Expansion Coefficient Of Composites Research Articles

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.

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.

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.

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].

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.

Bounds of the expansion coefficients of composites reinforced by spherically isotropic particles

The present paper is devoted to the study of expansional behaviours of a composite reinforced by spherically isotropic particles. An exact relation is derived between the effective expansion coefficient and bulk modulus of the composite by using the concept of uniform fields in the matrix which is proposed here. Through obtaining the Paul-type bounds of the bulk modulus by using the extreme principle of energy, bounds of the effective expansion coefficient are also derivded

Mechanical Property and Fatigue Bahavior of $Al/{Al_2}{O_3}$ Metal Matrix Composite

The metal matrix composites(MMC) are currently receiving a great deal of attention. These composites possess exellent mechanical and physical properties such as modulus, strength, wear resistance and thermal stability, which make them very attractive for use in automotive piston. In this study, (15%) composites are fabricated by the squeeze casting method. Mechanical properties such as tensile strength and ductility are performed at room and elevated temperature( and ), respectively. Through thermomechanical analyser, thermal expansion coefficient of composites are conducted for ranging from room temperature to (.And bending fatigue tests are also performed by the rotary bending machine at room temperature.The tensile strength and elastic modulus have been improved up to 38% and 35% by the addition of the reinforcements, respectively. Thermal expansion coefficients of MMCs which is located normal and parralel to the applied pressure are showed slightly different less than 10%. Fatigue strengh of the composite was improved by about 20% compared with that of unreinforced Al alloy. The results of this study will be used to understand the basic fracture behavior of MMCs and eventually to expand the applocation of MMCs as a machine parts undertaken various loadings.

Thermal expansion coefficients of fiber composites defined by the concept of the interphase

The thermal expansion behavior of unidirectional composites has been studied. In this analysis a model which introduces the concept of the boundary interphase has been used. The expansion coefficients of the composite were calculated by using this concept to determine the influence of the interphase which depends on the quality of adhesion between fiber and matrix. In the present paper it has been assumed that the interphase material was inhomogeneous with properties varying from the fiber surface to the matrix. Three laws of variation have been taken into consideration in order to derive expressions for the thermal expansion coefficients in which appeats the rôle of this interphase layer possessing physico-chemical properties different from those of the constituent phases. A thermal analysis method was used in order to find the extent of the interphase layer. The results are assessed by comparing them with those given by other theories.

Analysis of thermal expansion coefficients of composites reinforced with plane randomly oriented discontinuous carbon fibers (abstract)

Analysis of thermal expansion coefficients of composites reinforced with plane randomly oriented discontinuous carbon fibers (abstract)

Analysis of Thermal Expansion Coefficients of Composites Reinforced with Plane-Randomly Oriented Discontinuous Carbon Fibers

Analysis of Thermal Expansion Coefficients of Composites Reinforced with Plane-Randomly Oriented Discontinuous Carbon Fibers

Thermal Stresses and Thermal Expansion Coefficients of Short Fiber Composites With Sliding Interfaces

The paper analyzes thermal stresses and effective thermal expansion coefficients of the composites in which the fiber-matrix interface is allowed to slip. Thermal stresses are evaluated by introducing an eigenstrain in the fibers, which corresponds to the strain due to the mismatch of thermal expansion coefficients. For simplicity, the effect of friction is neglected. Boussinesq-Papkovich displacement potential method is used in the analysis. Then, the results for a single sliding fiber are used to predict the average thermal expansion coefficients of the composite containing finite concentration of fibers. It is observed that sliding at the fiber-matrix interface causes higher stress concentrations and affects significantly the average coefficients of thermal expansion of the composite.

Thermal and Mechanical Properties of High Thermal Expansion ZrO<sub>2</sub>-CaF<sub>2</sub> Composite Ceramics

Thermal and mechanical properties of two-phase composite sintered-materials consisting of ZrO2 with 3mol% Y2O3 and various volume fractions of CaF2 were measured. The composites were made by hot-pressing micronized powders at 1300°C under 30MPa pressure. No phase except ZrO2 and CaF2 was observed by the X-ray diffraction method in the composites, and no crack in sintering bodies was observed by scanning electron microscope. Thermal expansion coefficient increased with increasing CaF2 content, in agreement with the prediction obtained by the Turner's equation for thermal expansion coefficients of composites. Bending strength decreased with increasing CaF2 content. The composite containing 50vol% CaF2 showed a high thermal expansion coefficient of 15×10-6/°C and a bending strength was approximately 350MPa. These properties are similar to that of stainless steel and Al2O3, respectively.

一方向繊維強化複合材料の応力分布の近似解 引張および熱負荷

An approximate solution of the stress field in unidirectional composites was obtained for tensile and thermal loading conditions based on the Airy stress function. The hexagonal packing of unidirectional fibers was assumed as an ideal arrangement. This solution is applicable to the transverseisotropic fiber/isotropic matrix composite system. Explicit solutions for the local stress and average strain of composite were presented together with the instruction for the numerical process. The average strain became equal to the thermal expansion coefficient of composites when no tensile load was applied. The present results were compared with the previous exact solutions obtained for glass/polymer composites and were found to be satisfactorily accurate. Finally, the stress along the fibermatrix interface and the average axial stress in both matrix and fiber were presented as a function of fiber volume fraction for glass/epoxy and carbon/epoxy composites.

Marginal adaptation of BIS-GMA-based composites containing various diluents.

The aim of this study was to determine how otherwise acceptable diluent monomers affect the marginal adaptation of BIS-GMA-based composites. Based on the results of the investigation, the following conclusions can be drawn: 1. Addition to dimethacrylate diluents containing (CH2) recurring units generally yields composites having better marginal adaptation than do those containing (CH2 CH2 O) groups. Best marginal adaptation for a single diluent is obtained for compositions using 1, 4 and 1, 10-polymethylene glycol dimethacrylate as diluent. 2. Marginal adaptation is improved on lowering the diluent concentration. Optimum adaptation will be obtained for a formulation containing a minimum percentage of diluent with clinically acceptable working properties. 3. Volume changes on temperature cycling resulting from differences in thermal expansion coefficients of composites do not effect the marginal integrity as much as does curing shrinkage.