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The mechanical properties of composites produced without additives are limited by the matrix and fibers of constructed material. To increase the mechanical properties, micro or nano size particles can be added to the composite. In this study, A l 2 O 3 particles with a purity of 98% and a size of 0–50 μm were added to the epoxy material in the ratios of 1%, 2%, 3%, 4% and 5% by weight to optimize the parameter in order to enhance the mechanical properties of [110P/163 T/195T]s stacking sequenced woven composites. Tensile fatigue tests were performed with a computer-controlled fatigue test device with a 100 kN load cell, by applying R = 0.1 load ratio, 6 Hz frequency, and sine wave load form. Fatigue tests were conducted at different load levels. As a result, increase between 119%-2441% was observed in the fatigue cycle of micro- A l 2 O 3 reinforced woven composite materials compared to non-particles added epoxy woven composites. The highest damping rate was observed as 57.528 in 1% micro- A l 2 O 3 , and the lowest damping rate was observed as 26.312 in composite with no Al2O3 particles. The micro-structure morphologies of micro-Al2O3 reinforced woven composites were observed by SEM. [ABSTRACT FROM AUTHOR]

An economical and effective method was developed to optimize the interface of glass fiber fabric (GFf)-reinforced epoxy composites (GFfE) by dispersing aminosilane-functionalized graphene oxide (GO) on the fiber surface. The effects of γ-aminopropyltrimethoxysilane (APS) or APS hydrolysis on the dispersion of GO and the interfacial properties of resultant composites were investigated in detail. The results indicated that the uniform dispersion of GO in composites and strong fiber/matrix adhesion could be achieved, based on grafting of APS hydrolysis onto GO. The interlaminar shear, flexural and tensile strengths of resultant composites were improved by 28%, 22% and 19%, respectively; the storage modulus and dynamic glass transition temperature (1 Hz) were significantly enhanced, compared with pure GFfE. In particular, the work of fracture received from interlaminar load–deflection curves increased by 97%, indicating the toughening effect of GO. This work demonstrates that it is possible to enhance the strength, stiffness and toughness of fiber-reinforced composites by incorporating GO into the interface between the fiber and the matrix. [ABSTRACT FROM AUTHOR]

In the present research, a novel rate-dependent micromechanical model was presented to predict the stiffness and strength of unidirectional glass/epoxy composites. To predict the strain-rate dependent stress–strain behavior of glass fibers, using the Maxwell model with the aid of semi-empirical relations, a new viscoelastic constitutive model was proposed. Moreover, to predict the strain-rate dependent ultimate strength of brittle glass fibers, the elasto-plastic strain-rate dependent Cowper-Symonds material model was simplified by deleting the plastic terms. The strain-rate dependent mechanical properties of the polymer were also investigated by using the modified Goldberg model. Then, by modifying the Mori-Tanaka micromechanical model, a rate dependent micromechanical model was developed to predict the effective elastic properties (stiffness and strength) of unidirectional fibrous composites at arbitrary strain rates. The present model was called the strain-rate dependent Mori-Tanaka micromechanical model. As inputs, the present model just needs the viscoelastic and viscoplastic properties of fibers and polymer. Therefore, the present model reduces the necessary experimental data to predict the rate-dependent mechanical properties of unidirectional composites. For verification of the present model, the results were compared with experimental data and very good consistency in predicting the rate-dependent behavior of unidirectional composites was observed. [ABSTRACT FROM AUTHOR]

