Littérature scientifique sur le sujet « Laminate composite NCF »

Considering aeronautics requirements, academies and industries are developing matrixes and reinforcements with higher mechanical performance. The same occurs with the process where new studies focus on obtaining composites with suitable matrix/reinforcement interface. The use of epoxy resin and carbon fiber with high mechanical performance does not guarantee a composite with high mechanical properties, considering imperfections and void formation along the laminate in case of inappropriate processing parameters. The aim of this article was to analyze and quantify the mechanical behavior of polymer composite reinforced with continuous fibers using finite element methodology and postprocessing software simulation. In addition, the classical laminate theory and finite elements were used to simulate flexural and tensile tests of composite specimens. Simulation results were compared with experimental test results using a carbon fiber noncrimp fabric quadriaxial/epoxy resin composite processed by resin transfer molding. Although void volume fraction for structural materials presenting results under aeronautics requirements regarding of 2%, imperfections like lack of resin and impregnation discontinuity showed an influence in tensile and flexural experimental results. Experimental mechanical behavior decreased 10% of strength, in comparison with simulation results due to imperfection on impregnation measured by C-Scan map. Improvement in processing procedures could able to provide greater impregnation continuity, reducing defect formation and ensuring better matrix/reinforcement interface. As a final conclusion, the process plays a role as important as the characteristics of reinforcement and matrix and, consequently, the mechanical properties.

NCFs (Non-Crimp Fabrics) infused with epoxy resin are popular in the design of wind turbine blades and other complex systems due to their ability to conform to complex shapes. Past work in the development of a combination beam-shell modeling approach to simulate the forming of NCF composites has been demonstrated to capture the change in the orientations of the yarns during a forming process. The structural performance of these manufactured blades is often analyzed using finite element simulations that consider the material properties of the fibers and of the resin based on the rule of mixtures and orthotropic shells where the model is sectioned into zones that account for changes in the material properties due to variations in the orientations of the lamina and number of layers. With the availability of the beam-shell model, the use of zones can be removed if the individual contributions of the yarns (beam elements) and resin (shell elements) can be characterized and the orientations of the yarns resulting from a forming simulation can be used to account for the variations in the material properties of the composite throughout the blade. This research uses a combination of static flexure tests and impact modal tests to ascertain the material properties of the fibers and resin in a unidirectional and biaxial non-crimp fabric laminate plates. The material properties are used in a finite element model of the plate and the model is analyzed in flexure and in a free-free modal configuration to compare to experimental results. Two different approaches are used in the commercially available software Abaqus to model the plate. One approach uses a combination of beam and shell elements to represent the fibers and the resin, respectively. The other approach uses orthotropic shell elements to capture the unbalanced behavior of the fiber/resin composite. The beam/shell modeling approach better represents the overall behavior of a single-layer plate and can be extended to consider multiple plies.

Abstract New generation non-crimp fabric (NCF) offers an attractive thin and lightweight building block alternative in the design of composite materials and structures. Pre-assembly of multiple plies of parallel fibers, each laying in a different orientation would not require crimping of the fibers and would enable one-axis lay-up that can substantially reduce the labor, scrap, and manufacturing costs. A state-of-the-art tow-spreading technique enables ply thickness to be reduced to as low as one-third of the typical commercial high quality pre-preg ply thickness. The thin-ply NCF stacks result in well-dispersed plies of different fiber orientations and creates the so-called homogenized laminates without ply clustering. As an option, bi-angle thin-ply NCF offers two different fiber orientations with one being off-axis, e.g. at ϕ°, along with an on-axis 0° forming (0/ϕ) assembly. This allows to design in anisotropic properties within the NCF building block. An overview of several aspects of the thin-ply bi-angle NCF composites is provided to address associated benefits and opportunities in the lightweight structural composites design process.

