Performance Of Fiber Reinforced Composites Research Articles

Hygrothermal effects on the durability of resin‐infused thermoplastic E‐glass fiber‐reinforced composites in marine environment

AbstractThis paper presents a comparative assessment of hygrothermal effects on the mechanical and thermomechanical properties of resin‐infused thermoplastic E‐glass fiber‐reinforced composites (FRC) in the marine environment. The thermoplastic FRCs were immersed in seawater at two different aging temperatures, that is, 35 and 70°C. The quasi‐static tests were conducted on unaged and aged FRCs, followed by scanning electron microscopy (SEM) to determine the effect of the marine environment on the mechanical properties and damage progression. The specimens immersed at 70°C showed a significant drop of 46.7%, 39.7%, 22.6%, and 16% in mechanical properties (tensile, compression, flexural, and ILSS) mainly due to plasticization, matrix cracking, and fiber/matrix debonding. The specimens immersed at 35°C showed a reduction in tensile, compressive, and flexural strength of 10%, 14.7% and 1.9% respectively, with no significant effect on ILSS. In addition, dynamic mechanical analysis (DMA) reveals that prolonged aging induces an increase in glass transition temperature due to polymerization reactions. This work is intended to reveal the effect of extreme marine environment on the resin‐infused thermoplastic FRC and to provide a useful reference for their potential structural applications in the marine industry.Highlights Influence of aging conditions on the long‐term performance of FRCs. Hygrothermal aging leads to an increase in the glass transition temperature. The marine environment degrades mechanical properties of FRCs by up to 50%. Matrix cracking and fiber‐matrix debonding evolved as dominant failure modes.

Investigation of fiber content evaluation methods of carbon fiber reinforced thermoplastic composites

Thermoplastic-based composites are becoming the preferred material for structural and non-structural components in the composite production industries. One of the most critical elements determining the characteristics and performance of fiber-reinforced composites is the fiber content. The fiber volume fraction (Vf) of carbon/polyamide410 (C-PA410) composite is evaluated using standard acid digestion, the unique two-stage thermogravimetry (TGA) method and 2D image processing method, with Vf values of 24.0%, 23.1%, and 18.3%, respectively. For statistical purposes, a substantial number of samples from each composite batch were tested and analyzed. The two-stage TGA approach used in this study, involves measuring the constituent content of carbon fiber thermoplastic composites in nitrogen first and subsequently in air. The standard acid digestion and the two-stage TGA method used in this study provided comparable results. The 2D image processing method, on the other hand, yields a lower volume fraction of fiber. The two-stage TGA approach has been proven to be more convenient in terms of accuracy, safety, and speed. This technique has been validated by testing a control specimen of a material (Toray Cetex® TC910 PA6) with a known weight fraction.

A Multicontinuum-Theory-Based Approach to the Analysis of Fiber-Reinforced Polymer Composites with Degraded Stiffness and Strength Properties Due to Moisture Absorption

Marine energy generation technologies such as wave and tidal power have great potential in meeting the need for renewable energy in the years ahead. Yet, many challenges remain associated with marine-based systems because of the corrosive environment. Conventional materials like metals are subject to rapid corrosive breakdown, crippling the lifespan of structures in such environments. Fiber-reinforced polymer composites offer an appealing alternative in their strength and corrosion resistance, but can experience degradation of mechanical properties as a result of moisture absorption. An investigation is conducted to test the application of a technique for micromechanical analysis of composites, known as multicontinuum theory and demonstrated in past works, as a mechanism for predicting the effects of prolonged moisture absorption on the performance of fiber-reinforced composites. Experimental tensile tests are performed on composite coupons with and without prolonged exposure to a salt water solution to obtain stiffness and strength properties. Multicontinuum theory is applied in conjunction with micromechanical modeling to deduce the effects of moisture absorption on the behavior of constituent materials within the composites. The results are consistent with experimental observations when guided by known mechanisms and trends from previous studies, indicating multicontinuum theory as a potentially effective tool in predicting the long-term performance of composites in marine environments.

Resin-Rich Volumes (RRV) and the Performance of Fibre-Reinforced Composites: A Review

This review considers the influence of resin-rich volumes (RRV) on the static and dynamic mechanical and physical behaviour of fibre-reinforced composites. The formation, shape and size, and measurement of RRV in composites, depending upon different fabric architectures and manufacturing processes, is discussed. The majority of studies show a negative effect of RRV on the mechanical behaviour of composite materials. The main factors that cause RRV are (a) the clustering of fibres as bundles in textiles, (b) the stacking sequence, (c) the consolidation characteristics of the reinforcement, (d) the resin flow characteristics as a function of temperature, and (e) the composite manufacturing process and cure cycle. RRV are stress concentrations that lead to a disproportionate decrease in composite strength. Those who are considering moving from autoclave consolidation to out-of-autoclave (OOA) processes should be cautious of the potential effects of this change.

