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Carbon fiber-reinforced epoxy matrix composites using ambient- and moderate-temperature curing non-autoclave processes have broad applicability in marine, offshore, and naval applications. This research focuses on the characterization of moisture kinetics of ambient cured carbon/epoxy composites subject to immersion in seawater for up to 72 weeks after prior periods of extended thermal aging. A two-stage model is shown to best describe the overall kinetics and response. The level of maximum moisture uptake shows an increasing trend with the temperature and time of prior thermal aging, reaching asymptotic levels at the highest levels. The transition point is seen to represent a shift between the diffusion and relaxation-/deterioration-based dominant regimes, and the ratio of uptake at the transition point to the maximum uptake can be correlated to the relaxation coefficient. Diffusivity, as expected, generally increases with the temperature of prior aging and shows changes based on the level of post-curing and network changes with time. Moisture uptake kinetics and characteristics developed through the sequence of exposures provide a better understanding of phenomena towards the development of a future comprehensive model capable of long-term prediction based on the sequential prior history of exposure to elevated temperatures and immersion in seawater.

Combining exceptional crushing strength of hollow glass microspheres (HGM) with reinforcing properties of carbon nanotubes as well as carbon fibres with epoxy resins results in a design poised to meet the demand for advanced, lightweight and high strength materials required in a variety of industries, such as aerospace and automotive, particularly, in the manufacture of composite rocket motor casings. In this study, unidirectional laminates of HGM/multi-walled CNTs (MWCNTs)/carbon-epoxy (CE) composites (samples nomenclature A–F) of varying wt.% of HGM and constant 0.1 wt.% of MWCNTs by filament winding technique were fabricated and subsequently cured. The HGM (iM16K) was varied as 0.2, 0.4, 0.6, 0.8, 1.0 wt.% by maintaining a constant concentration of 0.1 wt.% of MWCNTs. The hardener, fine hard (FH5200) was utilized in combination with epoxy resin (Epofine 1555). The epoxy resin was heated to 60°C after the fillers were added. Thermogravimetric analysis, differential mechanical analyzer and thermal mechanical analyzer were used to estimate the thermal stability, glass transition temperature and coefficient of thermal expansion (CTE), respectively. HGM and MWCNTs dispersion in the fracture samples caused by transverse tensile loading was examined using scanning electron microscopy. The effect of variation of HGM and 0.1 wt.% constant MWCNTs on tensile and compressive properties in transverse fibre directions of these composites has been investigated. Transverse tensile strength and tensile modulus were improved by 29.07 and 12.33%, respectively, up on the addition of 0.2 wt.% of HGM and 0.1 wt.% of MWCNTs in CE composite. The other findings indicated that > 0.2 wt.% HGM along with constant concentration of MWCNTs had decreasing effect on transverse tensile strength, modulus and compressive strength. The MWCNTs agglomeration was identified as the cause of these mechanical property degradations. The addition of HGM and MWCNTs decreased the CTE of the composite and increased the glass transition temperature as HGM limits the thermal motions of the epoxy polymer chain’s molecular segments. The HGM/MWCNTs/CE composite was shown to be thermally stable up to 310°C.

A novel method is proposed to quickly predict the tensile strength of carbon/epoxy composites with resin-missing defects. The univariate Chebyshev prediction model (UCPM) was developed using the dimension reduction method and Chebyshev polynomials. To enhance the computational efficiency and reduce the manual modeling workload, a parameterization script for the finite element model was established using Python during the model construction process. To validate the model, specimens with different defect sizes were prepared using the vacuum assistant resin infusion (VARI) process, the mechanical properties of the specimens were tested, and the model predictions were analyzed in comparison with the experimental results. Additionally, the impact of the order (second–ninth) on the predictive accuracy of the UCPM was examined, and the performance of the model was evaluated using statistical errors. The results demonstrate that the prediction model has a high prediction accuracy, with a maximum prediction error of 5.20% compared to the experimental results. A low order resulted in underfitting, while increasing the order can improve the prediction accuracy of the UCPM. However, if the order is too high, overfitting may occur, leading to a decrease in the prediction accuracy.

