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Highlights Nanofillers incorporated into polymeric matrices have gained attention for enhancing the properties of materials, particularly nanocomposites, with improvements observed in mechanical and dynamic mechanical thermal properties. Among the nanofillers, calcium carbonate (NCC), montmorillonite‐type clays (MMT), and graphene nanoplatelets (GNP) are prominent. The novelty of this study lies in investigating the dynamic compression behavior using the split‐Hopkinson pressure bar (SHPB) method on laminated composites prepared with reinforced High‐density polyethylene (HDPE) films, including the hybrid effect of calcium carbonate with montmorillonite and calcium carbonate with graphene. The objective of this research is to evaluate the influence of incorporating 1% by mass of nanofillers in laminated composites made with aramid fabric interspersed with nanoreinforced HDPE films. The laminated composites were assessed through bending tests, SHPB, and dynamic mechanical thermal analysis (DMTA). In addition to the samples containing NCC, MMT, and GNP, hybrid samples were prepared by intercalating films containing each nanofiller. The mechanical properties increased by 44%, 48%, and 55% in flexural strength and 46%, 69%, and 88% in flexural modulus for the composites prepared with calcium carbonate, graphene, and the hybrid graphene/calcium carbonate films, concerning the composite containing HDPE film. Moreover, the samples containing HDPE film with 1% GNP demonstrated a 79% increase in toughness, while the hybrid sample, which contained interspersed films of HDPE with 1% GNP and 1% NCC, exhibited a 46% increase in toughness. These results indicate a superior toughness response under high strain rates, contributing to enhanced energy dissipation. These two samples exhibited highly potential for ballistic industrial applications. Laminated composites reinforced with NCC, MMT, and GNP nanofillers. Mechanical properties of laminated composites assessed using the Split‐Hopkinson pressure bar test and dynamic mechanical thermal analysis. Impact strength improvement through the incorporation of nanofiller into laminated composites. Enhanced energy dissipation in laminated composite materials. [ABSTRACT FROM AUTHOR]

The performance of composite materials and structures at high-velocity impacts reaching or exceeding their ballistic limit is crucial for assessing their strength and safety in aerospace applications. In this highly transient impact regime, composite materials are subject to multiple complex failure modes and their properties are susceptible to strain rate effects, making very challenging the simulation and understanding of their ballistic impact performance. This study presents: (1) a multi-scale computational framework for predicting the ballistic limit of composite plates, and (2) experimental results of ballistic impacts on carbon/epoxy plates. The multi-scale model uses a micromechanical approach to account for strain-rate dependency, to calculate micro-stress effects on the matrix and fiber properties, and to predict their coupled effect on effective composite properties. Intralaminar damage initiation and evolution are identified using the maximum stress criterion, but the degradation of properties in the matrix and fibers is predicted with the micromechanics model. Mixed-mode damage laws are implemented to simulate delamination, which guarantees accurate and reliable results. The proposed multi-scale model has been implemented and integrated into ABAQUS/Explicit (VUMAT). Experimental results from high-velocity steel ball impacts on woven IM-65 Carbon/RTM6 epoxy composite plates conducted on a high-speed impact test bench are also presented including non-destructive evaluation of the types of damage and failure. The experimental results are finally used to validate the model predictions for the ballistic limit and the predicted types of damage and failure. [ABSTRACT FROM AUTHOR]

Composite structure is widely used in various technological fields because of its superior material properties. Composite structure detection technology has been exploring efficient and fast damage detection technology. In this paper, image-based NDT technology is proposed to detect composite damage using deep learning. A data set was established through literature, which contained images of damaged and non-damaged composite material structures. Then, five convolutional neural network models Alexnet, VGG16, ResNet-34, ResNet-50, and GoogleNet were used to automatically classify the damage. Finally, the performance of five pre-trained network architectures is evaluated, and the results show that RESNET-50 technology can successfully detect damage in a reasonable computation time with the highest accuracy and low complexity using relatively small image datasets. [ABSTRACT FROM AUTHOR]

In this work, the fabrication of graphene/Al laminate composites was achieved for the first time using the pulse current diffusion bonding method. A complete bonding interface without obvious defects was obtained under the conditions of 530 °C for 10min. The electron backscatter diffraction results revealed that the Al alloy recrystallized under the action of Joule heat, and fine grains were formed at the graphene/Al bonding interface. The transmission electron microscopy results showed that the bonding interface of graphene/Al was composed of graphene/amorphous layer + nanocrystalline MgO and Al 2 O 3 /MgO/Al. This research offers novel insights into the preparation of graphene/metal layer-stack composite materials. [ABSTRACT FROM AUTHOR]

Copyright of Przegląd Elektrotechniczny is the property of Przeglad Elektrotechniczny and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

In this study, a novel delamination detection method for composite materials is proposed through the innovative use of You Only Look Once v8 (YOLOv8), vibration analysis, and 2D continuous wavelet transform techniques. The method detects the location and size of damage more accurately than existing methods and avoids manual intervention in the detection process. Damage detection performed on the simulation dataset shows that the method is able to accurately identify the delamination location with IoU = 0.9906 and an average accuracy of 91.32%. The proposed method is then compared with the widely used YOLOv5 model, and the superior performance of the YOLOv8 model is verified, with a 37.93% improvement in training speed and 0.81% improvement in detection accuracy. In addition, an experimental dataset of four composite laminates with delamination damage is constructed. By using transfer learning, the performance of the pretrained network achieves a good precision up to 1. The method proposed in this study expands the range of tasks that can be accomplished by mode shape analysis and is very effective in real experiments. [ABSTRACT FROM AUTHOR]

