Fibers In Fiber-reinforced Composites Research Articles

Study of Hygrothermal Aging for Basalt Fiber/Epoxy Resin Composites Modified with CeCl3.

With increasing attention being paid to environmental issues, the application of natural fibers in fiber-reinforced composites has attracted more and more attention. Composite materials with basalt fibers (BFs) as reinforcement have excellent properties and are widely used in many fields. Hydrothermal aging crucially influences the durability of basalt fiber/epoxy resin composites (BF/ERCs). In this study, BFs were used as reinforcing materials, whose surfaces were modified with a rare earth modification solution (CeCl3). The density, mechanical performance, and chemical properties of BF/ERCs subjected to hygrothermal aging were analyzed by the weight method, static mechanical performance testing, scanning electron microscopy (SEM), and Fourier transform infrared spectroscopy (FT-IR). The effects of the modification solution with different Ce concentrations on the water absorption, tensile, bending and interlaminar shear strength (ILSS) of BF/ERCs were investigated. The test results showed that the water absorption of BF/ERCs treated with a modification solution that contained Ce 0.5 wt % as the minimum value and the retention rate of the mechanical properties of BF/ERCs reached maximum values after hygrothermal aging.

Effect of Mercerization and Benzoyl Peroxide Treatment on Morphology, Thermal Stability and Crystallinity of Sisal Fibers

Studies on the use of natural fibers as replacement to man-made fiber in fiber-reinforced co mposites have increased and opened up further industrial possibilities. Natural fibers have the advantages of low density, low cost, and biodegradability. However, the main d isadvantages of natural fibers in co mposites are the poor co mpatibility between fiber and matrix and the relative high mo isture sorption. Therefore, chemical treat ments are considered in modify ing the fiber surface properties. In this study, Sisal fibers were modified using alkali and benzoyl pero xide solution of different concentration for different time intervals. Morphological changes, thermal stability and crystallinity of fibers were investigated using scanning electron microscope (SEM), TGA and XRD technique. Thermal stability of sisal fibers were decreased on mercerization. Whereas, sisal fibers treated with benzoyl pero xide the enhanced thermal stability. In case of XRD studies, sisal fibers show enhanced crystallin ity.

Buckling of fibers in fiber-reinforced composites

Elastic stability of fibers in fiber-reinforced composite materials subject to compressive loading is studied. The transversal buckling mode is considered, and two limiting cases, the dilute and non-dilute composites are analyzed. In the case of a non-dilute composite, the cylindrical model and the lubrication approximation are applied. The original problem is reduced to a problem of stability of a rod on elastic foundation. Through the solution of this problem a simple formula for the buckling load is obtained. In the case of a dilute composite, the solution of a problem of stability of a compressed rod in elastic plane is used. On the basis of the obtained solutions in two limiting cases the interpolation formulae are derived. These formulae describe buckling of fiber in the fiber-reinforced composite for any value of the fiber volume fraction. Comparison with known numerical and experimental results is carried out, and the sufficient accuracy of the derived formulae is demonstrated.

Elastic stability of a dual-coated optical fiber of finite length

Dual-coated optical fibers are fabricated at elevated temperatures and operated at low temperature conditions. It is imperative that the fibers remain elastically stable, i.e., do not buckle as a result of the thermal contraction mismatch of the dissimilar materials of the fiber and the secondary coating or, in the case of an optical fiber interconnect, of the fiber and the material of an enclosure, if any. We develop a simple and easy-to-use predictive model that enables one to establish the condition of elastic stability for a dual-coated optical fiber of finite length, and/or to select the coating materials with the most favorable physical properties for such a fiber, and/or to establish the adequate thickness of the primary coating. The fiber is idealized as a free-free beam (i.e., a beam not supported at the ends), and the effect of the embedding medium is mimicked by a continuous elastic foundation. The obtained results can be applied also, with some minor modifications, for the evaluation of the elastic stability of short fibers in fiber-reinforced composites, including nanocomposites.

Chemical Treatments of Natural Fiber for Use in Natural Fiber-Reinforced Composites: A Review

Studies on the use of natural fibers as replacement to man-made fiber in fiber-reinforced composites have increased and opened up further industrial possibilities. Natural fibers have the advantages of low density, low cost, and biodegradability. However, the main disadvantages of natural fibers in composites are the poor compatibility between fiber and matrix and the relative high moisture sorption. Therefore, chemical treatments are considered in modifying the fiber surface properties. In this paper, the different chemical modifications on natural fibers for use in natural fiber-reinforced composites are reviewed. Chemical treatments including alkali, silane, acetylation, benzoylation, acrylation, maleated coupling agents, isocyanates, permanganate and others are discussed. The chemical treatment of fiber aimed at improving the adhesion between the fiber surface and the polymer matrix may not only modify the fiber surface but also increase fiber strength. Water absorption of composites is reduced and their mechanical properties are improved.

