Experimental characterization of traditional composites manufactured by vacuum‐assisted resin‐transfer molding

The primary purpose of this study is to investigate the anisotropic behavior of different glass‐fabric‐reinforced polyester composites. Two commonly used types of traditional glass fabrics, woven roving fabric and chopped strand mat, have been used. Composite laminates have been manufactured by the vacuum infusion of polyester resin into the fabrics. The effects of geometric variables on the composite structural integrity and strength are illustrated. Hence, tensile and three‐point‐bending flexural tests have been conducted at different off‐axial angles (0, 45, and 90°) with respect to the longitudinal direction. In this study, an important practical problem with fibrous composites, the interlaminar shear strength as measured in short‐beam shear tests, is discussed. The most significant result deduced from this investigation is the strong correlation between the changes in the interlaminar shear strength values and fiber orientation angle in the case of woven fabric laminates. Extensive photographs of fractured tensile specimens resulting from a variety of uniaxial loading conditions are presented. Another aim of this work is to investigate the interaction between the glass fiber and polyester matrix. The experiments, in conjunction with scanning electron photomicrographs of fractured surfaces of composites, are interpreted in an attempt to explain the interaction between the glass fiber and polyester. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci, 2008     

Nanoclay Addition and Core Materials Effect on Impact and Damage Tolerance Capability of Glass Fiber Skin Sandwich Laminates

This study explores the effects of modified (OMMT) nanoclay and core material on low velocity impact behavior and damage tolerance capability of glass fiber reinforced (FRP) polyester resin – polystyrene foam (PS) sandwich laminates. The FRP and sandwich laminates are prepared by a compression molding technique for investigation. Low velocity impacts are carried out on all the fabricated laminates by using a instrumented drop weight impact tower with the energy level of 30 J and load–energy–time plots were recorded using data acquisition software. Post impact flexural tests have been conducted to evaluate the damage tolerance capability of the fabricated composite laminates. X-ray Diffraction (XRD) results have been obtained for the samples, where the nanoclay has indicated that intergallery spacing of the layered clay increases with the matrix. Scanning Electron Microscopy (SEM) has given the morphological picture of the nanoclay dispersion in the polymer fracture samples. The results of the study show that the impact properties and damage tolerance capability of the 4% nanoclay polyester sandwich have been greatly increased.     

Influence of carbon nanotubes on the thermal, electrical and mechanical properties of poly(ether ether ketone)/glass fiber laminates

Novel poly(ether ether ketone) (PEEK)/single-walled carbon nanotube (SWCNT)/glass fiber laminates incorporating polysulfone as a compatibilizing agent were fabricated by melt-blending and hot-press processing. Their morphology, mechanical, thermal and electrical properties were investigated and compared with the behavior of similar non-compatibilized composites. Scanning electron micrographs demonstrated better SWCNT dispersion for samples with polysulfone. Thermogravimetric analysis indicated a remarkable improvement in the thermal stability of PEEK/glass fiber by the incorporation of SWCNTs wrapped in the compatibilizer, ascribed to a significant thermal conductivity enhancement. Differential scanning calorimetry showed a decrease in the crystallization temperature and crystallinity of the polymer with the addition of both wrapped and non-wrapped SWCNTs. The laminates exhibit anisotropic electrical behavior; their conductivity out-of-plane is lower than that in-plane. Dynamic mechanical studies revealed an increase in the storage modulus and glass transition temperature in the presence of polysulfone. Mechanical tests demonstrated significant enhancements in stiffness, strength and toughness by the incorporation of wrapped nanofillers, whilst the mechanical properties of non-compatibilized composites only improved marginally. Samples with laser-grown SWCNTs exhibit enhanced overall performance. This investigation confirms that SWCNT-reinforced PEEK/glass fiber compatibilized composites possess excellent potential to be used as multifunctional engineering materials in industrial applications.     

