Composites Part C Open Access最新文献

With the rapid advancement in the manufacturing industry, there has been a massive rise in the demand for products made of fiber reinforced polymer composites as they have high stiffness and strength to weight ratios. They are widely used in the manufacturing of parts in aerospace and automobile industry. The manual draping process of prepreg on the mold is time intensive and requires a highly skilled worker to perform the task. Various techniques have been designed to automate the process of composite parts manufacturing using automated fiber placement (AFP), automated tape laying (ATL) and automated plies layup. These methods use robots equipped with an end effector designed to drape the prepreg. The system utilizes both single and multi-robot cells for the process of composites manufacturing. The aim of this paper is to review the techniques and strategies employed for conforming and grasping of prepreg. The paper will also delve into the process parameters that influence the composites manufacturing process and investigate the impact of correct and inaccurate selection of process parameters on the final product. The paper will also discuss the limitations, challenges and future prospects for automated composite part manufacturing.

Auxetic composite laminates, i.e. laminates with a NPR (Negative Poisson’s Ratio), are regarded as a promising solution to combat LVI (Low-velocity impact) delamination BVID (Barely visible internal damage) and ensuing property degradation, a cause for concern in aerospace components, mainly inflicted by fortuitous accidents during handling operations. In order to potentiate the auxetic effect through the minimization of the Poisson’s ratio, a thorough analysis of material properties and stacking sequences is required, as only a restricted domain of combinations can generate the desired effect, either in an IP (In-plane) or TTT (Through-the-thickness) configuration. This paper focuses on a MATLAB program developed for IP and TTT auxetic laminate design, based on the CLT (Classical Lamination Theory). Cases studies on NPR domain definition of C/E (Carbon/epoxy), G/E (Glass/epoxy) and hybrid C-G/E (Carbon-Glass/epoxy) laminates are presented. Moreover, the influence of fibre volume fraction on C/E and G/E laminates is analysed.

The selection of materials in the construction industry plays a pivotal role in advancing sustainability goals. Traditional materials derived from natural resources face inherent constraints linked to geographic limitation, growth time, and geometric inconsistency and therefore recent attention has shifted towards developing novel bio-based materials. Composites, offering varying properties and geometries, are becoming increasingly popular for customising materials for specific applications. Pultrusion, a technology for manufacturing linear fibre-reinforced composites, is a well-established and reliable method. This study delves into optimising pultrusion technology, which traditionally relies on synthetic fibres, by exploring the potential of natural alternatives, specifically hemp bast fibres. Additionally, it presents a customised formulation based on a plant-based resin and additives. This formulation is tailored for pultrusion to produce high-performance biocomposites for use as load-bearing components in structural applications, with an initial focus on bending structures. The study elaborates on the material composition and performance of these newly developed natural fibre pultruded profiles, showcasing their mechanical capabilities through rigorous experimentation and testing. The results demonstrate the material's mechanical capabilities showcasing a flexural strength of 260 MPa with a bending modulus of 21 GPa and a bending radius reaching 0.5 m. While this study focuses on the material formulation tested on laboratory-scale pultrusion, the findings will be later applied in an upscaled production at an industrial level, aiming to enhance overall sustainability in the construction industry.

In this study, lignin underwent chemical modification via acetylation of hydroxyl groups to enhance its interfacial connection with poly (lactic acid) (PLA). Further enhancement of the blend was attained by adding an impact modifier, Biomax Strong. Incorporating Biomax Strong into PLA-lignin blends resulted in improvements in material characteristics, particularly in impact strength and thermal stability. This blend exhibited a unique set of mechanical properties, characterized by a reduction in tensile modulus as well as an increase in ductility. This will allow a more versatile use of PLA in various applications. The observed improved impact strength highlights the synergistic effect of stress redistribution within the PLA matrix contributing to widespread applications of PLA based composites. This can clearly be observed for the compound containing PLA and 15 wt.% lignin, where the impact strength was approximately 15 kJ/m². With the addition of 5 wt.% impact modifier, the impact strength increased by 60 %, reaching approximately 25 kJ/m². This synergy effect reinforces the overall structure, improving the impact toughness behavior. The combination of Biomax Strong and lignin not only address the limitations of PLA but also introduces new opportunities for applications requiring a balance of impact strength, ductility, and thermal stability. These advancements indicate a promising future for composite materials in various applications.

