Search Results (12)

In recent times, fiber reinforced polymer composite materials have become more popular due to their remarkable features such as high specific strength, high stiffness and durability. Particularly, Carbon Fiber Reinforced Polymer (CFRP) composites are one of the most prominent materials used in the field of transportation and building engineering, replacing conventional materials due to their attractive properties as mentioned. In this work, a CFRP laminate is fabricated with carbon fiber mats and epoxy by a hand layup technique. Alumina (Al₂O₃) micro particles are used as a filler material, mixed with epoxy at different weight fractions of 0% to 4% during the fabrication of CFRP laminates. The important objective of the study is to investigate the influence of alumina micro particles on the mechanical performance of the laminates through characterization for various physical and mechanical properties. It is revealed from the results of study that the mass density of the laminates steadily increased with the quantity of alumina micro particles added and subsequently, the porosity of the laminates is reduced significantly. The SEM micrograph confirmed the constituents of the laminate and uniform distribution of Al₂O₃ micro particles with no significant agglomeration. The hardness of the CFRP laminates increased significantly for about 60% with an increase in weight % of Al₂O₃ from 0% to 4%, whereas the water gain % gradually drops from 0 to 2%, after which a substantial rise is observed for 3 to 4%. The improved interlocking due to the addition of filler material reduced the voids in the interfaces and thereby resist the absorption of water and in turn reduced the plasticity of the resin too. Tensile, flexural and inter-laminar shear strengths of the CFRP laminate were improved appreciably with the addition of alumina particles through extended grain boundary and enhanced interfacial bonding between the fibers, epoxy and alumina particles, except at 1 and 3 wt.% of Al₂O₃, which may be due to the pooling of alumina particles within the matrix. Inclusion of hard alumina particles resulted in a significant drop in impact strength due to appreciable reduction in softness of the core region of the laminates. Full article

This study investigates the effects of incorporating glass microspheres (GMSs) as fillers in carbon fabric–epoxy composites (CFECs) on their degradation behavior under environmental conditions such as moisture and ultraviolet rays. The GMS-filled composites were subjected to accelerated ageing and evaluated using dynamic mechanical analysis (DMA), the Charpy impact test, and inter-laminar shear strength (ILSS) tests. The results indicate that the addition of GMS fillers significantly improves the stiffness and viscoelastic behavior of the composites. However, the impact strength of the composites decreases with the addition of GMS fillers and accelerated ageing. The ILSS results demonstrate that the addition of GMS fillers improved the interfacial bonding between the carbon–epoxy matrix and fillers. This study provides insights into the mechanical properties of GMS-filled carbon–epoxy composites. Full article

Carbon/Phenolic Composites (CPCs) are essential to manufacture many portions of the nozzle assembly of Solid Rocket Motors (SRMs) which are essential both to preserve the independent access to space as well as for the homeland security. In our research, a feasible approach aimed at preliminary retrieving the in-plane and out-plane thermal diffusivity of CPCs through the Oxy-Acetylene Torch (OAT) tests was validated. The proposed approach showed to be effective and able to bypass some limitations of common protocols, especially in terms of capability to determine the thermal diffusivity of CPCs at high heating rates. A comprehensive work of comparison of the obtained data with state-of-the-art CPCs such as MX-4926 and FM-5014 has also been carried out, evidencing the effectiveness of the proposed method. Full article

Fiber Bragg grating sensors (FBGs) are promising for structural health monitoring (SHM) of composite structures in space owing to their lightweight nature, resilience to harsh environments, and immunity to electromagnetic interference. In this paper, we investigated the influence of low Earth orbit (LEO) conditions on the integrity of composite structures with embedded optical fiber sensors, specifically FBGs. The LEO conditions were simulated by subjecting carbon fiber-reinforced polymer (CFRP) coupons to 10 cycles of thermal conditioning in a vacuum (TVac). Coupons with embedded optical fibers (OFs) or capillaries were compared with reference coupons without embedded OFs or capillaries. Embedded capillaries were necessary to create in situ temperature sensors. Tensile and compression tests were performed on these coupons, and the interlaminar shear strength was determined to assess the influence of TVac conditioning on the integrity of the composite. Additionally, a visual inspection of the cross-sections was conducted. The impact on the proper functioning of the embedded FBGs was tested by comparing the reflection spectra before and after TVac conditioning and by performing tensile tests in which the strain measured using the embedded FBGs was compared with the output of reference strain sensors applied after TVac conditioning. The measured strain of the embedded FBGs showed excellent agreement with the reference sensors, and the reflection spectra did not exhibit any significant degradation. The results of the mechanical testing and visual inspection revealed no degradation of the structural integrity when comparing TVac-conditioned coupons with non-TVac-conditioned coupons of the same type. Consequently, it was concluded that TVac conditioning does not influence the functionality of the embedded FBGs or the structural integrity of the composite itself. Although in this paper FBG sensors were tested, the results can be extrapolated to other sensing techniques based on optical fibers. Full article