Mechanics of short fibers in filled styrene-butadiene rubber (SBR) composites

Different short fibers (glass, carbon, cellulose, polyamide, and polyester with aspect, length/diameter, ratio of 600, 860, 500, 83, and 330 respectively) were added to styrene-butadiene rubber (SBR) matrix filled with an inorganic semireinforcing mineral (sepiolite). In all cases, 18 parts by volume of fiber per 100 parts by mass of rubber were added. The fiber orientation attained (more than 60%) was evaluated by a ratio of directional mechanics on uncured samples. In glass and carbon fiber composites, because of decreases in fiber aspect ratio after mixing (10 and 35 respectively), no improvements in properties were obtained. The presence of fibers yields a large increase in green strength, stress at low strain, and tear strength. Logically, the elongation at break diminishes. The uncured and cured properties present a remarkable anisotropy. The adhesive employed (resorcinol-formaldehyde) to increase fiber-to-matrix adhesion enhanced the composite properties, especially in the case of polyester fiber composites. Thus, for polyester fiber composites, green strength became 15.85 kg/cm²; stress at 25% strain, 10.2 MPa; tensile strength, 6.3 MPa; elongation at break, 36%; tear strength, 70 N; and swelling in longitudinal direction, 1.06.     

The effect of glass-resin interface strength on the impact strength of fiber reinforced plastics

The effect of glass-resin interface strength on the impact energy of glass fabric (style 181) reinforced epoxy and polyester laminates has been determined. The interface strength was altered by surface treatment of the fabrics with silane coupling agents and with a silicone fluid mold release and the interlaminar shear strength was determined as a means to evaluate the interface strength. An instrumented Charpy impact test was used on unnotehed specimens and thus both initiation and propagation energies could be determined as well as dynamic strength. It was found that the initiation energy for both polyester and epoxy laminates increased with increasing interlaminar shear strength, The propagation energy and thus the total energy for polyester laminates displays a minimum at a critical value of interlaminar shear strength (ILSS). Below this critical value, the total impact energy increases with decreasing shear strength and the dominant energy absorption mode appears to be delamination. Above the critical value, the impact energy increases with increasing values of ILSS and the fracture mode is predominantly one of fiber failure. In all cases, even with mold release applied, the shear strength of epoxy laminates was above this critical value and-thus the total impact energy increases with Increasing values of ILSS. The maximum energy absorbed for the epoxy laminate and the polyester laminate is nearly identical. However, the maximum for the epoxy laminate occurs when the shear strength is maximized while for the polyester laminate the shear strength must be minimized. For the polyester laminate when delamination is predominant, it was found that the glass surface treatment affects the amount of delamination as opposed to the specific value of delamination fracture work.     

玻璃纤维增强树脂基复合材料疲劳性能的试验研究

介绍了对玻璃纤维增强树脂基复合材料层合板疲劳问题的研究。试验采用MTS809液压电磁伺服疲劳试验机,对多种铺层平板试验件进行研究。试验得出不同铺层方向层合板的应力应变、疲劳寿命与加载比的关系曲线,并将试验数据与理论模型预测值进行了对比,分析了玻璃纤维增强树脂基复合材料层合板的疲劳机理。     

Properties of cellulose-polyester composites

Cellulose fibers were used as reinforcement in unsaturated polyesters. Composites were prepared as laminates with cellulose fibers used in the form of paper sheets. The impregnation was carried out in a vacuum and resulted in a composite with uniform distribution of polyester around the fibers. The polyester was also detected in the lumen of the fibers. The tensile properties were evaluated and compared with tensile properties of glass fiber reinforced polyester. It is found that cellulose fibers increase the tensile strength and modulus of a polyester composite. Immersion of the cellulose-polyester composites in water caused a considerable water uptake. The presence of water in the composites decreased the tensile properties drastically. Scanning electron photomicrographs of the tensile fracture surfaces showed a lack of adhesion between the cellulose fibers and the polyester matrix in wet conditions.     