Composite materials are widely used in aircraft due to the urgent need for high-quality structures in aerospace engineering. In order to verify the effectiveness of complex bolt repairs on composite structures, compression tests have been performed on three types (intact, damaged, and repaired) of composite plate specimens, and finite element simulation results of these three types' specimens were obtained. The experimental results show that for damaged composite laminates, the strength recovery after bolt repair can reach an impressive 107%, and the delamination propagation caused by over-buckling deformation is considered to be the main cause of failure, which also suggests that although bolt repair can improve the strength of the specimens, it has a limited ability to inhibit delamination propagation. The simulation results of the finite element model in this paper are in good agreement with the actual experimental results, and the maximum error does not exceed 7.9%. In conclusion, this paper verifies the suitability of the proposed repair scheme in engineering applications and the correctness of the modeling method for repaired composite laminates. [ABSTRACT FROM AUTHOR]

Today, there is a high demand and increasing trend for multifunctional composite materials and components due to the combination of a wide range of favorable properties. However, undesired deformation leading to delamination, curvature, cracks, or even complete fracture frequently occurs during the co‐sintering process of metal–ceramic laminates (MCLs). To solve these issues, experimental work highly relies on the time‐consuming trial‐and‐error principle. This work aims to develop a thermo‐mechanical‐metallurgical model capable of predicting the densification, deformation, and delamination of MCLs during the co‐sintering process. It is found that the developed model successfully considers the inhomogeneous relative density distribution and phase transformation of the steel tape. In addition, a thin interlayer formed by a mixed slurry in the MCLs is modeled as cohesive elements to simulate the delamination process. The developed model is systematically validated by the experimental measurements and observations in terms of densification, deformation, and delamination during the co‐sintering process of the investigated laminate variants. [ABSTRACT FROM AUTHOR]

Composite materials are often exposed to repeated impact in their industrial applications, which can have serious consequences on their mechanical performance. Therefore, the key purpose of this investigation is to study experimentally and numerically the response of laminated composites and sandwich composites. This involves evaluating their mechanical response and the damage accumulation under repeated impacts. The numerical models developed using the ABAQUS/Explicit software were validated against experimental data obtained through a modified Charpy test, where initial impact energies of 30 J, 40 J, and 50 J were applied to the two composite types under investigation. This was achieved by comparing commonly used parameters such as absorbed energy and induced energy. The results confirm that the first impact is responsible for the damage and that the repetition of the impact has no fundamental effect on the shape of the damage, but slightly increases its surface area. The numerical results made it possible to accurately predict the absorbed energy values and traces of damaged areas observed experimentally. [ABSTRACT FROM AUTHOR]

Plastics reinforced with glass fiber have a significant likelihood of being replaced by natural fiber hybrid composites (NFHCs). Making holes helps in part assembly, which is a crucial activity in the machining of composite constructions. As a result, choosing the right drill bit and cutting parameters is crucial to creating a precise and high-quality hole in composite materials. The present study employs the Taguchi approach to examine the delamination behavior and hole quality of ramie–bamboo composite laminates consisting of epoxy and nano-fillers (SiC, Al2O3) with feed, spindle speed, and three distinct drill bit types. Surface roughness and delamination are significantly influenced by feed and spindle speed, as indicated by the results of the analysis of variance. It was found that the spindle speed had a major impact on the delamination factor and surface roughness, while the feed and drill bit type had a minor influence. The surface roughness (76.5%) and delamination factor (66.7%) are significantly affected by the spindle speed. [ABSTRACT FROM AUTHOR]

Copyright of Acta Materiae Compositae Sinica is the property of Acta Materiea Compositae Sinica Editorial Department and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Fiber‐reinforced elastic laminated composites are extensively used in several domains owing to their high specific stiffness and strength and low specific density. Several studies were performed to ascertain the factors that affect the composite plates' dynamic properties. This study aims to derive a mathematical model for the dynamic response of the processed composite material in the form of an annular circular shape made of polyester/E‐glass composite. The mathematical model was developed based on modified classical annular circular plate theory under dynamic loading, and all its formulas were solved using MATLAB 2023. The mathematical model was also verified with real experimental work involving the vibration test of the fabricated composite plate. The composite plate was processed by reinforcing the polyester matrix with E‐glass fibers with a 50% volume fraction each by using the handy lay‐up method. After fabrication, the composite plate was tested with a universal vibration tester, where the plate was impacted and released to free vibration, and the deflection was measured experimentally to compare it with the theoretical value calculated from the derived model. The plate was tested under two boundary conditions, namely, simply and built‐in supported. The findings show good agreement between theoretical and experimental plate deflections at different angles, particularly at built‐in supported boundary conditions. Also, a higher natural frequency was recorded at this condition compared to others, and this may be ascribed to the higher shear stresses involved due to large moments at the ends along with supporting. Meanwhile, the real experimental spectrum of the built‐in condition was higher than others, as the sig view curve revealed. [ABSTRACT FROM AUTHOR]

Highlights It is more and more difficult to identify defects in carbon fiber composite materials due to the difficulty in making defect samples and the single signal analysis method. In order to better solve the problem of defect identification in carbon fiber composite materials, this study uses ultrasonic phased array equipment to quantitatively locate and detect carbon fiber composite laminates with embedded delamination defects, so as to more intuitively and effectively display the appearance of different delamination defects. The time domain analysis of the collected ultrasonic original signal and the time‐frequency domain analysis using wavelet packet are carried out. A total of 6 eigenvalues were extracted to reflect the ultrasonic signals of different delamination defects. By using genetic algorithm to optimize BP neural network, the recognition accuracy of delamination defects of different sizes is more than 95%, and the recognition accuracy of delamination defects of different depths is 100%, so as to realize the effective intelligent recognition of delamination defects of different sizes and depths of carbon fiber composites. This study is of great significance to improve the accuracy and reliability of defect identification of carbon fiber composite materials. The ultrasonic phased array equipment is used to quantitatively locate the carbon fiber composite laminates with embedded delamination defects, so that the appearance of different defects can be displayed more intuitively and effectively. Using time domain analysis and time‐frequency domain analysis based on wavelet packet, the combination of the two can more comprehensively extract the effective features of the defect signal. The BP neural network is optimized by genetic algorithm, and the results can effectively and automatically identify different layered defects, which lays a good foundation for the rapid and accurate identification of more defects in the future. [ABSTRACT FROM AUTHOR]

