Search

In the present work, a combination of virgin polypropylene and E-glass fiber was subjected to ten (10) reprocessing cycles via extrusion and compression molding techniques to mimic recycling and its impacts on the bending properties of the composites. The samples were characterized using Fourier transform infrared (FTIR) spectroscopy, x-ray diffraction (XRD), scanning electron microscopy (SEM), and melt flow index (MFI). The results revealed a gradual depreciation in flexural properties after each reprocessing cycle. The XRD analysis indicated a substantial reduction of peak intensities, degrees of crystallinities, and average crystallite sizes, explaining the lowered flexural properties in addition to a possible reduction in glass fiber lengths (fiber attrition). Melt-processing behavior shows a progressive increase of MFI from 7 to 19.16 g/10 min, confirming the probable damage in molecular weight and loss of complex viscosity. Chemical and structural analysis showed no alteration in the polypropylene major functional groups. It is concluded that the reductions in molecular weight and composites' properties occurred due to chain scission from recycling effects; hence, glass fiber-reinforced polypropylene composites can be recycled only three (3) times unless it is refreshed by the addition of virgin parts to compensate for the lost property. [ABSTRACT FROM AUTHOR]

A novel marine composite structure (experimental tidal turbine blade) made up of a polyurethane (PU) foam/glass fiber/epoxy resin composite with multiwall carbon nanotubes (MWCNTs) is proposed herein to self-sense its strain under a structural test scenario. To achieve this, MWCNTs were deposited onto glass fiber fabric by spray-coating technique in order to form an effective electrical percolation network onto the external skin surface of the tidal turbine blade which enables piezoresistive capability. After MWCNT deposition, the blade was manufactured by means of one-shot resin transfer molding (RTM) in a closed and heated metallic mold specially designed with a blade geometry of 67 cm length. The results confirm that the spray coating technique is a viable method to deposit MWCNTs onto glass fiber surface and form electrical networks into the blade at a relatively low MWCNT concentration. Finite element analysis (FEA) predicted a suitable structural blade design with a maximum failure index value of 0.9 attained in the blade shear web. The measured longitudinal strains of the tidal turbine blade were in good agreement with the numerical strain values predicted with FEA. Electromechanical tests carried out on a structural test rig designed and instrumented for tidal turbine blades showed that the electrical resistance change response of carbon nanotube (CNT) network integrated into the blade was capable of following the mechanical curve response up to the blade limit load, confirming its ability to self-sense its strain in real time. [ABSTRACT FROM AUTHOR]

The growing awareness of socioeconomic and environmental issues and the high percentage of petroleum resources consumed and new environmental regulations have fueled efforts to develop innovative, cutting-edge, environmentally friendly materials with a wide range of applications. Due to environmental and sustainability concerns, the advancement of biocomposites has resulted in tremendous breakthroughs in green materials in this century. Their primary goal is to replace current synthetic petroleum-based composites with natural resources. Materials derived from nonrenewable petroleum-based sources are hazardous and expensive to produce; on the other hand, biocomposites derived from natural sources are biodegradable, recyclable, non-abrasive, and compostable and have properties comparable to synthetic fiber composites. Natural fibers are low-cost, lightweight, biodegradable, renewable, and environmentally friendly alternatives to synthetic fibers like glass and carbon fiber. The long-term viability of natural fiber-based composite materials has led to increased use in various production industries. However, the manufacturing process of natural fiber-based biocomposites is still plagued by some difficulties, such as poor adhesive propensity, moisture absorption, poor fire resistance, low impact strength, and low durability. This review provides a panoramic view to provide insight into different aspects of biocomposites based on natural fibers and polymers in terms of properties and applications, which will pave the way for future biocomposites research in academic and commercial contexts. [ABSTRACT FROM AUTHOR]

Gradient distribution of vascular structure made the bamboo wall structure so effective which improved the load-bearing capacity of such bio-mimicked energy absorption structures and modify the crush behavior of thin-walled composite tubes. In this research, the influence of the layering design and stacking sequence on the crush behavior, failure mechanism and absorbed energy of bamboo-inspired GFRP composite tubes is assessed experimentally and numerically. Quasi-static compression tests were conducted to explore seven permutations of Coarse Woven (CW), Fine Woven (FW), and Unidirectional (UD) E/glass fiber sheets, taking into account the longitudinal vascular bundles strengthened by organic matrix. Samples were fabricated employing a modified hand laying up method by using mechanical pressure to obtain better surface finishing and interlaminar adhesion compared to conventional hand layering up methods. To evaluate the corresponding crashworthiness parameters and characterize the crushing behavior of composite tubes, quasi-static axial compressive loading was done. The numerical simulations were validated versus experiments by a commercial finite element (FE) LS-DYNA integrating material model 54. The predicted load-displacement curves and failure mechanisms of FE analysis demonstrate acceptable correlations with visual observations during experimentation. Furthermore, the parametric numerical was performed to examine the effect of different distributions of vascular bundles. The FE analysis results revealed that the crushing behavior of bio-inspired composite tubes depended substantially on layering configuration and the stacking sequence design. The outcomes showed that the combination of woven and unidirectional fibers, respectively, located in the inner layer and hoop direction provide the optimal layering configuration design in terms of crush length efficiency, crush load efficiency, Specific energy absorption, stable progressive crushing, and better manufacturing quality. [ABSTRACT FROM AUTHOR]

Fibre architecture of glass fibre (GF) reinforced polymer composites has a major impact on the mechanical properties for structural applications. In this study, a novel continuous glass fibre non-woven GF mat based on Spirograph art pattern is laid using a customized mechanical system. Spirograph-based continuous glass fibre non-woven (SNW) mat of different patterns was prepared and GF laminate epoxy composites were fabricated with the aim of achieving quasi-isotropic mechanical properties. The samples were cut to dimensions of test specimens from various identical locations symmetrically from a circular-shaped SNW composite laminates which were subjected to flexural, impact, shear and modified compression with anti-buckling tests. One particular SNW pattern composite laminate exhibited 40.82% better impact and 49.01% better shear resistance than commercial 0°/90° woven roving mat composite. The developed SNW laminate composite had quasi-isotropic fibre orientation and better mechanical properties without any stitching and interlacing as in case of woven fibre laminate composite. [ABSTRACT FROM AUTHOR]