Delamination, a form of composite failure, is a significant concern in laminated composites. The increasing use of out-of-autoclave manufacturing techniques for automotive applications, such as compression moulding and thermoforming, has led to increased interest in understanding the delamination resistance of carbon-fibre-reinforced thermoplastic (CFRTP) composites compared to traditional carbon-fibre-reinforced thermosetting (CFRTS) composites. This study evaluated the mode I (opening) interlaminar fracture toughness of two non-crimp fabric (NCF) biaxial (0/90°) carbon/thermoplastic composite systems: T700/polyamide 6.6 and T700/polyphenylene sulphide. The mode I delamination resistance was determined using the double cantilever beam (DCB) specimen. The results were analysed and the Mode I interlaminar fracture toughness was compared. Additionally, the fractographic analysis (microstructure characterisation) was conducted using a scanning electron microscope (SEM) to examine the failure surface of the specimens.

There has been a lot of interest in understanding the low-velocity impact (LVI) response of thermoplastic composites. However, little research has focussed on studying the impact behaviour of non-crimp fabric (NCF)-based fibre reinforced thermoplastic composites. The purpose of this study was to evaluate the LVI responses of two types of non-crimp fabric (NCF) carbon fibre reinforced thermoplastic laminated composites that have been considered attractive in the automotive and aerospace industry: (i) T700/polyamide 6.6 (PA6.6) and (ii) T700/polyphenylene sulphide (PPS). Each carbon/thermoplastic type was impacted at three different energy levels (40, 100 and 160 J), which were determined to achieve three degrees of penetrability, i.e., no penetration, partial penetration and full penetration, respectively. Two distinct non-destructive evaluation (NDE) techniques ((i) ultrasonic C-scanning and (ii) X-ray tomography) were used to assess the extent of damage after impact. The laminated composite plates were subjected to an out-of-plane, localised impact using an INSTRON® drop-weight tower with a hemispherical impactor measuring 16 mm in diameter. The time histories of force, deflection and velocity are reported and discussed. A nonlinear finite element model of the LVI phenomenon was developed using a finite element (FE) solver LS-DYNA® and validated against the experimental observations. The extent of damage observed and level of impact energy absorption calculated on both the experiment and FE analysis are compared and discussed.

Unidirectional non-crimp fabrics (UD-NCF) are often used to exploit the lightweight potential of continuous fiber reinforced plastics (CoFRP). During the draping process, the UD-NCF fabric can undergo large deformations that alter the local fiber orientation, the local fiber volume content (FVC) and create local fiber waviness. Especially the FVC is affected and has a large impact on the mechanical properties. This impact, resulting from different deformation modes during draping, is in general not considered in composite design processes. To analyze the impact of different draping effects on the mechanical properties and the failure behavior of UD-NCF composites, experimental results of reference laminates are compared to the results of laminates with specifically induced draping effects, such as non-constant FVC and fiber waviness. Furthermore, an analytical model to predict the failure strengths of UD laminates with in-plane waviness is introduced. The resulting stiffness and strength values for different FVC or amplitude to wavelength configurations are presented and discussed. In addition, failure envelopes based on the PUCK failure criterion for each draping effect are derived, which show a clear specific impact on the mechanical properties. The findings suggest that each draping effect leads to a “new fabric” type. Additionally, analytical models are introduced and the experimental results are compared to the predictions. Results indicate that the models provide reliable predictions for each draping effect. Recommendations regarding necessary tests to consider each draping effect are presented. As a further prospect the resulting stiffness and strength values for each draping effect can be used for a more accurate prediction of the structural performance of CoFRP parts.

