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Flexural testing provides a rapid and straightforward assessment of fiber-reinforced composites’ performance. In many high-strength composites, flexural strength is higher than compressive strength. A finite-element model was developed to better understand this improvement in load-bearing capability and to predict the flexural strength of three different carbon-fiber-reinforced polymer composite systems. The model is validated against publicly available experimental data and verified using theory. Different failure criteria are evaluated with respect to their ability to predict the strength of composites under flexural loading. The Tsai–Wu criterion best explains the experimental data. An expansion in compressive stress limit for all three systems was observed and is explained by the compression from the loading roller and Poisson’s effects.

Cellulose sponges are an example of fiber-reinforced polymer composites. In the past few years, natural materials were considered to replace synthetic materials in the manufacture of sponges. These cellulose sponges have high water absorption which can be used as an absorbent. In this study, cellulose sponges were made from cellulose xanthate as a matrix and cellulose fibers as reinforcement with variations in reinforcement concentrations of 1%, 2%, 3%, 4%, and 5%. Sponge morphology, tensile strength, elongation, and water absorption for 2 and 24 hours of immersion were characterized. The morphology of cellulose sponges shows a thick layer that has cavities inside which is caused by melting glauber salt. The more viscose rayon fibers in the cellulose sponge, the higher the tensile strength of the cellulose sponge and the smaller the elongation at break. The water absorption of cellulose sponge is more than 100%. However, addition of viscose rayon did not significantly influence the absorption. &nbsp

In this paper, exploratory studies on the application of fibre-reinforced polymer composites in the construction of gearbox housing elements that are used for transport means, as an alternative to traditionally used materials, were undertaken. Composite materials with three types of reinforcement were used: a glass-chopped strand mat, glass fabric, and carbon fabric. The manufactured elements were subjected to weight assessment and vibroactivity tests, including the recording of vibration and noise. The obtained results were compared to the values recorded for housings made of steel. It has been found that composite housings, while maintaining geometric similarity, are characterised by at least 60% lower weight compared to steel housings. It has been shown that in the frequency range below 1 kHz, composite housings are characterised by the presence of resonant frequencies with higher amplitudes than steel housings. At higher frequency ranges&mdash, above 1 kHz&mdash, composite housings had a lower vibroactivity level than steel housing. They allowed a significant reduction in the level of vibration and noise in this frequency range. The results obtained indicate that composite gearbox housings can be a good alternative to steel-based solutions.

Fiber-reinforced polymer matrix composites continue to attract scientific and industrial interest since they offer superior strength-, stiffness-, and toughness-to-weight ratios. The research herein characterizes two sets of E-Glass/Epoxy composite skins: stressed and unstressed. The stressed samples were previously installed in an underground power distribution vault and were exposed to fire while the unstressed composite skins were newly fabricated and never-deployed samples. The mechanical, morphological, and elemental composition of the samples were methodically studied using a dynamic mechanical analyzer, a scanning electron microscope (SEM), and an x-ray diffractometer, respectively. Sandwich composite panels consisting of E-glass/Epoxy skin and balsa wood core were originally received, and the balsa wood was removed before any further investigations. Skin-only specimens with dimensions of ~12.5 mm wide, ~70 mm long, and ~6 mm thick were tested in a Dynamic Mechanical Analyzer in a dual-cantilever beam configuration at 5 Hz and 10 Hz from room temperature to 210 °C. Micrographic analysis using the SEM indicated a slight change in morphology due to the fire event but confirmed the effectiveness of the fire-retardant agents in quickly suppressing the fire. Accompanying Fourier transform infrared and energy dispersive X-ray spectroscopy studies corroborated the mechanical and morphological results. Finally, X-ray diffraction showed that the fire event consumed the surface level fire-retardant and the structural attributes of the E-Glass/Epoxy remained mainly intact. The results suggest the panels can continue field deployment, even after short fire incident.

To investigate the mechanical degradation of the shear properties of glass fiber-reinforced polymer (GFRP) laminates in bridge decks under hygrothermal aging effects, short-beam shear tests were performed following the ASTM test standard (ASTM D790-10A). Based on the coupled hygro-mechanical finite element (FE) analysis method, an inverse parameter identification approach based on short-beam shear tests was developed and then employed to determine the environment-dependent interlaminar shear modulus of GFRP laminates. Subsequently, the shear strength and modulus of dry (0% Mt/M&infin, ), moisture unsaturated (30% Mt/M&infin, and 50% Mt/M&infin, ), and moisture saturated (100% Mt/M&infin, ) specimens at test temperatures of both 20 &deg, C and 40 &deg, C were compared. One cycle of the moisture absorption&ndash, desorption process was also investigated to address how the moisture-induced residual damage degrades the shear properties of GFRP laminates. The results revealed that the shear strength and modulus of moisture-saturated GFRP laminates decreased significantly, and the elevated testing temperature (40 &deg, C) aggravated moisture-induced mechanical degradation. Moreover, an unrecoverable loss of shear properties for the GFRP laminates enduring one cycle of the moisture absorption&ndash, desorption process was evident.

This work describes a novel method of embedded damage detection within glass fiber-reinforced polymer composites. Damage detection is achieved by monitoring the spatially distributed electrical conductivity of a strain-sensitive multiwalled carbon nanotube thin film. First, thin films were spray-deposited directly upon glass fiber mats. Second, using electrical impedance tomography, the spatial conductivity distribution of the thin film was determined before and after damage-inducing events. The resolution of the sensor was determined by drilling progressively larger holes in the center of the composite specimens, and the corresponding electrical impedance tomography response was measured by recording the current-voltage data at the periphery of the monitored composite sample. In addition, the sensitivity to damage occurring at different locations in the composite was also investigated by comparing electrical impedance tomography spatial conductivity maps obtained for specimens with sets of holes drilled at different locations in the sensing area. Finally, the location and severity of damage from low-velocity impact events were detected using the electrical impedance tomography method. The work presented in this study indicates a paradigm shift in the available possibilities for structural health monitoring of fiber-reinforced polymer composites. © The Author(s) 2013.