Injection molding is a common process for manufacturing thermoplastic polymers. Preconnected to fabrication, mechanically loaded parts are examined in structural simulation. A crucial prerequisite for a valid structural simulation for any material is the underlying material data. To determine this data, different phenomena must be considered such as influences of load type, strain rate, environmental conditions and in case of fiber reinforced materials the fiber orientation (FO) in the considered area. Because of rheological effects, injection molded parts often possess a non-homogeneous FO distribution. This makes it challenging to create testing plates for specimen extraction with a well-defined FO over thickness and width in the considered area. In this paper, a novel testing part is introduced with an unidirectionally oriented testable area. It shows a FO degree of more than 0.75, which has been validated with μ-CT measurement and two thermoplastic materials: polyamide and polybutylene terephthalate, both reinforced with 30 weight percent of short glass fibers. In order to resolve influences of the already addressed FO distribution in injection molded parts, tensile test specimens need to be extracted out of specially designed plates via milling and cannot be injection molded directly. Experiments were carried out to study possible effects of preparation on the mechanical properties of specimens with both materials and two milling parameter sets. The first milling parameter set creates reproducible surface roughnesses, whereas the second parameter set shows a correlation between FO and roughness value: when milling perpendicularly to the main FO lower roughnesses are reached than milling in fiber direction. Uncertainties of the normalized rupture strain from orthogonally extracted specimens seem to be larger than the values from those extracted in fiber direction. [ABSTRACT FROM AUTHOR]

The demand for durable and sustainable eco-friendly materials in recent times has caused many researchers to consider the use of plant fibers in composite development. In this research, the suitability of treated pawpaw fiber as a substitute for glass fiber was considered. The pawpaw fiber was extracted from the plant stem by dew retting and treated before been incorporated into the epoxy matrix. Two distinct fiber structures in linear and network forms were identified, separated, and used for the development of the composites. The composites were produced by incorporating a fixed amount of pawpaw fiber with a varied amount of glass fiber within 3–15 wt% in epoxy-based polymer matrix after which mechanical and biodegradation tests were carried out on the developed samples. Fractured surface morphology was also observed using a scanning electron microscope. The results revealed that the fiber structures influence the properties of the material. While mechanical properties were mostly enhanced by treated linear structure pawpaw fiber, biodegradation was highly promoted by treated network structure pawpaw fiber. Tensile (except for strain), hardness, and flexural properties were enhanced by the linear-structured treated pawpaw fiber, while biodegradability, impact, and tensile strain were improved by the network-structured treated pawpaw fiber compared to the control sample. [ABSTRACT FROM AUTHOR]

In this work, we examine the relationships between the microstructure and the mechanical properties of glass fiber–reinforced polyamide 6,6 composite materials (V f = 54%). These materials made by thermocompression incorporate different grades of high fluidity polyamide-based polymers and two types of quasi-UD glass fiber reinforcement. One is a classic commercial fabric, while the other specially designed and manufactured incorporates weaker tex glass yarns (the spacer) to increase the planar permeability of the preform. The effects of the viscosity of the polymers and their composition on the wettability of the reinforcements were analyzed by scanning electron microscopy observations of the microstructure. The respective influences of the polymers and the spacer on the mechanical performance were determined by uniaxial tensile and compression tests in the directions parallel and transverse to the warp yarns. Not only does the spacer enhance permeability but it also improves physical and mechanical properties: tensile longitudinal Young's modulus increased from 38.2 GPa to 42.9 GPa (13% growth), tensile strength increased from 618.9 MPa to 697 MPa (3% growth), and decrease in ultimate strain from 1.8% to 1.7% (5% reduction). The correlation of these results with the damage observed post mortem confirms those acquired from analyses of the microstructure of composites and the rheological behaviors of polymers. [ABSTRACT FROM AUTHOR]

Tensile quasi-static and fatigue behaviors of out-of-autoclave, quasi-isotropic, E-glass/epoxy composites with woven and stitched fiber architectures are compared. Some specimens were cyclically loaded to failure, while others were tested for residual modulus and ultimate strength. Both laminates survived 107 cycles at a maximum stress of 94.8 MPa but failed prior to 107 cycles at a maximum stress greater than or equal to 124.1 MPa. For the stress-lifetime diagram and residual strength, the woven laminate had superior properties below 104 cycles and the stitched laminate had superior properties above 105 cycles. While intralaminar crack density was higher in the stitched laminate, the woven laminate demonstrated a higher percentage of delaminated area. [ABSTRACT FROM AUTHOR]

This article focuses on 3D printing of continuous glass fiber reinforced composites-polylactic acid by fused deposition modeling. An innovative continuous fiber reinforced composite 3D printer and self-made continuous glass fiber reinforced filament-polylactic acid are applied to study the influences of process parameters including printing temperature, speed, layer height, and fiber volume fraction on mechanical properties of continuous glass fiber reinforced composites-polylactic acid printing samples. Tensile and three-point bending tests are carried out to explore the mechanical responses of printed samples. Experimental results show that the mechanical properties of continuous glass fiber reinforced composites-polylactic acid printing samples are better than those of polylactic acid samples. The tensile and flexural strengths of the specimens are increased by 400% and 204% when the fiber volume fractions are about 5.21% and 6.24%, respectively. The microscopic observations of the fracture surfaces of the tensile samples are also conducted to analyze the influences of layer heights on tensile strength and failure mechanism. [ABSTRACT FROM AUTHOR]

The objective of this work was to explore different types of deformations (buckling, bending, and relaxation) on the properties of laminated composites based on polyester as the matrix and glass fiber in two forms: woven and chopped strand mat. The specimens were produced with the same thickness but with different number of ply. Also, a thin gelcoat based on clay particles was applied on the chopped strand mat samples to get a third series. The results showed that using the same thickness, the mechanical properties, especially in terms of bending and buckling, are influenced by the layers' number. Furthermore, a sports application, which is the main objective of this work, is presented as an applied investigation for a leg prosthesis. Three different running blades "Flex-foot Cheetah" were manufactured to be experimentally and numerically (ANSYS ACP software) characterized to simulate real conditions. The results showed a good agreement between the experimental and numerical values in terms of total displacement, which is around 50 mm, the produced blade has been tested in quasi-static and dynamic compression, and results showed that the relaxation behavior depends on the structure design and the used materials. [ABSTRACT FROM AUTHOR]

This article presents an experimental study on the quasi-static crushing performance of carbon fiber reinforced polymer (CFRP) rods consisting of unidirectional carbon fibers wrapped by braided glass fibers. Rods with and without a taper are tested and then inserted in extruded and expanded polystyrene foam and cardboard panels. Hybrid columnar aluminum tube–CFRP rod structures are also tested in all panel materials. These results are compared to those based on glass fiber reinforced polymer (GFRP) rods, GFRP rods in polystyrene foams, and to GFRP rods in cardboard from a previous study. Tapered CFRP rods exhibit progressive crushing behavior with specific energy absorption superior to GFRP rods, with values of 82 kJ/kg and 65 kJ/kg, respectively. Moreover, the highest specific energy absorption (111 kJ/kg) is obtained in hybrid columnar aluminum tube–CFRP tapered rods, exceeding values of aluminum tubes (89 kJ/kg) and equivalent structures containing GFRP rods (102 kJ/kg). Within panels, cardboard produces the largest increase in mean load of CFRP and GFRP rods due to most constraining fiber splaying during crushing, followed by extruded foam, and lastly expanded foam. However, crushing displacement is most restricted in cardboard due to earlier final compaction. The smallest variations in crushing load occur in extruded polystyrene due to greater homogeneity throughout the foam structure. [ABSTRACT FROM AUTHOR]

