Elastic waves in multilayered plate reinforced by inextensible fibres

In this article the propagator matrix method is employed to obtain the overall transfer matrix which gives dependence of displacements and stresses on the one face of the multilayered plate in terms of those on the opposite face. Attention is restricted to waves propagating in the plane parallel to stress free plate faces where we examine waves travelling at any angle to one of the families of fibres. The plate is of finite thickness but of infinite lateral extent. Each of the laminae is formed from same material reinforced by one family of inextensible fibres laying in the plane of the laminae. Results are presented for eight-ply laminated plate with symmetric arrangements of the laminae. Frequency spectrum for first 10 modes is presented for specific plate with (/2, –/4, /4, 0)_s lay up, and specific fibre reinforced material.     

Fabrication, mechanical properties and thermal stability of a novel glass matrix composite material reinforced by short oxycarbide fibres

An aluminosilicate glass matrix composite material reinforced by randomly oriented SiC-based (Tyranno) chopped fibres was fabricated. Slurry dipping and hot-pressing techniques were used to prepare dense composites containing 45 vol% fibres uniformly dispersed in the glass matrix. The mechanical properties and fracture mechanisms of the composite under flexion and compression loading were studied. In flexure, the composite showed higher modulus and strength than the unreinforced glass. However, in compression, the strength of the composite was lower than that of the monolithic glass. Considering the potential application of the material at high temperatures, the thermal aging behaviour of the composite in air at temperatures between 500 and 700°C was investigated. The composite retained its room-temperature compressive strength after exposure for 26 h at 500°C. The variation of compressive strength measured after exposures at higher temperatures was ascribed to mechanisms of fibre/matrix interface oxidation and to the softening of the glass matrix.     

Tensile properties and thermal expansion behaviors of continuous molybdenum fiber reinforced aluminum matrix composites

The tensile properties and thermal expansion behaviors of continuous molybdenum fiber reinforced aluminum matrix composites (Mo_f/Al) have been studied. The Mo_f/Al composites containing different volume percents of Mo fibers were processed by diffusion bonding. The strengths of unidirectional Mo_f/Al composites were close to the rule-of-mixtures. The strengths of 0°/90° dual-directional composites increased with fiber content, while those of 45°/135° composites remained relatively low. The coefficients of thermal expansion (CTEs) of the composites decreased as the fiber content increased, close to the values of Mo fibers. With increasing temperature, the CTEs of unidirectional composites increased, while those of dual-directional composites decreased due to large accumulated thermal stresses. The CTEs of 45°/135° composites were lower than those of 0°/90° composites because of contraction effect. At temperatures above 250 °C, the CTEs of the dual-directional composites gradually increased due to matrix yielding and interfacial decohesion.     

Experimental investigation and FE simulation of spherical indentation on nano-alumina reinforced copper-matrix composite produced by three different techniques

Preparation of metal matrix composites with homogenously distributed reinforcement is a difficult process. The process can be even more complex when the reinforcement particles are nano-particles. In this paper, three different techniques (dry mixing, mechanical alloying and mechanochemical) were applied to produce Cu-Al₂O₃ nano composite with three different Al₂O₃ content (2.5, 7.5 and 12.5 .wt.%). XRD, SEM and EDX analysis were conducted to analyse the physical and structural properties of the produced samples. Rockwell hardness test and compression test were applied to determine the mechanical properties of the produced composites. A 2D axisymmetric FE model was implemented using commercial software to predict the Rockwell hardness of the prepared samples. The results show that dry mixing and mechanical alloying techniques are valid for production of metal matrix composites with large reinforcement particle size and low reinforcement content. However, mechanochemical technique can be used to produce Cu-Al₂O₃ nano composite with high reinforcement weight fractions. Homogenously distributed dispersed nano alumina copper matrix can be achieved by applying mechanochemical technique and as a result, the mechanical and physical properties can be improved. The hardness predicted by the presented FE model correlates well with the experimental observation.     

Fibre reinforced gypsum binder composite, its microstructure and durability

The effect of E-type glass fibre on the strength and durability of gypsum binder composites was studied under different climatic conditions and by accelerated methods. After 50 cycles of wetting and drying at 60°C an irregular deposition of gypsum binder products was found at the surface of glass fibres. Durability of E-type glass (borosilicate) fibres employed as reinforcement in the gypsum binder composites was examined after immersion into aqueous extract of gypsum binder at temperature 27° to 60°C. The exposed glass fibres were studied by scanning electron microscope and by weight loss determination. Deterioration of E-type glass fibres was observed at 50° and 60°C on exposure to aqueous gypsum binder extract which is directly related to the durability of gypsum binder composites. It is concluded that gypsum binder composites should be used under 50°C.