Reducing vehicle weight is crucial for enhancing fuel efficiency and reducing emissions in transportation. Traditional composite materials offer improved energy absorption over metals yet are limited by brittleness. This study introduces an innovative approach, inspired by the mantis shrimp's natural defense mechanisms, to enhance the crashworthiness and energy absorption of composite structures, optimizing safety and performance. Utilizing a bio-inspired design, we developed corrugated Carbon Fiber Reinforced Polymer (CFRP) crash box structures, aiming to optimize their energy absorption capabilities and crash force efficiency (CFE) for potential applications in transportation safety. Through a series of quasi-static axial compression tests, the corrugated structures' performance was evaluated against traditional crash box designs. The experimental results demonstrate that the bio-inspired configurations improved crashworthiness characteristics. Strategic manipulation of layer numbers and corrugations led to superior CFE values, indicative of safer, more controlled collision behavior. The “7N-6L” configuration featuring seven corrugations with six layers of CFRP demonstrated the highest efficacy, achieving an optimal CFE of 1.08. This configuration demonstrated a Specific Energy Absorption (SEA) of 1.56 J/g and an Energy Absorption (E_a) of 42.56 J. Furthermore, compared to conventional steel crash boxes, the CFRP crash box with 7N-6L corrugated structure showcased competitive energy absorption capabilities with significantly reduced mass, absorbing 2850 J with a CFE of 0.91, nearly matching the ideal CFE and highlighting its superior lightweight performance. These results underline the potential of integrating bio-inspired designs to develop robust, lightweight structures for improved crashworthiness, paving the way for safer and more sustainable transportation solutions.

Fiber reinforced polymer (FRP) bars have become increasingly popular, while the studies on durability of FRP bars are primarily on small-diameter FRP bars. This study investigated the tensile strength retention in glass FRP (GFRP) bars of different diameters (13 mm and 25 mm) after immersion in an alkaline solution (pH=12.6) at various temperatures (20 °C, 40 °C and 60 °C) for 1, 2, 3, and 6 months. The results reveal that the degradation of GFRP bars was slow at 20 °C, accelerated but not pronounced at 40 °C and considerable at 60 °C. Particularly, the 13 mm diameter GFRP bars exhibited a more significant reduction in tensile strength, with a decrease of 20.12 % after 6 months, while the 25 mm diameter bars only decreased by 13.23 %. Results reveal that, importantly, degradation of GFRP bars is primarily attributed to the diffusion of the moisture and alkalis, which disrupts the bond between the fibers and the matrix, causing interface damage. Finally, based on the Arrhenius theory, it is predicted that the tensile strength retention of 13 mm and 25 mm diameter GFRP bars will be 66.4 % and 79.8 %, respectively, after 50 years of exposure at an average annual temperature of 35 °C. The important finding that the small-diameter FRP bars are more vulnerable to the alkaline exposure than larger diameter bars suggests that the current studies on durability of FRP bars are conservative to be referred in practice.

In this study, we examine to derive the solutions of effective elastic moduli and thermal expansion coefficient for composite materials containing ellipsoidal fillers oriented randomly in the material using homogenization theories, which are the self-consistent method and the Mori–Tanaka method. This analysis is carried out by micromechanics combining Eshelby’s equivalent inclusion method for each theory. The solutions for effective elastic moduli and thermal expansion coefficient obtained on each theory are expressed by common coefficients composed of both the physical properties of the constituents of the composite material and geometrical factors depending upon the shape of the fillers. Moreover, these solutions enable us to calculate effective elastic moduli and thermal expansion coefficient for composite materials that contain randomly oriented fillers of various shapes and physical properties. By taking the limit of eliminating the existence of the matrix for these solutions, we can derive effective physical properties of polycrystalline materials. Using the obtained solutions, we investigate the effects of the shape of the fillers on the effective elastic moduli and thermal expansion coefficient. As a result, we confirm that these effective properties fall within the lower and upper bounds, and find that a characteristic result appears when the shape of the fillers is flake or oblate. Through comparisons between the analytical and experimental results, we confirm the practical usability of the solutions obtained in this analysis. Furthermore, we determine originally the shape factor for the filler and can show that this factor has the potential to provide guidelines for the optimal design of filler shape to improve the effective elastic properties of materials.

