Composites with Agglomerated Carbon Nanotubes

In this paper, a micromechanics model is presented, which can predict the thermal expansion coefficients (CTE) of composites with agglomerated carbon nanotubes (CNTs). In the present model, two aggregation parameters are introduced. The Mori-Tanaka method and rule of mixture model are adopted to estimate the effect of CNT agglomeration on the thermal expansion coefficients of composites. The aim of the present paper is to investigate the CTEs of CNTs reinforced composites, with an emphasis on the influence of two agglomeration parameters on the CTEs. It is noted that the carbon nanotube agglomeration has a strong influence on the thermal expansion coefficients of composites.

New Nanocomposite Materials with Improved Mechanical Strength and Tailored Coefficient of Thermal Expansion for Electro-Packaging Applications

In this research, copper nanocomposites reinforced by graphene nanoplatelets (GNPs) were fabricated using a wet mixing method followed by a classical powder metallurgy route. In order to find the best dispersion technique, ball milling and wet mixing were chosen. Qualitative evaluation of the structure of the graphene after mixing indicated that the wet mixing is an appropriate technique to disperse the GNPs. Thereafter, the influence of graphene content on microstructure, density, hardness, elastic modulus, and thermal expansion coefficient of composites was investigated. It was shown that by increasing the graphene content the aggregation of graphene is more obvious and, thus, these agglomerates affect the final properties adversely. In comparison with the unreinforced Cu, Cu–GNP composites were lighter, and their hardness and Young’s modulus were higher as a consequence of graphene addition. According to the microstructural observation of pure copper and its composites after sintering, it was concluded that grain refinement is the main mechanism of strengthening in this research. Apart from the mechanical characteristics, the coefficient of thermal expansion of composites decreased remarkably and the combination of this feature with appropriate mechanical properties can make them a promising candidate for use in electronic packaging applications.

Composites from poly(lactic acid) and bleached chemical fibres: Thermal properties

Poly (lactic acid) (PLA) reinforced with bleached kraft soft wood (BKSW) biocomposites with fibre content up to 35% were processed by kinetic mixing and injection moulding. The cellulosic filler was a commercial chemical bleached kraft soft wood pulps composed of well individualized fibres free from lignin with diameter about 20 μm and length within micron scale. The effect of fibre addition on the thermal properties of composites was investigated using differential scanning calorimetry (DSC), dynamic mechanical analysis (DMA), thermal gravimetric analysis (TGA) and thermo-mechanical analysis (TMA). In a previous work, it was demonstrated that fibre inclusion on PLA enhanced the modulus as well as the strength. Fibre addition promoted the crystallization of PLA by favouring the heterogeneous nucleation and accelerating the crystallization kinetic, without adversely altering the thermal stability. The DMA analysis confirmed the strong stiffening effect brought by the addition of fibres at the glassy as well as the rubbery domains. The presence of fibres had also a beneficial effect on the dimension stability by lowering the thermal expansion coefficient of composites.

負の熱膨張率を有する材料と複合材料の熱膨張率制御への応用

負の熱膨張率を有する材料と複合材料の熱膨張率制御への応用

Evaluation of elastic properties and thermal expansion coefficient of composites reinforced by randomly distributed spherical particles with negative Poisson’s ratio

In this contribution, numerical studies are carried-out in order to evaluate the elastic effective properties, including Young modulus, Poisson’s ratio, shear modulus and linear thermal expansion coefficient of composites reinforced by randomly distributed spherical particles. The spherical inclusion and matrix can be made from auxetic materials. In this numerical, the volumetric fraction of randomly uniform spherical inclusion can reach up to 60.27% of total volume. Different scenarii are carried-out to build graphical results that can suggest the designer to choose an appropriate combination of parameter to make the expected materials.

Deformation Mechanisms in NiTi-Al Composites Fabricated by Ultrasonic Additive Manufacturing

Thermally active NiTi shape memory alloy (SMA) fibers can be used to tune or tailor the effective coefficient of thermal expansion (CTE) of a metallic matrix composite. In this paper, a novel NiTi-Al composite is fabricated using ultrasonic additive manufacturing (UAM). A combined experimental-simulation approach is used to develop and validate a microstructurally based finite element model of the composite. The simulations are able to closely reproduce the macroscopic strain versus temperature cyclic response, including initial transient effects in the first cycle. They also show that the composite CTE is minimized if the austenite texture in the SMA wires is 〈001〉B2, that a fiber aspect ratio >10 maximizes fiber efficiency, and that the UAM process may reduce hysteresis in embedded SMA wires.

Calculation of Effective Coefficient of Thermal Expansion for Composite ‘Glass-Eucryptite’ Changing during Sintering

In this work, thermal expansion coefficient of composite is calculated on the base of the model transient zone formation between spherical inclusion and matrix. Effective properties of particle surrounded by transient zone are used when composite properties are calculated. Different models leads to qualitative results similar to each other. Quantitative results depend on sintering temperature and time, on inclusion sizes and volume part of inclusions.

