Volume Fraction Of Glass Fibers Research Articles

Viscosity analysis of photopolymer and glass‐fibre composites for rapid layered manufacturing

Refers to how the mechanical properties of polymer‐based composite objects produced via rapid layered fabrication methods can be improved significantly using short discontinuous fibres as reinforcements. Notes in this context, that the viscosity of the uncured fibre‐photopolymer composite liquids affects the raw‐material handling, the layer formation and the draining operations. Assesses the effects of aspect ratio, surface coating and volume fraction of short glass fibres on the viscosity of the fibre‐photopolymer composite liquids. Based on extensive experimentation and analysis, concludes that the shear viscosity of the composite liquids increases with increasing fibre‐volume fraction, showing that this effect is more pronounced at low shear rates than at high shear rates. Reveals, similarly, that the aspect ratio of the dispersed fibres has a stronger effect on the increase of viscosity at low shear rates and that the surface coating of the dispersed fibres also affects the viscosity of the composite liquids.

Hybrid Effect in the Mechanical Properties of Short Sisal/Glass Hybrid Fiber Reinforced Low Density Polyethylene Composites

Hybrid composites of low density polyethylene (LDPE) reinforced with intimately mixed short sisal and glass fibers were prepared by solution mixing technique. The mechanical properties of these composites have been investigated with reference to the effects of orientation and composition of fibers in them. It has been observed that the composites contining longitudinally oriented fibers exhibit better mechanical properties than those with randomly oriented ones. Also it is seen that the mechanical properties increase with increase in the volume fraction of glass fibers in the hybrid composites. The effict of chemical modification of sisal fibers on the properties of 50:50 sisal/glass fiber composites has also been studied. The hybrid effect was calculated by the additive rule of hybrid mixtures using the mechanical properties of individual composites. A positive hybrid effect was echibited by the composites for all the mechanical properties except for elongation at break.

ITER central solenoid model coil impregnation optimization

The success of the vacuum-pressure impregnation of the International Thermonuclear Experimental Reactor central solenoid is critical to success of the magnet system. Analysis of fluid flow through a fabric bed is extremely complicated, and complete analytical solutions are not available, but semiempirical methods can be adapted to model these flows. Several of these models were evaluated to predict the impregnation characteristics of a liquid resin through a mat of reinforcing glass fabric, and an experiment was performed to validate these models. The effects of applied pressure differential, glass fibre volume fraction, resin viscosity and impregnation time were examined analytically. From the results of this optimization, it is apparent that use of elevated processing temperature resin systems offer significant advantages in large scale impregnation due to their lower viscosity and longer working life, and they may be essential for large scale impregnations.

The influence of fibre aspect ratio on the deformation of discontinuous fibre-reinforced composites

The fundamental theory for discontinuous fibre reinforcement of plastics is reviewed and compared to experimental data obtained from a range of single-fibre composite tests. Given that the theory provides an adequate description of fibre reinforcement, predictions for the critical fibre length in model composites based on glass fibres embedded in a range of matrices with different volume fractions have been made. The model has been used to predict the modulus for unidirectional discontinuous glass fibre-reinforced composites with a high volume fraction of glass fibres with different mean fibre lengths, diameters and matrices. From this study the concept of a critical aspect ratio, required for effective composite performance, has been defined generally for this type of material. The critical aspect ratio has been found to depend upon fibre diameter, matrix modulus and fibre volume fraction. A brief review of this class of material in the scientific literature has been made in the areas of deformation and failure. To aid the developments in the theory behind discontinuous fibre composites, a series of deformation experiments have been performed on model discontinuous glass fibre/nylon 6,6 compounds produced by extrusion and pultrusion compound technology. The materials were processed using multilive feed technology, to produce effective representations of unidirectional discontinuous glass-fibre composites. Given that the model compounds contained variations in fibre lengths and diameters, the deformation experiments performed were a fundamental test of the theory presented for the critical fibre aspect ratio and the results of theory and experiment have been compared. Based on the predictions of the model and the experimental work, conclusions are offered on the type of fibre that should be used for discontinuous fibre-reinforced composites.