The current study focuses on studying the effect of reinforcement of carbon fabric (CF) decorated with in-situ grown silver (Ag) nanoparticles (NPs) on the performance properties of epoxy composite. The Ag NPs were grown on carbon fabric by reducing silver nitrate. The main objective of developing such an innovative reinforcement was to improve thermal conductivity, interlaminar strength, and tribological properties of CF-epoxy composites. The growth of NPs on the surface of CF was confirmed through scanning electron microscopy (SEM), energy dispersive X-Ray spectroscopy (EDAS), X-ray photoelectron spectroscopy (XPS), and X-ray diffraction studies. The development of composites was conducted by the impregnation method, followed by compression molding. It was observed that in-situ growth of Ag NPs enhanced thermal conductivity by 40%, enhanced inter-laminar shear strength by 70%, enhanced wear resistance by 95%, and reduced the friction coefficient by 35% in comparison to untreated CF. Full article

Interest in the use of natural fibres as an alternative for artificial fibres in polymer composite manufacturing is increasing for various engineering applications. Their suitability for use in outdoor environments should be demonstrated due to their perceived hydrophilic behaviour. This study investigated the water absorption behaviour of hybrid flax fibre-reinforced epoxy composites with 0%, 0.5%, 1% and 1.5% graphene by weight that were immersed in water for 1000, 2000, and 3000 h. The flexural and interlaminar shear strength before and after immersion in water was then evaluated. The results showed that graphene nanoparticles improved the mechanical properties of the composites. The moisture absorption process of hybrid natural fibre composites followed the Fickian law, whereas the addition of graphene significantly reduced the moisture absorption and moisture diffusion, especially for hybrid composites with 1.5% graphene. However, the flexural and ILSS properties of the composites with and without graphene decreased with the increase in the exposure duration. The flexural strength of hybrid composites with 0%, 0.5%, 1% and 1.5% graphene decreased by 32%, 11%, 17.5% and 13.4%, respectively, after exposure for 3000 h. For inter-laminar shear strength at the same conditioning of 3000 h, hybrid composites with 0.5%, 1% and 1.5% graphene also decreased by 13.2%, 21% and 17.5%, respectively, compared to the dry composite’s strength. The specimens with 0.5% graphene showed the lowest reduction in strength for both the flexural and interlaminar tests, due to good filler dispersion in the matrix, but all of them were still higher than that of flax fibre composites. Scanning electron microscope observations showed a reduction in voids in the composite matrix after the introduction of graphene, resulting in reduced moisture absorption and moisture diffusion. Full article

In the current research, the effect of cyclic temperature variation on the mechanical and thermal properties of woven carbon-fiber-reinforced polymer (CFRP) composites was investigated. To this, carbon fiber textiles in twill 2/2 pattern were used as reinforced phase in epoxy, and CFRPs were fabricated by vacuum-assisted resin-infusion molding (VARIM) method. Thermal cycling process was carried out between −40 and +120 °C for 20, 40, 60 and 80 cycles, in order to evaluate the effect of thermal cycling on mechanical and thermal properties of CFRP specimens. In this regard, tensile, bending and short beam shear (SBS) experiments were carried out, to obtain modulus of elasticity, tensile strength, flexural modulus, flexural strength and inter-laminar shear strength (ILSS) at room temperature (RT), and then thermal treated composites were compared. A dynamic mechanical analysis (DMA) test was carried out to obtain thermal properties, and viscoelastic properties, such as storage modulus (E’), loss modulus (E”) and loss factors (tan δ), were evaluated. It was observed that the characteristics of composites were affected by thermal cycling due to post-curing at a high temperature. This process worked to crosslink and improve the composite behavior or degrade it due to the different coefficients of thermal expansion (CTEs) of composite components. The response of composites to the thermal cycling process was determined by the interaction of these phenomena. Based on SEM observations, the delamination, fiber pull-out and bundle breakage were the dominant fracture modes in tensile-tested specimens. Full article

Many high-strength composite materials have been developed for aircraft structures. GLAss fiber REinforced aluminum (GLARE) is one of the high-performance composites. The review of articles, however, yielded no study on the impact damage of heated GLARE laminates. This study, therefore, aimed at developing a numerical model that can delineate the continuum damage of GLARE 5A-3/2-0.3 laminates at elevated temperatures. In the first stage, the inter-laminar interface failure of heated GLARE laminate had been investigated at room temperature and 80 °C. The numerical analysis employed a three-dimensional GLARE 5A-3/2-0.3 model that accommodated volumetric cohesive interfaces between mating material layers. Lagrangian smoothed particles populated the projectile. The model considered the degradation of tensile and shear modulus of glass fiber reinforced epoxy (GF/EP) at 80 °C, while incorporated temperature-dependent critical strain energy release rate of cohesive interfaces. When coupled with the material particulars, an 82 m/s bird impact at room temperature exhibited delamination first in the GF/EP 90°/0° interface farthest from the impacted side. Keeping the impact velocity, interface failure propagated at a slower rate at 80 °C than that at room temperature, which was in agreement with the impact damage determined in the experiments. The outcomes of this study will help optimize a GLARE laminate based on the anti-icing temperature of aircraft. Full article

