Influence Of Fiber Volume Fraction Research Articles

Pressure infiltration of sol/gel processed short fibre ceramic matrix composites

Using pressure infiltration short fibre-reinforced ceramic matrix composites with uniform and dense microstructure can be made. Based upon this processing technique, composites composed of silica sol, alumina particles, and alumina short fibres were fabricated. The related processing parameters studied in this work include infiltration rate, fibre volume fraction Vf, particle size, and infiltrate viscosity. An optimal infiltration rate was 4 mm min-1, at which rate the composite with Vf of 8.1% and particle size of 3 μm has the highest green density. An equilibrium between particle packing strength and applied load must be obtained during the infiltration to obtain high green density and composite strength. The influence of fibre volume fraction and particle size on composite green density is in a synergistic manner because it involves particle–fibre interactions, fibre–fibre interactions, and sedimentation. Furthermore, the increase of sol viscosity results in more sedimentation in the infiltrate and lower composite green density. The fracture toughness of composites is 38% higher than that of monolithic alumina. © 1998 Chapman & Hall

Recycled content in polymer matrix composites through the use of A‐glass fibers

AbstractThe utility of recycled A‐glass (primarily composed of soda‐lime‐silicate) fibers as reinforcement for structural composites has been studied. A series of plaques of unsaturated polyster composite were resin transfer molded with an A‐glass continuous strand mat (CSM) and a control with E‐glass CSM. The influence of fiber volume fraction on the physical and thermo‐mechanical properties of the resultant composites were investigated, both before and after environmental exposure. At the maximum fiber fraction considered (nominally 29 vol%), the use of A‐glass reinforcement lowered the warp direction tensile modulus from 8.6 to 7.6 GPa and strength from 139 to 100 MPa, relative to the control. Similar results were observed for both the flexural and the tensile properties, irrespective of fiber fraction and test direction (warp vs. weft), for the A‐glass reinforcement. Environmental exposure was found to affect equally the properties of A‐glass and E‐glass fiber reinforced composites. Based upon microscopic analyses and constituent properties, the lower mechanical properties of the A‐glass fibers composites have been linked to the lower properties of A‐glass fibers relative to E‐glass fibers. The experimental results were also used to test a micro‐mechanics models for random fiber reinforced composites. Reasonable correlation was found between the experimental results and the theoretical predictions. To offset their lower mechanical properties, A‐glass fibers could be used as a reinforcement in composite applications by simply increasing the fiber fraction relative to their E‐glass counterpart.

Transverse squeeze flow of concentrated aligned fibers in viscous fluids

This paper examines the effect that aligned long fiber reinforcement has on the processing characteristics of thermoplastic composites. More specifically, the influence of fiber volume fraction on the transverse shear viscosity of unidirectional composites is explored. Through both experimental evaluation and theoretical modeling, the study focuses on the flow behavior of a model material consisting of unidirectional nylon or glass fibers algned in a clay matrix. The flow behavior of a commercially produced material (APC-2) composed of unidirectional carbon fibers aligned in a thermoplastic polyether ether ketone (PEEK) matrix is also examined. An experimental technique has been employed that characterizes both the bulk transverse shearing viscosity and the fluid mechanics of such highly filled fiber-resin systems in squeeze flow. Squeeze flow experiments were performed for the model material containing various fiber volume fractions and, with specially designed hot platens, for the carbon fiber-PEEK composites. Flow visualization techniques have been developed to measure the velocity profile of the material during flow. A cell model is proposed to calculate the effect of fiber volume fraction on the transverse shear viscosity of aligned fiber composites and, hence, the squeeze force requirements of such materials. The cell model, which calculates individual fiber interactions based on the lubrication approach with a viscous Newtonian or Carreau fluid, demonstrates the effects of varying the fiber volume fraction, fiber diameter and the shear thinning nature of the matrix fluid on the force requirement under constant squeeze rates. Comparisons are made between the experimenttally measured squeeze force and the cell model predictions. Good agreement is found at high fiber volume fractions as the lubrication flow assumptions become more accurate.