In this paper, the energy absorption performance of braided composite tubes under combined shear-compression loading is investigated. ABAQUS/Explicit is employed to analyze the energy absorption of braided composite tubes, and quasi-static compression tests are carried out. Braided composite materials absorb energy through the damage accumulation in laminate. Thus, to maximize energy absorption performance, a progressive crushing mode should be induced. While extensive research has been conducted on cases of axial loading, understanding of the energy absorption performance of braided composite tubes under combined shear-compression loading remains limited. Experimental results reveal that under both axial and combined shear-compression loading at 30 degrees, the braided composite tube exhibits a progressive crushing mode. The test results are utilized to validate the finite element model. Through finite element analysis, it is confirmed that the damage accumulation in laminate is maximized due to the induction of a progressive crushing mode. It means that the energy absorption principles of braided composites apply similarly to combined shear-compression loading, allowing for the maintenance of superior energy absorption performance of braided composites under various load angles. [ABSTRACT FROM AUTHOR]

This research focuses on investigating the buckling strength of thin-walled composite structures featuring various shapes of holes, laminates, and composite materials. A parametric study is conducted to optimize and identify the most suitable combination of material and structural parameters, ensuring the resilience of structure under both mechanical and thermal loads. Initially, a numerical approach employing the finite element method is used to design the C-section thin-walled composite structure. Later, various structural and material parameters like spacing ratio, opening ratio, hole shape, fiber orientation, and laminate sequence are systematically varied. Subsequently, simulation data from numerous cases are utilized to identify the best parameter combination using machine learning algorithms. Various ML techniques such as linear regression, lasso regression, decision tree, random forest, and gradient boosting are employed to assess their accuracy in comparison with finite element results. As a result, the simulation model showcases the variation in critical buckling load when altering the structural and material properties. Additionally, the machine learning models successfully predict the optimal critical buckling load under mechanical and thermal loading conditions. In summary, this paper delves into the study of the stability of C-section thin-walled composite structures with holes under mechanical and thermal loading conditions using finite element analysis and machine learning studies. [ABSTRACT FROM AUTHOR]

The determination and verification of repair tolerance of patch-repaired laminates based on progressive failure analysis method was studied. The axial tensile tests of intact, perforated, and repaired specimens of T700SC/EC240A composite laminates were carried out. The damage process of composite laminates under tensile load was numerically simulated using the progressive damage degradation model of 3D Hashin–Ye failure criterion. A method for determining the repair tolerance of patch-repaired laminates was proposed, and the upper and lower limits of repair the composite laminates were derived. The result verified by the strength index of Boeing Company showed that the method for determining the repair tolerance proposed is reasonable and feasible. [ABSTRACT FROM AUTHOR]

This study investigates the vibration behavior of delaminated cylindrical shells composed of symmetric cross-ply composite material are partially or completely filled with fluid. An incompressible, non-viscous and irrotational internal fluid is considered. The classical shell theory and Helmholtz's equation with the velocity potential function are employed to derive the governing equation for the vibration of delaminated symmetric cross-ply laminated cylindrical shells. The primary focus is to understand the impact of varying fluid heights, densities and velocities on the natural frequencies of the shells, as well as the effects of shell length, thickness-to-radius ratio, and delamination's position in the thickness and circumferential directions. The study findings indicate that the natural frequencies decrease considerably as the height of the fluid increases and that the delamination position significantly influences the observed frequency variations. Moreover, the internal fluid density and shell length affected natural frequencies. This research contributes not only to our knowledge of the behavior of cylindrical shells with delamination and fluid filling but can also assist in designing structures that mitigate undesirable vibrations and promote the creation of more efficient and dependable structures. [ABSTRACT FROM AUTHOR]

Developing constitutive models that can be used to model composite structural systems subjected to impact loads where modeling damage, failure, and delamination are critical is a challenging task. Often processing experimental data to develop the composite material model and, especially, the delamination model can be tedious, subjective, and error prone. In this paper, procedures for characterizing the behavior of laminated unidirectional composites (UDCs) are explained. First, laboratory tests are conducted to obtain the orthotropic material properties of a commonly used composite, IM7-8552. The obtained data are used in the MAT_213 model in LS-DYNA. Second, fracture-related tests, i.e., double-cantilever beam (DCB) and end-notched flexure (ENF) tests, are conducted to obtain the load-displacement responses. Finally, an inverse analysis approach is used by combining response surface methodology (RSM) and gradient-based numerical optimization to find the optimal values of the traction-separation law (TSL) parameters to build the constitutive model for modeling delamination. The developed cohesive zone element (CZE) model is then validated using the experimental results of a quasi-isotropic tension test. It is shown that the overall process of analyzing the experimental data and building a finite-element model is simpler, and the results from the validation test indicate that the developed methodology can yield accurate predictions. [ABSTRACT FROM AUTHOR]

In recent decades, composite materials have been widely used in several fields. The challenge in recent years has been to find an effective and automatable repair technique for these materials. Low-speed impact tests were carried out on panels made from prepregs in carbon fibre and epoxy resin. An innovative repair technique has been tested by injecting resin into the delamination due to the impact event. After the first impact, some panels were repaired and re-impacted, while others were impacted twice consecutively. The data analysis and damage detection by an ultrasound technique demonstrate that the absorbed energy of the twice-impacted panels is lower than that of the repaired ones, demonstrating a configuration similar to that of the panels impacted only once. The results of this research have demonstrated the effectiveness of the repairs. [ABSTRACT FROM AUTHOR]