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Résumé L’effet de la fibre de verre de type E sur la force et la durabilité des matériaux liants à base de gypse a été étudié sous différentes conditions climatiques et par des méthodes accélérées. Après 50 cycles de mouillage et séchage à 60°C, une déposition irrégulière de liants à base de gypse a été dévouverte à la surface des fibres de verre. La durabilité des fibres de verre (borosilicate) de type E utilisées afin de renforcer les matériaux liants à base de gypse a été examinée après immersion dans un extrait aqueux du liant à base de gypse à une température de 27 à 60°C. Les fibres de verre exposées ont été scannées et étudiées à l’aide d’un microscope électronique et leur perte de poids a été déterminée. Une détérioration des fibres de verre de type E a été observée à 50 et 60°C après exposition à l’extrait aqueux du liant à base de gypse, qui est directement lié à la durabilité des liants à base de gypse. En conclusion, les composites liants à base de gypse doivent être utilisés à une température inférieure à 50°C.

     

Thermal expansion behaviour of ultra-high modulus carbon fibre reinforced magnesium composite during thermal cycling

The thermally induced strain response of unidirectional P100S/AZ91D carbon fibre-reinforced magnesium composite was studied over five cycles in the ±100 °C temperature range. A temperature-dependent one-dimensional model was employed to predict the anticipated response to the cycling thermal environment. Strain hysteresis was observed during cycling and attributed to matrix yielding. First cycle residual plastic strains were modelled with reasonable agreement. Experimental results deviated from predictions during subsequent cycles with continued thermal ratcheting shifting the hysteresis loops to higher strains with increasing cycles. This was thought to be associated with interfacial debonding and frictional sliding at fibre/matrix interfaces. The effect of thermal treatment on composite expansion behaviour was investigated and the results discussed in terms of minimising thermally induced deformations during anticipated service conditions. Treatments were found to affect the first cycle behaviour, reducing in particular residual plastic strain generation. Matrix yield strength was exceeded over the thermal cycle due to a lack of sufficient hardening, and since interfacial conditions were unaltered, interfacial sliding and thermal ratcheting could not be eliminated. The potential for improvement of C/Mg composite thermal strain response was explored in the light of the current findings.     

Behaviour of composite soil reinforced with natural fibres

Next to the food shortage, the housing shortage is one of the most crucial problems on earth. To improve this situation and make it possible to build more houses, particularly for low-income families, it is necessary to examine all locally available materials which can be used for construction. Bamboo, sisal and coconut fibres are materials which are available in abundance in Brazil and are not used in civil construction. To increase the amount of information concerning the physical and mechanical behaviour of these materials several research programmes were executed at Pontifical Universidade Católica in Rio de Janeiro (PUC-Rio) and Universidade Federal da Paraiba (UFPb) under the general supervision of the first author. In this paper new results are presented concerning the application of sisal and coconut fibres in conjunction with three types of locally appropriate soil for the production of composite soil blocks reinforced with sisal and coconut fibres.     

Effect of thermal cycling on the microstructure of continuous carbon fibre reinforced copper matrix composites

Copper reinforced by continuous carbon fibres is a candidate material for heat sinks of electronic modules. The thermal expansion can be matched to the adjacent ceramics and the thermal conductivity is higher than that of alternative materials. Because the material is expected to work in cyclic thermal conditions during application its structure must withstand such a load without any severe damage. The structure of unidirectionally and cross-ply fibre reinforced samples was observed before and after thermal cycling by optical microscopy and Scanning Electron Microscopy (SEM). SEM was used for examining the fibre-matrix interface before and after thermal cycling. Optical microscopy showed the arrangement of individual monolayers. The influence of adding copper foils between individual monolayers on the structure of the material is reflected in a reduction in the number of cracks in monolayers.     