This paper deals with detection of macro-level crack type damage in rectangular E-Glass fiber/Epoxy resin (LY556) laminated composite plates using modal analysis. Composite plate-like structures are widely found in aerospace and automotive structural applications which are susceptible to damages. The formation of cracks in a structure that undergoes vibration may lead to catastrophic events such as structural failure, thus detection of such occurrences is considered necessary. In this research, a novel technique called as node-releasing technique in Finite Element Analysis (FEA), which was not attempted by the earlier researchers, is used to model the perpendicular cracks (the type of damage mostly considered in all the pioneering research works) and also slant cracks (a new type of damage considered in the present work) of various depths and lengths for Unidirectional Laminate (UDL) ([0]S and [45]S) composite layered configurations using commercial FE code Ansys, thus simulating the actual damage scenario. Another novelty of the present work is that the crack is modeled with partial depth along the thickness of the plate, instead of the through the thickness crack which has been of major focus in the literature so far, in order to include the possibility of existence of the crack up to certain layers in the laminated composite structures. The experimental modal analysis is carried out to validate the numerical model. Using central difference approximation method, the modal curvature is determined from the displacement mode shapes which are obtained via finite element analysis. The damage indicators investigated in this paper are Normalized Curvature Damage Factor (NCDF) and modal strain energy-based methods such as Strain Energy Difference (SED) and Damage Index (DI). It is concluded that, all the three damage detection algorithms detect the transverse crack clearly. In addition, the damage indicator NCDF seems to be more effective than the other two, particularly when the detection is for damage inclined to the longitudinal axis of the plate. The proposed method will provide the base data for implementing online structural health monitoring of structures using technologies such as Machine Learning, Artificial Intelligence, etc.

Ce travail consiste à une étude expérimentale et numérique du comportement et de la résistance de matériaux composites stratifiés soumis à un impact faible vitesse/faible énergie. L’objectif principal porte sur le développement d’un modèle robuste capable de prévoir la réponse de composites stratifiés en statique et dynamique, en se basant sur des observations expérimentales précises. Des essais d’impacts ont été réalisés au moyen d’une tour de chute instrumentée par caméras rapide pour suivre l’évolution des endommagements en temps réel. L’étude éléments finis 3D d’impact en dynamique explicit permet de juger de l’applicabilité des critères de rupture et des méthodes d’évolution des dommages. Divers modèles d'endommagement progressif sont mis en œuvre pour prédire l'initiation et l'accumulation des dommages dans un stratifié composite NCF. Des éléments cohésifs sont également insérés entre les plis adjacents pour rendre compte de la délamination entre plis. Dans un deuxième temps, le modèle a été valider pour la simulation de manière fiable l’évolution des mécanismes jusqu’à la rupture, dans des situations de chargement quasi-statique. Dans ce cas, le composite NCF est modélisé à l’aide d’un modèle unitaire constitutif à l’échelle méso, et présentant des régions idéalisées de la matrice polymère et des mèches imprégnés. Le modèle unitaire idéalisé est défini sur la base de données provenant d’analyse d’image. La méthodologie proposée est générique, elle utilise une représentation par éléments 3D de la pièce pour l’analyse globale, ainsi que la non-linéarité de la matrice et la réponse local à l’endommagement
This work consists of an experimental and numerical study of the behavior and strength of laminated composites subjected to a low velocity/low energy impact. The main objective is to develop a robust model capable of predicting the static and dynamic response of laminated composites, based on accurate experimental observations. Impact tests have been performed using a drop tower instrumented with high-speed cameras to monitor the evolution of damage in real time. The 3D finite element study of impact in explicit dynamics allows to judge the applicability of the failure criteria and the damage evolution methods. Various progressive damage models are implemented to predict the initiation and accumulation of damage in an NCF composite laminate. Cohesive elements are also inserted between adjacent plies to account for inter-ply delamination. In a second step, the model has been validated to reliably simulate the evolution of the mechanisms until failure, under quasi-static loading situations. In this case, the NCF composite is modeled using a unitary constitutive model at mesoscale, and presenting idealized regions of the polymer matrix and impregnated wicks. The idealized unitary model is defined on the basis of data from image analysis. The proposed methodology is generic, using a 3D elemental representation of the part for the global analysis, as well as the non-linearity of the matrix and the local response to the damage