Copyright of Acta Materiae Compositae Sinica is the property of Acta Materiea Compositae Sinica Editorial Department and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Accurate modeling of layered composite structures often requires the use of detailed finite element models which can sufficiently resolve the kinematics and material behavior within each layer of the composite. However, individually discretizing each material layer into finite elements presents a prohibitive computational expensive given the large number of thin layers comprising some laminated composites. To address these challenges, an 8‐node layered solid hexahedral finite element is formulated with the aim of striking an appropriate balance between efficiency and fidelity. The element is discretized into an arbitrary number of distinct material layers, and employs reduced in‐plane integration within each layer. The chosen reduced integration scheme is supplemented by a novel physical stabilization approach which includes layerwise enhancements to mitigate various forms of locking phenomena. The proposed framework additionally supports the inclusion of interlaminar enhanced displacements to better represent the kinematics of general layered composite materials. The described element formulation has been implemented in the ParaDyn finite element code, and its efficacy for modeling laminated composite structures is demonstrated on a variety of verification problems. [ABSTRACT FROM AUTHOR]

AbstractComposite materials are widely used in various aircraft due to their high specific strength, stiffness, corrosion resistance, and robust design flexibility. However, when subjected to complex loading conditions, composite structures are susceptible to damage, necessitating prompt repair upon aircraft return. Analyzing the re-damage process of repaired structures is crucial for assessing aircraft structural reliability, lifespan, and determining whether a repeat flight is warranted. In this study, a prediction method was proposed for re-damage behavior through meso-modeling and energy analysis of the repaired composite bolted joint. First, this article established a meso-mechanical model for composite laminates, analyzed force transfer characteristics at the fiber − matrix interface, and derived equations for stress field. Additionally, a strain energy distribution model was developed for composite bolted repaired joint near fibers and repaired area, proposing a damage prediction method based on the strain energy criterion. This method could anticipate the location, type, sequence, and magnitude of damage. Finally, simulation calculations yielded mechanical characteristics of the repaired area under typical load conditions, while loading tests verified the feasibility of the prediction method. This study offered an effective means of predicting performance degradation in composite structures and provided a vital direction for optimal spacecraft structure repairing methods and parameters. [ABSTRACT FROM AUTHOR]

Composite materials are increasingly used in a broad range of applications due to their recognizable mechanical properties and the high strength-to-weight ratio. The aim of the current study is to improve the mechanical properties and fracture toughness of composite laminates. Several types of fabrics, such as glass, carbon, and Kevlar, and micro-particles are adopted to create composite laminates via the vacuum infusion method. The mechanical performances of the proposed laminates were evaluated via tensile and flexural strength tests. Moreover, the impact strength tests were conducted to examine their dynamic performances. Results showed that woven laminates such as glass woven, carbon woven, and Kevlar woven composites with micro-particles revealed better tensile properties compared with those without micro-particles. For instance, enhancement in the Young's modulus with around 5%, 6%, and 13% were resulted from the glass, carbon, and Kevlar fabrics with fillers, respectively. Furthermore, higher impact strength and fracture toughness were obtained from the laminates of glass, carbon and Kevlar with inclusion of thermoplastic particles. For example, the glass, carbon and Kevlar fabrics composites with fillers samples showed improvement in the fracture toughness with around 24%, 17% and 14%, respectively. In addition, numerical simulation findings of flexural failure load and damage failure modes were in accordance with experimental results both qualitatively and quantitatively. [ABSTRACT FROM AUTHOR]

Quasi-brittle materials such as composite laminates, concrete, and toughened ceramics are subject to size effects in which the nominal strength decreases with increasing specimen size. Analyzing the joining of such materials is very important. Mechanically bolted joints are a widely used and suitable method for joining composite laminates in aircraft materials. Two-parameter cohesive laws—linear, constant, and exponential—were implemented analytically to analyze tearing, bearing stress, and remotely applied stress. An extended 2-D finite element model was created to validate the remote applied stress. The model provides reasonably acceptable results that can be used as fast design data for the selection of such materials and optimization of composite bolted joints. [ABSTRACT FROM AUTHOR]

This study focuses on optimizing carbon/epoxy laminate configurations to maximize the flutter speed of composite structures using a Fast Tree Regression algorithm. Initially, a seed dataset was created, using finite element method (FEM) modal analysis for common stack-ups used in composite fins and UAV components. The FEM analysis, based on the Lanczos algorithm for extracting modal frequencies in bending and torsion, was verified through experimental modal analysis using an AS-4/3501-6 composite system. Custom software was developed to interface with the FEA modal software, enabling the generation and augmentation of laminate dataset scenarios. The seed dataset was expanded until the coefficient of determination (R2) reached at least 0.95. Various regression algorithms, including Fast Forest Regression, Fast Tree Regression, Sdca Regression, and Lbfgs Poisson Regression, were evaluated. The Fast Tree Regression algorithm was selected for further analysis due to its superior performance. This algorithm was applied to a design space of nearly 2000 potential laminate candidates, focusing on symmetric lay-ups to avoid undesirable coupling between bending and torsion in UAV and missile control surfaces. The final optimized lay-ups, exhibit the highest Delta function values (the squared difference of modal frequencies in torsion and bending), indicating the expected highest flutter speeds. The results demonstrate the efficacy of tailored composite materials in achieving specific aerodynamic performance goals. [ABSTRACT FROM AUTHOR]

AbstractCarbon fiber-reinforced polymer (CFRP) is prone to machining defects, including burrs and tearing, during milling. These defects are closely associated with interface delamination while milling force plays a crucial role in their occurrence. In this paper, a nonlinear explicit finite element (FE) model is developed to predict the milling force and analyze the delamination damage occurring during the milling of unidirectional CFRP (UD-CFRP). The proposed FE model is validated through numerical comparison with experimental data for milling force. Moreover, a detailed study is conducted to examine the influences of spindle speed, feed rate and depth-of-cut on the side-milling performance and damage response of UD-CFRP. This study provides valuable insights into the effects of machining parameters on milling force and delamination damage in CFRP, thereby supporting the optimization of machining technology for this composite material system. [ABSTRACT FROM AUTHOR]