The undesired residual stresses in fiber reinforced polymer composites are developed during their manufacturing processes due to the thermal and chemical shrinkage of the polymer matrix, which negatively affect the performance of the composites. Applying tensile stress to the reinforcement fibers during the curing of the matrix can reduce or eliminate the undesired residual stresses. Furthermore, the undesired tensile residual stress within the matrix can be replaced with beneficial compressive residual stress which can improve the mechanical properties of the composites. In this study, theoretical stress analysis was performed in order to determine the value of the optimum compressive residual stress that is associated with the highest tensile strength. This value was determined based on the tensile testing result of prestressed composites with a 40% fiber volume fraction. For the composites with different fiber volume fractions, a new approach was introduced to estimate the optimum fiber prestressing level which generates the optimum compressive residual stress within the matrix and consequently, the highest tensile strength can be achieved. In order to validate this approach experimentally, prestressed composites with 25 and 30% fiber volume fraction were prepared by applying the estimated optimum fiber prestressing levels during curing of matrix and tensile testing was performed. The result of the stress analysis showed that the value of the optimum compressive residual stress corresponding to the highest tensile strength is 2.5 MPa approximately. The tensile testing results confirmed the validity of the new approach in estimating the optimum fiber prestressing level for the composites with different fiber volume fractions. For both prestressed composites with 25 and 30% fiber volume fraction, the highest tensile strength was achieved when the theoretically estimated optimum fiber prestressing level was applied to the fibers during the curing of the matrix. [ABSTRACT FROM AUTHOR]

A new composite manufacturing process, resin transfer pressing, is introduced in this paper. In this process, nonwoven fabrics made of recycled carbon fibers are oversaturated with thermoset resin, i.e. they contain excess resin. The oversaturated nonwoven fabrics are prefabricated and used as resin carrier in a press process, where they are placed in a heated mold together with a dry textile-based preform. During pressing, the resin is pressed out and transferred from the nonwoven into the non-impregnated preform and hence impregnates the whole reinforcement. This study examines the oversaturation of nonwoven fabrics, the resin transfer pressing laminate manufacturing and the surface quality of the laminates. The ability of a nonwoven fabric to be oversaturated with resin is defined by the saturation degree, which was determined as up to 12 for glass fiber nonwoven fabrics and up to 60 for recycled carbon fiber nonwoven fabrics. Different laminates are manufactured by resin transfer pressing, and the impregnation quality is evaluated. With an optimized stacking sequence, a pore content <1% was achieved. The use of recycled carbon fiber nonwovens in the resin transfer pressing process leads to a less wavy surface compared to a wet compression molding manufactured laminate, showing a decrease of waviness Wz25 of 11% minimum. [ABSTRACT FROM AUTHOR]

Distribution of stresses in fiber/matrix interface in UD flax fiber reinforced composites is investigated under transverse loading and compared with conventional synthetic fibers. Micro-scale finite element models with representative volume elements are generated with various fiber packing types and fiber volume ratios. The study is performed for various strain values, which take into account the material nonlinearity of matrix. The results show that significantly lower stress concentrations exist in the case of flax fibers compared to glass fiber composites, explaining the absence of transverse cracks until failure in previously conducted transverse tension tests. Increase in the applied transverse strain causes a further decrease in the stress concentrations due to the nonlinear behavior of the matrix. [ABSTRACT FROM AUTHOR]

The mechanical properties of fiber-reinforced polymer composites depend on several aspects such as the characteristics of constituents, fiber volume fraction, and manufacturing techniques. Fiber prestressing is considered a very attractive manufacturing technique that can be used to produce fiber-reinforced polymer composites with high mechanical properties. This technique has the potential to eliminate or reduce some manufacturing problems like fiber waviness. In the present study, a new approach was used to prepare prestressed fiber-reinforced polymer composites. Unidirectional E-glass fiber-stitched mats were impregnated with epoxy matrix through vacuum-assisted resin transfer molding process. Once the infusion was done, a pre-calculated tensile force was applied to the fiber mats through a hydraulic tensile machine. The impregnated fiber mats were left under tension and vacuum during curing of the epoxy matrix (24 h). Five prestressed samples were prepared by using five different prestressing levels 20, 40, 60, 80, and 100 MPa. In addition, non-prestressed (control) sample was prepared for the purpose of comparison. The influence of fiber prestressing on fiber waviness, fiber volume fraction, and void content was investigated. Flexural, tensile, and compression tests were performed to observe the effect of fiber prestressing on the mechanical properties. The results have shown the success of this new approach in producing prestressed fiber-reinforced polymer composites with high mechanical properties comparing to non-prestressed composites. The microstructure analysis has shown dramatical reduction in fiber waviness for the prestressed samples over control sample. All prestressed samples have shown higher fiber volume fraction and lower void content comparing to the control sample. Also the results have shown as the prestressing level increases, fiber volume fraction increase and void content decreases. Prestressing levels of 40 and 60 MPa were found to be the best candidates, they have led to an increase in tensile strength, compressive strength, and flexural strength by 24.2%, 72.5%, 28% and 28.6%, 100.4%, 26.1%, respectively, comparing to the non-prestressed sample. Ease of implementation and promising results of this new approach would attract the attention toward it. Automotive industry is one potential nominee to apply this approach during manufacturing of fiber-reinforced polymer leaf spring. [ABSTRACT FROM AUTHOR]

Currently, there is a tendency to develop materials that have an increasingly specific purpose for a particular application and the composites can be part of these types of materials. In addition, there is a search for replacement of synthetic fibers with natural ones, because of concerns about the environment. Hybridization of glass fiber composites with sisal fibers can result in improved performance by combining the benefits of each fiber with various applications. Many studies are developed on these types of composites, sisal/glass hybrids, varying certain parameters, such as matrix, orientation of fibers, treatment of fibers, stacking of layers, composition of elements, method of manufacture, among others, characterizing the various types of properties. The present work organizes the researches on the hybrid composites of sisal/glass, in chronological order, highlighting the specifications and parameters used and the main results obtained. [ABSTRACT FROM AUTHOR]