The wear resistance of glass fibre reinforced epoxy composites

Polymers are usually characterized by low moduli and strength. Epoxy, as a thermoset material, has a low wear resistance. Additions of glass fibres improve the elastic modulus and tensile strength and can improve the wear resistance. The composites were prepared by pultrusion of the glass fibres after saturation of epoxy. The fibre volume fraction was varied up to 50%. Tensile and wear tests were carried out to examine the improvement in the composite properties. A small deviation of the tensile strength and the elastic modulus from the calculated values using the rule of mixture was observed due to the existence of porosities. The wear resistance increases with increasing the sliding velocity, with decreasing the applied contact pressure and with selecting the most favourable glass fibre volume fraction.

An Analytical Model for Estimating the Coefficient of Thermal Expansion of Random Fiber Reinforced Composites

The coefficient of thermal expansion (CTE) of random glass fiber rein forced polyethylene (PE) and polypropylene (PP) composites prepared using the patented aqueous wet laid process has been measured over a temperature range of 150°C (from -40°C to 110°C). It was found that there were two CTE values for both PE and PP/glass fiber filled composites in this range, namely a low temperature value (from —40°C to a transition value) and a high temperature value (from the transition temperature to 110°C). Predictions were calculated from a model based on Halpin-Pagano laminate analogy, the Halpin-Tsai equations, and Schapery's energy method. Excellent estimates were obtained for the CTE values of PE and PP matrix random fiber composites with varying length and volume fraction of short glass fibers. A computer program developed for the analysis of the data significantly reduced the analysis time.

The study of microfracture and fracture toughness for transverse loading of FRP composites.

Fracture toughness tests were carried out on compact tension specimens to obtain the fracture toughness for transverse loading of unidirectional glass fiber reinforced plastics. The fracture toughness decreases as the radius of the notch tip and the volume fraction of glass fibers decrease. During the fracture toughness tests, acoustic emission signals corresponding to the microfracture of the fiber reinforced composite were detected. By use of a crack initiation model based on the microfracture, the influence of the radius of the notch tip and the volume fraction of glass fibers on the fracture toughness was explained.

Microstructural efficiency and fracture toughness of short fiber/thermoplastic matrix composites

This paper outlines the fracture behavior of composites with thermoplastic matrices of different fracture toughness K cm (increasing in the order PPS → PET ( I) → PET ( II) → ETFE → PC). In particular, the way in which the fracture toughness of these composite systems, K cc, is affected by the volume fraction, orientation and distribution of short glass fibers across the plaque thickness (fiber length ≈ 200 μm, fiber diameter ≈ 10 μm), and by the quality of their interfacial bonding to the matrix is discussed. SEM studies were carried out to define the microstructural details and the dominant mechanisms of energy adsorption during breakdown of the composites. In general, an increase in composite toughness can be expected with increasing extent of reinforcement if the matrix is in a brittle condition (here also verified by K c-tests at lower temperatures) and if the fibers are well bonded and mostly oriented perpendicular to the crack front. An opposite tendency may occur for matrices which behave in a highly ductile manner even in the presence of fibers. The probability of this behavior is favored in poorly bonded systems. The results are discussed in terms of a ‘microstructural efficiency factor’ M, which mainly considers the relative contributions of fiber and matrix related mechanisms to energy dissipation during breakdown of a composite (‘energy absorption ratio’ n) as well as the reinforcement content and its arrangement in the matrix (‘reinforcing effectiveness parameter’ R).

Transversely reinforced 1-3 and 1-3-0 piezoelectric composites

Abstract Piezoelectric PZT-polymer 1-3 and 1-3-0 composites were transversely reinforced with glass fibers to increase the hydrostatic piezoelectric coefficients for possible use in hydrophone applications. Modeling of these composites theoretically showed that the dhgh figure of merit is a function of the volume fractions of PZT rods, glass fibers, and polymer porosity, and of the Poisson's ratio and compliance of the polymer matrix. Experimental results showed significant enhancements of the dhgh figure of merit with the addition of glass fibers. Comparisons of the theoretical predictions and the experimental results were made.

Elastic properties of intermingled hybrid composites

AbstractThe combination of different types of fibers in a common matrix, known as a hybrid composite, has the potential of achieving a balance between composite strength and ductility, as well as a more cost‐effective use of expensive fibers, not re‐alized in a single‐fiber compostie. The elastic properties of a continuous Kevlar®/glass intermingled hybrid composite have been investigated. Theoretical predictions utilizing a self‐consistent model and a bound approach are compared to the influence of the relative Kevlar®/glass fiber volume fraction on the elasstic material properties.