L’industrie aéronautique concentre ses efforts sur l’amélioration de la performance de ses avions, tout en réduisant leur poids et limitant l’impact environnemental. Une partie de cet objectif est assurée par l’utilisation des matériaux composites stratifiés à fibres longues. Les fissures matricielles, dans les plis où les fibres ont des orientations éloignées de la direction principale du chargement, sont le premier mode d’endommagement observable dans un stratifié. Tandis que ces fissures se propagent dans des tunnels et augmentent en nombre, deux proches fissures matricielles de deux plis voisins peuvent se croiser formant une enveloppe avec le bord libre. Des délaminations locales peuvent y être générées. L’évolution et l’interaction de ces deux modes d’endommagement ainsi que l’accumulation de l’endommagement sous des sollicitations spécifiques sont des informations cruciales pour bien comprendre les mécanismes et prévoir avec exactitude la dégradation des propriétés mécaniques du matériau endommagé. Ce mémoire aborde l’initiation et l’évolution des fissures matricielles et des délaminations inter-couches des matériaux stratifiés. Dans la première partie, des essais mécaniques en statique et en fatigue cyclique sont menés sur des stratifiés NCF ( Non Crimp Fabric) quasi-isotropes Epoxy/ fibres de carbone. L’objectif est de développer une méthodologie efficiente pour déterminer l’évolution de l’endommagement sous chargement cyclique tout en économisant le temps et le coût des tests et de la caractérisation. Un modèle simple basé sur la distribution de Weibull permet de prévoir la densité des fissures matricielles. Une partie des paramètres du modèle est déterminée par de simples tests quasi statiques et l’autre partie est déterminée grâce a un nombre limité des essais cycliques. Dans les régions où des fissures matricielles croisent le bord de l´échantillon, des délaminations locales se sont créées à cause d’un état de contraintes élevées. L’effet des paramètres du chargement appliqué sur la longueur moyenne de délaminations inter-couches est caractérisé et lié ensuite à la perte de rigidité résultante. Dans la deuxième partie, la présence du délaminage local et son effet sur la rigidité du composite stratifié sont examinés à l’aide d’une analyse numérique par éléments finis. La simulation était réalisée en traction unidirectionnelle pour composites stratifiés avec des longueurs de délaminage différentes, afin d’étudier l’influence de la progression des délaminations sur l’ouverture moyenne des lèvres des fissures matricielles et la réduction de la rigidité axiale. Les derniers résultats sont utilisés pour simuler le comportement du composite dans le cas de flexion 4-points. La rigidité de flexion est considérablement réduite par les fissures matricielles accompagnées de délaminations. Une approche, basée sur le concept de la rigidité effective du pli endommagé est utilisée. La matrice de rigidité effective obtenue est alors une fonction de la densité des fissures matricielles dans les plis et de la longueur de délamination développée entre les plis du stratifié. La rigidité effective est utilisée pour déterminer la rigidité de flexion pour le stratifié endommagé. La courbature ainsi calculée est en bon accord avec celle obtenue par une modélisation 3D FEM dans le cas de la flexion 4-points ou il y a les deux modes d’endommagement
Aerospace industry is devoted to improving the aircraft performance while reducing its weight and limiting the emissions. Part of this objective can be accomplished with the use of high-performance long fibre reinforced polymer laminated composites. Being the first mode of damage under loading, intralaminar cracks initiate at the free edge of the off-axis plies and propagate along the respective fibre orientation. While these cracks grow as tunnels and increase in number, at some point two close cracks in plies of different off-axis orientation could intersect forming an envelope with the free edge. As loading continues, local delamination is expected within this envelope. The evolution and interactions of the different damage modes and the accumulation of damage under a specific loading are crucial in order to have a good understanding of the mechanisms and hence an accurate prediction of the mechanical properties´ degradation. This thesis is devoted to initiation and evolution of intralaminar cracking in plies and interlayer delamination in composite laminates. In the first part, quasi-isotropic Carbon Fibre/ Epoxy non-crimp fabric (NCF) laminates were studied under both quasi-static and cyclic loadings. The objective was to develop an efficient testing methodology for statistical damage evolution determination in Fatigue. The sequence of damage occurrences (intralaminar cracks in the different layers, delaminations at the different interfaces) loaded under quasi-static and tension-tension fatigue is first captured. To save characterisation time and costs, a simple model for predicting intralaminar cracking in laminates under cyclic loads was proposed and validated under low stress cyclic loads and low crack density. The model is based on Weibull distribution for the probability of cracking where part of parameters is obtained in quasi-static tests and part in a limited number of cyclic tests. The predictions of dependency of the cracking on the stress and number of cycles are validated against experimental observations of cracking in the 90-plies of quasi-isotropic NCF laminates as well as in tape based cross-ply laminates. In position where intralaminar cracks meet the specimen edge, local delaminations initiate due to the high 3D stress state. The delamination is further assisted by cracks in other off-axis plies, usually linking them. The average delamination length dependence on loading parameters is characterized and linked with the extent of the laminate stiffness reduction, showing using a simple ply-discount analysis that delaminations are the main reason for very large axial modulus reduction. In the second part, local delaminations and their effect on laminate stiffness are analysed using FEM. Expressions for the crack opening displacement (COD) determined using FEM are obtained and a modelling approach based on GLOB-LOC is performed for intralaminar crack case with local delaminations starting from the intralaminar crack. The delamination length is used as a parameter and studies are performed for different materials. Strong effect of delaminations on COD and on the axial modulus of the laminate is found. Finally, the last findings are used to simulate the damaged composite laminate behaviour in 4-point bending test. The bending stiffness of the laminate is significantly reduced by intralaminar cracks with delaminations. An approach, using the concept of the effective stiffness of the damaged ply is used. The so obtained effective stiffness matrix is a function of intralaminar crack density in the ply and the delamination length. The effective stiffness is used to calculate the bending stiffness of the damaged laminate. The laminate curvature calculated in this way is in a very good agreement with the curvature obtained in 3-D FEM simulations of the test with explicitly including cracks and delaminations in the model