Introduction/purpose: The aim of this study is to examine the buckling and free vibration behavior of laminated composite plates reinforced with carbon nanotubes when various sources of uncertainty are taken into account with 1 the main focus being the existence of porosity. Methods: A porous laminated plate model is developed using a high order shear deformation theory. Different configurations of functionally graded aligned single-walled carbon nanotubes throughout the thickness of each layer are being investigated. The effective properties of materials are evaluated through the extended rule of mixture while considering an upper bound for the effect of porosity. The governing equations are derived and solved using the virtual work principle and Navier's approach. The validity of the current formulation is confirmed by comparing the results with the existing data from literature sources. The impact of numerous parameters such as porosity, carbon nanotube volume fraction, reinforcement distribution types, lamination scheme, and the number of layers on the buckling and free vibration responses is investigated in detail. Results: A key finding of this study is the significant reduction in buckling resistance of laminated FG-CNTRC plates due to porosity, contrasting with the minor impact on the free vibration response. Conclusion: The results of this paper emphasize the critical role of porosity in structural integrity and provide novel insights into the behaviour of advanced composite materials. [ABSTRACT FROM AUTHOR]

To investigate the load-bearing capacity and failure modes of unidirectional fiber-reinforced laminates subjected to uniaxial loads, finite element analyses were conducted to predict mechanical responses such as plastic accumulation and damage evolution. The Ladeveze constitutive model based on the 2D continuum damage theory was introduced and a user material subroutine was developed based on this model to consider the plastic behavior of the composites, where the isotropic plastic strengthening was assumed. Subsequently, a LS-DYNA finite element simulation model for unidirectional laminate plates was established to explore typical failure behaviors under loading conditions of longitudinal tension, longitudinal compression, transverse tension, and in-plane shear, respectively. A comparative analysis with experimental results was carried out to validate the efficacy of the developed subroutine. Finally, a logarithmic rate-dependent correction function was introduced to predict the damage modes of composite materials under various strain rate loads. The sensitivity of the rate effect in unidirectional fiber-reinforced laminates and its correlation with load-bearing components were investigated. [ABSTRACT FROM AUTHOR]

This paper presents a mesoscale damage model for composite materials and its validation at the coupon level by predicting scaling effects in un-notched carbon-fiber reinforced polymer (CFRP) laminates. The proposed material model presents a revised longitudinal damage law that accounts for the effect of complex 3D stress states in the prediction of onset and broadening of longitudinal compressive failure mechanisms. To predict transverse failure mechanisms of unidirectional CFRPs, this model was then combined with a 3D frictional smeared crack model. The complete mesoscale damage model was implemented in ABAQUS®/Explicit. Intralaminar damage onset and propagation were predicted using solid elements, and in-situ properties were included using different material cards according to the position and effective thickness of the plies. Delamination was captured using cohesive elements. To validate the implemented damage model, the analysis of size effects in quasi-isotropic un-notched coupons under tensile and compressive loading was compared with the test data available in the literature. Two types of scaling were addressed: sublaminate-level scaling, obtained by the repetition of the sublaminate stacking sequence, and ply-level scaling, realized by changing the effective thickness of each ply block. Validation was successfully completed as the obtained results were in agreement with the experimental findings, having an acceptable deviation from the mean experimental values. [ABSTRACT FROM AUTHOR]

This study analyzed the effect of incorporating graphene nanoplatelets in the fiber-matrix interphase on the behavior of a multiscale composite laminate based on carbon fibers and epoxy resin subjected to contact loads. The selected loading mode was the contact between an elastic surface and a cylinder. The multiscale composite material used was a quasi-isotropic laminate with graphene nanoplatelets (GnPs) added at the fiber-matrix interface. The specimens were prepared with 0.0%, 0.1%, and 0.25% by-weight GnPs. Laminate beams were used according to the ASTM D7264 standard, and contact was studied in two configurations, applying the load at the edge of the laminate and in the other, in the plane of the test pieces. The normal strains in the contact region were determined experimentally using the interferometric Moiré technique. These results were compared with estimations using the Hertz contact theory and the finite element method (FEM). The normal strains in the contact area of specimens with fibers modified with 0.1% GnPs were lower than those with 0.25% or fibers without surface modification. Excellent agreement between the experimental results along lines in the contact zone with those estimated with the FEM. The normal strains in a direction perpendicular to the applied load obtained by the Hertz theory for the maximum deformation were slightly higher than those obtained by FEM. Except for those calculated for the normal strain in εy for the load in the direction of the thickness, although the distribution was very similar to those obtained by FEM as well as the experimental one. [ABSTRACT FROM AUTHOR]

In the past decade, polymer‐based glass fiber‐reinforced laminate composites have gained significant popularity in various mass transit applications, including marine, aircraft, and automotive industries. However, it is crucial to consider the degradation and potential failure of these materials, especially in mass transit networks. To address this concern, fractographic analysis has emerged as a valuable approach for investigating fracture surfaces, extracting vital information, and facilitating the development of new materials. Furthermore, it sheds light on the underlying physical mechanisms that contribute to composite failure. This paper primarily focuses on examining flaws, failure modes, and performing fractography analysis on fiber‐reinforced polymer (FRP) laminate composites subjected to various loading conditions such as tension, compression, flexure, impact, shear, and fracture. Fractography, as an indispensable method, plays a pivotal role in the comprehensive development of composite structures and has become a reliable tool for composite engineers. The outcomes of this study are expected to serve as a foundation for identifying areas that require further investigation in terms of fracture analysis and failure modes specific to FRP composite materials, particularly those used in marine applications. Highlights: Introduction to FRP laminate composites in marine structures.Concise analysis of failure modes in FRP laminate composites.SEM fractography review of FRP laminate composites under varied loading conditions.Comprehensive study on tensile, flexural, impact, compression, shear, and fracture toughness failure modes.Summarization of identified defects in FRP composites. [ABSTRACT FROM AUTHOR]

