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Sustainable hybrid composites, made of two different natural plant fiber types, are increasingly being attracted by composite researchers, for their cost effectiveness and ability to control mechanical performances through varying weight ratios of different fibers. In contrast, their lower mechanical properties are reported in the literature, because of strength variations of different fiber types and an improper fiber‐matrix stress distribution. Therefore, it is aimed to develop sustainable hybrid composites from two dry fiber preforms—woven fabric and short fiber preform—originated from same fiber type (jute). A highly packed short fiber preform is used as the core layer, while woven fabrics (plain/twill–rib/twill–diamond) are used in the skin layers for producing sandwiched hybrid jute composites. Mechanical tests and scanning electron microscopy images show that hybridized plain fabric/short fiber preform composites have better mechanical properties (≈58 MPa tensile strength/≈117 MPa flexural strength/≈112.12 kJm−2 impact strength with an ≈487.4% improvement) compared to other fabric structures hybrid/nonhybrid composites. This enhancement is related to the interlocking of short fibers with long plain fabric leading to a strong fiber‐matrix interfacial bonding. Thus, this developed hybrid composites, can be applied in many semi‐structural applications, wherein composites’ low cost and mechanical performances are primary concerns. Sustainable hybrid composites are developed using two different dry‐fiber preforms from the similar jute fiber type. Woven fabric and highly packed short jute fiber preform are used as skin and core layers respectively, in these sandwiched hybrid jute composites. Plain fabric/short fiber preform hybrid composites show improved mechanical properties. They are cost‐effective and can be used in semistructural composite applications.

Aiming at the research and development technology of high-precision load connecting frame structure with special-shaped variable cross-section reinforced by internal cross bars, the two-step weaving and stitching fiber preform forming process scheme and the general RTM product forming process scheme of load connecting frame are discussed by using the comparison method; The virtual simulation of RTM glue injection process is studied by using ESI Group software, and the results show that the completion time of the glue injection process with four sprues is about 29.4% of that of the glue injection process with only one sprue, which guides the design of RTM molding design; The key process of product manufacturing, such as the glue injection and curing process of the product and the quality control process during the technological process, are analyzed, and the performance of the final product is evaluated. Through the research on the manufacturing process, we have overcomed the major constraints on several molding technologies, such as the two-step fiber preform molding technology of weaving and stitching, the RTM molding design and processing technology of complex and special-shaped composite products, the split molding technology, and combination finishing processing technology after secondary bonding. The results prove that the formed products have better forming quality, dimensional accuracy and thermal cycle dimensional stability. The nondestructive testing results of composite parts show that the internal structure of the product is good. The fiber volume fraction is controlled at (55 ± 3)%, the flatness of the important surface of the product is 0.05 mm and 0.03mm respectively, and the dimensional accuracy of the important interface is controlled within ± 0.02 mm. The dimensional stability after the thermal cycle test is good, and all indicators of the product meet the user’s requirements, which achieved expected goals. The success on the manufacturing of these products provides a technical basis for the design and manufacture of high-precision and high stiffness composite structures for deep space exploration and manned spaceflight.

The core refractive index n2 of silica-based optical fiber preform heated to 2000 °C was determined experimentally for the first time. The measurements were carried out in the process of preform temperature reduction. It was shown that n2 could increase up to ~1.75 in the visible spectral range at temperatures of ~2000 °C (n2 ≈ 1.46 at room temperature). This fact suggests that pressures close to or exceeding the ultimate strength of silica glass (~20 GPa) occur in the preform core region. The local extra pressure is argued to be a possible cause of the well-known “starburst” phenomenon at the core–cladding interface of preforms with certain core compositions. The observed effect of radial cracks can be interpreted as the result of silica cladding destruction under the action of extra-high pressure in the core.

It is very important to predict any defects occurring by undesired fiber deformations to improve production yields of resin transfer molding, which has been widely used for mass production of carbon fiber reinforced composite parts. In this study, a simple and efficient analytic scheme was proposed to predict deformations of a multi-layered fiber preform by comparing the forces applied to the preform in a mold of resin transfer molding. Friction coefficient of dry and wet states, permeability, and compressive behavior of unidirectional (UD) and plain woven (PW) carbon fabrics were measured, which were used to predict deformations of the multi-layered fiber preforms with changing their constitution ratios. The model predicted the occurrence, type, and position of fiber deformation, which agreed with the experimental results of the multi-layered preforms.