This research investigates the effectiveness of bio-sourced flax fiber-reinforced polymer in comparison with a traditional system based on carbon fiber-reinforced epoxy polymer in order to confine recycled aggregate concretes. The experimental investigation was conducted on two series of concrete including three mixtures with 30%, 50%, and 100% of recycled aggregates and a reference concrete made with natural aggregates. The concrete mixtures were intended for a frost environment where an air-entraining agent was added to the mixture of the second series to achieve 4% air content. The first part of the present work is experimental and aimed to characterize the compressive performance of confined materials. The results indicated that bio-sourced composites are efficient in strengthening recycled aggregates concrete, especially the air-entrained one. It was also found that the compressive strength and the strain enhancement obtained from FRP confinement are little affected by the replacement ratio. The second part was dedicated to the analytical modeling of mechanical properties and stress–strain curves under compression. With the most adequate ultimate strength and strain prediction relationships, the full behavior of FRP-confined concrete can be predicted using the model developed by Ghorbel et al. to account for the presence of recycled aggregates in concrete mixtures.

Since the early development, the sectors where the composite materials are being used have been growing gradually. Nowadays, these materials have extensive application in the structural components in the aerospace, defense, transportation, civil, and energy industries. The composites, especially carbon fabric/epoxy resin, have excellent in-plane properties. However, the susceptibility to delamination from out-of-plane loads, due to the lack of fibers oriented through the thickness, is still one of the weaknesses of this kind of materials. The introduction of reinforcement through the thickness has the potential to increase out-of-plane properties of composite materials. This can be accomplished by different reinforcement methods, such as Z-pinning, stitching, and tufting. This work aimed to develop and implement a simplified method of through-the-thickness reinforcement, based on tufting reinforcement. The experimental methodology was developed in a CNC router machine where glass fiber and polyamide were used as the main reinforcement materials in different square patterns (5 × 5 and 7 × 7) and applied in laminated carbon/epoxy composites manufactured by vacuum resin transfer molding process. Then, efficiency of the reinforcement was evaluated by means of mechanical testing, i.e., tensile and end-notched flexure testing in order to evaluate the ability to improve the interlaminar fracture strength. Results showed that the presence of the reinforcements provided around 27% increase in the delamination resistance compared to the non-reinforced composites in the thickness direction.

In this work, it was aimed to develop carbon fiber reinforced epoxy thermoset resin composite tapes for flexible rapier weaving machines. Five different types of epoxy resin (Flex, Norm Medium, Norm Slow, Norm Hard and MGS-LR) and three different types of carbon fabric (200 g/m² plain weave, 200 g/m² unidirectional and 300 g/m² unidirectional) were employed. For laminate production, vacuum assisted resin infusion method was used. The number of carbon fabric layers and their placement or direction in the reinforcement were also changed to obtain different composite properties. It was calculated based on rapier dynamic motion analysis that rapier tapes were subjected to maximum around 500 N at 800 rpm running speeds and below 300 N under 600 rpm industrial running speeds. Load elongation and 3-points bending tests were applied to composite samples. The results were evaluated and compared with the results of a commercially used carbon reinforced composite rapier tape. It was shown with the solution of dynamic rapier motion analysis and load-elongation curve measurements that elongation under 0.1 mm at 500 N was obtained for a 150 mm sample length which is close to commercial rapier tape. Although bending force was calculated well below its breaking value when it is bent to 150–200 mm radius of curvature (radius of rapier drive wheel) for a sample length of 150 mm, both maximum bending force and maximum bending strength values remained under those of commercial composite rapier tape and needed improvement with further studies.

Carbon fiber reinforced polymer composites are widely used in the rehabilitation, repair, and strengthening of civil, marine, and naval infrastructure and structural systems. In these applications, they are exposed to a range of exposure conditions, including humidity and immersion, which are known to affect the durability of the resin and the fiber–matrix interface over long periods of time. This paper presents results of long-term hygrothermal aging of wet layup carbon/epoxy composites including through acceleration by temperature focusing on the development of a comprehensive understanding of moisture uptake kinetics and its effects on glass transition temperature and interface and inter-/intra-laminar dominated performance characteristics. A two-phase model for uptake that incorporates both diffusion- and relaxation-/deterioration-dominated regimes, as well as a transition regime, is shown to describe uptake well. The inclusion of damage terms to the diffusion and relaxation coefficients is seen to capture changes well, with the effective diffusion and relaxation coefficients increasing with fiber volume fraction and temperature. Effects of uptake, including at elevated temperatures, reflective of accelerated aging, on glass transition temperature and flexural strength are correlated, emphasizing a three-stage progression of overall response in line with the moisture uptake changes. The drop in glass transition temperature per percent increase in moisture uptake was seen to range from a low of 4.38% per % increase in moisture content, for the highest volume fraction at the highest temperature, to a high of 6.95% per % increase in moisture content, for the intermediate volume fraction at the lowest temperature. The composites with heavier fabric showed the greatest drop in both glass transition temperature and flexural strength, indicating a level of correlation between these characteristics as well. It is shown that both glass transition temperature and flexural strength show steep initial decreases, followed by a regime with slower decrease and, then, an asymptotic or near-asymptotic response with time of immersion, suggesting a close correlation with moisture uptake, which forms the basis for future modeling.