The thermal expansion of carbon-fibre reinforced plastics

The thermal expansion characteristics of a series of carbon-fibre fabric reinforced plastic laminates over the approximate temperature range 90 K to 440 K have been determined. The reinforcements included Morganite Type II fibres in a plain weave and a two-by-two twill weave and Courtaulds Grafil E/XAS fibres in a two-by-two twill weave, a five-shaft satin weave and in an unwoven unidirectional disposition. The results show that the ratio of fibre tow densities in the principal fibre directions, the crimp in the reinforcing fibres and the laminate stacking sequence all influence the magnitudes and temperature dependences of the linear thermal expansion coefficients, as well as the detailed manner in which the dimensions respond to changes of temperature. Volume shrinkage effects resulting from temperature cycling are also reported. The linear thermal expansion coefficients of Courtaulds Grafil E/XAS carbon fibres in directions parallel, ^f , and perpendicular, _¶ ^f , to the fibre axis have been estimated as ^f =–2.6× 10^–7 K^–1 and ^f =2.6×10^–5 K^–1.     

On the thermal expansion of composite materials and cross-property connection between thermal expansion and thermal conductivity

The paper focuses on the quantitative characterization of heterogeneous microstructures from the point of view of the material’s thermal expansion. First, we derive expression for the second rank thermal expansion contribution tensor of an inhomogeneity and specify it for various inhomogeneity shapes. Case of a spheroidal inhomogeneity in an isotropic material is discussed in detail. Thermal expansion contribution tensor is used as a basic building block to calculate effective thermal expansion of a heterogeneous material and to derive explicit cross-property connection between thermal expansion and thermal resistivity of a composite. We compare our results with experimental data available in literature and with other approaches.     

Elastic constants and thermal expansion of aluminum-SiC metal-matrix composites

The elastic behavior and the thermal expansivity of metal-matrix composites have been investigated using ultrasonic velocity and strain gage measurements. The composites used in this study consisted of three aluminum alloys reinforced with different concentrations of SiC particles. The results show that the elastic constants increase and the coefficients of thermal expansion decrease with particle content. The results also show that the behavior of elastic constants with reinforcement can be best represented by the calculations of the upper and lower bounds of Hashin and Shtrikman. The behavior of thermal expansion, however, agrees with bounds developed by Schapery. In addition, both properties are found to be related through a model linking the strain to the elastic and thermal stresses in the composite. This relationship gives promise for the nondestructive characterization of the composites using these measurements.     

Elastic and thermal expansion anisotropy of oriented linear polyethylene

A two-phase composite laminate model is proposed for representing biaxially oriented sheets of linear polyethylene. Thermoelastic analysis of the model yields predictions of the complete elastic and thermal expansion anisotropy. These predictions are compared with experimental measurements of elastic compliance and thermal expansivity obtained with the same oriented sheets. Using only one adjustable parameter (Poisson's ratio of non-crystalline linear polyethylene), extensive qualitative agreement is obtained between model predictions and experimental results. Discrepancies which are observed are attributed to the influence of the interfacial regions which exist between adjacent stacks of lamellar crystals in the real oriented sheets.     

Design of composite structures reinforced curvilinear fibres using FEM

This paper describes a method of modelling a curvilinear reinforcement structure, for a composite plate with a hole that allows trajectories of fibres to be adapted to geometric discontinuities (holes, notches, bolts, etc.). For this method, it is assumed that the trajectories of fibres are curvilinear and continuous, as well as located along the trajectories of maximum principal stress. On the basis of these trajectories, the functionally graded material is simulated by means of the finite element method (FEM). Each element of this structure has its own mechanical properties, depending on the fibre direction and a change in the distance between the fibres. It is demonstrated that the maximum value of the stress concentration factor in the fibre direction for the plate with the curvilinear reinforcement structure reduces by 3.2 times in comparison with the same plate with a rectilinear reinforcement structure (orthotropic material).     

Synthesis process and microstructure of carbon fibres/graphite/copper composites by spark plasma sintering

Carbon fibres/graphite/copper composites are prepared by mechanical alloying and spark plasma sintering at different temperature in this study, and the microstructure evolution is investigated during sintering. The curves of punch displacement, mould temperature, furnace chamber vacuum, and voltage against time were recorded and discussed. The results show that the carbon fibre/graphite/copper composite presents neat and pure interface. Copper element is found in carbon fibres and graphite, which may be due to discharge. The microhardness of the obtained composites is up to 160?HV. The highest relative density in this test is 96.5%. The microstructure evolution process during SPS is associated with sparking, joule heat, pressure, and deformation. The sintering process is uneven at initial stage.     