An experimental study is performed to investigate the electro-mechanical response of three-dimensionally conductive multi-functional glass fiber/epoxy laminated composites under quasi-static tensile loading. To generate a threedimensional conductive network within the composites, multi-wall carbon nanotubes are embedded within the epoxy matrix and carbon fibers are reinforced between the glass fiber laminates using an electro-flocking technique. A combination of shear mixing and ultrasonication is employed to disperse carbon nanotubes inside the epoxy matrix. A vacuum infusion process is used to fabricate the laminated composites of two different carbon fiber lengths (150 mm and 350 mm) and four different carbon fiber densities (500, 1000, 1500, 2000 fibers/mm2). A four circumferential probe technique is employed to measure the in-situ electrical resistance of composites under tensile load. Although composites of both carbon fiber lengths showed significant decrease of sheet resistance under no mechanical load conditions, composites of 350 mm long carbon fibers showed the lowest resistivity of 10 X/sq. Unlike the resistance values, composites of 350 mm carbon fibers showed a significant decrease in Young's modulus compared to 150 mm counterparts. For the electro-mechanical response, composites containing carbon fibers of 150 mm long demonstrated a maximum value of percentage change in resistance. These results were then compared to both 350 mm and no added carbon fibers under quasi-static tensile loading. [ABSTRACT FROM AUTHOR]

Nowadays, fiber-reinforced composites have gained attention due to their improved potential for replacing the conventional materials in various applications. Kenaf fiber has been widely used as reinforcement in composites over the past few years which is a most attractive alternative due to its rapid growth at different climatic conditions and ensuring low cost; kenaf fiber has gained some attention to replacing the glass fiber composite and making it purely an eco-friendly composite. However, for enhancing its properties in different applications, an appropriate characterization is very important. Hence, many researches have been conducted in recent years, for the characterization of kenaf fiber and its composites. In this paper, a state-of-the-art review of these characterizations is presented. [ABSTRACT FROM AUTHOR]

This article proposes to develop novel functionally graded materials-based thermoplastic composites and present investigations on their mechanical and thermal properties. An especially designed mold and punch are used to fabricate functionally graded materials and homogeneous composites. Punch is a rotating member of the mold with a cavity at the center along the axis where the material is filled to produce desired samples. The punch rotates for 2 min at 1800 r/min for the gradation of fibers in functionally graded materials towards the outermost zone of the punch cavity. The punch is placed stationary for the fabrication of homogeneous composites. Functionally graded materials and homogeneous composites are fabricated with 15 wt.% and 30 wt.% glass fibers-reinforced polybutylene terephthalate. Neat polybutylene terephthalate is also fabricated for comparative study. The gradient of fiber distribution in functionally graded materials is verified by ignition loss test, hardness measurement, and scanning electron microscope analysis. Mechanical, fracture toughness, and thermo-mechanical peculiarity of functionally graded materials are investigated and compared with neat polybutylene terephthalate and homogeneous composites. Functionally graded materials outperform neat polybutylene terephthalate and homogeneous composites. This manufacturing technique shows a promising potential for fabrication of thermoplastics-based functionally graded materials which otherwise is difficult to produce because of their inherence characteristic to solidify at fast rate. [ABSTRACT FROM AUTHOR]

This research was undertaken to investigate the influence of the sizing components, principally coupling agents and film formers, of glass fiber on the interface of reinforced polyurethane composites. The contents of film-forming agents and coupling agents were, respectively, checked by acetone extraction and heat treatment. The categories and chemical structures of the film-forming agents, which mainly exist in the extracting solutions, were investigated by nuclear magnetic resonance spectroscopy. The coupling agents, which mainly existed on the extracted glass fiber surfaces, were analyzed by X-ray photoelectron spectroscopy. Then, the interfacial adhesion properties between glass fibers of untreated, extracted and heat-treated and polyurethane resin were measured with micro-droplet test. The results show that the interfacial shear strength of the glass fiber-reinforced polyurethane composite mainly depends on the coupling agents, in which the N-containing groups play a dominant role. The film formers also take some effects, in which the hydroxyl groups have the greatest contribution. [ABSTRACT FROM AUTHOR]

Glass fiber reinforced plastics are used in variety of industrial and constructional applications for their superb mechanical and physical properties. Delamination is one of the most important and prevalent damages in machining of glass fiber reinforced plastics. Diamond core drills have the capability of simultaneously drilling and grinding of fiber reinforced plastics, which results in hole quality improvement. Rotary ultrasonic-assisted drilling is the new machining process to drill holes on fiber reinforced plastics and has attracted increasing attention in recent years. In this paper, thrust force and delamination in rotary ultrasonic-assisted drilling of glass fiber reinforced plastics using diamond core drill have been investigated. A proper ultrasonic system for a core drill in ABAQUS was designed and fabricated. Influence of ultrasonic vibration and then tool grain size, fiber-volume fraction and machining parameters including spindle speed and feed rate on thrust force and delamination was investigated. Higher thrust force induces more delamination. As a result of the study, less delamination was achieved in ultrasonic-assisted mode by using a tool with larger grain size onto lower fiber-volume fraction composites. Additionally, experiments showed that lower spindle speed and higher feed rate induce more delamination. [ABSTRACT FROM AUTHOR]

This research article investigated the notch sensitivity of two different glass fibre architectures, namely short and 2D plain-woven glass fibres reinforced with unsaturated polyester and epoxy matrix composites fabricated by the hand lay-up technique. This was carried out through open hole tension tests at different ratios of the specimen hole diameter to the specimen with three different values (0.1, 0.2, 0.5) compared to the unnotched specimen. The notch sensitivity of these composites was evaluated using the residual tensile strength by the application of Whitney–Nuismer Mathematical Model. The results showed that by using polyester matrix, the notch sensitivity of composites reinforced with plain-woven glass fibre is higher than that of short glass fibre at different D/W ratios. On the other hand, on testing epoxy matrixes, the notch sensitivity of composites reinforced with plain-woven glass fibre is lower than that of short glass fibre at different D/W ratios. [ABSTRACT FROM AUTHOR]

The structural design of the bolted fiber reinforced polymer elements is typically governed by the capacity of the joint rather than the fiber reinforced polymer member, while the joint capacity is typically governed by the shear strength of the fiber reinforced polymer. Here, the possibility of improving the shear strength of bolted joints is investigated in the unidirectional glass fiber reinforced polymer plates by incorporating the multiwalled carbon nanotubes during glass fiber reinforced polymer fabrication. Glass fiber reinforced polymer double-shear bolted lap joints were fabricated using up to 1.0 wt% multiwalled carbon nanotubes–-epoxy nanocomposites. Finite element modeling using multicontinuum theory and element deletion techniques was performed to explain the joint behavior. The experimental investigations show that incorporating multiwalled carbon nanotubes improved the shear strength, ductility, and energy absorption significantly. Microstructural analysis proves that a chemical reaction between multiwalled carbon nanotubes and epoxy improves the shear strength of the matrix. [ABSTRACT FROM AUTHOR]

