Search Results (51)

With the continuous development of new aircraft, the application of low-cost composite materials technology still encounters numerous challenges and issues. The development of low-cost composite technology, while ensuring the high reliability of aircraft components, has become a common concern among aerospace composites. The research presented in this paper examines the findings related to the conformity verification process of an electric aircraft in China. This is an all-composite structural general aviation aircraft certified under CCAR Part 23. This study focuses on the quality characteristics of low-cost wet vacuum bagging composites, addressing the causes and effects of high porosity in the manufacturing process. Based on the research findings, a relationship between porosity and the strength of wet vacuum bagging composites is established. Consequently, a safe and reliable method for ensuring airworthiness conformity of low-cost composites is proposed and implemented in the aircraft type’s conformity verification. Furthermore, this paper discusses the development trends of low-cost composites for general aviation, providing valuable insights for the advancement of low-cost technologies in the future. Full article

Nanocomposite laminates containing carbon fibers, epoxy, and multiwalled carbon nanotubes were fabricated using a vacuum bag process. Ecofriendly ionic liquid (5 wt%)-treated multiwalled carbon nanotubes (pristine and nickel-coated) were added to the epoxy independently, in amounts ranging from 1 wt% to 3 wt%, in order to tailor the mechanical, electrical, and thermal performance of manufactured carbon fiber epoxy composite laminates. These nanocomposite laminates were later characterized through flexural testing, dynamic mechanical analysis, impedance spectroscopy, thermal conductivity tests, and FTIR spectroscopy to evaluate their suitability for battery pack applications. The findings showed that both types of multiwalled carbon nanotubes exhibited multifaceted effects on the properties of bulk hybrid carbon fiber epoxy nanocomposite laminates. For instance, the flexural strength of the composites containing 3.0 wt% of ionic liquid-treated pristine multiwalled carbon nanotubes reached 802.8 MPa, the flexural modulus was 88.21 GPa, and the storage modulus was 18.2 GPa, while the loss modulus peaked at 1.76 GPa. The thermal conductivity of the composites ranged from 0.38869 W/(m · K) to 0.69772 W/(m · K), and the electrical resistance decreased significantly with the addition of MWCNTs, reaching a minimum of 29.89 Ω for CFRPIP-1.5 wt%. The structural performance of hybrid nanocomposites containing ionic liquid-treated pristine multiwalled carbon nanotubes was higher than that of the hybrid nanocomposite of ionic liquid-treated Ni-coated multiwalled carbon nanotubes, although the latter was found to possess better functional performance. Full article

Structural batteries, also known as “massless batteries”, integrate energy storage directly into load-bearing materials, offering a transformative alternative to traditional Li-ion batteries. Unlike conventional systems that serve only as energy storage devices, structural batteries replace passive structural components, reducing overall weight while providing mechanical reinforcement. However, achieving uniform and efficient coatings of active materials on carbon fibers remains a major challenge, limiting their scalability and electrochemical performance. This study investigates ultrasonic spray coating as a precise and scalable technique for fabricating composite cathodes in structural batteries. Using a computer-controlled ultrasonic nozzle, this method ensures uniform deposition with minimal material waste while maintaining the mechanical integrity of carbon fibers. Compared to traditional techniques such as electrophoretic deposition, vacuum bag hot plate processing, and dip-coating, ultrasonic spray coating achieved superior coating consistency and reproducibility. Electrochemical testing revealed a specific capacity of 100 mAh/g_LFP with 80% retention for more than 350 cycles at 0.5 C, demonstrating its potential as a viable coating solution. While structural batteries are not yet commercially viable, these findings represent a step toward their practical implementation. Further research and optimization will be essential in advancing this technology for next-generation aerospace and transportation applications. Full article

Monitoring of real-time flow and defects in the vacuum-assisted resin infusion (VARI) process can provide important guidelines for full impregnation of dry reinforcement. A weak fiber Bragg grating array was employed to obtain quasi-distributed monitoring results in real-time. Sensitivity testing of different kinds of coated optical fiber sensors (OFs) was carried out first, and the polyacrylate-coated OF showed a greater wavelength-shift response than the polyimide-coated one. Then, two- and three-dimensional flow monitoring tests were carried out. During the resin-filling stage, three trends of strain curve were identpified in relation to the different placement setups of embedded OFs, the resin flow direction, and the different vacuum-bagging methods. The monitoring criteria were analyzed and the results were compared with the visual inspection, showing good agreement and indicating the ability of the fiber Bragg grating array. Finally, defects including dry spots and voids were introduced and reflected in the maximum changed strains of FBGs due to the smaller stress relaxation, indicating the potential to characterize the local flow state and permeabilities experimentally based on these quasi-distributed sensing methods. Full article