In order to investigate the effects of different functional groups on graphene on the mechanical behavior of carbon fiber reinforced epoxy composites were fabricated by hand layup technique. In this study, three different variety of functionalized graphene (–NH 2 , –COOH, and –OH) with varying weight percent (i.e. 0.1, 0.3, and 0.5 wt%) was considered. Tensile, interlaminar, and three-point flexural tests were conducted to evaluate the effects of graphene concentration and fiber stacking sequence (i.e. 0/90° and 0/90/ ± 45°) on composites. The microstructures of the composites were characterized by a scanning electron microscope. Experimental results showed that pristine and functionalized graphene significantly improved the mechanical properties of carbon fiber epoxy composites. Compared to neat carbon fiber epoxy composites, the maximum tensile strength of 33.34% and 26.35% were noticed for 0/90°–COOH–0.5 and 0/90/ ± 45°–NH 2 –0.3 stacked functionalized graphene modified carbon fiber epoxy composites, respectively. Moreover, 48.44% and 59.1% flexural strength were recorded for 0/90°–COOH–0.3 and 0/90/ ± 45°–OH–0.5 stacked functionalized graphene modified carbon fiber epoxy composites, respectively. Furthermore, maximum interlaminar shear strength (ILSS) of 120.25% was observed for 0/90/ ± 45° stacked carbon fiber epoxy composites. Finally, the results obtained with graphene as reinforcement filler can cause a significant improvement in the mechanical performance of fiber composites. Henceforth, they can also be considered as a promising candidate for designing composites for structural applications.

High-temperature engineering thermoplastic fillers are gaining popularity for enhancing the toughness of the inherently brittle composites, making them a potential candidate for low velocity impact applications. The incorporation of pre-formed immiscible thermoplastic filler into a thermoset matrix to boost its toughness offers many advantages over the miscible phase-separated filler. In this study, immiscible polyether ether ketone (PEEK) microparticles were utilized to increase the toughness of the carbon epoxy composite. A vigorous mechanical stirring was employed to properly distribute the PEEK particles in the matrix. The wet compression molding technique was used to make the composites. The effectiveness of the PEEK particles was analyzed by considering the coefficients of thermal expansion (CTE) in the axial and through thickness directions, dynamic mechanical analysis (DMA), and thermal conductivity of the composite material. The significant increase in the damping factor by 49% of the composite material reflects the strong influence of the PEEK particles in the impact behavior of the epoxy matrix-based composite material. However, a decrease in the behavior of the storage modulus by 23% and thermal conductivity by 24% of the hybrid composite is found in this study. The CTE in the longitudinal direction was found to be decreased, while in the Z-direction it is found to be increased with the increasing temperature. The glass transition temperature of the composite was found to be increased with the addition of the PEEK particles.

Recently, many structural parts using composite materials are being applied to small aircraft and UAV in the world. The aim of this work is to design the engine intake structure of a small aircraft. For structural safety evaluation, a finite element analysis method was applied. In this work, structural design and numerical analysis of air intake and s-duct structures for small aircraft were performed. The target structure is composed of an s-duct and a cylindrical intake structure. Firstly, an investigation of the mechanical properties of carbon/epoxy material was conducted. The distributed pressure load and acceleration condition was applied to the structural design. The structural design load was investigated considering safety factors. The structural analysis was performed to analyze the validity of the design results. Through the structural analysis using the finite element analysis method, it was confirmed that the designed air intake structure is safe. The manufacturing of the prototype structure will be carried out based on the designed result.