In this study, the impregnated fibre bundle test, a common method used by carbon and glass fibre manufacturers to determine the properties of fibres used in composites, was adapted for natural fibres and validated by a round robin test on one type of natural fibres, namely flax fibres. Five European laboratories have carried out in parallel the impregnated fibre bundle test, on the same batch of hackled flax (long fibres), to check the applicability and reliability of this modified method on natural fibres. The results were compared to the more traditional single fibre test on elementary fibres. The back-calculated fibre stiffness shows a very low scatter between the five laboratories of less than ±5% (59.8 ± 2.4 GPa, as measured between 0 and 0.1% strain). The fibre ultimate tensile strength of 527 ± 138 MPa has a higher scatter, compared to stiffness values, as this property is highly sensitive to imperfections and flaws. [ABSTRACT FROM AUTHOR]

The objective of this study is to characterize the damage in glass fiber reinforced composite laminated reinforced with nanosilica particles subjected to tensile, flexural, and transverse loadings. Tensile, three-point bending, quasi-static indentation test, and ballistic impact tests were used in order to obtain the perforation response, flexural and tensile behavior of the composites and nanocomposites. Experimental test series was carried out to determine the tensile and flexural strength and stiffness, impact energy absorption, and failure mechanisms of composites in the presence of nanoparticle. Hand lay-up method has been used to manufacture nanocomposites constituted of 12 layers of 2D woven glass fibers with 40% fiber volume fraction. The composites were reinforced by adding organically modified nano-silica in a 0%, 0.5%, 1%, and 3% ratio in weight with respect to the matrix. Results revealed that in 0.5 wt.% nanoparticles, energy absorption and tensile strength are maximum, but flexural strength has the highest value in 3 wt.%. Furthermore, the highest energy absorption, elastic energy, and energy absorption at maximum force in quasi-static penetration occur in 0.5% nanosilica content. In the case of ballistic tests, effect of nanosilica is more tangible than in quasi-static indentation. Nanocomposite at 0.5% nanosilica recorded higher ballistic limit and energy absorption in comparison with other composites and nanocomposites. SEM images showed that fracture surfaces in 0.5 wt.% nanocomposites are rough and engender more crack tips in comparison with other specimens, which contributes to higher energy absorption in static and dynamic tests. [ABSTRACT FROM AUTHOR]

For both environmental and economic consideration, the use of recycled glass fiber-reinforced flame retardant poly(butylene terephthalate) (RGFFRPBT) is of significant importance. In the study, the mechanical, thermal, rheological, and flame retardant properties of RGFFRPBT granulated by different extruders were evaluated. To explore the relationship between the screw structure and the properties of the extruded RGFFRPBT, the carboxyl content (CC), and intrinsic viscosity ([η]) of the processed polymer and the average GF length (L¯) were investigated. Increasing the shear force of the extruder caused both [η] and L¯ to decrease, whereas the CC increase. Variations of these parameters had a different effect on the properties of the RGFFRPBT. Both of mechanical and thermal properties of extruded RGFFRPBT deteriorated with the increase of screw shear force, while the thermal flowability improved. Furthermore, all the extruded products were classified as V-0 with LOI of 32.2%, and passed the glow wire ignition temperature test (GWIT). The results confirmed that the degradation of properties of RGFFRPBT can be controlled by screw-type extrusion. RGFFRPBT granulated by a single screw extruder with 30 mm diameter and length to diameter ratio of 30 was found to produce material with properties meeting the requirements for electronic and electrical applications. [ABSTRACT FROM AUTHOR]

This paper aims at comparing the mechanical behaviour of different composite materials constituted of twill flax and glass fabrics-reinforced liquid thermoplastic and thermoset resins. The main objective is to study the possibility of thermoplastic to replace thermoset matrix, and flax fibre to replace glass fibre. For this purpose, the studied composites were fabricated using the vacuum infusion technique. Next, they were subjected to several monotonic and load-unload tensile tests in order to determine their mechanical properties and their evolution with damage. Two elastic damage and elastic-plastic damage models were also considered to predict their behaviour. The obtained results show that the used thermoplastic resin could constitute an interesting alternative to the thermoset resin for the vacuum infusion process. Furthermore, the flax fibre composites, in particular those based on the thermoplastic resin, present specific tensile moduli close to those of glass composites. [ABSTRACT FROM AUTHOR]

The objective of this paper is to present an investigation of resistance welded thermoplastic joints using stainless steel wire mesh and polyethylene terephthalate (PET) with unidirectional E-glass fiber reinforcement. Five weld pressures and six heating element types were investigated to achieve high quality welds. Scanning electron microscope (SEM) images of welded heating element cross-sections were analyzed to provide a phenomenological description of the weld. Welded joints were also subjected to experimental lap shear evaluation and joint strengths were compared with values from the literature to assess the overall quality of welded joints. Characteristic B-basis strengths and corresponding SEM images are compared to lead to a recommended weld pressure of 345 kPa with a stainless steel wire mesh with 100 openings per inch. [ABSTRACT FROM AUTHOR]

Barely visible impact damage in composites can result in hidden damage such as delamination and cracking. Triboluminescence is currently being looked at as a way of inundating composites with a sensory level mechanism for impact events. ZnS:Mn doped resin sensing plates are embedded within glass fiber-reinforced composites and are impacted at low velocities (3.45–3.51 m/s). The damage created by the impact can be seen under black light analysis and allows for quick visual inspection of the composite. The striker during impact registers a bounce which can be used to determine final impact velocity, which in turn defines the force at impact. By measuring the amount of time between consecutive impacts, an indirect estimation of impact force was made using the temporal occurrence of triboluminescence. Triboluminescent emissions occurred for impacts greater than 300 N. The measured impact energy averaged 36.79 J (±0.48). The calculated impact force and impact energy corresponded to the amount of damage area found on the composite, showing that triboluminescent crystal inclusion into composites can provide damage sensing capability to woven fiber composites. [ABSTRACT FROM AUTHOR]