Stability and vibration control are major challenges for applications in which laminated composite beams are being used. Using composite base materials with higher strength and/or using appropriate layout orientation are the two potential methods to improve the dynamic performance of laminated composite structures. However, using composite materials with higher strength significantly increases the manufacturing cost. Recently, layers/segments of Magnetorheological (MR) fluids have been added to the common laminated beams, the so-called MR-laminated beam, to improve the dynamic characteristics of such structures. The present work investigates the effect of base materials and applied magnetic field on the dynamic response of MR-laminated beams. Different composite materials, including E-glass, carbon fiber, and Kevlar, have been used as base materials to build the sandwich MR-laminated beam. The hollow spaces of the sandwich beam are filled with MR fluid to fabricate a testing sample for experimental purposes. A modified layerwise theory, N-layer, has been used to determine the vibration response of the structures. It is concluded that applying a magnetic field increases the natural frequency of the MR-laminated beam. In fact, applying 1400-Gauss magnetic fields to a low-cost material like E-glass provides the same natural frequency as that of the fiber-carbon without magnetic fields. [ABSTRACT FROM AUTHOR]

The article examines the accuracy of homogenization processes in describing the behavior of materials with microstructure. It discusses how composite materials such as laminates or fiber-reinforced plastics are produced by cleverly combining individual material components at the microscopic level. Homogenization allows for the mathematical prediction of the effective behavior of such composite materials. The article also addresses the homogenization of the wave equation for materials with periodic microstructure. It is shown that classical homogenization is unable to capture the long-term change in waveforms. It is emphasized that homogenization results should be viewed with caution as they may not adequately represent reality. [Extracted from the article]

In defense and military applications, the growing use of radar technology necessitated the development of effective stealth solutions for military equipment like drones and fighter jets. This paper explored a new approach that glass fiber mat coated with various concentrations of grapheme embedded polyvinylidene fluoride (PVDF) nanofibers using electrospinning technique and stacked the Graphene/PVDF/Glass fiber mat layers by epoxy resin and hardener to form the glass fiber laminate composite by hand layup technique to enhance the electromagnetic wave absorption. These research findings demonstrated that composite materials were more successful than metals at absorbing electromagnetic waves. The tailored composite showed above 80% increase in electromagnetic absorption over conventional metal in the X-band (8–12 GHz), although having a minimum thickness of 3 mm. According to X-ray diffraction, PVDF/Graphene nanofibers had improved electroactive β-phase behavior when compared to pure PVDF nanofibers. The PVDF/graphene nanofibers which have an average diameter of 80–160 nm, were seen using scanning electron microscopy. The tailored composites also had simple configuration and mechanical characteristics that were improved when compared to plain glass fiber laminate composite. In comparison to all other configurations, experimental findings showed that the composite with 0.5 wt% Gp/PVDF had a wide band absorption of above 90% in all the frequencies. This innovative method of fabrication of the tailored Gp/PVDF nanofibers coated glass fiber laminate composite provided a promising strategy in the manufacture of military equipment and stealth fighters. [ABSTRACT FROM AUTHOR]

Biostructures found in nature exhibit remarkable strength, toughness, and damage resistance, achieved over millions of years. Observing nature closely might help develop laminates that resemble natural structures more closely, potentially improving strength and mimicking natural principles. Bio-inspired Carbon Fiber-Reinforced Polymers (CFRP) investigated thus far exhibit consistent pitch angles between layers, whereas natural structures display gradual variations in pitch angle rather than consistency. Therefore, this study explores helicoidal CFRP laminates, focusing on the Non-Linear Rotation Angle (NLRA) or gradual variation to enhance composite material performance. In addition, it compares the strength and failure mechanisms of the gradual configuration with conventional helicoidal and unidirectional (UD) laminates, serving as references while conducting transverse tensile tests (out-of-plane tensile). The findings highlight the potential of conventional and gradual helicoidal structures in reinforcing CFRP laminates, increasing the failure load compared to unidirectional CFRP laminate by about 5% and 17%, respectively. In addition, utilizing bio-inspired configurations has shown promising improvements in toughness compared to traditional unidirectional laminates, as evidenced by the increased displacement at failure. The numerical and experimental analyses revealed a shift in crack path when utilizing the bio-inspired helicoidal stacking sequence. Validated by experimental data, this alteration demonstrates longer and more intricate crack propagation, ultimately leading to increased transverse strength. [ABSTRACT FROM AUTHOR]

The crack propagation in composite material due to thermal loading and environmental conditions is a serious issue. The study of the fracture propagation in a composite laminate will help understand the response of the structures under various loads. In the present study, a composite laminate is modelled with an elliptical cut-out and the fracture behaviour of the structure under the application of the thermal load is studied. Finite element analysis was used to obtain the stresses in the structure. Thermal load is applied on the laminate in the form of a constant temperature. The temperatures used in the present study are 30°C, 80°C, 130°C, and 180°C. The stresses in the laminate increased with the increase in the thermal load. The stresses in the normal direction are major stresses in the structure. The stresses in the composite laminate at the thermal load of 180°C is nearly nine times the stress at the 30°C in certain conditions. [ABSTRACT FROM AUTHOR]

Fibre metal laminates (FMLs) are the most interesting composite materials of the past decade. They possess the properties of both polymer composites and metallic alloys. However, there is a problem with corrosion when the outer layers are made of aluminium or magnesium. The electrochemical changes that occur during the corrosion process and the mechanisms associated with the corrosion phenomenon are still being investigated. Recently, self-healing phenomena have emerged as a useful approach to prevent corrosion. However, there is limited research on the combination of FMLs and self-healing layers. Therefore, the main purpose of this article is to evaluate the self-healing ability of a magnesium/PEO layer based on microcapsules in a corrosion environment. It was observed that the corrosion mechanism in magnesium alloys is very complex. However, the use of a barrier layer with PEO treatment and microcapsules yielded positive anti-corrosion results. The FML samples were subjected to a 6-week corrosion test, and the addition of microcapsules to the layers showed positive results. In contrast, the samples without microcapsules exhibited intergranular corrosion. In the future, comprehensive tests using self-healing microcapsules in FMLs could greatly enhance their anti-corrosion properties and improve the integrity of the structure. [ABSTRACT FROM AUTHOR]