The introduction of new type of nanomaterials has provided challenges in a deeper level understanding of mechanical behavior and failure mechanisms of fiber-reinforced composites. In this study, a comparison of low-velocity impact behavior of E-Glass epoxy composites modified with 10 wt% nanosilica and 2.5 wt% Nafen™ alumina nanofibers manufactured using vacuum-assisted resin transfer molding is reported. Low-velocity impact tests at three impact energies of 29 J, 39 J, and 50 J are conducted and impact responses, such as impact strength, absorbed energy, and damage area are determined and compared for the two nanoparticles. The damage sustained by composite samples is evaluated by optical microscopy and infrared thermography. Nanosilica-incorporated composites showed rigid behavior, whereas alumina nanofiber-modified composites showed increased stiffness at increased energy of impact as observed from the initial stiffness and deflection of samples. The degree of damage in case of 10 wt% nanosilica-modified composites is reduced by 7.04%, 3.96%, and 7.92% for energy levels of 29 J, 39 J, and 50 J respectively when compared to nonmodified composites, whereas 2.5 wt% alumina nanofiber-modified composites showed 1.66%, −7.35%, and 26.39% for energy levels of 29 J, 39 J, and 50 J, respectively. [ABSTRACT FROM AUTHOR]

Fluid diffusion in fiber reinforced composites is typically anisotropic. Diffusivity in the fiber direction is faster than in the transverse direction. The reason for this behavior is not yet fully understood. In this work, dealing with glass fiber epoxy composite immersed in distilled water, an experimental procedure for determination of anisotropic diffusion constants from a laminate is presented. The method has the advantage that it does not require sealing of the samples edges because 3-D anisotropic diffusion theory is implemented for obtaining the diffusion constants. A microscale model is presented, where matrix and fiber bundles are modeled separately. The matrix properties have been obtained experimentally and the fiber bundle properties have been deduced by the composite homogenized diffusivity model. The analysis indicates that the anisotropic diffusion of the composite is due to inherent anisotropic properties of the fiber bundles. [ABSTRACT FROM AUTHOR]

The objective of the present investigation is to study the alteration in flexural performance of glass/epoxy (GE) composite with and without multiwalled carbon nanotube (MWCNT) after liquid nitrogen conditioning. The epoxy resin was first modified by 0.1, 0.3, and 0.5 wt% MWCNT, which was then used along with E-glass fibers to fabricate laminates. Flexural strength and modulus were evaluated by 3-point bend test. Out of these four compositions, the maximum strength in the as-fabricated condition was obtained for GE composite with 0.1 wt% CNT, which is 32.74% higher as compared to GE composite. Decrease in strength and modulus was observed for short time span of liquid nitrogen conditioning i.e. 0.25 h. Long cryogenic conditioning resulted in increment in strength. To understand the failure mechanisms, post failure analysis was carried out using scanning electron microscope. The design parameters are calculated using Weibull distribution model. [ABSTRACT FROM AUTHOR]

Determination of gel point is important for a modelling assessment of residual stresses developed during curing of composite materials. Residual stresses in a composite structure may have a detrimental effect on its mechanical performance and compromise its integrity. In this article, the evolution in bending stiffness of a glass/epoxy composite material during an isothermal curing process is examined to identify different material stages and behaviour. Differential scanning calorimetry and dynamic mechanical analysis are used to analyse the material behaviour. Gelation is identified as a clear onset in bending stiffness, and vitrification is seen as a decrease in the bending stiffness rate. Often gel point predictions for composite materials are based on neat matrix measurements. However, the results presented in this article demonstrate that the gel point is affected by the presence of the fibre reinforcement. [ABSTRACT FROM PUBLISHER]

Glass fiber epoxy composites are widely used in industries. Liquid epoxidized natural rubber was added to epoxy as the matrix for a fiber-reinforced composite in order to improve its mechanical properties whilst E-glass fiber was used as the composite reinforcement. Flexural test, Izod impact test, tensile test, thermogravimetric analysis, and scanning electron microscopy were performed to investigate the effect of liquid epoxidized natural rubber addition and glass fiber loadings on the mechanical properties of the composite. It was observed that the flexural strength and flexural modulus of the samples increased with increasing glass fiber percentage with 9% as the maximum weight percentage recorded. The tensile strength and Young’s modulus increased with increasing glass fiber content until it reached the maximum value at 9 wt% of glass fiber. The same trend was observed with the impact value of the samples. All the tests were conducted for the composite with and without liquid epoxidized natural rubber addition. The presence of liquid epoxidized natural rubber improved the mechanical properties of the composites due to the plasticizing effect of the rubber particles in the matrix. Thermogravimetric analysis revealed the thermal stability of the composites whilst the scanning electron microscopy shows a heterogeneous dispersed phase of morphology. There was poor adhesion between the matrix polymer and glass fibers due to the use of untreated glass fibers. [ABSTRACT FROM PUBLISHER]