Mechanical properties of a commercial out-of-autoclave non-crimp fabric epoxy prepreg (AR2527 NCF) composite were investigated in detail for the manufacturing plant elevations. To simulate the effects of elevation, the vacuum pump used for pulling vacuum from the laminate during debulking and curing was adjusted to provide two different vacuum pressures: 1) 96 kPa corresponding to 450 m elevation in Wichita KS, and 2) 84 kPa corresponding to 1550 m elevation in Denver CO. One laminate for each vacuum pressure was cured in an oven using manufacturer’s recommended cure cycle and subsequently, the laminates were machined into appropriate mechanical test coupons tested at room temperature. It was observed that the average short beam shear, combined loading compression, and flexural strength of the prepreg dropped 5%, 9%, and 12% as a result of 1100 m increase in the elevation. It was also observed that the two laminates had similar porosity (∼4%). The decrease in mechanical properties of the prepreg was attributed to the increase in resin content of the laminate.

Fiber-reinforced plastic (FRP) composites comprising unidirectional non-crimp fabrics (UD-NCFs) have recently gained considerable traction for fabrication of liquid composite molded parts. However, the variations in the microstructure of UD-NCF composites poses challenges in predicting and optimizing their properties. Additionally, their mechanical properties are influenced by process-induced defects, including variations in the relative position and shape of the tows, in-plane tow misalignment, out-of-plane tow crimping, and non-uniform fiber volume fraction. Thus, there is a need to develop robust tools to predict the mechanical properties of NCF composites that capture the critical manufacturing-induced defects. In this study, a multiscale finite element (FE) modelling approach is proposed to predict the in-tow (micro) and lamina-level (meso) effective properties of UD-NCF composites in order to support the use of artificial neural networks (ANNs) for the same purpose. First, a microscopic analysis was conducted to capture the material micro and mesoscale structure and process-induced defects. Second, microscale and mesoscale FE models were constructed based on the microscopic analysis, where process-induced defects were included within the associated representative volume elements (RVEs). The developed multiscale modeling approach was intended to generate an adequate amount of reliable training and testing data for ANN models. Finally, micro and mesoscale ANN models were developed, trained, and tested to predict the relations between inputs (i.e., constituent properties and material structure parameters) and outputs (i.e., in-tow and lamina-level effective properties). The trained ANN models reduced the calculation time from hours in multiscale FE modeling to seconds without sacrificing accuracy.