Residual monomers and degree of conversion of partially bioresorbable fiber-reinforced composite

The aim of this study was to evaluate the total quantity of residual monomer (bis-phenyl glycidyl dimethacrylate, i.e. Bis-GMA, and triethylene glycol dimethacrylate, i.e. TEGDMA), residual monomer release into water and the degree of monomer conversion (DC%) of glass fiber-reinforced composites (FRC) with a partially bioresorbable polymer matrix. Another aim was to find out whether the curing mode affects the quantity of residual monomer and degree of conversion. Glass fibers were preimpregnated with a bioresorbable poly(hydroxyproline) amide and non-resorbable Bis-GMA–TEGDMA resin system. Specimens were immersed in water for 1, 3 or 7 days (37 °C) to determine the quantity of leached residual monomers, or in the solvent tetrahydrofuran for 3 days to determine the total quantity of residual monomers by high performance liquid chromatography. DC% was measured by Fourier transform infrared spectroscopy. The quantity of residual monomer of the specimens decreased when the specimens contained glass fibers, and/or poly(hydroxyproline) amide, and/or when it was post-cured. The majority of the residual monomers were leached out during the first 24 h of immersion in water. The DC% of the specimens increased when post-cured. Also glass fibers in the composite increased the DC% in contrast to Bis-GMA–TEGDMA resin only. In conclusion, use of poly(hydroxyproline) amide as a sizing of the glass fibers in FRC does not increase the quantity of residual monomers. These results suggest that this new kind of partially bioresorbable FRC has potential for biomedical applications.

A numerical estimation of the effects of a cylindrical hole and imperfect bonding on stability of a fibre in an elastic matrix

A simple numerical model based on three-dimensional analytical considerations is proposed for an estimation of the local effects of a cylindrical hole in the matrix as well as of fiber-matrix interface imperfections on compressive stability of fibers in fiber-reinforced composites. The geometry of the model includes an inclusion (a fiber) in a matrix with the assumption of an imperfect bonding at the interface and a cylindrical hole in the closest neighborhood. Then the problem formulation is idealized in two directions, providing a possibility of establishing lower and upper bounds for critical loads for the case of a matrix with a cylindrical hole of a non-circular cross-section as well as for the case of interface imperfections with the possibility of sliding without discontinuity of the displacements normal to the interface. The model takes into account the distinct difference in the properties of the fiber and the matrix and the spatial character of the problem at the microlevel. It is based on individual consideration of the fiber and the matrix with a hole with the necessity of satisfying certain idealized bonding conditions between them.

Stress transfer in a model composite containing a single embedded fiber

Elastic stress transfer between the matrix and the fibers in fiber-reinforced composites is examined in the present study. Specifically, experimental results of a model composite consisting of a glass matrix and a single embedded alumina-zirconia fiber are analyzed. The composite is subjected to both tensile loading parallel to the fiber axis and residual stresses. Stress transfer occurs at both the interface along the fiber length and the ends of the fiber. The stress-induced axial stain along the fiber length was determined previously using fluorescence spectroscopy. Assuming a bonded interface and bonded fiber ends, a modified shear lag model is developed and the analytical solutions are consistent with the experiment results.

Acid treatment for functionalizing polyethylene fiber surfaces for enhanced adhesion to epoxy resins

The utility of high-strength, high-modulus polyethylene fibers in fiber-reinforced composites is limited due to its poor interfacial adhesion to various polymeric matrices. One way to overcome this limitation is to introduce reactive functionalities on the fiber surface capable of covalently bonding to matrix resins. Ultra high-strength polyethylene (UHSPE) fibers were treated with chlorosulfonic acid. The surface acid groups were found to considerably improve the interfacial adhesion between polyethylene fibers and epoxy resins as shown by the microbond test. These surface functionalities were found to improve the fiber wettability, as shown by contact angle measurements using the Wilhelmy balance method. Colorimetric measurements of methylene blue absorption were used to quantify the surface concentrations of the acid groups. It was possible to functionalize the UHSPE fiber surfaces using this method to obtain fibers that formed a stronger adhesive bond with epoxy resins; this was achievable without sacrificing other fiber mechanical properties.

Probabilistic study of debond length and pull-out length of fibers in a random short-fiber-reinforced composite.

A better understanding of the debond and pull-out processes of fibers in fiber-reinforced composites is needed because they affect the fracture toughness of the composites. In this paper, a new stochastic model is proposed to predict the probability distributions of debond and pull-out lengths of fibers in a short-fiber-reinforced SMC composite. By considering that fibers in a short-fiber-reinforced SMC composite are discontinuous and that their dircection is random, the probability distributions of debond and pull-out lengths are predicted. It is found that the debond length becomes shorter and the pull-out length becomes longer than those in unidirectional continuous-fiber-reinforced composites. Furthermore, the influences of the fiber-matrix interfacial condition on the debond and pull-out lengths are clarified.

Harmonic waves in one-, two- and three-dimensional composites: Bounds for eigenfrequencies

Harmonic waves in one-, two- and three-dimensional elastic composites with periodic structure are considered. Based on a new quotient recently proposed by Nemat-Nasser, lower and upper bounds for the eigenfrequencies are developed. For illustration waves propagating normal to the layers in layered composites, and normal to the fibers in fiber-reinforced composites, are considered. These examples show that the new quotient is very effective and yields very accurate results for the considered class of problems. While these results are of interest in their own right, they can be used to check the effectiveness of various approximate theories which recently have been proposed by various authors.