The use of thin-ply composite materials has rapidly increased due to their tailorable mechanical properties and design flexibility. Considering an adhesively bonded composite joint, peel stress stands out as a key contributor leading to failure among other primary stress factors. Therefore, the reinforcement of carbon fiber-reinforced polymer (CFRP) laminates throughout the thickness could be considered as an approach to improve the joint strength. Using thin plies locally between the conventional CFRP layers in a laminate can enhance the strength, as the sudden change in stiffness means that the load transfer is not monotonous. Consequently, the following study examined the effect of altering thin plies gradually throughout the thickness on the behaviour of the CFRP laminates when subjected to transverse tensile loading. To achieve this goal, the CFRP laminates were gradually modified by using different commercially accessible prepreg thin plies, leading to an improved overall structural performance by reducing stress concentrations. Besides conducting an experimental study, a numerical assessment was also carried out utilizing Abaqus software with a Representative Volume Element (RVE) at the micro scale. The comparison of reference configurations, which involved various thin plies with different thicknesses and traditional CFRP laminates, with the suggested gradual configuration, demonstrated a notable enhancement in both strength and material cost. Furthermore, the proposed RVE model showed promising capability in accurately forecasting the strength of fabricated laminates. [ABSTRACT FROM AUTHOR]

Natural fiber‐reinforced composites exhibit excellent mechanical properties. However, achieving a balance between excellent mechanical properties and optimal acoustic performance remains a challenge. In this study, four composite laminates with different stacking orders were fabricated using polyester fiber mats (WFs) and palm sheaths (WPs) through a hot‐press process. Moreover, the effects of different stacking orders on the mechanical and acoustic properties of the composite were investigated. The results revealed that the incorporation of polyester fiber felts and the modification of the layup sequence of WP and polyester fiber felts significantly improved the mechanical and acoustic properties of the composites. Scanning electron microscopy images revealed a strong bonding between palm fibers and polyester fibers at the epoxy resin interface. Compared with pure palm fiber composites, the alternately stacked palm fibers and polyester fibers (WP/WP/WF/WP/WF) exhibited the highest mechanical properties, with a significant enhancement of 142.67% and 16.90% in flexural and tensile strengths, respectively. Additionally, the peak absorption coefficient of polyester fiber felts, positioned in the surface layer of the composite material, within the 2580–3400 Hz frequency band significantly increased from 0.07 to 0.44. Therefore, this study indicates that modifying the stacking order improves the mechanical and acoustic properties of the composites, making them suitable for use in acoustic engineering materials for buildings and decorative panels for furniture, including perforated panels and acoustic screens. Highlights: The fabric‐like textured structure significantly enhanced the overall performance of the composites.The stacking order significantly influenced the overall properties of the composite.Alternately stacked polyester fiber felts and palm fibers exhibited excellent mechanical performance.The polyester fiber felts positioned on the surface layer of the composites exhibited superior mechanical performance.A laminate with "green" attributes and good acoustic properties was fabricated. [ABSTRACT FROM AUTHOR]

Under the background of poor plantation forests, shortage of timber resources, and rich bamboo resources in China, as a kind of biomass engineering material, laminated veneer lumber (LVL) has the advantage of efficiently utilizing the existing resources. Due to its excellent mechanical properties, it can realize the standardization and serialization of the production of other characteristics, and has shown a broad application prospect. Combined with the development of China's wood-based panel industry, this paper outlined the origin and development of LVL, focused on analyzing the structural characteristics of LVL from the perspective of composite mechanics, and introduced the characteristics of veneer grading and LVL billeting. Moreover, the two types of LVL reinforcement methods, namely, phenolic resin impregnation and composite of fiber materials were summarized. Finally, the evaluation standards of LVL at home and abroad were compared and discussed, and a number of suggestions were then put forward based on the current situation of the development of China's wood construction industry and the problems existing in the application process of LVL. [ABSTRACT FROM AUTHOR]

The paper presents a critical review and new accomplishments on the equivalence of the first-order displacement-based zigzag theories for laminated composite and sandwich structures. Zigzag theories (ZZTs) have widely spread among researchers over the last few decades thanks to their accuracy in predicting the response of multilayered composite and sandwich structures while retaining the simplicity of their underlying equivalent single-layer (ESL) theory. The displacement field consists of two main contributions: the global one, able to describe the overall structural behaviour, and the local layer-wise one that considers the transverse shear continuity at the layer interfaces that describe the "zigzag" displacement pattern typical of multilayered structures. In the framework of displacement-based linear ZZTs, various assumptions have been made on the local contribution, and different theories have been deduced. This paper aims to provide a unified formulation for first-order ZZTs, highlighting some common aspects and underlying equivalencies with existing formulations. The mathematical demonstrations and the numerical examples prove the equivalence of the approaches to characterising local zigzag enrichment. Finally, it is demonstrated that the kinematic assumptions are the discriminants of the ZZTs' accuracy. [ABSTRACT FROM AUTHOR]

The aim of this research is to investigate basalt as a natural mineral-based fibre together with a vitrimeric resin as a sustainable alternative to standard composite materials. Vitrimers combine the properties of thermoset and thermoplastic polymers, enabling the repair of specimens and hence prolonging the lifetime of the composite material. The micro-mechanical characteristics between the basalt fibres and the vitrimer resin are reported and shown to match those of a standard Skyflex K51 epoxy resin. Discontinuous (4 mm) basalt fibres were employed to produce aligned discontinuous fibre-reinforced composites (ADFRCs) using the high-performance discontinuous fibre (HiPerDiF) technology. The mechanical characteristics of the laminates were investigated through tensile testing and the fracture zones were analysed under a scanning electron microscope. By normalising the results by their respective fibre volume fraction, it was discovered that the vitrimer–basalt ADFRCs exhibited, on average, a 4% higher strength and a 25% higher stiffness compared to their basalt epoxy counterparts. The repair potential of the vitrimer ADFRC specimens was explored during low-temperature compression repair. Two approaches were tested using double-sided local- and full-patch repair. Both successfully recovered a significant amount of their prime strength. In conclusion, the potential of the sustainable vitrimer–basalt composite is shown by its competitive mechanical performance. Combining this with the manufacturing flexibility, repair potential, and recyclability of the material, the vitrimer–basalt composite seems to be a competitive alternative to standard glass epoxies. [ABSTRACT FROM AUTHOR]