Although there are different models for determining bond strength and development length of glass fiber-reinforced polymer bar in normal concrete, they cannot evaluate the interfacial behavior of glass fiber-reinforced polymer bar in self-consolidating concrete accurately. This study presents more precise and efficient models for bond strength and development length of glass fiber-reinforced polymer bar in self-consolidating concrete than existing equations. The performance of a model depends very much on test data. Previous researches do not have enough data of bond strength and development length of glass fiber-reinforced polymer bar in self-consolidating concrete. So, more extensive data are needed to investigate the efficiency and accuracy of a model. To solve this problem, direct pull-out tests are performed in this study. Unlike existing models for bond strength and development length, proposed models perform very well for predicting bond strength and development length of glass fiber-reinforced polymer bar in self-consolidating concrete. The new models considerably decrease the deviation of existing models. [ABSTRACT FROM AUTHOR]

A numerical study was performed to investigate the tensile properties of unidirectional fiber-reinforced composites containing co-polypropylene and short glass fiber (SGF) using a three-dimensional representative volume element (RVE) and finite element method (FEM). The initiation and propagation of interfacial crack were simulated based on a bilinear cohesive zone method (CZM). The FE simulation indicated that the transverse tensile strength of composite reinforced by SGF was strongly affected by the interface strength, critical fracture energy owing to interfacial debonding as well as loading direction. By increasing of SGF aspect ratio, the anisotropy of tensile strength was slightly affected; however, the anisotropy of modulus was noticeably elevated. The results of FE analysis indicated the proposed CZM can be used to simulate the crack-induced softening mechanism of reinforced thermoplastic polymers. [ABSTRACT FROM AUTHOR]

The entrance flow of long glass fiber reinforced polypropylene has been studied. It is demonstrated that longer glass fibers are easier to break and accumulate at the entrance. As the length of the die and shear rate increase, the fiber breakage increases for long glass fiber reinforced polypropylene. Comparison of fiber breakages of long and short glass fiber reinforced polypropylene indicates that short glass fiber mainly breaks before and at the entrance and remains almost unchanged in the die, while longer glass fibers still break after the entrance within the die. It is demonstrated that fiber accumulation increased when increasing the length of the die and shear rate. The pressure is found to oscillate at the entrance and this pressure accumulation and release should be related to the fiber interactions and fiber breakage at the entrance. It is also found that the presence of long glass fibers would lead to significantly higher viscosity which would decrease when increasing the shear rate. [ABSTRACT FROM AUTHOR]

To improve the comprehensive performances of polypropylene/ethylene-α-octene copolymer foams, short glass fiber was introduced to prepare polypropylene hybrid composite foams. Then, the effects of short glass fiber on the foaming qualities, interfacial morphologies, mechanical properties and energy absorption behavior of polypropylene hybrid composite foams were investigated. Results showed that the foaming qualities of the hybrid composite foams were improved greatly. The minimum average cell diameter and maximum cell density were achieved with adding 30% short glass fiber. From the analysis of interfacial structures, the interfacial interactions were mainly occurred in the polypropylene/short glass fiber and polypropylene/ethylene-α-octene copolymer pairs rather than short glass fiber/ethylene-α-octene copolymer pair. With increasing content of short glass fiber, the mechanical properties (excluding elastic modulus) of polypropylene hybrid composite foams were increased first and then declined. Within the study range, the energy absorption capability of polypropylene hybrid composite foams could be doubled with 30% short glass fiber added. The energy-absorption ratio was improved only with relative higher short glass fiber content, of which, however, the improvement was not as remarkable as that shown in the energy absorption capability. [ABSTRACT FROM AUTHOR]

This article investigated the preparation, microstructures, and performance of long-fiber-reinforced thermoplastic polycarbonate/poly(butylene terephthalate) alloys through the joint processing of melt blending followed with a melt pultrusion. The mechanical evaluation demonstrated that the resulting composites achieved significant improvements in tensile strength, flexural strength and modulus, and notched impact strength. Such a prominent reinforcement effect is attributed to the feature that the residual fiber length within the injection-molded long-fiber-reinforced thermoplastic composite specimens is much longer than that of the short-fiber-reinforced ones. This takes full advantage of the strength of the reinforcing fibers themselves. The improvement in impact toughness is due to the energy dissipation by both the fiber pullout and fiber fracture as a result of the long-fiber-reinforcing effectiveness. The scanning electron microscopy investigation confirmed that the fiber pullout and fiber breakage concurred on the impact and tensile fracture surfaces, and the former was more significant than the latter. Meanwhile, the scanning electron microscopy observation also indicated a good interfacial adhesion between the thermoplastic matrix and fibers, which results in the subsidiary enhancement of mechanical properties. The study of dynamic mechanical analysis revealed the long-fiber-reinforced thermoplastic polycarbonate/poly(butylene terephthalate) composites achieved a remarkable increase in storage modulus but presented a considerable decrease in loss-factor magnitude compared to the pristine alloys. The thermal stabilities of the composites were also slightly improved in the presence of long glass fibers according to the results of thermogravimetric analysis. [ABSTRACT FROM AUTHOR]

This paper deals with durability of glass fiber-reinforced polymer composites under sustained loads and simultaneously exposed to either saltwater or tap water. The tensile properties of the specimens before and after conditioning were evaluated along with their moisture uptaking behavior to reveal the durability of the specimens under combined effects. The mass change curves under saltwater and tap water immersion exhibited dual-stage diffusion process. The first stage followed Fickian profile, while mass loss occurred in the second stage with increasing immersion time, attributed to hydrolysis of resin. The weight gain in saltwater was greater than that in tap water. Moreover, the mass change curves under varying percentage of sustained loadings exhibited similar trends, while the maximum moisture uptake was obviously affected by the loading conditions. Based on Fick’s second law, the diffusion coefficients in the first stage under different conditions were determined through the least-square regression technique. It was observed that the tensile strength and modulus were increasing initially upon immersion, which was attributed to curing beyond the initial cure during manufacture. Then, the tensile properties decreased with continued immersion in saltwater or tap water. After 180 days of immersion, the tensile properties degraded at a smaller rate, both for specimens with and without sustained loading. For the saltwater immersion of 360 days, the tensile properties decreased significantly as the sustained loading increased. However, the tap water immersion had less detrimental effect on tensile properties of glass fiber-reinforced polymer. Furthermore, based on Arrhenius concept coupled with fracture mechanics principle, a new model was proposed to describe the combined effects of immersion and sustained load. [ABSTRACT FROM AUTHOR]

Bamboo fibre has gained significant interest as a sustainable reinforcement fibre in natural fibre/polymer composites, which is as a result of specific mechanical properties and being a biodegradable material compared to glass fibres. The article also gives a summary of how to improve the mechanical properties of bamboo fibre reinforced polypropylene (BFRP) composites as presented in various researches and the methodology of attaining these ultimate properties of bamboo fibres with polymeric matrices leading to improved BFRP. Mechanical properties of BFRP composites are improved by introducing coupling agent. Fibre treatment and nanoclay addition, in the right proportion, as reported have improved mechanical properties of BFRP composite. [ABSTRACT FROM AUTHOR]

