Contrast on tensile and flexural properties of glass powder reinforced epoxy composites: Pilot study

Epoxy resin was filled with glass powder to optimize the tensile and flexural strength of the composite for structural applications by a research center in the University of Southern Queensland (USQ). To reduce costs, the center wishes to fill as much glass microspheres as possible subject to maintaining sufficient strength of the composites in structural applications. This project varies the percentage by weight of the glass powder in the composites. After casting the composites to the molds, they were cured at ambient conditions for 24 h. They were then postcured in a conventional oven and subjected to tensile and flexural tests. The contribution of the study was that if tensile and flexural properties were the most important factors to be considered in the applications of the composites, the maximum amount of glass powder can be added to the resin will be five (5) percent. It was also found that the fractured surfaces examined under scanning electron microscope were correlated with the tensile and flexural strength It is also hoped that the discussion and results in this work would not only contribute toward the development of glass powder reinforced epoxy composites with better material properties, but also useful for the investigations of tensile and flexural properties in other composites. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2011     

The effects of curing cycles on properties of the epoxy system 3221/RH glass fabric composites

In this work, the epoxy system 3221 and its glass fabric laminates were thermally cured under different curing temperatures. The curing degree of the resin was increased with elevated reaction temperature. Dynamic mechanical analysis was performed on the laminate coupons and glass transition temperature (T_g) and relative stiffness (E′) of composites were measured before and after soaked in distilled water at 70°C. A shift in glass transition temperature to higher values and the splitting of the tan δ curve were observed with extent of cure under dry conditions. T_g values shifted to lower temperatures after immersion. Under wet condition, the change in T_g1 was very small when the curing degree was up to 96%. The relative stiffness experienced a reduction both in initial modulus and the initial sharp drop temperature after immersion. It also suggested that the excessively high curing temperature (>130°C) had a negative effect on the retention of relative stiffness under wet condition. Both the interlaminar shear strength and dielectric properties of laminates were determined before and after immersion. The compared results demonstrated that the elevated curing temperature played a good influence on both of the properties before aged. However, for samples cured above 130°C, lower retention of interlaminar shear strength and poor dielectric properties were observed during immersion due to their higher moisture contents. POLYM. COMPOS., 2008. © 2008 Society of Plastics Engineers     

Preparation and properties of silicon nitride/glass fiber/epoxy composites

Silicon nitride/glass fiber (Si₃N₄/GF) hybrid fillers are performed to prepare the Si₃N₄/GF/epoxy composites. Results showed the thermal conductivities of the Si₃N₄/GF/epoxy composites that are improved with the addition of Si₃N₄, and the thermal conductive coefficient λ is 1.412 W/mK with 38 vol% modified Si₃N₄/GF hybrid fillers (30 vol% Si₃N₄ + 8 vol% GF), seven times higher than that of pure epoxy resin. The flexural strength and impact strength of the composites are optimal with 13 vol% modified Si₃N₄/GF hybrid fillers (5 vol% Si₃N₄ + 8 vol% GF). The dielectric constant and dielectric loss of the composites are increased with the increasing addition of Si₃N₄. For a given Si₃N₄/GF hybrid fillers loading, the surface modification can further improve the thermal conductivities of the Si₃N₄/GF/epoxy composites. POLYM. COMPOS., 35:1338–1342, 2014. © 2013 Society of Plastics Engineers     

Effects of fiber length on the tensile strength of epoxy/glass fiber and polyester/glass fiber composites

In discontinuous fiber-reinforced composites, the shear strength at the fiber–matrix interface plays an important role in determining the reinforcing effect. In this paper, a method was devised to accurately determine this shear strength, taking the strength distribution of glass fiber into consideration. Calculated strength values based on the shear strenght obtained by the method were in better agreement with the experimental observations than those calculated by employing the shear strength obtained on the assumption that the fiber strength was uniform. The tensile strength of composites increases with increasing aspect ratio of the reinforcing fibers. This trend is almost the same regardless of the kind of matrix, the nature of interfacial treatment, and the environmental temperature. When composites are reinforced with random-planar orientation of short glass fibers of 1.5 times the mean critical fiber length, the tensile strength of composite reaches about 90% of the theoretical strength of composites reinforced with continuous glass fiber. Reinforcing with glass fibers 5 times the critical length, the tensile strength reaches about 97% of theoretical. However, from a practical point of view, it is adequate to reinforce with short fibers of 1.5–2.0 times the mean critical fiber lenght.     