FDM-Based 3D Printing of Polymer and Associated Composite: A Review on Mechanical Properties, Defects and Treatments.

Fused deposition modelling (FDM) is one of the fastest-growing additive manufacturing methods used in printing fibre-reinforced composites (FRC). The performances of the resulting printed parts are limited compared to those by other manufacturing methods due to their inherent defects. Hence, the effort to develop treatment methods to overcome these drawbacks has accelerated during the past few years. The main focus of this study is to review the impact of those defects on the mechanical performance of FRC and therefore to discuss the available treatment methods to eliminate or minimize them in order to enhance the functional properties of the printed parts. As FRC is a combination of polymer matrix material and continuous or short reinforcing fibres, this review will thoroughly discuss both thermoplastic polymers and FRCs printed via FDM technology, including the effect of printing parameters such as layer thickness, infill pattern, raster angle and fibre orientation. The most common defects on printed parts, in particular, the void formation, surface roughness and poor bonding between fibre and matrix, are explored. An inclusive discussion on the effectiveness of chemical, laser, heat and ultrasound treatments to minimize these drawbacks is provided by this review.

Global sensitivity analysis for fiber reinforced composite fiber path based on D-MORPH-HDMR algorithm

This study presents a quantitative sensitivity analysis for the assessment of fiber reinforced composites (FRCs). Global sensitivity analysis (GSA) approach is based on the variance based method incorporating Random Sampling-High Dimensional Model Representation (RS-HDMR) expansion in which component functions are determined by diffeomorphic modulation under observable response preserving homotopy (D-MORPH) regression. The advantage of the D-MORPH regression lies in its capability to solve linear algebraic equations with a limited number of sample points. The main purpose is to investigate the influence of fiber path, regarded as the design variable, on the formability and structural performance of FRCs. Wherein, spring-back and load-carrying capacity are two meaningful problems to be addressed. Two typical FRCs are included that an L-shaped part with straight fiber path using autoclave manufacturing process and a variable stiffness composite cylindrical shell under pure bending. The work not only focuses on the ranking of design variables but also hopes to find out their interactions represented by the second order global sensitivity indexes. After being tested by three typical numerical functions, the GSA algorithm highlights that spring-back of FRC using autoclave manufacturing process is most sensitive to fiber orientation angles on plies close to the tool. And buckling performance of the VS cylinder is dominated by fiber orientation angles at compression/tension regions.

Highly tunable interfacial adhesion of glass fiber by hybrid multilayers of graphene oxide and aramid nanofiber.

The performance of fiber-reinforced composites is governed not only by the nature of each individual component comprising the composite but also by the interfacial properties between the fiber and the matrix. We present a novel layer-by-layer (LbL) assembly for the surface modification of a glass fiber to enhance the interfacial properties between the glass fiber and the epoxy matrix. Solution-processable graphene oxide (GO) and an aramid nanofiber (ANF) were employed as active components for the LbL assembly onto the glass fiber, owing to their abundant functional groups and mechanical properties. We found that the interfacial properties of the glass fibers uniformly coated with GO and ANF multilayers, such as surface free energy and interfacial shear strength, were improved by 23.6% and 39.2%, respectively, compared with those of the bare glass fiber. In addition, the interfacial adhesion interactions between the glass fiber and the epoxy matrix were highly tunable simply by changing the composition and the architecture of layers, taking advantage of the versatility of the LbL assembly.

Adhesion of RFL-coated aramid fibres to elastomers: The role of elastomer–latex compatibility

The performance of fibre-reinforced composites is strongly dependent on the nature and the strength of the fibre–matrix interface. Good interfacial bonding is required to ensure load transfer from matrix to reinforcing fibres. For rubber-reinforced composites, resorcinol formaldehyde latex (RFL) is known as a fibre surface coating which is able to provide good adhesion between rubber and fibres. In the present study, aramid fibres are investigated, because of their significantly higher modulus and strength, compared to other commercial fibres. Their adhesion after being coated with RFL, in compounds based on natural rubber (NR) and in NR blended with a small amount of styrene butadiene rubber (SBR) is investigated. It is shown that though having very similar tensile properties, the latter compound has much better adhesion to RFL which is also less sensitive to RFL ageing, compared to the pure NR compound. It is argued that an interphase region is formed between RFL and the elastomer, which is stronger for the compound containing SBR due to its enhanced compatibility with the latex part of the RFL.