Vinyl ester resins are widely used as thermoset matrix materials for laminated composites, particularly in naval and automotive applications, due to their strength, chemical resistance, and ease of processing. However, their brittleness limits their use, especially in cold conditions. This study investigates the toughness of core–shell rubber (CSR)-modified resins in composites with natural fibers. This research compares the properties of the neat resin matrix and the CSR-modified matrix. After optimizing the resin curing process with catalysts, various treatments were tested to analyze their mechanical and thermal properties. Using the vacuum bagging process, flax and glass fibers were used as reinforcements to assess the effects of matrix modifications. Flax fibers were chosen for their sustainability as a potential alternative to glass fibers. Mechanical testing was performed, comparing the performance of flax-based composites to those with glass fibers. Water absorption tests on flax composites followed the ISO 62 standard. Additionally, interlaminar shear strength and SEM micrography studies were conducted to examine the morphology and fiber–matrix adhesion, linking the microscopic structure to mechanical properties. Results indicate that while glass-reinforced composites have superior properties, flax composites offer a sustainable alternative, making them a promising choice for future applications. Full article

The limited recyclability of fibre-reinforced thermoset composites has fostered the development of alternative thermoplastic-based composites and their manufacturing processes. The most common thermoplastic-based composites are often costly due to their availability in the form of prepreg materials and to the high pressure and temperatures required for their manufacturing. Yet, the manufacturing of economic and recyclable composites, made of semi-preg composite materials using traditional composite manufacturing technologies, has only been proved at a laboratory scale through the manufacturing of flat plates. This work reports the manufacturing of a real structural part, a wing spar section with complex geometry, made of commingled polyamide 12 (PA12) fibres and carbon fibres (CFs) semi-preg and by oven vacuum bagging (OVB). The composite layup was studied using finite element analysis, and processing simulation assisted in the determination of the PA12/CF preform for OVB. Processing of two forms of semi-preg materials was first evaluated and optimised. The material selection for part manufacturing was mainly defined by the materials’ processability. The spar section was manufactured in two OVB stages and was then mechanically tested. The mechanical test showed a linear strain response of the prototype up to the maximum load and validated the optimised layup configuration of the composite structure. Full article

One of the garlic processing methods is fermentation, which produces black garlic with completely different chemical, physical, sensory, culinary, and health-enhancing properties. Our study aimed to compare the influence of various processing conditions on the quality indicators of black garlic (BG). Samples of white garlic (WG) were placed in laboratory climatic chambers. BG1 samples were packed in plastic bags and vacuumed, BG2 and BG3 samples were packed in textile mesh bags. BG1 samples were fermented in 70% humidity at 50 °C for 28 days, BG2 samples in 85% humidity at 60 °C for 99 days, and BG3 samples in 80% humidity at 80 °C for 14 days. The dependence of changes in chemical composition, color, and texture of garlic on fermentation conditions was analyzed. Proximate composition analyses and antioxidant activity of WG and BG were performed using standard methods. It was established that regardless of the fermentation conditions, BG’s chemical composition became richer than WG’s. They significantly increased vitamin C content (1.5–5.8 fold), titratable acidity (14.7–21.0 fold), protein (1.4–3.2 fold), fiber (4.6–7.0 fold), and ash (1.2–3.9 fold) content, amount of total phenolic compounds (6.6–9.6 fold) and antioxidant activity (5.3–9.9 fold). Fermented garlic turned dark in color and soft and sticky in texture. The higher fermentation temperature (80 °C) but the shorter time (14 days) had the greatest positive effect on the quality of black garlic. Full article

Following the vision of the European Commission, organisations and workers establishing Industry 5.0 approaches aspire to more future-proof, resilient, sustainable, and human-centred European industries. In this contribution, we explore how technological innovations that contribute to a “win–win” interaction with involved stakeholders may be advanced in a human-centred and transparent proceeding supported by impartial expert translators who provide information or knowledge-based guidance for decision-makers, initiators and implementers in manufacturing innovation driven by sustainability. We elaborate a stepwise procedure for agreeing on milestones and conjointly treading the path towards solving innovation challenges during a translation process. We exemplify the technological aspects of such a process using an innovation case aiming at identifying parameters for enhancements in a vacuum-bagging process applied to the manufacturing of composite parts from prepregs based on condensation-curing matrix resins made from renewable resources. In detail, we present a straightforward design of an experimental approach varying the dwelling temperature and the temperature ramps during the curing of stacked prepregs. In this way, we demonstrate that for cured composites comprising a poly(furfuryl alcohol)-based matrix, the porosity and connected mechanical properties achieved with autoclave-free curing processes sensitively depend on these process parameters. Applying the resulting data-based model is shown to support decision-making for sustainable composite manufacture. Full article