Multi-walled triaxial hollow fibers with two different outer wall materials are fabricated by core-sheath electrospinning process and integrated into epoxy matrix with or without primary glass fiber reinforcement to produce composites with enhanced mechanical properties. The morphologies of multi-walled hollow fibers are tailored by controlling the materials and processing parameters such as polymer and solvent types. The triaxial hollow fiber fabrication is achieved through using a nozzle containing concentric tubes, which allows for the transport of different fluids to the tip of the nozzle under the applied high voltage. In comparison to uniaxial electrospun fibers, the hollowness of electrospun fibers enables one to manufacture new reinforcing agents that can improve the specific strength of composites. It is shown that the mechanical properties of epoxy matrix composite incorporated with electrospun fibers as primary fiber reinforcement can be significantly tailored by properly selecting the wall materials, diameters, and the amount of electrospun fibers. We have also presented that triaxial electrospun hollow fibers as co-reinforcement in the glass fiber-laminated epoxy matrix composites enhance the flexural modulus by 6.5%, flexural strength by 14%, the onset of first layer of glass fabric failure strain by 12.5%, and final failure strain by 20%. [ABSTRACT FROM AUTHOR]

Due to its good mechanical performances and design flexibility, long glass fiber-reinforced polypropylene (hereinafter referred to as LGFRP) composite has been increasingly used in the automotive industry, in which the LGFRP components are likely to sustain different strain rates loading during a crash event. The objectives of this study are to investigate the correlations between the LGFRP and strain rates 10[sup -3]s-1 to 50 s-1, and the corresponding failure modes of LGFRP. Therefore, tensile and compression tests are conducted at different strain rates and the corresponding microstructures of the specimens are investigated with scanning electron microscope. The experimental results show that the failure strain and ultimate strength increase as increasing strain rate. The elastic modulus is sensitive to strain rate in tensile tests, but less sensitive to strain rate in compression tests. The main failure modes of the specimens are the matrix crack and fiber pull-out. The defects such as bubbles, shrinkage cavities, or dry fibers of the specimens play important roles in the initiation and propagation of cracks during the tensile and compression tests. [ABSTRACT FROM AUTHOR]

Pultrusion is one of the several manufacturing processes for polymer composites. It involves resin-impregnated fibers that passed through a heated die, while the resin cures to produce a solid profile in the desired shape. Many processing variables such as die temperature, pull speed, fiber impregnation, resin viscosity, among others, affect the composite quality and the process efficiency. In fact, a good understanding and careful control of all these variables are needed to avoid defective profiles as well as to achieve better processing conditions. In this paper, the relationship between the resin bath temperature and the mechanical properties of pultruded rods such as tensile strength, elastic modulus, and hardness was established. The effect of resin viscosity on the fibers wet-out, cure position inside the die and the void formation was also investigated. The results showed that the rods made at higher bath temperatures presented higher tensile strength, elongation at break and hardness, but lower modulus of elasticity. This behaviour was correlated with the void content yielded during the profile formation. [ABSTRACT FROM AUTHOR]

Nylon 6,6 nanofibers were interleaved in the mid-plane of glass fiber/epoxy matrix composite laminates for Mode I and II fracture mechanic tests. The present study investigates the effect of the nanofibers on the laminates’ mechanical response. Results showed that Nylon 6,6 nanofibers improved specimen’s fracture mechanic behavior: the initial energy release rates GIC and GIIC increased 62% and 109%, respectively, when nanofibrous interlayer was used. Scanning electron microscope micrographs showed that nanofiber bridging mechanism enhances performances of the nanomodified specimens, still able to link the layers when the matrix is broken. [ABSTRACT FROM AUTHOR]

This paper reports the effect of temperatures (30℃ to 80℃, with incremental steps of 5℃) and orientations of the glass fibers (0°, 30°, 45°, 60° and 90°) on the dynamic properties (the loss factors and the natural frequencies) of polypropylene honeycomb sandwich composites. The impulse technique has been employed to calculate the natural frequency and loss factor of the sandwich specimens under different temperatures. The natural frequency and loss factor values have also been calculated theoretically using Blevins's formulae for natural frequency, and Yim et al.'s transverse shear effect, respectively. The values of damping loss factor and the natural frequency/stiffness are the maximum at 0° fiber orientation in the skins of the sandwich specimen. The loss factor of the same oriented specimen increases sharply with the increase in temperature. The main reasons for the above are the higher in-plane strength of skins and lower transverse shear strength of the honeycomb core. Hence, the 0° fiber oriented sandwich specimen is more desirable than the other fiber oriented specimens at all temperatures. A good agreement is observed between the experimental and theoretical values. [ABSTRACT FROM AUTHOR]

This paper aims to address the responses of the AWJM parameters to two different reinforcement sources, viz, bi-directional glass mat (synthetic) and coconut sheath (natural) fibre, in a polymer matrix composite. The machining quality of the cut (kerf taper angle and surface roughness) was analysed, using the multi-objective response based on the L9 (34) orthogonal array, using the Taguchi-based experimental grey relational analysis. The mechanical performance of the composites was studied before and after machining, to observe the interfacial adhesion between the fibre and the matrix due to the cutting force, using scanning electron microscopy (SEM). Only very little reduction in tensile strength was found after the machining of the composite in each case, and it indicates lesser stress formation due to the cutting forces. The machining performance of two different composite materials with the same wt % of fibre content was found experimentally; it showed significant changes in the results for both the materials. However, the abrasive particle size was identified as the most significant parameter influencing the quality of the cut in both the composites. A higher crack resistance was found in the glass mat composites due to their better interfacial adhesion capability. [ABSTRACT FROM AUTHOR]

To improve the performance of short glass fiber reinforced polypropylene (SGF/PP) foam composites, the maleic anhydride (MAH) grafted PP (PP-g-MAH) and MAH grafted ethylene-α-octene copolymer (EOC-g-MAH) were introduced as the interfacial compatibilizers. Then, the effects of compatibilizers on the cellular structures, interfacial morphologies, and mechanical properties of SGF/PP foam composites were investigated and compared in detail. Results showed that the foaming qualities of composites were remarkably improved in the presence of either PP-g-MAH or EOC-g-MAH. The best samples were achieved with minimum average cell diameters and maximum cell densities, when the content of either PP-g-MAH or EOC-g-MAH was added up to 8%. Increased compatibilizers promoted the wettability of PP to SGF, and PP-g-MAH showed the more obvious influence on enhancing SGF–polymer interfacial bonding that that of EOC-g-MAH. Mechanical tests claimed that mechanical properties, except for compression strength, were all strengthened with growing compatibilizers. It was emphasized that EOC-g-MAH had much advantage of improving the impact toughness, whereas the PP-g-MAH was more beneficial of increasing the flexural and compression strength of SGF/PP foam composites. [ABSTRACT FROM AUTHOR]