This study investigates novel polymer composites through the hybridization of jute and recently explored Rosa hybrida (RH) fiber. The jute /Rosa hybrida fiber preforms are made with various weight ratios (100/0, 75/25, 50/50, 25/75, and 0/100) and then incorporated into the epoxy matrix by the hand lay-up technique to fabricate composites. Their water absorption, mechanical properties (tensile, flexural, impact, and hardness), and morphologies are then evaluated. It is found that the water absorption of composites reduces with increasing RH fiber, and the 25% jute/75% RH fiber composite displays minimum water absorption. The tensile and flexural properties, and hardness of hybrid composites decrease as the RH fiber content increases, and the hybrid comprising 75% jute and 25% RH fiber exhibits better tensile modulus and strength of 2 GPa and 41.93 MPa, and flexural modulus and strength of 1.55 GPa and 91.27 MPa, respectively, and hardness of 82.7 Shore D among other hybrids, whereas the impact strength of composites tends to enhance with rising RH fiber loading, and the hybrid of 25% jute/75% RH offers a maximum impact strength (17.67 kJ/m 2 ) among other hybrids. Additionally, the tensile and flexural properties, hardness of 100% jute fiber composite, and impact strength of 100% RH fiber composite are found to be noteworthy. Fracture morphologies also show that composites fail because of fiber pullout, jute and RH fibers fracture, fiber-matrix debonding, and voids. This study provides some insights to promote the application of jute / RH fiber-based composites in the internal structures of automobiles (e.g., seat foundations and dashboards), aircraft (e.g., interior panels, overhead storage compartments, and seating structures), and construction (e.g., wall panels and partitions). Graphical Abstract

Liquid resin infusion processes are becoming attractive for aeronautic applications as an alternative to conventional autoclave-based processes. They still present several challenges, which can be faced only with an accurate simulation able to optimize the process parameters and to replace traditional time-consuming trial-and-error procedures. This paper presents an experimentally validated model to simulate the resin infusion process of an aeronautical component by accounting for the anisotropic permeability of the reinforcement and the chemophysical and rheological changes in the crosslinking resin. The input parameters of the model have been experimentally determined. The experimental work has been devoted to the study of the curing kinetics and chemorheological behavior of the thermosetting epoxy matrix and to the determination of both the in-plane and out-of-plane permeability of two carbon fiber preforms using an ultrasonic-based method, recently developed by the authors. The numerical simulation of the resin infusion process involved the modeling of the resin flow through the reinforcement, the heat exchange in the part and within the mold, and the crosslinking reaction of the resin. The time necessary to fill the component has been measured by an optical fiber-based equipment and compared with the simulation results.

Three-dimensional (3D) biodegradable polyglycolic acid fiber (PGA) preforms were developed as temporary scaffolds for three-dimensional tissue regeneration applications. Three-dimensional biodegradable polyglycolic acid fiber (PGA) preforms including various degrees of interlaced structures called 3D plain, semi-interlaced, and orthogonal woven preforms were designed. Analytical relations and finite element model-based software (TexGen) on fiber volume fraction and porosity fraction were proposed to predict scaffolds’ stiffness and strength properties considering micromechanics relations. It was revealed that yarn-to-yarn space, density, and angles of all 3D PGA fiber preforms were heterogeneous and demonstrated direction-dependent features (anisotropy). Total fiber volume fractions (Vfp) and porosity fraction (Vtpr) predicted by analytic and numerical modelling of all 3D scaffolds showed some deviations compared to the measured values. This was because yarn cross-sections in the scaffolds were changed from ideal circular yarn (fiber TOW) geometry to high-order ellipse (lenticular) due to inter-fiber pressure generated under a tensile-based macrostress environment during preform formation. Z-yarn modulus (Ez-yarn) and strength (σz-yarn) were probably critical values due to strong stiffness and strength in the through-the-thickness direction where hydrogel modulus and strengths were negligibly small. Morphology of the scaffold showed that PGA fiber sets in the preform were locally distorted, and they appeared as inconsistent and inhomogeneous continuous fiber forms. Additionally, various porosity shapes in the preform based on the virtual model featured complex shapes from nearly trapezoidal beams to partial or concave rectangular beams and ellipsoid rectangular cylinders. It was concluded that 3D polyglycolic acid fiber preforms could be a temporary supportive substrate for 3D tissue regeneration because cells in the scaffold’s thickness can grow via through-the-thickness fiber (z-yarn), including various possible mechanobiology mechanisms.