Effect of loading‐unloading cycles on impact‐damaged jute/glass hybrid laminates

The production of glass/plant fiber hybrid laminates is a possibility for obtaining semistructural materials with sufficient impact properties, and a better life cycle analysis (LCA) profile than fiberglass. The simplest and possibly the most effective configuration for the production of these hybrids would involve the use of a plant fiber reinforced laminate as the core between two glass fiber reinforced laminates. A main limitation to the use of composites including plant fibers is that their properties may be significantly affected by the presence of damage, so that even the application of a low stress level can result in laminate failure. In particular, it is suggested that when loading is repeatedly applied and removed, residual properties may vary in an unpredictable way. In this work, E‐glass/jute hybrid reinforced laminates, impacted in a range of energies (10, 12.5, and 15 J), have been subjected to post‐impact cyclic flexural tests with a step loading procedure. This would allow evaluating the effect of damage dissipation offered by the plant fiber reinforced core. The tests have also been monitored by acoustic emission (AE), which has confirmed the existence of severe limitations to the use of this hybrid material when impacted at energies close to penetration. POLYM. COMPOS., 2009. © 2009 Society of Plastics Engineers     

Bending properties of compression molded three-layer long fiber polypropylene composites

The results of studies on bending properties of three-layer long fiber polypropylene composites are presented. Thirteen samples with glass fibers of various lengths (i.e., 13, 25, 50 mm and continuous fiber length) in the laminates were prepared by stamping. Bending properties of shorter lengths exhibited a large scatter. On substitution of the middle layer with a continuous glass fiber the scatter was reduced. These results have been explained on the basis of flow models and X-ray shadowgraphs, which showed that both slippage flow and orientation of the glass fiber during stamping are the major phenomena responsible for the scatter.     

Mechanical properties of vinylester/glass and polyester/glass composites fabricated by resin transfer molding and hand lay‐up

This paper reports the comparative performance of vinylester/glass and polyester/glass laminates fabricated by resin transfer molding (RTM) and hand lay‐up. A resin transfer mold was designed and fabricated for preparing the laminates. Void content was much lower in Spartan II RTM specimens than in that of hand lay‐up. Ultimate tensile strength, Young's modulus, flexural strength, flexural modulus, impact strength, and interlaminar shear strength of RTM specimens were superior to that of the hand lay‐up for both vinylester/glass and polyester/glass. The improvements for vinylester/glass were 44%, 28%, 88%, 84%, 36%, and 78% for the respective properties. The corresponding improvements for polyester/glass were 21%, 52%, 70%, 74%, 57%, and 82%, respectively. Particle impact erosion rate was lower in RTM specimens than that of the hand lay‐up. J. VINYL ADDIT. TECHNOL. 21:166–173, 2015. © 2014 Society of Plastics Engineers     

Use of acoustic emission to characterize corrosion fatigue damage accumulation in glass fiber reinforced polyester laminates

The acoustic emission technique has been used to characterize fatigue damage accumulation in glass fiber woven roving (0/90°) polyester laminates after prolonged exposure in sea water. Comparisons were made with fatigue tests of “as-received” laminate under similar loading conditions. Pre-exposure has been found to substantially reduce the fatigue strength of the composite. Acoustic emission monitoring during fatigue testing has shown that the amplitude distribution of the acoustic events shifts from predominantly low amplitude (40–55 dB), associated with matrix cracking, in as-received specimens, to intermediate amplitude (55–75 dB) associated with delamination and debonding after pre-exposure. Optical microscopy of fatigued samples has verified these failure mode changes. The number of recorded high amplitude events (≥ 80 dB) associated with fiber fracture is the same in both cases, which indicates that the glass reinforcement is unaffected by pre-exposure.     

Structural degradation and mechanical fracture of hybrid fabric reinforced composites

This investigation involves the study of accelerated environmental aging in two polymer composite laminates reinforced by hybrid fabrics based on carbon, Kevlar and glass fibers. Composite laminate configurations are defined as a laminate reinforced with E‐glass fiber and Kevlar 49 fiber hybrid fabric (GK) and another laminate reinforced with E‐glass fiber and AS4 carbon fiber hybrid fabric (GC). Both laminates were impregnated with epoxy vinyl ester thermosetting resin (Derakane 470‐300) consisting of four layers. Morphological studies (photo‐oxidation process and structural degradation) of environmental aging were conducted, in addition to comparative studies of the mechanical properties and fracture characteristics under the action of uniaxial tensile and three‐point bending tests in specimens in the original and aged conditions. With respect to uniaxial tensile tests for both laminates, good mechanical performance and little final damage (small loss of properties) was caused by the aging effect. However, for the three‐point bending tests, for both laminates, the influence of aging was slightly higher for all parameters studied. The low structural deterioration in the laminates is attributed to the high performance with the heat of the matrix (Derakane 470‐300) and the characteristics of the hybrid fabric, exhibiting fiber/matrix interface quality. POLYM. ENG. SCI., 56:657–668, 2016. © 2016 Society of Plastics Engineers     