This paper presents the test results of an experimental study to investigate the effect of elevated temperatures on the bond properties of glass fiber-reinforced polymer bars in concrete. For this purpose, a total of 39 pullout specimens with glass fiber-reinforced polymer bars were cast for bond strength tests. In addition to the laboratory temperature, specimens were exposed to heating regimes of 100, 200, 300 and 350℃ for a period of 1, 2 or 3 h. The test results are presented in terms of bond strength, bond–slip relationship, and mode of failure. All specimens failed by shearing of the concrete corbels surrounding the bars and almost no damage was seen in the glass fiber-reinforced polymer bars. The results showed that the bond strength decreased as the temperature or exposure period increased. Reductions of about 20% of the original bond strength were recorded after exposure to 100 and 200℃ for 3 h. Significant reductions of about 50% in the bond strength were recorded after exposure to 350℃ for periods of 2 and 3 h. A modification to the ACI (American Concrete Institute) and CEB-FIP (Comité Euro-International du Béton-Fédération Internationale de la Précontrainte) equations was developed to consider the effect of elevated temperatures and it showed good agreement with test results. [ABSTRACT FROM AUTHOR]

The effects of various types and amounts of fumed silica and graphite nanoplatelets on the microstructure and thermomechanical properties of polypropylene composites containing 5, 10, and 20 wt% of short glass fibers have been analyzed. Hybrid composites were produced by melt compounding and compression molding. The aspect ratio of the short glass fiber decreased with the fiber loading and the nanofiller amount. The tensile strength and elastic modulus increased, while the elongation at break decreased as the content of both short glass fiber and nanofiller increased. A two-population model, based on the Halpin–Tsai and Tsai–Pagano composite theories, was used to predict the elastic modulus of the nano-micro hybrid composites. Experimental values appear to be reasonably consistent with model predictions. Tensile energy to break under impact conditions increased with the short glass fiber content but decreased with nanofiller amount. Moreover, storage modulus and creep stability were remarkably enhanced in short glass fiber composites by the presence of both nanofillers. [ABSTRACT FROM AUTHOR]

Microwave curing of epoxy/glass fiber composites was investigated in this paper. By studying the reaction characteristics of the resin matrix, detailed curing processes were established. With the use of a self-designed pressure-exerting device, the resin weight fraction of the composites was controllable. The glass transition temperature was measured by differential scanning calorimetry, and the mechanical properties were determined by three-point-bend and uniaxial tensile tests at room temperature. The tensile failure surfaces of both microwave and thermally cured composites were observed with scanning electron microscope. A comparison of the microwave and thermal processes was conducted to evaluate the advantage of microwave curing process. The microwave process (a) and thermal process (b) were regarded as the optimized process for each curing method. It was concluded that the epoxy/glass composites cured by microwave radiation had slightly higher Tg, comparable flexural strength and better tensile properties. Furthermore, the microwave process had a great advantage in saving the cycle time. [ABSTRACT FROM AUTHOR]

Glass fibers reinforced polymer composites have been prepared by various manufacturing technology and are widely used for various applications. Initially, ancient Egyptians made containers by glass fibers drawn from heat softened glass. Continues glass fibers were first manufactured in the 1930s for high-temperature electrical application. Nowadays, it has been used in electronics, aviation and automobile application etc. Glass fibers are having excellent properties like high strength, flexibility, stiffness and resistance to chemical harm. It may be in the form of roving’s, chopped strand, yarns, fabrics and mats. Each type of glass fibers have unique properties and are used for various applications in the form of polymer composites. The mechanical, tribological, thermal, water absorption and vibrational properties of various glass fiber reinforced polymer composites were reported. [ABSTRACT FROM AUTHOR]

Bond behavior of sand-coated deformed glass fiber reinforced polymer rebars was experimentally investigated in this study. A total of 84 specimens, including 30 beam specimens, 48 Losberg pullout specimens, and six RILEM/CEB/FIP pullout specimens, were constructed and tested under monotonic loading. Two failure modes including pullout failure and splitting failure were observed. The pullout failure occurred when the embedment length of specimens was less than 5 times glass fiber reinforced polymer rebar diameter, while the splitting failure occurred when embedment length was more than 5 times rebar diameter. The specimens with the embedment length of 5 times bar diameter failed either by glass fiber reinforced polymer rebars pulling out or by concrete splitting. The results also showed that bond strength of sand-coated deformed glass fiber reinforced polymer rebars was, on average, 59–127% that of the deformed steel rebars. With higher concrete strength, higher bond strength of sand-coated deformed glass fiber reinforced polymer rebars was obtained. When rebar diameter or embedment length increased, bond strength of sand-coated deformed glass fiber reinforced polymer rebars decreased. Based on these results, formulas for the bond strength and the development length of glass fiber reinforced polymer rebars were proposed, considering the effects of concrete strength, bar diameter, embedment length, and rebar outer surface. [ABSTRACT FROM AUTHOR]

Various chemical treatments such as mercerization (alkali treatment), permanganate treatment, and benzoyl chloride treatment were performed on palmyra palm leaf stalk fibers. Composites were fabricated by hand layup method followed by compression molding process using unsaturated polyester as matrix. Two types of composites were fabricated, one by using treated continuous palmyra palm leaf stalk fibers and other by hybridizing nonwoven glass fiber mat and alkali treated continuous palmyra palm leaf stalk fibers with bilayer arrangement. In both the cases palmyra palm leaf stalk fiber is laid unidirectionally for composite fabrication. The composites were tested for its tensile, flexural, impact, and dynamic mechanical properties. There was an increase of 33% in tensile, 55% in flexural, and 50% in impact strength for benzoyl, permanganate, and alkali treated composites, respectively, compared to untreated fiber composites. But all the treated fiber composites did not show much variation in properties. Hybridization resulted in 54, 36, and 58% improvement in tensile, flexural, and impact properties, respectively, in comparison to unhybridized treated unidirectional palmyra palm leaf stalk fiber composites. Reinforcement of alkali treated fibers and hybridization of glass fibers enhanced the loss and storage modulus of the composites, increased glass transition temperature (Tg), and also reduced the tan δ peak. A positive shift in tan δ was also evident for all the composites. [ABSTRACT FROM AUTHOR]