Influence Of Fiber Volume Fraction Research Articles

Prediction of orthotropic mechanical properties of plain‐weave composites with matrix voids using unit cells at multi‐scales

AbstractA numerical procedure for predicting the orthotropic mechanical properties of plain‐weave composites with matrix voids through a combined approach of the representative volume element method and finite element analyses is presented. The representative volume element method was implemented using two unit cells established at different length scales with equation boundary conditions. By considering the presence of randomly scattered voids throughout the matrix induced during the manufacturing process, it was assumed in the simulation that the spatial distribution of matrix voids is completely random. The procedure was exemplified with a glass fiber‐reinforced (plain‐weave fabric) epoxy composite with matrix voids. Sensitivity studies were conducted to quantify the influence of fiber volume fraction and mechanical properties of the constituent phases on the orthotropic mechanical properties of the composite. The numerical procedure, which can be implemented in ABAQUS, is an efficient tool for guiding the design of plain‐weave composites at materials level and also provides effective properties of such composites for the design optimization of engineering structures made of such composite materials. © 2012 Society of Chemical Industry

Study of Thermal Stress of Iron-Boron Alloy Casing

The outer casing of heater made of iron-boron alloy is brittle fractured easily. It is a an effective way to add continuous fibers in brittleness material to improve the mechanical properties of composites. Temperature and thermal stress distribution of iron-boron alloy casing and the influence of thickness on the thermal stress of the casing is computed with finite element method, and the thermal stress distribution and influence of fiber volume fraction of continuous fiber-reinforced composites is studied. The result indicates that the external surface is in tensile stressed condition, and the internal surface is in compression stressed condition; the thermal stress increases with the thickness. The compression stress of the matrix decreases and the tensile stress increases with the increasing of the fiber volume fraction.

Kajian Pengaruh Fraksi Volume Serat Akibat Perlakuan Alkali Terhadap Ketangguhan Impak Komposit Limbah Serat Aren-Polyester

The purpose of this study is to investigate the influence of fiber volume fraction of the impact strength of palm fiber-unsaturated polyester composite and investigate the mechanism of fracture caused by impact loads. This research material is palm fiber (Arenga pinnata), unsaturated polyester matrix yukalac BQTN-EX 157 type, hardener metyl etyl ketone peroxide (MEKPO), alkali solution (NaOH) and H2O. Testing with Charpy impact tester, impact test specimens prepared according to standard test ASTM D-5942. While the macro picture is used for the analysis of the fracture. The results showed that the most optimum impact toughness of palm fiber-polyester composite reached 0.011 J/mm2 on volume fraction (Vf) 40%. While the interaction characteristics of palm-fiber bond strength polyester showed matrix cracking behavior of failure on volume fraction (Vf) 10% to 30%, and fiber pull out the volume fraction (Vf) 40% and 50%, the same fracture behavior between the matrix and fibers in volume fraction (Vf) 40% indicates that fiber and matrix has a strong bonding interaction.

Prediction of effective thermal conductivities of woven fabric composites using unit cells at multiple length scales

Abstract

A study on interfacial properties of jute-PP composites

In this work jute fiber has been treated with Maleic Anhydride grafted PP (MAgPP) and also Vinyl trimethoxy silane (VTMO) at various concentration levels and the tensile, interfacial, and moisture regain properties of the composites are studied in detail. Tensile and flexural tests are carried out to characterize the mechanical properties and fiber pull out test is carried out to characterize the interfacial properties. It has been found that both MAgPP and VTMO treatments improve the tensile properties of the resultant composites. MAgPP treatment yields higher increase in composite tensile properties. Fiber pull out tests also indicate better interfacial strength for MAgPP treated fibers. The influence of fiber volume fraction on tensile and flexural properties is carried out for composites with MAgPP treated jute fibers.

Mechanical Properties of Aerogel-Ceramic Fiber Composites

Aerogel composites were prepared by immersing ceramic fiber into silica aerogel precursor via supercritical fluid drying. The mechanical behavior of silica aerogel composites was investigated with shrinkage, tension, bending and compression. The influences of fiber volume fraction, aerogel density and heat treatment were examined. After reinforced by ceramic fiber, the shrinkage of aerogel and aerogel-fiber composites was retarded obviously. The mechanical property of aerogel-fiber composites increased first and then decreased with increasing fiber volume fraction from 5.8% to 11.5%. For a given fiber volume fraction, the mechanical strength enhanced with increasing aerogel density. In addition, the mechanical property of aerogel composites did not decrease but increased after heat treatment at 600°C.