The influence of surface modifications of glass on glass fiber/polyester interphase properties

Unsized glass fibers and planar glass substrates were subjected to low temperature plasma or wet-chemical process to modify the fiber or substrate surface and thus influence the interphase properties of the glass/polyester system. Plasma-polymerized thin films (interlayers) of organosilicon monomers (hexamethyldisiloxane and vinyltriethoxysilane) were deposited in an RF helical coupling plasma system on the glass surface. Commercial silane coupling agent (vinyltriethoxysilane) was coated onto an unmodified glass surface from an aqueous solution. Bonding at the glass/interlayer interface was analyzed by employing a micro-scratch tester together with an optical polarizing microscope for the planar samples. The results revealed that the adhesion bonding could be controlled by plasma process parameters. Scanning electron and atomic force microscopies enabled characterization of the film surface morphology. Chemical composition and chemical structure of prepared interlayers were characterized using X-ray photoelectron and infrared spectroscopies. Microcomposites (macrocomposites) were tested to evaluate the interfacial shear strength (short-beam strength) of the glass fiber/polyester interphase using the microbond test (short-beam shear). Our study indicated that the most efficient interphase could be prepared by plasma polymerization or wet-chemical process using the vinyltriethoxysilane monomer. The short-beam strength was 110% higher than that for untreated fibers in both cases.     

Composites containing glass spheres and fibers. I. Young's and flexural moduli

Experiments on sphere-filled aligned fiber reinforced polyester resins show that the Young's and flexural moduli of the composites are increased by the presence of the spheres. The increase is particularly marked for composites made with flexible resins, and has potential for improving the properties of aligned fiber laminates. The moduli in the absence of fibers do not fit well with existing theory, and agreement with finite element analysis is only observed in the case of the rigid polyester. When fibers are present synergistic effects are observed.     

Surface roughness of fiber reinforced plastic laminates fabricated using rubber pressure molding technique

The rubber pressure molding (RPM) technique for fabricating fiber reinforced plastic (FRP) laminates is a new development in manufacturing technology of FRP composites. The technique is based on the matching die set, where the die is made of hard metal like steel and the punch from the flexible rubber‐like material, natural rubber (NR). A split steel die and rubber punch are designed and fabricated to prepare the FRP product. The same split die is also used to cast the rubber punch. The use of flexible rubber punch applies hydrostatic pressure on the surface of the product. The rubber used to make the punch for pressing the component during curing process contains carbon black as filler material. The present study was carried out to investigate the effect of carbon black loading on the surface roughness of the FRP components produced by RPM technique. Natural rubber with different loading of carbon black (0 to 120 phr) was used for making the punch to fabricate the laminates through RPM technique. A number of FRP laminates with polyester resin and glass fiber were prepared to perform the experimentation. It was observed that as the loading of carbon black in rubber punch is increased from 0 to 120 phr, there is a significant decrease in the surface roughness of laminates. The surface roughness values of FRP laminates are correlated with a proposed model. POLYM. COMPOS. 27:504–512, 2006. © 2006 Society of Plastics Engineers     

Comparison of the Mechanical and Thermo-Mechanical Properties of Unfilled and SiC Filled Short Glass Polyester Composites

This paper presents a comparison between particulate filled (SiC particles) and unfilled glass polyester composites on the basis of their mechanical and thermo-mechanical properties. The results show that particulate filled composites have a decreasing trend in mechanical properties when compared to the unfilled glass polyester composites. In particulate filled composites, the tensile and flexural strength of the composites decrease with the addition of 10 wt.-% SiC particles but increase with 20 wt.-% SiC particles. In the case of the unfilled glass polyester composite, the tensile and flexural strength of the composites increase with an increase in the fiber loading. However, higher values of tensile strength and flexural strength of particulate filled glass polyester were found than that of the unfilled glass polyester composite. In the case of thermo-mechanical and thermal properties, the particulate filled composites show better dynamical and thermal properties when compared to the unfilled glass polyester composites. The mechanical and thermal properties (i.e. thermal conductivity) are also calculated using FE modeling (ANSYS software) and the results from this simulation shows good agreement with the experimental results.     