Glass fiber reinforced polymers (GFRPs) are used extensively in many industries because of their low cost and high mechanical properties. Even if composite manufacturing processes are well controlled and allow to fabricate near net shapes, machining operations are still necessary to complete the manufacturing. As a composite material, GFRP machining remains difficult because of its heterogeneous and anisotropic character. This work intends to investigate the effect of graphene addition to the epoxy matrix of GFRP on its machinability. The epoxy was filled with 1 wt% graphene by mixing, sonicating, and then being used to produce unidirectional GFRP laminate by hand layup methods. Thermocouples were bonded on a chemical vapor deposition (CVD) diamond coated tool in order to record cutting temperatures during the trimming process. The cutting forces were recorded and the resulting surface roughness after trimming was measured to qualify properly the machinability of the modified GFRP. Compared to the reference material (GFRP without graphene), the additive improved the machining process by decreasing the cutting temperature and forces as well as the surface roughness without deteriorating the inter-laminar shear strength. Full article

The effects of reinforcement structures and hybrid types on the inter-laminar shear strength (ILSS) of carbon-glass hybrid fibers/bismaleimide composites under thermo-oxidative aging conditions were investigated. The process resulted in progressive deterioration of the matrix and fiber/matrix interfaces, in the form of chain scissions, weight loss, and fiber/matrix debonding, which significantly led to the decrease of the ILSS of composites. Moreover, the three-dimensional orthogonal woven hybrid composites (3D composites) showed higher ILSS retention rate than those of the laminated orthogonal hybrid composites (laminated composites). No delamination occurred in the aged 3D composites like in the aged laminated composites. This was because the Z-binder yarns in the 3D composites resisted the inter-laminar shear load, although the resin was damaged and the adhesive force between fiber bundles and resin decreased seriously after thermo-oxidative aging. Meanwhile, the ILSS retention rate of the laminated composites with the carbon fiber as intermediate layers was higher than that of the laminated composites with the glass fiber as the intermediate layers. This was because the carbon fiber/bismaleimide interface bonding performance was stronger than that of the glass fiber/bismaleimide at the same thermo-oxidative aging condition. Full article

During the production of fiber-reinforced composite materials, liquid resin is introduced into the fiber material and cured, i.e., hardened. An elevated temperature is needed for this curing. Microwave curing of composites has been investigated for some time, but it has mostly been done using small domestic or laboratory equipment. However, no investigation has been carried out using an industrial-sized chamber-microwave for glass fiber-reinforced plastic (GFRP). Here, we show that microwave curing produces laminates of the same quality as oven-cured ones. The study shows that, if the process is done right, GFRP samples can be produced with an industrial scale microwave. Even if not fully cured, microwave samples show a glass transition temperature measured with DMA (T_g-DMA) that is comparable to the T_g-DMA according to the proposed cure cycle on the data sheet. Specific microwave-cured configurations show better inter-laminar shear strength than oven specimens. The results show that microwave-based heat introduction can be a beneficial curing method for GFRP laminates. A microwave-optimized process is faster and leads to better mechanical properties. Full article

Thermally reduced graphene oxide (TRGO) was incorporated as a reinforcing filler in the epoxy resin to investigate the effect on the mechanical properties of carbon fiber (CF)/epoxy composites. At first, the epoxy matrix was modified by adding different wt % of TRGO from 0.05 to 0.4 wt % followed by the preparation of TRGO/CF/epoxy composites througha vacuum-assisted resin transfer molding process. The prepared TRGO was characterized by using Fourier transform infrared spectroscopy, Raman Spectroscopy and field emission scanning electron microscopy (FE-SEM) techniques. It was observed that the wrinkled structure of synthesized TRGO may be helpful to interlock with the epoxy resin and CF.The inter-laminar shear strength, in-plane fracture toughness and impact strength increased by ~67%, 62% and 93% at 0.2 wt % of TRGO loading in the CF/epoxy composites as compared to the CF reinforced epoxy. The mechanical properties of the hybrid composites decreased beyond the 0.2 wt % of TRGO incorporation in the epoxy resin. The fracture surfaces of the hybrid composites were studied by FE-SEM image analysis to investigate the synergistic effect of TRGO in the CF/epoxy composite. This study suggested that TRGO could be used asgood nanofiller to resist the matrix and fiber fracture. Full article