The main objective of this study was to investigate the mechanical and thermal properties of bamboo, as well as interlaminar hybrid composites reinforced with both bamboo and synthetic fibres in an epoxy matrix. Bamboo and glass, aramid, and carbon bidirectional fabrics were used with a bi-component epoxy matrix to fabricate the composite materials using the vacuum bagging process. The synthetic fabrics were placed on the outer layers, while the bamboo fabrics were used as the core of the hybrid composites. The developed composites were characterized and compared in terms of morphological, physical, and mechanical properties. Further, thermogravimetric (TGA) analysis was used to measure and compare the degradation temperature of the composites studied. Finally, a Scanning Electron Microscopy (SEM) analysis was performed in order to examine the fracture surfaces of the specimens tested. It was found that the fibre hybridization technique significantly improved the general mechanical properties. TGA analysis showed an increase in the thermal stability of the composites obtained by incorporating the synthetic fibres, confirming the effect of hybridization and efficient fibre matrix interfacial adhesion. The results from this work showed that the use of synthetic fibre reinforcements can help to significantly improve the mechanical and thermal properties of bamboo fibre-reinforced composites. Full article

Low fiber-direction compressive strength is a well-recognized weakness of carbon fiber-reinforced polymer (CFRP) composites. When a CFRP is produced using 3D printing, the compressive strength is further degraded. To solve this issue, in this paper, a novel magnetic compaction force-assisted additive manufacturing (MCFA-AM) method is used to print CFRP laminates reinforced with carbon nanofiber (CNF) z-threads (i.e., ZT-CFRP). MCFA-AM utilizes a magnetic force to simultaneously levitate, deposit, and compact fast-curing CFRP prepregs in free space and quickly solidifies the CFRP laminate part without any mold nor supporting substrate plate; it effectively reduces the voids. The longitudinal compressive test was performed on five different sample types. ZT-CFRP/MCFA-AM samples were printed under two different magnetic compaction rolling pressures, i.e., 0.5 bar and 0.78 bar. Compared with the longitudinal compressive strength of a typical CFRP manufactured by the traditional out-of-autoclave–vacuum-bag-only (OOA-VBO) molding process at the steady-state pressure of 0.82 bar, the ZT-CFRP/MCFA-AM samples showed either comparable results (by −1.00% difference) or enhanced results (+7.42% improvement) by using 0.5 bar or 0.78 bar magnetic rolling pressures, respectively. Full article

The goal of this paper is to fabricate innovative diaphragm headphones using graphene oxide paper (GOP) and GOP/epoxy nanocomposites (GOPC). Initially, graphene oxide suspension is fabricated, and the vacuum filtration method is adopted to make GOP. Then, vacuum bag molding is used to fabricate GOPC from GOP. Hot pressing and associated molds are adopted to fabricate line-indented (GOPC-L) or curve-indented patterns (GOPC-C) on the GOPC. The performances of one kind of GOP and three kinds of GOPC diaphragm headphones are analyzed based on their sound pressure level (SPL) curves achieved by the Soundcheck measurement system. There are four important processing parameters that will influence the performance of the diaphragm, including material type GOP versus GOPC, indented pattern type, sonication time on suspension, and graphene weight fraction in suspension. Compliances of various diaphragms are measured by the Klippel LPM laser measurement system. The results indicate that effects of sonication time and graphene weight fraction on SPL of GOP and GOPC headphones are in reverse, and this is associated with their difference on compliance (modulus), mass, damping ratio, and microstructure uniformity. Either GOPC-L or GOPC-C seems to improve the microstructure of the GOPC, and leads to better SPL performance. The correlation between the previous four factors and SPLs of four kinds of diaphragm headphones is proposed by using scanning electron microscope (SEM) to examine the microstructure of these diaphragms. Full article