This study presents the effect caused by the saline environment (artificial seawater) on the physical and tribological properties of laminated composite materials reinforced with aramid fibers when they are subjected to erosive wear by sand particles. Composite materials made by epoxy resin and reinforced with glass fiber, carbon fiber and hybrid fiber (aramid with carbon) were studied. The laminates were superficially reinforced with layers of Kevlar fiber and prepared by the vacuum-assisted resin infusion process. The samples were subjected to a seawater accelerated aging process at 70°C for 1122 h. To reproduce erosive wear conditions of marine structural components, sea sand was used as solid particle under conditions of 4.5 bar of pressure, impact speed of 4.7 m/s and impact angle of 90°. The results showed that aged materials absorb more impact energy with respect to unaged counterparts, causing less material loss and a less depth in the wear track. The information generated by this research work may serve for the design and durability analysis of marine structures such as tidal turbine blades. [ABSTRACT FROM AUTHOR]

This study explores the fire behavior of wood–glass and jute–glass hybrid laminates, with a focus on the influence of jute and wood veneers as new materials for composite production. Five-layer hybrid laminates were manufactured using the vacuum infusion process (VIP). Combustion and carbonization performances were assessed using a cone calorimeter based on the ISO 5660 method. This study evaluates flammability through key parameters including ignition time, heat release rate, and smoke production. The results indicated that the ignition time was significantly longer (ca. 64 s) for the glass–jute laminate (GJGJG), compared to the wood–glass laminate (WGWGW) (ca. 53 s). The heat release rate of laminates containing organic components was higher than the sample composed only of glass mat (G5) but their rates were all lower than the polyester reference resin. WGWGW, compared to the GJGJG sample, was able to produce a good-quality protective shield and, therefore, postpone the occurrence of the heat release peak. In this way, the fire growth rate index (FIGRA) best performance was accomplished by the WGWGW sample (2.7 ± 0.3 kW/m2 × s), which was even better than that of the G5 sample. The total-smoke-released value was highest for polyester, 7361 ± 839 m2/m2, followed by WGWGW, 2873 ± 188 m2/m2, and J5, 2484 ± 216 m2/m2. Among the hybrid laminates, the best performance was obtained by GJGJG, 1860 ± 49 m2/m2, but compared to the G5 laminates, it was only ~36% higher. The specific extinction area (SEA) is a smoke parameter related to the mass of the samples; the best result was obtained by WGWGW with 697 ± 31 m2/kg. Finally, the neat polyester and all laminates achieved UL 94HB classification, with firing rates below 40 mm/min. [ABSTRACT FROM AUTHOR]

The study of the failure mechanisms of a composite material is essential for the efficient design of structures. The analysis of the effect of transverse biaxial loads, both at micromechanical and macromechanical level, is required for an integral vision of the whole mechanism of damage. In a previous work by the authors a transverse biaxial testing campaign was performed on cruciform specimens; in the present work a FEM model that successfully reproduces the coupons elastic state is presented in order to understand the failure occurrence and to make failure predictions avoiding the complexity of the experimental process. [ABSTRACT FROM AUTHOR]

We employ the Baker–Campbell–Hausdorff formula to derive closed-form expressions for the effective properties, including emergent Willis coupling, of a one-dimensional heterogeneous poroelastic medium consisting of a periodically repeating two-layer unit-cell. In contrast to the elastic and fluidic analogs, the Willis coupling of this periodic poroelastic medium does not vanish in the low-frequency limit. However, the effective wavenumber and impedance of this asymmetric lamellar material demonstrate symmetric reflection and absorption behavior that is indicative of symmetric structures in the low-frequency limit due to the effect of Darcy's law on the dynamic effective density, which is inversely proportional to frequency. These closed-form expressions are validated against results obtained by direct numerical evaluation. The scattering coefficients, particularly the two reflection coefficients for incidence from either side of a finite length asymmetric structure, are different at non-zero frequencies but still in the metamaterial limit and are correct when the Willis coupling is included. The results show that asymmetry in poroelastic layers results in direction-dependent absorption coefficients, one of which could be optimized based on layer properties and asymmetry factors. As a consequence, the frequency range of validity of these scattering coefficients is wider when the Willis coupling matrix is accounted for than in its absence. This work paves the way for better control of elastic and acoustic waves in multiphase materials by considering poroelastic behavior. [ABSTRACT FROM AUTHOR]

Composite materials are increasingly used in aircraft structural components with complex structures like L, C, or T shapes, which can cause delamination failure in the thickness direction under complex loading. This research focuses on the experimental investigation of the effect of different adhesive reinforcement phases with an adhesively bonded external patch to examine the residual strength and delamination resistance of repaired glass/epoxy curved samples. The damaged region in curved samples was repaired using adhesive reinforcement phases like neat epoxy, chopped glass fiber, and particulate glass fiber, along with adhesively bonded external patches like hybrid patches of glass/Kevlar (HP G/K), glass/carbon (HP G/C), and intraply patch carbon/Kevlar (IP C/K). The findings show that chopped glass fiber HP G/C patch-repaired curved samples had a curved beam strength (CBS) and interlaminar tensile strength (ILTS) recovery of 222.87% and 149.54%, respectively, as compared to damage area removed samples. In addition, it exhibited higher peak force, residual strength, and less elongation when compared to HP G/K and IP C/K patch-repaired curved samples. According to the findings of this research, composite angle brackets in aircraft structural components can be repaired utilizing an adhesively bonded HP G/C patch filled with chopped glass fiber at the dressed site. Highlights • The effect of patch hybridization on repaired curved laminates was studied. • Four-point bending test was conducted on indented and repaired samples. • Residual strength and delamination behavior were studied. • Chopped glass fiber HP G/C patch repaired samples had higher CBS and ILTS. • Delamination onset and propagation were assessed using Photographic images. [ABSTRACT FROM AUTHOR]