The thermal expansion of carbon fibre reinforced plastics

Measurements of the principal linear thermal expansion coefficients of a tridirectional (–45°, 0°, +45°) carbon fibre reinforced plastics laminate are reported in the approximate temperature range 90 K to 500 K. A quantitative evaluation of the in-plane results in thermoelastic terms has yielded an agreement with these results consistent with the approximations and uncertainties involved. The qualitative agreement with expectations based upon the behaviour of unidirectional and bidirectional laminates is also demonstrated. The account concludes with an examination of some effects which are peculiar to multidirectional laminates.     

Study on graphite fiber and Ti particle reinforced Al composite

Graphite fiber and Ti particle-reinforced aluminum matrix composite were produced by squeeze casting technology. A small amount of needle aluminum carbide at graphite fiber and Al interface was observed, and TiAl₃ intermetallic compound at Ti particle and Al interface was detected. Tensile strength and bending strength of the composite have been measured. The fracture surface of the composite after tensile and bending tests was observed; graphite fiber-reinforced Al was brittle fracture, whereas Ti particle-reinforced Al was ductile fracture. The corresponding fracture mechanism was discussed.     

电子封装SiCp/356Al复合材料制备及热膨胀性能

采用无压渗透法制备了SiCp／356Al复合材抖．用SEM和XRD对复合材料组织形貌和物相进行了研究，测定了复合材料在50-400℃温度区间的热膨胀系数。分析了复合材料热膨胀性能的影响因素。结果表明SiCp／356Al复合材料中SiC颗粒分布均匀，无明显新相形成，复合材料的热膨胀系数比基体合金的热膨胀系数显著降低，复合材料热应力引起热膨胀性能的变化随温度的不同而不同。     

Effect of expansion temperature of expandable graphite on microstructure evolution of expanded graphite during high-energy ball-milling

Two expanded graphites (EG), marked as EG-1 and EG-2, were prepared by rapid heating of expandable graphite to 600 and 1000 °C, respectively, and ball milled in a high-energy mill (planetary-type) under air atmosphere. The microstructure evolution of the ball-milled samples was characterized by X-ray diffraction (XRD) and high resolution transmission electron microscopy (HRTEM). XRD analysis shows that the evolution degree of the average crystallite thickness along the c-axis (L_c) of EG-2 is lower than that of EG-1 during the milling process. From the HRTEM images of the samples after 100 h ball-milling, slightly curved graphene planes can be frequently observed both in the two EGs, however, EG-1 and EG-2 exhibit sharply curved graphene planes and smoothly curved graphene planes with high bending angles, respectively.     

Preparation and characterization of polyaniline/exfoliated graphite composite via a combination method of in situ polymerization and thermal expansion

Polyaniline/exfoliated graphite (PANI/EG) composite was prepared via a combination method of in situ polymerization and thermal expansion and characterized, using scanning electron microscope (SEM), Fourier transform infrared spectroscopy (FTIR) and X-ray diffraction (XRD). In the in situ polymerization, PANI/graphite intercalation compounds (GIC) composite was synthesized by GIC and aniline. In the thermal expansion, PANI/EG composite was prepared by PANI/GIC composite. The characterization showed that the morphology of PANI/EG composite was analogous to foam and the surface of PANI/EG composite had many micro-apertures. When PANI/GIC composite was synthesized by 0.80 g of GIC and 2.00 g of aniline, PANI/GIC composite would be exfoliated to PANI/EG composite at 200 °C, which had 75.00 mL·g⁻¹ of the expansion volume and 0.01Ω⁻¹ cm⁻¹of the conductivity.     

Effect of Bi2O3 coating of whisker on thermal expansion behaviour of aluminium composite reinforced by aluminium borate whisker

Abstract

The thermal expansion behaviours of aluminium composites reinforced by ABOw with and without Bi₂O₃ coating are studied. The results show that the coating could influence the thermal expansion behaviour of composite. The coefficient of thermal expansion (CTE) of the composite with Bi₂O₃ coating is higher than that of the composite without coating. In addition, the heat treatment influences the thermal expansion behaviours of composite with Bi₂O₃ coating. The CTEs of the heat treatment composites are lower compared to as cast composite. At the same time, the quenching can boost the CTE of the composite compared with the annealing.