Tensile properties of natural fabric Hildegardia populifolia/polycarbonate toughened epoxy composites

The environmentally friendly composites of natural fabric Hildegardia populifolia/polycarbonate toughened epoxy were prepared. The effect of fabric content and the orientation of the fibers in the fabric on the tensile properties of the composites was studied. The effect of alkali treatment of the fabric and a silane coupling agent on the tensile properties was also studied. The tensile properties improved with alkali treated fabric content when a coupling agent was used. Polym. Compos. 25:563–568, 2004. © 2004 Society of Plastics Engineers.     

Fundamental study on fiber-reinforced epoxy composites using glass fabric treated by low-temperature ammonia plasma

Glass fabrics were treated with NH₃ plasma for interfacial control in glass fiber-reinforced plastics (GFRPs) with epoxy resin. The tensile strength of the GFRPs was improved by the use of glass fabrics treated with NH₃ plasma. The plasma technique was also applicable to non-heat-treated glass fabrics, on which starch had remained, for improvement of the strength of their FRPs. As a result, with non-heat-treated glass fabrics treated with NH₃ plasma, the GFRPs showed a very high tensile strength.     

Influence of silicon carbide filler on mechanical and dielectric properties of glass fabric reinforced epoxy composites

Fiber‐reinforced polymeric composites (FRPCs) have emerged as an important material for automotive, aerospace, and other engineering applications because of their light weight, design flexibility, ease of manufacturing, and improved mechanical performance. In this study, glass‐epoxy (G‐E) and silicon carbide filled glass‐epoxy (SiC‐G‐E) composite systems have been fabricated using hand lay‐up technique. The mechanical properties such as tensile strength, tensile modulus, elongation at break, flexural strength, and hardness have been investigated in accordance with ASTM standards. From the experimental investigations, it has been found that the tensile strength, flexural strength, and hardness of the glass reinforced epoxy composite increased with the inclusion of SiC filler. The results of the SiC (5 wt %)‐G‐E composite showed higher mechanical properties compared to G‐E system. The dielectric properties such as dielectric constant (permittivity), tan delta, dielectric loss, and AC conductivity of these composites have been evaluated. A drastic reduction in dielectric constant after incorporation of conducting SiC filler into epoxy composite has been observed. Scanning electron microscopy (SEM) photomicrographs of the fractured samples revealed various aspects of the fractured surfaces. The failure modes of the tensile fractured surfaces have also been reported. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2009     

中温固化环氧/杂环芳纶（布）预浸料及其复合材料性能研究

试验研究了044B杂环芳纶布性能、3233/044B预浸料制备及其复合材料力学性能.结果表明,044B杂环芳纶布性能较好,3233/044B复合材料的常规性能和耐热性较好,夹层结构的滚筒剥离强度高,树脂具有韧性,适用于复合材料夹层结构.该预浸料已用于航空复合材料制件.     

Interfacial properties of glass fiber/brittle-ductile dual-matrix composites using micromechanical techniques and acoustic emission

The interfacial adhesion and microfailure modes of glass fiber-reinforced brittle unsaturated polyester/modified epoxy composites were investigated via micromechanical techniques and acoustic emission (AE). Various silane coupling agents caused different degrees of interfacial adhesion and subsequent microfailure modes. In the brittle matrix layer, the number of matrix fragments was significantly influenced by the type of silance coupling agents. The more cracks, the higher the interfacial adhesion under both dry and wet conditions. This is attributed to the chemical and hydrogen bondings in two interphases. The results obtained from microdroplet and fragmentation tests were correlated by associating with the AE technique. The sequential occurrence of mainly three groups of AE were as follows: the first group originated mainly from brittle matrix cracking. The second and the third groups resulted in fiber breakage and ductile matrix cracking and debonding. For dual-matrix specimens the micromechanical tests provide reliable information with regard to the interfacial adhesion and characterize the microfailure modes when combined with the AE technique.     

Hybrid multi‐scale epoxy composites containing conventional glass microfibers and electrospun glass nanofibers with improved mechanical properties

A mechanically flexible mat consisting of structurally amorphous SiO₂ (glass) nanofibers was first prepared by electrospinning followed by pyrolysis under optimized conditions and procedures. Thereafter, two types of hybrid multi‐scale epoxy composites were fabricated via the technique of vacuum assisted resin transfer molding. For the first type of composites, six layers of conventional glass microfiber (GF) fabrics were infused with the epoxy resin containing shortened electrospun glass nanofibers (S‐EGNFs). For the second type of composites, five layers of electrospun glass nanofiber mats (EGNF‐mats) were sandwiched between six layers of conventional GF fabrics followed by the infusion of neat epoxy resin. For comparison, the (conventional) epoxy composites with six layers of GF fabrics alone were also fabricated as the control sample. Incorporation of EGNFs (i.e., S‐EGNFs and EGNF‐mats) into GF/epoxy composites led to significant improvements in mechanical properties, while the EGNF‐mats outperformed S‐EGNFs in the reinforcement of resin‐rich interlaminar regions. The composites reinforced with EGNF‐mats exhibited the highest mechanical properties overall; specifically, the impact absorption energy, interlaminar shear strength, flexural strength, flexural modulus, and work of fracture were (1097.3 ± 48.5) J/m, (42.2 ± 1.4) MPa, (387.1 ± 9.9) MPa, (12.9 ± 1.3) GPa, and (30.6 ± 1.8) kJ/m², corresponding to increases of 34.6%, 104.8%, 65.4%, 33.0%, and 56.1% compared to the control sample. This study suggests that EGNFs (particularly flexible EGNF‐mats) would be an innovative type of nanoscale reinforcement for the development of high‐performance structural composites. © 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015 , 132, 42731.     