Fabrication and mechanical response of commingled GF/PET composites

The mechanical properties and the response to mechanical load of continuous glass fiber reinforced polyethylene terephthalate (GF/PET) laminates have been characterized. The laminates were manufactured by compression molding stacks of novel woven and warp knitted fabrics produced from commingled yarns. The laminate quality was examined by means of optical and scanning electron microscopy. Few voids were found and the laminate quality was good. Resin pockets occurred in the woven laminates, originating from the architecture of the woven fabric. The strength of the fiber/matrix interface was poor. Some problems were encountered while manufacturing the laminates. These led to fiber misalignment and consequently resulted in tensile mechanical properties that were slightly lower than expected. Flexural failures all initiated as a result of compression, and it is possible that the compression strength of the matrix material, rather than its tensile strength, might limit the ultimate mechanical performance of the composites. Flexural failures for both materials were very gradual. The warp knitted laminates were stronger and stiffer than the woven laminates. The impact behavior was also investigated; the woven laminates exhibited superior damage tolerance compared with the warp knitted laminates.     

Hybrid fiber fabric composites from poly ether ether ketone and glass fiber

Poly ether ether ketone (PEEK) polymer was extruded into filaments and cowoven into unidirectional hybrid fabric with glass as reinforcement fiber. The hybrid fabrics were then converted into laminates and their properties with special reference to crystallization behavior has been studied. The composite laminates have been evaluated for mechanical properties, such as tensile strength, interlaminar shear strength (ILSS), and flexural strength. The thermal behavior of the composite laminates were analyzed using differential scanning calorimeter, thermogravimetric analyzer, dynamic mechanical analyzer (DMA), and thermomechanical analyzer (TMA). The exposure of the fabricated composite laminates to high temperature (400 and 500°C) using radiant heat source resulted in an improvement in the crystallanity. The morphological behavior and PEEK resin distribution in the composite laminates were confirmed using scanning electron microscope (SEM) and nondestructive testing (NDT). Although DMA results showed a loss in modulus above glass transition temperature (T_g), a fair retention in properties was noticed up to 300°C. The ability of the composite laminates to undergo positive thermal expansion as confirmed through TMA suggests the potential application of glass–PEEK composites in aerospace sector. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci 117:1446–1459, 2010     

Comparison of water permeation behaviour in poly(dimethylsiloxane), poly(ether ether ketone), and glass fibre reinforced composites using dielectric spectroscopy

Abstract

This paper describes the use of dielectric spectroscopy to characterise the absorption of water by three different classes of polymeric materials: an elastomer, poly(dimethylsiloxane); a thermoplastic, poly(ether ether ketone); and two composites, polyester and vinyl ester glass fibre reinforced laminates (GRP). Novel approaches have been used to assess water absorption by the elastomer and the GRP and the results are critically assessed. The data for all the materials are discussed in the context of their molecular structures. The applicability and limitations of these dielectric methods for the assessment of water absorption in polymeric materials that have considerably different physical properties is demonstrated.     

Properties of unidirectional kenaf fiber–polyolefin laminates

The objective of this research was to evaluate the effect of kenaf fiber orientation and furnish formulation on the properties of laminated natural fiber–polymer composites (LNPC). The uniaxial fiber orientation provided property enhancement of the LNPC. The randomly oriented kenaf fibers, regardless of fiber contents in the laminates, provided an equal performance compared to the composites made of 25% fiber glass reinforced polyvinyl ester resin in the same laboratory processing conditions. Thermal properties of the laminates obtained from thermal gravimetry with differential scanning calorimetry (TG‐DSC) showed that the melting point (T_m) of the polypropylene (PP) film laminates decreased, and the crystallization peak increased as the kenaf fiber content in the laminates increased. The surface morphology results of the kenaf fiber and fractures of the laminates showed that some fibers pulled out from the matrix. The mechanical properties increased as the kenaf fiber content increased. The tensile stress of the laminated composites fabricated with unidirectional fiber orientation was about 2–4 times higher than those with the randomly oriented samples. POLYM. COMPOS., 2010. © 2009 Society of Plastics Engineers