This article deals with the effect of drilling parameters (feed, speed, and drill pre-wear) on the machinability parameters (thrust force, torque, peel-up and push-out delaminations, surface roughness, and bearing strength) in drilling woven glass fiber-reinforced. The results show that at high feeds (0.45 mm/rev), the drill point acts as a punch that pierces the laminate with approximately constant push-out delamination size irrespective to the value of the thrust force. Surface roughness increases with the increase of drill pre-wear due to the generated heat that assisted by the low thermal properties of polymeric composites. Drilling at high feeds reduces the stiffness of the specimens and its ultimate bearing loads. Artificial neural network and multivariable regression models were developed for predicting the bearing strength of drilled holes. [ABSTRACT FROM PUBLISHER]

An effort was made to study the effect of hygrothermal ageing at varying intervals of time on the interphase of the fiber-reinforced polymer composites. Silane-coated glass fibers and epoxy as matrix were used to fabricate the micro-composite. Absorbance peaks of OH stretching bands were focused to study the curing mechanism of epoxy matrix and effect of hygrothermal exposure at the interphase of the micro-composite by Fourier transform infrared (FTIR) imaging. The differential scanning calorimeteric (DSC) was carried out to monitor the glass transition temperature of hygrothermally aged samples after each interval. The FTIR results shows existence of gradient in degree of curing from the interphase to the bulk matrix and with the increase in ageing time the water absorption increases at the interphase leading to improvement in the adhesion initially, as it is reflected in the results obtained with DSC analysis, i.e., increases in glass transition temperature with the ageing time was reported. Obtained improved results may be attributed to moisture induced additional ring opening polymerization of epoxide molecule and/or formation of strong hydrogen double bonds with the epoxy matrix by water molecule. Microstructural analysis was done for hygrothermally treated samples by scanning electron microscope (SEM). [ABSTRACT FROM AUTHOR]

This study reports the method of recovery of glass fibers from glass/epoxy composites through the solvent method. It is possible to decompose epoxy resin with a yield of more than 99 wt% soluble products in a nitric acid solution (8 M) at 90°C for 5 h. The decomposition rate of epoxy resin increases with an increase in temperature and concentration of acid solution. The glass fibers can be recovered with very little contamination and they have a tensile strength reduction of 3.5% under decomposition conditions of T=70°C, t=250h, C=6M and α=6g/100mL. These fibers can be used as reinforcement to prepare new composites. The interlaminar shear strength (ILSS) of recovered short fiber-reinforced composites produce strength reductions of only 2.5% compared with pristine composites. [ABSTRACT FROM AUTHOR]

Polymer matrix composites using renewable resources are currently of great interest. A novel soy-based resin system for pultrusion was synthesized at University of Missouri-Rolla (UMR). Due to relatively low reactivity of soy-based resin and short curing time of pultrusion, it is important to set up the process parameters properly in order to obtain a high quality pultruded product. In the present work, a combination of experimental and numerical methods is used to investigate the effect of pultrusion process variables on the cure of composites. A mathematical model has been developed and implemented in the commercial ABAQUS finite element package to predict the temperature and degree of cure of soy-based composites. The kinetic parameters of the soy-based epoxy resins are obtained from a differential scanning calorimeter (DSC). Glass fiber-reinforced composite samples are manufactured using a pultrusion machine. For experimental verification, an online monitoring system is used to measure the temperature profiles inside the die. The degrees of cure of pultruded soy-based composites are measured by DSC. The experimental findings are in good agreement with the finite element prediction. The results indicate that the novel soy-based epoxy resin system is suitable for application in the pultrusion process. [ABSTRACT FROM AUTHOR]