Surface structure of silane-treated glass beads and its influence on the mechanical properties of filled composites

The surface treatment of glass beads, chosen as a model filler, was carried out using four different silane coupling agents with multilayer coverage. For this purpose, silanes having an aminopropyl or a methacryloxypropyl group as an organofunctional group with di- or tri-alkoxy structures were used. The amount of silane detected on the bead surface was four to six times that required for a monolayer coverage. The topography of the silane layer on the bead surface was observed using an atomic force microscope. The topography was strongly affected by the composition of the silane solution and the number of alkoxy groups in the silane. The effects of the organofunctional group and the number of alkoxy groups of the silanes on the mechanical properties of bead-filled poly(vinyl chloride), chosen as a typical ductile polymer, were investigated. A higher yield stress was observed for the silane with an aminopropyl group than for that with a methacryloxypropyl group. Furthermore, for each organofunctional group, the yield stress was higher for the silane with a dialkoxy structure than for that with a trialkoxy structure. However, their effects on the elongation-at-break were contrary to the above tendencies.     

改性空心玻璃微珠/环氧树脂复合材料力学性能研究

采用偶联剂对玻璃微珠表面进行改性处理,借助超声波振动,使改性空心玻璃微珠在环氧树脂中均匀、稳定分散,增强了玻璃微珠与环氧树脂之间的相容并探讨了改性空心玻璃微珠对环氧树脂力学性能的影响。结果表明,复合材料中改性空心玻璃微珠添加质量分数为3%时,其拉伸强度达到最大值68.54 MPa,与空白样相比提高了20.3%;冲击强度达到最大值24.42 kJ/m2,比纯环氧树脂提高了166%;KIC(断裂韧性)达到最大值2.338 MPa/m2,是空白试样的2.27倍,增韧效果较为明显。     

Role of silanes in adhesion. Part II. Dynamic mechanical properties of silane-treated glass fiber/polyester composites

—Glass fiber/unsaturated polyester composites, prepared by impregnating glass braid with varying thickness coatings (from 200 Å up to 1600 Å thick) of polyester resin, were tested with a DuPont Dynamic Mechanical Analyzer. The effects of the polyester resin thickness and silane treatments on the dynamic mechanical properties of the composites were evaluated. The results are supported by Fourier transform infrared spectroscopy of the composite materials. It is shown that both the concentration and the organo-functional group of the silane coupling agent influence the damping, storage, and loss moduli as well as the glass transition temperature (T_g) of the matrix resin in the closest vicinity to the glass/resin bondline. In the absence of a silane inner layer, a low T_g, 'soft' boundary layer exists due to inhibition of the polyester resin cure by the glass surface. It is noted that a reactive silane, such as γ-methacryloxypropyltrimethoxysilane, promotes the formation of a 'soft' or 'rigid' (high T_g) boundary layer, depending on the concentration of the silane in the treating solution. On the other hand, a non-reactive silane, such as methyltrimethoxysilane, produces a 'rigid' interphase in the entire range of concentrations of the silane solution. An attempt was made to correlate the dynamic mechanical properties of the boundary layer with the fiber/polymer interfacial shear strength. Upon pretreatment of glass fibers with silane coupling agents, the relative magnitude of the loss modulus, E", and the nature of the boundary layer (T_g) seem to be better indicators of efficient stress transfer from the polymer to the glass fiber in the composite system than tan δ. Efficient stress transfer is characterized by a low value of E" and 'soft' boundary layers. The results suggest that the mere presence of glass/polyester chemical bonding is insufficient to ensure effective stress transfer. A strong bond results from the synergistic effect of glass/silane/polymer chemical bonding and a 'soft' boundary layer.     