This work aims to obtain recycled carbon fibre and develop an application for this new material. The carbon fibres were obtained by recycling aerospace prepreg waste via the pyrolysis process. The recycled fibres were combined with an Araldite LH5052/Aradur LY5053 epoxy resin/hardener system using manual lay-up and vacuum bagging processes. For comparison, the same resin/hardener system was used to produce a composite using commercial carbon fibre. The recycled and commercial composites were subjected to flexural, tensile and Mode I testing. Fracture aspects were analysed via scanning electron microscopy (SEM). The pyrolysis process did not affect the fibre surface as no degradation was observed. The fracture aspect showed a mixture of failure in the recycled composite laminate and interlaminar/translaminar failure near the surface of the commercial composite caused by flexural stress. Flexural and tensile tests showed a loss of mechanical strength due to the recycling process, but the tensile values were twice as high. The sand ladder platform was the project chosen for the development of a product made with recycled carbon fibres. The product was manufactured using the same manufacturing process as the specimens and tested with a 1243 kg car. The method chosen to design, manufacture and test the prototype sand ladder platform made of recycled carbon fibre was appropriate and gave satisfactory results in terms of high mechanical strength to bending and ease of use. Full article

Within the rapidly growing market for fiber-reinforced plastics (FRPs), conventional production processes involving molds are not cost-efficient for prototype and small series production. Therefore, new flexible forming techniques are increasingly being researched, many of which have been inspired by incremental sheet metal forming (ISF). Due to the different deformation mechanisms of woven reinforcement fibers and metal sheets, ISF is not directly applicable to FRP. Instead, shear and bending of the fibers need to be realized. Therefore, a new dieless forming process for the production of FRP supported by metal wire mesh as an auxiliary material is proposed. Two standard tools, such as hemispherical punches, are used to locally bend a reversible layup of metal wire mesh and woven reinforcement fiber fabric enclosed in a vacuum bag. Therefore, the mesh aids in introducing shear into the material due to its ability to transmit compressive in-plane forces, and it ensures that the otherwise flexible fabric maintains the intended deformation until the part is cured or solidified. Basic experiments are conducted using thermoset prepreg, woven commingled yarn fabric, and thermoplastic organo sheets, proving the feasibility of the approach. Full article

Currently, biobased epoxy resins derived from plant oils and natural fibers are available on the market and are a promising substitute for fossil-based products. The purpose of this work is to investigate novel lightweight thermoset fiber-reinforced composites with extremely high biobased content. Paying attention to the biobased content, following a cascade pathway, many trials were carried out with different types of resins and hardeners to select the best ones. The most promising formulations were then used to produce flax fiber reinforced composites by vacuum bagging process. The main biocomposite properties such as tensile, bending, and impact properties as well as the individuation of their glass transition temperatures (by DSC) were assessed. Three biocomposite systems were investigated with biobased content ranging from 60 to 91%, obtaining an elastic modulus that varied from 2.7 to 6.3 GPa, a flexural strength from 23 to 108.5 MPa, and Charpy impact strength from 11.9 to 12.2 kJ/m². The properties reached by the new biocomposites are very encouraging; in fact, their stiffness vs. lightweight (calculated by the E/ρ³ ratio) is comparable to some typical epoxy–glass composites. Full article

This research aimed to explore the porosity characteristics of a “hybrid” layup composite; this involved combining a fully impregnated prepreg and a dry fiber fabric via the the vacuum-bag-only (VBO) manufacturing process to create unidirectional carbon-fiber laminates sized at 15 × 15 cm². This investigation delved into several VBO process parameters encompassing the debulking technique, curing cycle, laminate saturation index, and thickness. The primary goal was to comprehend how these factors impacted the porosity levels within the laminate. Elevating the dwelling temperature during the curing cycle, employing a saturation index beyond 1.57, and utilizing thicker laminates emerged as strategies for decreasing the void content in the laminate. By implementing the optimal parameters identified through this research, we produced composite laminates that exhibited a substantial reduction in porosity. Furthermore, the study extended to modifying the two-stage curing cycle into a multi-stage cure cycle. This modification provided evidence that the incorporation of more dwell stages contributed to a further reduction in porosity. This study also featured a comparative analysis involving two types of laminates: one with prepreg fibers oriented at 0° and dry fibers oriented at 90° and another laminate with a sole 0° layup using a combination of prepreg and dry fibers. The findings suggest that the cross-layup allowed the prepreg fibers to conform more effectively to the protruding weft, thus eliminating voids induced by the weft. In conclusion, this research underscores the potential for a significant reduction in porosity within hybrid layup composites manufactured using the VBO process. Full article