Micromechanical Analysis of Thermal Expansion Coefficients

Thermal expansion coefficients play an important role in the design and analysis of composite structures. A detailed analysis of thermo-mechanical distortion can be performed on microscopic level of a structure. However, for a design and analysis of large structures, the knowledge of effective material properties is essential. Thus, either a theoretical prediction or a numerical estimation of the effective properties is indispensable. In some simple cases, exact analytical solutions for the effective properties can be derived. Moreover, bounds on the effective values exist. However, in dealing with complex heterogeneous composites, numerical methods are becoming increasingly important and more widely used, because of the limiting applicability of the existing (semi-)analytical approaches. In this study, finite-element methods for the calculation of effective thermal expansion coefficients of composites with arbitrary geometrical inclusion configurations are discussed and applied to a heterogeneous lightning protection coating made from Dexmet&#174 copper foil 3CU7-100FA and HexPly&#174 epoxy resin M21. A short overview of some often used (semi-)analytical formulas for effective thermal expansion coefficients of heterogeneous composites is given in addition.

Modeling of thermal expansion coefficients of composites with disc shaped inclusions and related systems

The subject of thermal expansion, particularly negative thermal expansion, is a topic of great practical importance in view of its relevance in many everyday applications and the consequences which may arise when the thermal expansion if not controlled. This paper presents a detailed analytical model of a composite system, which enables control of the thermal expansion through the use of the thinning that is observed when a conventional material is mechanically stretched (the Poisson's effect). It is shown that the model can predict the thermal expansion of such systems to an extent comparable to more complex finite element simulations. The proposed model also permits optimization of the system to exhibit maximum negative thermal expansion, or, thermal expansion of a desired magnitude.

Further studies on Mori–Tanaka models for thermal expansion coefficients of composites

The relations of Mori–Tanaka (M–T) model for thermal expansion coefficients (CTEs) of composites are derived following a regular procedure to compare with other two different expressions of M–T model often used for modeling thermal properties of nanocomposites. It is verified that by correcting the related parameters mis-determined all the relations are consistent and can provide same predicting results. This clarifies the confused information in literature concerning the M–T model on CTEs. Some issues are discussed and attentions are suggested in appropriate use of different relations of M–T models. Comparisons of M–T model with other related theory models on CTEs are made by numerical results, which show some advantages of M–T relations over other models in applications. The related expressions of M–T model on CTEs are summed up under self-consistent coordinate systems for convenience of practical use.

Combined numerical/experimental investigation of particle diameter and interphase effects on coefficient of thermal expansion and young's modulus of SiO2/epoxy nanocomposites

AbstractA combined numerical/experimental approach is used to study the effects of the particle/matrix interphase on the coefficient of thermal expansion (CTE) and Young's modulus of SiO2/epoxy nanocomposites having nanoparticle reinforcements of different sizes. Our experiments showed that the composite CTE decreases and composite Young's modulus increases with decreasing nanoparticle diameter at the same volume fraction, but our finite element (FE) model predictions did not match the expected trends when the interphase was not accounted for. The new models include an interphase region around the nanoparticle which results in an “effective particle volume fraction” that is larger than the actual particle volume fraction. The results from the models are compared with the experimental results and the new models are accurately fitted to the experimental results using the interphase thickness as a curve‐fitting parameter. We believe that this is the first published report on the use of combined numerical/experimental investigations of both elastic stiffness and thermal expansion characteristics to demonstrate the existence of a particle size‐dependent “effective particle volume fraction” due to the particle/matrix interphase region in a nanoparticle‐reinforced composite. POLYM. COMPOS., 2012. © 2012 Society of Plastics Engineers

Influence of the elastic properties of the phases on the coefficient of thermal expansion of a metal matrix composite

Copper matrix composites reinforced with low thermal expansion ceramic particles, i.e. SiO2, AIN and diamond, in the range of ceramic volume fractions between 0.55 and 0.85 have been prepared by gas pressure infiltration and are characterized by their coefficient of thermal expansion (CTE). It is shown that the composite CTE is strongly affected by the ratio between the stiffness of the matrix and that of the particles. For the Cu/SiO2 composites, the CTE is above the rule of mixture in agreement with elastic theory. (C) 2010 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.