Dynamic Stability Behavior of 3D Braided Composite Plates Integrated with Piezoelectric Layers

This article presents a dynamic stability analysis of a simply supported 3D braided composite laminated plate with surface-bonded piezoelectric layers, subjected to electrical and periodic in-plane mechanical loads. The braided composite plate is produced by the four-step 1 × 1 technique. It is assumed that the yarn is transversely isotropic, and the matrix is isotropic. A fiber inclination model is used to predict the effective stiffness matrices of the braided composite laminates. Theoretical formulations are based on Reddy’s higher order shear deformation plate theory and include piezoelectric effects. Double Fourier series is employed to convert the dynamic governing equations into a linear system of Mathieu—Hill equations from which the boundary points on the unstable regions are determined by Bolotin’s method. Numerical illustrations show the influence of fiber volume fraction, braiding angle, inclination angle, static load level, applied voltage, and aspect ratio on the dynamic stability, buckling and free vibration of the braided composite plate.

Influence of Fiber Volume Fraction and Fiber Type on Mechanical Properties of FRLACC

This article presents results of an experimental study conducted to investigate the influence of fiber volume fraction, fiber type, and presence of fly ash on mechanical properties of fiber-reinforced, lightweight aggregate, cellular concrete (FRLACC). Steel fibers are added at Vf of 0.5, 1.0, and 1.5%, and 25% of cement weight is replaced with fly ash in the control and FRLACC specimens that had shown the highest compressive strength in our preceding work. With the addition of 0.5% Vf of fibers, the increase in compressive strength of the polypropylene FRLACC specimens is slightly higher than that of the steel FRLACC specimens, whereas decreases in their peak load and modulus of rupture over those of control specimens are observed. The findings of the experimental study also show that the utilization of 25% fly ash is more efficient in improving the mechanical properties of the steel FRLACC specimens than those of the polypropylene FRLACC specimens.

Failure and volume fraction dependent mechanical properties of composite sensors and actuators

Composite actuators and sensors manufactured by combining a ferroelectric ceramic such as lead zirconate titanate and a passive phase such as a polymer are used in a variety of applications including SONAR, vibration damping, change of structural shape (morphing), and structural health monitoring. The composite route provides specific advantages, including tailored piezoelectric response, high strain, a degree of flexibility, and increased damage tolerance compared with conventional dense monolithic ceramic materials. For piezoelectric fibre composites, where fine-scale brittle ceramic fibres of 40–800 μm diameter are introduced into a ductile polymer matrix, the composite strength and failure mechanism ultimately depend on the mechanical properties of each phase and their volume fraction. This article examines the mechanical properties of piezoelectric fibres and the matrix phase and discusses the possible influence of fibre volume fraction on mechanical properties and failure mechanism of the composite. The data are of particular use in determining the failure stress, failure strain, and failure mechanism of composite actuators and sensors subjected to high levels of stress, for example, in applications where such devices are embedded into host structures.

Influence of fibre volume fraction on mode II interlaminar fracture toughness of glass/epoxy using the 4ENF specimen

Glass reinforced composites are used in many structural applications. Their fibre content can vary considerably according to the manufacturing route, typically from 30% to 70% by volume. This paper presents results from an experimental study of the influence of fibre volume fraction on the mode II interlaminar fracture toughness, G IIc, using the 4ENF (four point end notched flexure) specimen. Results show that G IIc increases with decreasing fibre content. This effect is caused by plastic deformation energy dissipation in the thicker resin-rich interlaminar layer in lower fibre content composites.

Influence of fiber volume fraction on mode III interlaminar fracture toughness of glass/epoxy composites

The influence of fiber volume fraction on the mode III interlaminar fracture toughness, G IIIC, of a glass/epoxy composite was examined using the edge-cracked torsion specimen. It was found that G IIIC corresponding to onset of crack propagation substantially increased with decreasing fiber volume fraction. The fracture surfaces of broken specimens were inspected in optical and scanning electron microscopes. The higher initiation fracture toughness for the low fiber volume fraction composite is attributed to the increased matrix volume allowing for increased plastic deformation energy dissipation in the matrix resin prior to macroscopic crack propagation. In addition to the primary delamination crack, both the low and high fiber volume fraction specimens displayed intralaminar matrix cracks in the 90° plies adjacent to the crack plane, and such cracks were particularly numerous in the low fiber volume fraction specimens which contribute to the resistance to crack propagation.