On fibre debonding effects and the mechanism of transverse-ply failure in cross-ply laminates of glass fibre/thermoset composites

The mechanism of transverse-ply failure in cross-ply laminates of glass fibre thermoset composites has been investigated. It is shown that fibre debonding initiates failure, the debonds subsequently joining up to form a transverse crack nucleus. In the epoxy system investigated fibre debonding causes an observable whitening effect and small modulus change; this effect is reversible in that rebonding can be brought about by further heat treatment. It is shown that in the case of the polyester system the larger thermal strains introduced during the curing cycle cause debonding of the composite and therefore the whitening effects are not observed on application of load. Simple models for the prediction of the observed effect of glass fibre volume fraction on transverse failure strain are proposed.

Determination of the planar distribution of glass fibres in opaque matrix composites

A scanning technique using a photodiode has been developed for estimating the glass fibre volume fractions in composites with opaque matrices. The information is derived from light transmitted along the reinforcing fibres by total internal reflection. The method described has advantages over a previous method based on photographic techniques and it is possible to gain information about the uniformity of fibre distribution within the composite. Results obtained with glass fibre reinforced cement and plaster specimens are described. The transmission of light through the composite is proportional to the volume fraction of glass fibres up to a limiting value of ∼6% Inhomogeneous fibre distribution can be detected using this technique. For cement samples the curing history is important as the degree of interaction between the cement and the glass has a marked influence on the glass transmittance.

Crack growth in hybrid fibrous composites

A preliminary analysis is made of the energetics of transverse crack growth in a brittle elastic matrix bridged by elastic fibres fictionally bonded to the matrix. Studies made of the stability of a crack of finite length in a brittle polymeric material reinforced with steel wires are found to be in reasonable agreement with the predictions of the theory. It is proposed that the stability of transverse cracks in a very brittle matrix could be increased substantially by the inclusion of a second fibre component designed specifically to increase the work of fracture of the matrix. This has been shown to be possible using a very small volume fraction of glass fibres as a matrix toughening component and it has also been observed that stable transverse matrix crack growth can be achieved with composite systems of this type. This principle might have applications in the design of hybrid composites utilizing either a brittle polymeric or ceramic matrix.

Photoelastic analysis of an orthotropic ring under diametral compression.

N this paper an improved model material for photoorthotropic-elasticity, with better transparency and more favorable fiber distribution, is described. A unidirectional ly reinforced circular ring, subjected to diametral compression at 0°, 45°, and 90° to the reinforcement direction, is investigated. The resulting isochromatic fringes are converted to tangential stresses on the inner and outer boundaries after correction for the residual birefringence of the model material. The stress distributions are compared with the corresponding values for an isotropic ring. Contents Two different methods have been employed so far in the preparation of unidirectiona lly reinforced model materials for transmission photoelastic applications. The method used by Pih and Knight1 as well as by Sampson2 involves filament winding and the application of vacuum to eliminate entrapped air. The method employed by Dally and Prabhakaran3 utilizes commercial glass fabrics and does not require the application of vacuum. However, the twist of the yarns in the glass fabric gives rise to two problems. First, air entrapped between the fibers is not completely removed by the simple squeezing operation and consequently maximum possible transparency is not achieved, in spite of careful matching of the refractive indices of the matrix and the glass reinforcement. Secondly, the glass fibers are grouped together in discrete bundles resulting in poor fringe resolution in regions of high fringe gradient.4 To eliminate the disadvantages of twisted yarns while retaining the simplicity of fabrication technique, in the present study woven roving has been used as the reinforcement. With only ten plies of the glass roving, a thicker laminate (0.18 in.) was obtained. Far greater transparency was achieved, without resorting to vacuum. Most important of all, the photoelastic response was much better, with improved fringe resolution. In Fig. 1 the lightfield isochromatic fringe pattern for a notched beam in four-point bending is presented for the old and new model materials. The reason for the difference in fringe resolution is apparent from the photomicrographs. The glass fibers in the material prepared from roving are more uniformly distributed, thus better justifying the treatment of the heterogeneous orthotropic material as a homogeneous orthotropic material. A circular ring, with the outside and inside diameters 3 in. and 1.5 in., respectively, was machined from a f-in.-thick unidirectionally-reinforeed laminate consisting of 35% volume fraction of glass fibers. The machining stresses were annealed by heating the