Influence of reinforcement weight fraction on microstructure and properties of submicron WC–Co p/Cu bulk MMCs prepared by direct laser sintering

Direct metal laser sintering (DMLS), due to its flexibility in materials and shapes, exhibits a great potential for fabricating complex shaped bulk metal matrix composites (MMCs). In the present work, the submicron WC–10% Co particulate reinforced Cu matrix composites were prepared using DMLS. The influence of reinforcement content on the sintered densification and the attendant microstructures, e.g. the dispersion homogeneity of the reinforcing particulates and the interfacial bonding ability, was investigated using scanning electron microscopy (SEM), energy disperse X-ray (EDX) spectroscopy, and atomic force microscope (AFM). It shows that using a low reinforcement content of 20 wt.% results in a poor densification with severe balling phenomena, due to a higher average composite coefficient of thermal expansion (CTE) and a superheating of the melt. A heterogeneous microstructure with a significant particulate aggregation is obtained at a high reinforcement content of 40 wt.%, because of a limited liquid formation and the resultant high liquid viscosity and reduced Marangoni effect. Using an optimal reinforcement content of 30 wt.% leads to a uniform distribution of the reinforcing particulates and a compatible interfacial microstructure, so as to obtain a favorable sintered density of 90.3% theoretical density.

Effect of an inhomogeneous interphase on the thermal expansion coefficient of a particulate composite

This work is a study of the thermal properties of composite materials containing isotropic spherical inclusions surrounded by an inhomogeneous interphase, embedded in an isotropic matrix. By modelling the thermal and mechanical properties of the interphase as continuous radial functions, a replacement technique is used to derive a differential equation which models the thermal expansion coefficient of the composite. The results are generalised for a wide class of functions describing the inhomogeneous properties of the interphase. When the mechanical properties of the interphase are described by a power law profile a closed form solution is obtained for various thermal expansion profiles. The results are displayed graphically against various other theoretical models and with experimental results. A comparison of the results for different values of the problem parameters is also presented. The present model showed good agreement with the experimental results of Holliday and Robinson [Holliday L, Robinson J. Review: the thermal expansion of composites based on polymers. J Mater Sci 1973;8:301–11].

Towards model-based engineering of underfill materials: CTE modeling

Polymeric composite based underfill materials, with well-controlled coefficient of thermal expansion (CTE) are critical to flip-chip and other advanced high-density integrated circuit packaging technologies. The use of underfills beneath the flip-chip integrated circuits leads to an increase in reliability by reducing the strain on the solder bumps during thermal cycling imposed by the CTE mismatch between the chip and substrate. A fundamental understanding of the composite CTE of underfill materials is critical to the manufacture of high performance underfill materials and is critical to market expansion of flip-chip technology for high density packaging applications. This work presents a novel model for predicting the effective CTE of underfills and other polymeric composite materials by considering the effect of an interphase zone surrounding the filler particles in a polymer matrix. A microscopic model is also introduced for the volume fraction of the interphase as a function of filler concentration as well as filler–filler overlapping. The CTE model resolves several conflicts regarding the effect of filler concentration, filler size and filler–polymer interaction on the effective CTE of underfill and other polymeric composite materials. The results are demonstrated to be critical for accurate flip-chip reliability predictions based on finite-element and other modeling techniques.

An analytical approach to evaluate the coefficients of thermal expansion of textile composite materials

AbstractAn analytical approach is developed to evaluate the coefficients of thermal expansion (CTE) of textile reinforced composites. At the micro level, a cylindrical composite model is employed to model the fiber/matrix thermal and mechanical interactions. The effects of voids and fiber coating on the thermal expansion coefficients of composites are considered at this level. The cylindrical model was then embedded in a macro hybrid finite element solutio structure to calculate the value of the CTE for textile composites. AS‐4/epoxy balanced plain weave textile composites were manufactured. Five different fiber volume fractions were tested for CTE. Evaluatio of the thermal expansion coefficients using the current model was compared to experimental data for in‐plane and out‐of‐plane directions.

Thermal expansion of metal–ceramic composites: a three-dimensional analysis

The thermal expansion response of macroscopically isotropic metal–ceramic composites is studied through micromechanical modeling. Three-dimensional finite element analyses are carried out for the entire range of phase concentration from pure metal to pure ceramic, using the aluminum–silicon carbide composite as a model system. Particular attention is devoted to the effects of phase connectivity, since other geometrical factors such as the phase shape and particle distribution play a negligible role in affecting the overall coefficient of thermal expansion (CTE) of the composite. Three types of phase connectivity, i.e. metal-matrix, ceramic-matrix and interpenetrating (where both phases form a continuous network in space), are considered. It is found that for fixed phase concentrations, the composite CTE depends strongly on the phase connectivity, with the metal- and ceramic-matrix cases showing the highest and lowest CTE values, respectively. The numerical results are compared with analytical predictions. The combined effects of phase connectivity and metal plasticity are examined by numerically varying the thermal history. The correlation between the constrained metal yielding and the composite CTE is identified. The three-dimensional analysis allows the thermal deformation behavior of interpenetrating composites to be examined in a realistic manner. The results presented in this paper are important in the design and characterization of composites in applications such as electronic packaging and functionally graded materials.