An experimental study was performed to characterize the evolution of damage in a unidirectional Non-Crimp Fabric (NCF) carbon fiber/snap-cure epoxy composite under in-plane quasi-static tensile loads. The NCF composites were manufactured using a High Pressure-Resin Transfer Molding (HP-RTM) process and comprised a fast-curing epoxy resin and heavy tow unidirectional carbon fiber NCF layers. Laminates with stacking sequences [0/±45/90] and [±45/0 ] were subjected to axial and transverse quasi-static tensile loads and an in-situ Edge replication (ER) technique was used to capture the damage evolution at predefined intervals. An imprint of the composite microstructure, as observed on the edges of a test coupon, was created on a cellulose acetate replicating tape, which was then observed under the microscope. The onset and progression of ply cracks and delamination, which were the two major damage modes present, were quantified and correlated with the stress-strain curves and changes in stiffness. The influence of stacking sequence and ply thickness are also captured.

The purpose of this research was to determine the influence of material properties on the impact response of a laminate, whereby specimens were fabricated and cured under a vacuum and high temperature using three types of pre-impregnated (prepreg), carbon fibers, namely unidirectional fiber, plain weave woven fiber, and non-crimp fiber (NCF). Each carbon fiber panel, usually known for its low-impact properties, of 16 plies underwent impact testing using a low-velocity impactor and visual damage inspection by C-scan in order to measure the damage area and depth, before and after impact testing. These panels were treated with UV exposure and moisture conditioning for 20 days each. Water contact angles were taken into consideration to determine the hydrophobicity and hydrophillicity of the respective prepreg materials. Experimental results and damage analysis showed that UV exposure and moisture conditioning showcased the variation in impact response and behavior, such as load-carrying capacity, absorbed energy, and impact energy of the carbon fiber panels. This study illustrates that non-crimp carbon fiber laminates were far more superior relative to load capacity than woven and unidirectional laminates, with the NCF-AS laminate exhibiting the highest load capacity of 17,244 lb/in (pre-UV) with only 0.89% decrease after UV exposure. This same laminate also had a 1.54% decrease in sustaining impact and 31.4% increase in wettability of the panel. Moreover, the study shows how symmetric and asymmetric stacking sequences affect the impact behavior of non-crimp fiber laminates. These results may be useful for expanding the capacity of carbon fiber, lowering costs, and growing new markets, thus turning carbon fiber into a viable commercial product.

The fiber waviness is inevitable in non-crimp fabric (NCF) reinforced composites. It is very challenging to accurately and efficiently predict the material behavior with fiber waviness. This work presents a machine learning approach to the prediction of material behavior of NCF composites under a compressive load. The out-of-plane fiber orientations are first extracted from micrographs of NCF laminates. A digital twinning process is followed to create finite element (FE) models with elementwise fiber orientations. Based on the FE models, a physics-based damage model is employed to generate high-fidelity simulation datasets, capturing the kink-band due to the fiber waviness. With the simulation datasets, convolutional neural network (CNN) models are developed to take the images of the fiber orientations and predict the corresponding stiffness, strength, and stress-strain curves of the NCF composites. The results show that the CNN models can capture spatial information of the fiber orientation and efficiently predict the corresponding material behavior with a high accuracy. In addition, the correlations of the fiber orientations and the final material behaviors are investigated based on the developed CNN models.