The mechanical properties of composite materials are strongly related to the fiber–matrix interface properties. This study focuses on the click chemistry modification of short flax fibers using the Cu(I)-catalyzed Huisgen cycloaddition type, to strengthen the fiber–fiber interface for composite applications. The flax fibers are functionalized in three steps: a mechanical fibrillation pre-treatment of the fibers surface, followed by a chemical cleaning treatment to eliminate pectin, lignin, hemicelluloses and waxes, allowing exposure of the hydroxyl groups in flax fibers in view of the final treatment of click chemistry. The chosen strategy allows the adaptation of propargylation and tosylation reactions to flax fibers in aqueous media. FTIR and EDX analysis of fibers treated at intermediate stages confirmed the presence of various surface functions of modified fibers with a very high degree of substitution. The properties obtained are strongly improved for reinforcements containing covalent fiber–fiber contacts. Tensile, tearing and bursting tests performed on dry mat reinforcements showed increases in the tensile index, elongation at break, tensile stiffness, burst and tear indexes of 519%, 355%, 201%, 304% and 421%, respectively. Resin transfer molding (RTM) was used to fabricate epoxy composites made of click chemistry-treated short fiber flax mats at a fiber volume content ( V f ) of 40%. Tensile tests results showed the positive effect of the click chemistry treatment, with increases in the tensile modulus, strength and strain at break of 41.5%, 64.3% and 30.8%, respectively. Marked improvements in strength and Young's modulus were obtained for composites made of pre-compacted and cross-linked flax-mat preforms.

By embedding optical fiber sensors into fiber preforms and utilizing liquid molding processes such as resin transfer molding (RTM), intelligent composite materials with self-sensing capabilities can be fabricated. In the liquid molding process of these intelligent composites, the quality of the final product is highly dependent on the resin flow and impregnation effects. The embedding of optical fibers can affect the microscopic flow and impregnation behavior of the resin; therefore, it is necessary to investigate the specific impact of optical fiber embedding on the resin flow and impregnation of fiber bundles. Due to the difficulty of directly observing this process at the microscopic scale through experiments, numerical simulation has become a key method for studying this issue. This paper focuses on the resin micro-flow in RTM processes for intelligent composites with embedded optical fibers. Firstly, a steady-state analysis of the resin flow and impregnation process was conducted using COMSOL 6.0 obtaining the velocity and pressure field distribution characteristics under different optical fiber embedding conditions. Secondly, the dynamic process of resin flow and impregnation of fiber bundles at the microscopic scale was simulated using Fluent 2022R2. This study comprehensively analyzes the impact of different optical fiber embedding configurations on resin flow and impregnation characteristics, determining the impregnation time and porosity after impregnation under different optical fiber embedding scenarios. Additionally, this study reveals the mechanisms of pore formation and their distribution patterns. The research findings provide important theoretical guidance for optimizing the RTM molding process parameters for intelligent composite materials.

Liquid composite molding (LCM) is a class of fast and cheap processes suitable for the fabrication of large parts with good geometrical and mechanical properties. One of the main steps in an LCM process is represented by the filling stage, during which a reinforcing fiber preform is impregnated with a low-viscosity resin. Darcy’s permeability is the key property for the filling stage, not usually available and depending on several factors. Permeability is also essential in computational modeling to reduce costly trial-and-error procedures during composite manufacturing. This review aims to present the most used and recent methods for permeability measurement. Several solutions, introduced to monitor resin flow within the preform and to calculate the in-plane and out-of-plane permeability, will be presented. Finally, the new trends toward reliable methods based mainly on non-invasive and possibly integrated sensors will be described.