Influence of fiber volume fraction and aspect ratio in resol–sisal composites

AbstractVegetable fibers are being used as reinforcements in polymeric matrices with a wide variety of applications. Among these fibers, sisal is of particular interest due to the high impact strength and moderate tensile and flexural properties of its derivated composites. Because of its low cost and affinity, a phenol–formaldehyde resin, resol, has been selected as the matrix to obtain resol–sisal composites. The influence of fiber length and volume fraction on flexural properties has been studied. An optimum for the fiber length as well as for the fiber volume fraction was found. The improvement of the properties occurred up to a length of about 23 mm. The use of longer fibers lead to reduced properties because they tended to curl and bend during processing. Besides, actual composite densities were lower than theoretical ones mainly due to the presence of voids. This undesirable porosity produced a reduction in flexural properties at high fiber contents. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 89: 2714–2722, 2003

Probabilistic Study of Visible Length of Fibers under the Surface of a Short Fiber Reinforced Composite

The so-called 'visible length' under the surface of a short fiber reinforced composite was examined, assuming that fibers under the composite surface could be observed. The fibers under the surface are overlapped by other fibers. The length of the part between other overlapping fibers is the visible length. Relative position of the fiber in the composite can be classified into six categories when the fiber was observed from the composite surface. In each category, projection length of the fiber to the composite surface was calculated. The result was substituted for the method proposed before and the visible length distribution was obtained. It was found that the average visible length in the composite dose not significantly changes, if the average fiber length exceeds 30 times of the fiber diameter. Furthermore the influence of fiber volume fraction on the visible length was clarified.

Forming performance and biodegradability of woodfibre–Biopol™ composites

Abstract A Taguchi approach to experimental design has been used to analyse the hotpressing and vee-bending of woodfibre–Biopol™ composites. Analysis of the hotpressing process clearly shows that platen temperature is the parameter with the most influence on tensile performance of the composite sheet produced. In bending (a common manufacturing situation), geometric conformance is maximised when forming time is 60 s, forming rate is 250 mm/min and forming radius/thickness ratio is 2 for the composite sheets studied in this paper. A study of the influence of fibre volume fraction on the biodegradability of these sheets show that these composites are highly biodegradable, often degrading at a rate greater than that of pure Biopol™. The results also suggest that a woodfibre mass fraction of ∼15% maximises the degradation of the woodfibre–Biopol™ composites.

Three‐dimensionally braided carbon fiber–epoxy composites, a new type of material for osteosynthesis devices. I. Mechanical properties and moisture absorption behavior

AbstractIn recent years, three‐dimensionally (3D) braided composites have attracted a great deal of attention because of their high‐impact damage tolerance and fatigue life, superior fracture toughness, and so forth, and have been used in aeronautics, military, and transportation. These advantages make them strong candidates for osteosynthesis devices. In this study, 3D braided carbon fiber–epoxy (C3D/EP) composites were produced via a simple vacuum impregnation technique. The load‐deflection curve, mechanical properties, and influence of fiber volume fraction, braiding angle, and axial reinforcing fibers were examined to determine their suitability for internal fixation devices. It is found that the C3D/EP composites have excellent toughness and do not show brittleness when fractured because of their relatively high void content. The flexural, shear, and impact strengths of the C3D/EP composites are excellent. It was shown that a C3D/EP composite with a stiffness similar to load‐bearing bones can be made while maintaining enough strength. It is concluded that a relatively higher void content and braiding angle is more suitable for the C3D/EP composites from the viewpoint of requirements of fracture fixation materials. The moisture absorption behavior and changes in mechanical properties caused by moisture uptake were evaluated. Results show that absorbed moisture slightly decreases mechanical properties of the C3D/EP composites. Contrary to the unreinforced epoxy, the moisture absorption behavior of the C3D/EP composites cannot be described with Fick's law of diffusion, probably because of the presence of voids and/or 3D fiber structure. The exact mechanisms should be proposed in further investigations. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 85: 1031–1039, 2002

Influence of Fiber Volume Fraction on the Mechanical and Thermal Properties of Unidirectionally Aligned Short-Fiber-Reinforced SiC Composites.

The aim of this study were to fabricate a short-fiber-reinforced SiC composites by hot-pressing using an Al2O3-Y2O3-CaO mixture as sintering additive, and, to investigate the effect of processing parameters on the mechanical and thermal properties of SiC/SiC composites containing BN-coated Hi-Nicalon short fibers. Fibers were mostly aligned within planes perpendicular to the hot-pressing direction. The composite fabricated by this process achieved nearly full density after hot-pressing at 1700°C. The bending strength increased with increasing sintering temperature and decreased with increasing testing temperature. The fracture behavior of the SiC/SiC composites showed a completely brittle fracture. Results of scanning electron microscopy (SEM) investigation showed that there were pulled-out fibers in the tensile stress zone of the fracture surface, but the degree of pull-out was low. On the basis of these results, the influence of fiber volume fraction on the mechanical and thermal properties of the SiC/SiC composites is discussed.