Adhesion of RFL-coated aramid fibres to sulphur- and peroxide-cured elastomers

The performance of fibre-reinforced composites is strongly dependent on the nature and the strength of the fibre–matrix interface. Good interfacial bonding is required to ensure load transfer from matrix to reinforcing fibres. For rubber-reinforced composites, resorcinol formaldehyde latex (RFL) is known as a fibre surface coating which is able to provide good adhesion between rubber and fibres. But the performance of this substance in many cases can be largely affected due to exposure of the coated fibres to air and light. Moreover, most data available in the literature concern sulphur-cured elastomers only. In the present study, aramid fibres are investigated, because of their significantly higher modulus and strength compared to other commercial fibres. The adhesion of these fibres in compounds based on sulphur-cured natural rubber and peroxide-cured ethylene propylene diene rubber is investigated after being coated with RFL which is the most common adhesive coating for various sort of fibres, including aramid. The effect of physical interaction between fibres and rubbers is shown to be minor, and the effect of ageing of RFL on its ability to bond with rubbers using peroxide and sulphur curing systems are shown. As a result of ageing, ozone is able to decrease the double bonds of the latex part of the RFL, which negatively affects the RFL–rubber adhesion in sulphur-cured systems, while it has almost no effect in peroxide-cured systems. It is also discussed that, unlike in sulphur vulcanization in which bonding happens just between the latex in the RFL and rubber, peroxide is able to generate bonds between elastomer and the resin structure of the RFL-coating.

Plasma polymers used for controlled interphase in polymer composites

The performance of fiber-reinforced composites is strongly influenced by the functionality of composite interphases. Sizing, i.e. functional coating (interlayer), is therefore tailored to improve the transfer of stress from the polymer matrix to the fiber reinforcement by enhancing fiber wettability, adhesion, compatibility, etc. The world market is dominated by glass reinforcement in unsaturated polyester. However, commercially produced sizing (wet chemical process) is heterogeneous with respect to the thickness and uniformity, and hydrolytically unstable. Companies search for new ways of solving the above problems. One of the alternative technologies is plasma polymerization. Plasma polymer films of hexamethyldisiloxane, vinyltriethoxysilane, and tetravinylsilane, pure and in a mixture with oxygen gas, were engineered as compatible interlayers for the glass fiber/polyester composite. The interlayers of controlled physicochemical properties were tailored using the deposition conditions with regard to the elemental composition, chemical structure, and Young’s modulus in order to improve adhesion bonding at the interlayer/glass and polyester/interlayer interfaces and tune the cross-linking of the plasma polymer. The optimized interlayer enabled a 6.5-fold increase of the short-beam strength compared to the untreated fibers. The short-beam strength of GF/polyester composite with the plasma polymer interlayer was 32% higher than that with commercial sizing developed for fiber-reinforced composites with a polyester matrix. The progress in plasmachemical processing of composite reinforcements enabled us to release a new conception of composites without interfaces.

Progressive Failure Analysis of Composites

Recent developments in the aircraft industry towards substantially improving fuel economy and extending flight range have accelerated interest in the use of advanced composites as primary structural materials. The airframes of next-generation airliners will have substantial parts made of light-weight composites. This means that the engineering demands on the performance of fiber-reinforced composites will become greater. There is therefore a need to better understand and predict the multiple complex failure mechanisms in composite structures, and to devise more reliable failure theories and damage progression models. There is a large body of literature on progressive damage analysis in composites, much of which employs damage mechanics and material stiffness degradation methods. This article reviews some of the more recent work in this area and describes the issues pertinent to application in composite structures. The authors' ongoing research efforts in modeling and prediction of progressive damage through the relatively novel element-failure method (EFM), which has been coded into a user-defined UEL code in Abaqus, are discussed. In particular, results for notched composite laminates and pin-loaded (PL) analyses are shown and compared to experimental data. Although EFM is the computational platform on which the damage is advanced in the structure, the results are dependent on the choice of the failure criterion. Various failure criteria are used throughout the cases discussed herein, from the more traditional Tsai—Wu (TW) criterion to the very recently proposed micromechanics-based failure (MMF) criterion. The EFM may also be used with cohesive elements, with the former intended for modeling in-plane damage progression, while the latter for delamination onset and propagation. This hybrid EFM-cohesive element approach is illustrated with an analysis of double-notched composite laminate. The computational models are relatively robust up to and including ultimate load, and enable the mapping of extensive damage patterns in composite structures. They represent a suite of computational tools that extend the capability to model damage and failure propagation beyond initial failure prediction.