In this study, Symmetric cross-ply linear width tapered laminated composite beam is considered. Due to the variety of width tapered composite beams and the complexity of the analysis, no closed-form analytical solution is available at present regarding free vibration response. Therefore in the present work, the Ritz method is used for the free vibration analysis with considering uni-axial compressive and tensile force. The elastic stiffness of the width tapered composite beam is analyzed compared to uniform laminated composite beam. Free vibration which is significant to investigate the dynamic characteristics of the structure using Ritz method with and without effect of axial tensile and compressive force is analyzed. The analysis is based on 1D laminated beam theory. The governing equations are obtained by means of Hamilton’s principle. Tsai-Wu failure analysis is considered to find the tensile and compressive failure force for each ply in the laminate. Buckling analysis is conducted to find the critical buckling force for the laminated composite beam-column subjected to different sets of boundary conditions. Simply supported, Clamped-free, Clamped-Clamped edge boundary conditions are considered. A detailed parametric study is conducted on tapered composite beams made of NCT/301 graphite-epoxy to investigate the effects of the ratio of the width of the thick section to thin section, boundary conditions, effects of axial and compressive force on natural frequency and buckling analysis.

Abstract This manuscript introduces the challenges in the fabrication of graphene sheet reinforced non-crimp fabric (NCF) composite laminates and their influence on the interlaminar strength of the composite laminates. In the current work, the laminates were fabricated using non-crimp carbon fabric prepreg along with 50,120 and 240 μm thick graphene sheets at the mid-plane. Double Cantilever Beam (DCB) tests are done as per ASTM 5528 using INSTRON electromechanical testing system. Modified Beam Theory method used to compute Mode I fracture toughness, using load, displacement, specimen dimension, and crack opening displacement. The graphene sheets are brittle; little bonding between the graphene and matrix observed during the fabrication process results in a fragile interface. To overcome this problem, graphene sheets were converted into a lattice structure. The lattice structure used in the present research had horizontal, vertical, and square grids. Effects of sheet thickness, grid pattern were evaluated by Mode I fracture toughness, with and without nanoengineered enhanced laminates. Axio Image upright microscope used to compare the bonding at the midplane after the DCB test. The results indicate that the composite laminates fabricated using lattice graphene structure had better interlaminar strength than the laminates fabricated with straight graphene sheets.

<div class="section abstract"><div class="htmlview paragraph">Introducing a groundbreaking exploration into the mechanical properties of epoxy hybrid biocomposites, this study unveils a comprehensive analysis encompassing tensile strength, flexural properties, impact resistance, and hardness characteristics. The materials under scrutiny include hemp fiber (H), kenaf fiber (K), and coconut powder (CP), both in their untreated state and after undergoing alkaline processing. This research marks a significant milestone in understanding these sustainable materials and their potential for enhancing composite materials. In this endeavour, hemp is the basis material, while kenaf and coconut are filler elements. The total weight proportion of hemp was kept constant while the other two fibre fillers were changed. The unprocessed laminate sample significantly improves tensile, flexural, and impact strength with increasing coconut fiber loading. The improved interlinking capacity of the natural fibre composites (NFC) and an epoxy matrix is also to blame for the composite’s efficient resistance competency. Furthermore, the creation of powerful hydrogen bonds due to the increased polarisation of the epoxy matrix improved the bending characteristics of the hybrid natural composites. Untreated specimens’ impact strength was enhanced by up to 20% wt. of CP and K. The addition of more CP and K had a detrimental effect. Furthermore, as coconut fibre loading increased, the hardness value of unprocessed samples declined steadily. The mechanical properties of unprocessed material and chemically modified hybrid samples were evaluated. Compared to unprocessed composite samples, the results of alkali-treated composite samples demonstrate more excellent tensile, flexural, compression, impact strength, and hardness. SEM examinations on the fractured surface of hybrids revealed that surface alteration of the fibre occurred, which increased fibre-matrix interaction.</div></div>