Mechanical properties of glass fiber composites with an epoxy resin modified by a liquid crystalline epoxy

The effect of liquid crystalline networks on epoxy + glass fiber composites is investigated. The matrix obtained from in‐situ curing of liquid crystalline (LC) diglycidyl ether of 4,4‐dihydroxybiphenol (DGE‐DHBP) with diglycidyl ether of bisphenol F (DGEBP‐F) by anhydride curing agent was used as the matrix for polymer composites. Impact, tensile, and flexural testing results are compared between the unmodified and modified systems. The interlaminar fracture toughness of commposites in the shear mode was determined by end notch flexure (ENF) tests. Scanning electron microscopy is used to study the fracture surfaces to understand the mechanism of fracture and interphase formation between the fiber and the matrix.     

Effect of coupling agents on the mechanical properties of mica/epoxy and glass fiber/mica/epoxy composites

The effect of coupling agents, two silane and one zirconate, on the mechanical properties of mica/epoxy and glass fiber/mica/epoxy composites has been investigated. The results showed that tensile modulus and flexural strength and modulus values were improved by the surface treatment of the coupling agents. The property retention was also found to be better in the case of coupling agent-treated mica/epoxy samples after boiling in water for 2h. In the case of glass fiber/mica/epoxy composites, the flexural modulus and interlaminar shear strength values improved with increase in mica content, but the effect of coupling agents was not pronounced.     

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     

耐高温高导热环氧树脂／玻纤／BN复合材料的制备

以4,4-二氨基二苯砜（DDS）和内亚甲基四氢邻苯二甲酸酐（NA）为复配固化剂,采用高温模压成型法制备耐高温高导热环氧树脂／玻纤／氮化硼（BN）复合材料。探讨了BN用量和偶联剂处理对复合材料冲击强度、导热性能和电阻率的影响。结果表明：当nDDS：nNA=3：1时,复合材料的耐热性能最佳。当BN质量分数为8％时,复合材料的冲击强度最高;导热性能随BN用量的增加而增加,当BN用量为15％时,热导率为0．7560W／（mk）,此时复合材料仍保持较高的体积、表面电阻率;当BN填充量为一定值时,偶联剂处理使冲击强度和导热性能得到进一步提高。     

Mechanical properties of glass fabric/polyester composites: Effect of silicone coatings on the fabrics

An experimental investigation was carried out to study the effect of a silicone coating on the mechanical properties of polyester/woven glass fabric composites, fabricated by resin transfer molding. E‐glass woven fabrics were coated with a silicone elastomer by solution dip coating. The effect of variation of silicone amounts on the impact resistance, toughness, and mechanical properties of the composite was determined. Short beam shear tests were performed to assess the effect of coating on the adhesion of the fiber to the matrix. The coated specimens exhibited worse interlaminar shear strength over that of uncoated fabrics. Three‐point bending tests were also performed to investigate the effect of the coating on flexural properties. Whereas flexural strength and Young's modulus decreased with increasing amount of coating, the toughness, represented by the area under the stress–strain curve, presented a maximum. Finally, notched Izod impact tests were carried out and the curve for the energy absorbed during impact versus the amount of coating also appeared to have a maximum, indicating an interesting slot for optimum impact performance. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 91: 1300–1308, 2004     

Electrostatic discharge properties of knitted copper wire/glass fiber fabric reinforced polypropylene composites

This paper presents a study on the development conductive knitted fabric reinforced thermoplastic composites, with the intention to use them in electrostatic discharge applications. Conductive knitted fabric composites are made using polypropylene as the matrix material, glass fibers as the reinforcement, and copper wires as the conductive fillers. To facilitate knitting of stiff copper wires and glass fibers, uncommingled yarns comprising copper wires, glass fibers, and polypropylene fibers are produced using a hollow spindle spinning method. Several kinds of conductive composite laminates are made by changing the fabric knit structure, stitch density, and the composition of yarns. The electrostatic discharge (ESD) attenuation of various laminates is measured at voltage potentials 8kV and 12 kV. The variations of ESD properties of composite laminates with the fabric knit structure, stitch density, and the amount of copper are described.     

Multilayered epoxy/glass fiber felt composites with excellently acoustical and thermal insulation properties

In this article, a series of epoxy composites consisting of multilayered ultra-fine glass fiber felts (GFFs) were produced by a hand lay-up process. The incorporation of GFFs greatly enhances the sound-absorption and sound-insulation properties of epoxy composites. It can be mainly attributed to great numbers of voids introduced into the matrix and the increasing interfacial area between glass fiber and epoxy resin, which is confirmed by scanning electron microscopy results. Furthermore, the thermal insulation performance of epoxy/glass fiber felt (EP/GFF) composites is continuously improved with the growing GFF layer, and meanwhile EP/GFF composites exhibit the satisfactory mechanical property. Such novel EP/GFF composites can serve as promising structural, heat-insulated, and soundproof materials in many multifunctional systems including buildings, aircrafts, constructions, vehicles, etc. © 2018 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2019 , 136, 46935.