This work aimed to investigate the low velocity impact behaviour of short jute fibre non-woven preform epoxy matrix composites experimentally. Dry fibre preforms were developed using an optimised process and a laboratory made preforming device. The effects of alkali and poly vinyl alcohol (PVA binder) treatments on impact performances of jute composites were investigated and compared at 3 J and 6 J impact energy levels. To identify the failure modes of tested composites, the X-ray µCT tomography was employed. The results demonstrated that the developed untreated short jute fibre preform reinforced composites absorbed a higher impact energy, when they were compared to treated (alkali or PVA binder) composites. For untreated composites, maximum impact forces at 3 J and 6 J energies, were found as ⁓2478 N and ⁓2319 N, respectively; for the PVA treatment these values were measured as ⁓2457 N and ⁓2216 N, while, at same energy levels, alkali treated composites showed the lowest values as ⁓1683 N and ⁓1440 N, respectively. Untreated jute fibre contains natural matrices such as hemicellulose, lignin and waxes, which ensured a positive response to absorb more energy upon impact loading. In contrast, the alkali treatment facilitates a highly fibre packed composite structure, which accelerated the impact crack propagation in tested composites, resulting in lower resistance to impact energy. Although, PVA treated composites showed reduced impact properties compared to untreated composites due to the PVA polymer brittleness on the treated fibre surface during the impact incidents, this treatment demonstrated better impact responses over the alkali treatment. The application of PVA binder on alkali-treated fibres provided an extra support to fibres and a better fibre/matrix interface and hence, this combined treatment demonstrated a slightly better impact resistance (⁓2027 N and ⁓1874 N impact forces at 3 J and 6 J respectively) compared to only alkali treated fibre composites. The SEM fracture images and the X-ray µCT damage analysis revealed different impact damage modes, which supported the observed impact results. The obtained results from this investigation could be helpful for using short jute fibre composites in various load demanding applications where impact incidents are likely to be happened.

This article deals with a detailed experimental study dedicated to the evaluation of the overall mechanical behaviour of a bio-based composite structure used in transportation industries. The sandwich structure is designed to increase the lightening, vibration damping, and composite recyclability. The considered materials consist of a Flax/Elium® laminate composite for skins associated with a balsa core. The sandwich structure was obtained using a one-shot liquid resin infusion process. Low-velocity impact tests were carried out on different sandwich configurations with the aim of characterizing the effects of the stacking sequence and the density and thickness of the core. Furthermore, an experimental comparative analysis was conducted involving two composite laminate types: Glass/Elium and Flax/Elium to enhance the specific behaviour of flax fibre composite to be used as skins in the sandwich structures. The impact tests were carried out at low velocities and at different levels of impact energy using a drop-weight test bench. Notable damage mechanisms have been identified, and a chronological sequence of their development has been suggested. Ultrasonic analyses using C-Scan imaging were applied to the opposite side of the impacted specimen. The research proves the efficient energy-absorbing capability of the biobased sandwich structure during impact. Finally, this study enables a deeper understanding of various parameters that influence the behaviour of sandwiches during low-velocity impacts, thereby facilitating more informed material selection for practical applications.

The present paper is focused to understand the reinforcement mechanisms exerted by GO nanosheets to both strengthen and toughen cement-matrix composites since, despite intensive research, such mechanisms are still not completely clear. To such an aim, the mechanical characteristics (that is, mechanical strengths and fracture toughness) of a cement-matrix nanocomposite, with the 0.05 % of GO used as an additive, are experimentally investigated at different curing times. Since reinforcement mechanisms are closely related to cement hydration products, they are qualified and quantified by chemical, mineralogical and microstructural analyses performed at the above times of curing. The present investigation leads to the conclusion that the role of both CSH and AFt content is dominant in strengthen and toughen of cement matrix-nanocomposites with GO used as an additive.