Electrical conductivity characterization and variation of carbon fiber reinforced cement composite

Electrical conductivity of carbon fiber reinforced cement composite (CFRCC) was measured. The conductivity of specimens increased by several orders of magnitude while the volume fraction of fibers reached a higher value than the critic concentration. The microstructure associated with electrical percolation phenomena was observed. The mechanism of conduction was interpreted as being due to fibers touching each other. The changes of electrical conductivity under three different loading levels were investigated. The percolation threshold value decreased with loading. The relative changes of electrical conductivity both under single loading and cyclic loading could sense the stress in non-elastic, elastic and fracture region with sensitive response. The influences of fiber volume fraction and fiber length on the sensitivity of electrical conductivity measurement were discussed. The results provide some new information for the fabrication of conductive and intrinsically smart carbon fiber reinforced cement composites.

Thermal expansion behavior of aluminum alloys reinforced with alumina planar random short fibers

The thermal expansion behavior of two aluminum alloys (Al-4%Cu and Al-12%Si) reinforced with alumina planar random short fibers has been studied, both experimentally and theoretically. The metal matrix composites (MMCs) were manufactured by pressure infiltration of molten metal into short fiber preforms with a planar random distribution of fibers. Dilatometric testing was used to investigate the influence of fiber volume fraction and architecture, and the effects of thermal cycling between 25 °C to ∼560 °C. Thermal expansion measurements showed that, by increasing the fiber content in the composites, both the thermal strains and the effective coefficient of thermal expansion (CTE) were reduced in the whole temperature range. Furthermore, the thermal strains of MMCs increased almost linearly up to a critical temperature, T cr, where the metallic matrix began to yield macroscopically due to internal thermal stresses. For temperatures higher than T cr the thermal strains of MMCs showed a marked hysteresis during heating/cooling cycles due to the elasto-plastic response of the metallic matrix. In this temperature range, the thermal expansion curves deviated appreciably from linearity and the planar (in the plane of fibers) and transverse (normal to the plane of fibers) responses were very different: while the planar CTE was strongly reduced, the transverse CTE increased sharply with temperature, being even larger than the CTE of the unreinforced alloy. Thermal cycling produced a net dimensional change of composites during the first 2-3 cycles but, on the subsequent cycles, the permanent deformation disappeared almost completely and the successive thermal expansion curves were identical. Experimental results were compared to the theoretical predictions of an analytical model based on the Eshelby's equivalent inclusion method, and an excellent agreement was obtained.

Influence of fiber volume fraction on dynamic damage in woven glass fabric composites: An experimental study

Experiments have been carried out to study the damage fracture growth and the associated damage mechanisms in woven glass fiber reinforced polyester composites. The initiation and propagation history of the damage has been recorded at few microsecond intervals using a high speed Cranz-Schardin camera. The images obtained are analyzed using IDRISI, an image processing tool. Three different fiber volume fractions, 2.4, 5.3 and 33.0 percent are considered. The influence of notch orientation are studied by varying the initial notch orientation between 0° and 45°. On the basis of the studies, it is observed that irrespective of initial notch orientation, the damage propagates in a direction perpendicular to the loading direction. For low fiber volume fractions, the damage is in the form of matrix cracking and interface debonding while delamination dominates for specimens with high fiber volume fractions. The damage velocity in low fiber volume fraction specimens are found to be higher than the terminal velocity of the crack in unreinforced polyester resin. Fractographic studies are also carried out and the results are presented.

The Influence of Fibre Volume Fraction on the Mode I Interlaminar Fracture Toughness of a Glass-Fibre/Vinyl Ester Composite

This paper investigates the influence of fibre volume fraction on the mode I interlaminar fracture toughness G Ic of a glass-fibre/vinyl ester composite. Two fibre volume fraction parameters are defined; a global value for the composite specimen and a value for the fibre-dense intralaminar regions. The range of global fibre volume fraction studied was 32–52 %. Results show that G Ic values for crack initiation are independent of fibre volume fraction and similar to matrix resin G Ic . Variations in the G Ic for steady-state crack propagation, and the amount of fibre bridging, are not completely explained by changes in global fibre volume fraction. Instead they are consistent with fibre volume fraction in the fibre-dense intralaminar regions, through which the crack preferred to grow. It is concluded that this latter parameter is more relevant for G Ic characterisation as a function of fibre volume fraction.