Volume fraction effects on interfacial adhesion strength of glass-fiber-reinforced polymer composites

Abstract The performance of fiber-reinforced composites is often controlled by the properties of the fiber–matrix interface. Good interfacial bonding (or adhesion), to ensure load transfer from matrix to reinforcement, is a primary requirement for effective use of reinforcement properties. Thus, a fundamental understanding of interfacial properties and a quantitative characterization of interfacial adhesion strength can help in evaluating the mechanical behavior and capabilities of composite materials. A large number of analytical techniques have been developed for understanding interfacial adhesion of glass-fiber-reinforced polymers. Among these techniques, the vibration damping technique has the advantage of being non-destructive as well as highly sensitive for evaluating the interfacial region, and it can allow the materials industry to rapidly determine the mechanical properties of composites. In the present study, a simple optical system was contributed for measuring the damping factor of uniaxial fiber-reinforced polymer composites in the shape of cantilever beams. The interfacial damping factors in glass-fiber-reinforced epoxy resin composites were correlated with transverse tensile strength, which is a qualitative measurement of adhesion at the fiber–matrix interface. Four different composite systems were tested in this study. In each system, three different surface treatments of glass-fiber at three different volume fractions were evaluated. The experimental results show an inverse relationship between damping contributed by the interface and composite transverse tensile strength.

The use of automated image analysis for the investigation of fabric architecture on the processing and properties of fibre-reinforced composites produced by RTM

The use of resin transfer moulding (RTM) as an economic means of producing high performance fibre-reinforced composites is critically limited by the permeability of the fabrics employed. Commercial fabrics are available where the architecture of their reinforcement is designed to cluster the fibres, giving higher permeabilities than conventional fabrics. This has been shown to improve processing times but there is evidence that such clustering is detrimental to mechanical performance. The objective of this work was to relate variations in permeability, mechanical performance and microstructure. This was achieved by producing carbon/epoxy plates of differing weave styles by RTM in a transparent mould. Permeabilities were calculated. Interlaminar shear, tensile and compressive tests were performed and fractal analysis was carried out to obtain fractal dimensions for the three fabrics. Variations in permeabilities and mechanical properties can be related to observed differences in the microstructure.

Pullout of Inclined Flexible Fiber in Cementitious Composite

The performance of fiber-reinforced composites is strongly dependent on the debonding/pullout behavior of the fibers. In cementitious composites, fibers are usually distributed in a quasi-random manner. It is therefore important to study the pullout of fibers that are inclined to a crack. For flexible fibers, a simple model of a string passing over a frictional pulley has been developed to describe inclined fiber pullout. The existing model is based on experimental results obtained from specimens with initially bent fibers. To evaluate the validity of the experimental results and the model, pullout tests are carried out with polypropylene fibers using (1) specimens with initially straight fibers; and (2) specimens with initially bend fibers. Significant differences are found between the two set of results. Since the pullout behavior of initially straight fibers is more representative of that in real composites, a new model for flexible fiber pullout is developed. By considering (1) the increase of both interfacial friction and snubbing factor with sliding; and (2) spalling of matrix at fiber exit point in the new model, excellent fitting of the experimental results can be obtained.

Influence of processing damage on performance of fiber-reinforced composites

The effect of processing-induced fiber damage, or equivalently the effect of fiber length in discontinuouslyreinforced composites, on the tensile stress-strain behavior of a fiber-reinforced ceramic or metal matrix is determined as a function of the extent of initial fiber damage and the pristine fiber strength distribution. The analysis combines a generalization of the analysis employed for the undamaged fiber problem [Curtin, W. A. (1991) Theory of mechanical properties of ceramic-matrix composites. J. Am. Ceram. Soc. 74, 2837–2845] and numerical simulations to predict the stress-strain curve, ultimate tensile strength and strain, fiber pullout, and work of pullout in terms of the underlying micromechanical material parameters. The results show that the characteristic scale of initial damage required to weaken the composite substantially is always of the order of one fiber break per length δ c , where δ c is the critical fiber slip length in the undamaged composite (typically ~ 1 mm). Overall, the effect of damage on tensile strength, failure strain, and pullout is found to be fairly small, which is attributed to the load carrying capacity of broken fibers due to the sliding resistance of the fiber/matrix interface. However, the detailed stress-strain behavior of the composite is modified. The analysis is applied to a Nicalon/CAS composite in which “premature” fiber damage has been observed. The inclusion of initial fiber damage into the theory accurately accounts for the excess strain, lower tangent modulus, and lower ultimate strength (relative to the predictions in the absence of initial fiber damage) observed in this material.