Si-Ti-C-O繊維結合型セラミックスの力学的特性に及ぼす繊維体積率の影響

Si-Ti-C-O繊維結合型セラミックスの力学的特性に及ぼす繊維体積率の影響

An experimental study of residual stresses in SiC-fiber-reinforced Ti-based composites

Composites of two Ti-based alloys (Ti14Al21Nb and Tiv6Al4V (weight per cent)) containing SCS-6 SiC fibers have been characterized microstructurally and are used as model systems in which to study the influence of fiber volume fraction and post-consolidation deformation on residual axial fiber strains. The magnitude and extent of local chemical strengthening of the matrix due to interstitial C diffusion have also been measured. A novel matrix etching technique was used to measure the axial fiber residual stress in the composites, and analysis of electron backscattered channeling patterns was employed as a qualitative means of measuring the extent of the local plastic yielding in the matrix. The measured fiber residual strain was found to depend on fiber volume fraction and was reduced significantly by the application of a mechanical load in excess of the matrix yield stress. Significant fiber-to-fiber variation in axial residual strain is measured in the (Ti14Al21Nb)SiC composite, and this variation is discussed with respect to contributions from variations in local fiber volume fractions (i.e. fiber spacing), matrix plasticity, and fiber bending resulting from the cross-weave process. In general, measurements of elastic residual fiber strains are in good agreement with analytical model predictions.

Finite element simulation of powder consolidation in the formation of fiber reinforced composite materials

Finite element codes are developed to analyze powder consolidation due to time-independent plasticity and time-dependent plasticity (power law creep and diffusional creep). For time-dependent plasticity, a new algorithm is proposed to obtain a prediction of the plastic strain increment when solving for the nodal displacement increment. This eliminates the use of an ad hoc Newton loop. A set of newly developed micromechanical models are adopted as the constitutive laws for power deformation, where the influence of deviatoric stresses on densification is taken into account. The densification maps are constructed for the powder consolidation in the formation of fiber reinforced composite materials. The influence of fiber volume fraction, powder particle size, temperature and fiber arrangement is investigated.

High heat flux composites for plasma-facing materials

Vapor grown carbon fiber (VGCF) has been shown to have the highest thermal conductivity of all carbon fiber currently available. This property holds potential of increasing the thickness and longevity of fusion reactor plasma-facing materials. The use of VGCF as a reinforcement in carbon/carbon composites has been explored, as well as methods of joining these plasma-facing materials to copper alloy heat pipes. In extensive study of VGCF/carbon matrix composites, the influence of fiber volume fraction, density, densification method, and heat treatment on composite properties were investigated. Joining of VGCF/carbon composites to copper and beryllium to copper using a novel alloying method was studied. The joint interface was examined by RBS analysis and thermal conductance.

A cohesive crack model to study the fracture behaviour of fiber-reinforced brittle-matrix composites

A cohesive crack model analysis of the fracture resistance and ductility of fiber-reinforced brittle-matrix composites was performed. The bulk material is assumed to behave as a linear elastic solid. The constitutive equation for the cohesive crack is obtained through micromechanical considerations based on the shear lag model of fiber-matrix interaction and on the statistical nature of fiber failure. A parametrical study of the influence of fiber volume fraction, fiber strength and flaw distribution, interfacial shear stress and specimen geometry on the fracture resistance of these composites was carried out. The results illustrate the role of each of these factors in overall composite toughening, and suggest various strategies to improve the composites' performance.

Origin of Hysteresis Observed During Fatigue of Ceramic‐Matrix Composites

Possible mechanisms for the hysteresis in stress‐strain response observed during fatigue of fiber‐reinforced ceramics are examined analytically. In the model developed, the microstructure of a unidirectional composite is divided into adjacent cells, each containing a single fiber. The compliance of each cell is modeled by a series of springs, with frictional sliding of fibers represented by sliding blocks. Fatigue damage is modeled by allowing fibers to debond and fracture on a random cycle‐by‐cycle basis. The magnitude of the interfacial shear between the fibers and matrix is shown to play a significant role in determining the extent of hysteresis observed during fatigue loading of unidirectional composites. Practical considerations, such as the influence of fiber volume fraction on macroscopic fatigue behavior, are also discussed.

Influence of Fiber Volume Fraction on Failure Mechanisms of Poly (ethylene terephthalate) Reinforced by Short Glass Fibers

Influence of Fiber Volume Fraction on Failure Mechanisms of Poly (ethylene terephthalate) Reinforced by Short Glass Fibers

The thermal expansion of carbon fibre reinforced plastics. Part 2, The influence of fibre volume fraction : Yates, B. et al. Journal of Materials Science Vol 13 No 2 1978 pp 433–440

The thermal expansion of carbon fibre reinforced plastics. Part 2, The influence of fibre volume fraction : Yates, B. et al. Journal of Materials Science Vol 13 No 2 1978 pp 433–440