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Highlights Artificial intelligence (AI) techniques are increasingly used for structural health monitoring (SHM) of polymer composite structures. However, to be confident in the trustworthiness of AI models, the models must be reliable, interpretable, and explainable. The use of explainable artificial intelligence (XAI) is critical to ensure that the AI model is transparent in the decision‐making process and that the predictions it provides can be trusted and understood by users. However, existing SHM methods for polymer composite structures lack explainability and transparency, and therefore reliable damage detection. Therefore, an interpretable deep learning model based on an explainable vision transformer (X‐ViT) is proposed for the SHM of composites, leading to improved repair planning, maintenance, and performance. The proposed approach has been validated on carbon fiber reinforced polymers (CFRP) composites with multiple health states. The X‐ViT model exhibited better damage detection performance compared to existing popular methods. Moreover, the X‐ViT approach effectively highlighted the area of interest related to the prediction of each health condition in composites through the patch attention aggregation process, emphasizing their influence on the decision‐making process. Consequently, integrating the ViT‐based explainable deep‐learning model into the SHM of polymer composites provided improved diagnostics along with increased transparency and reliability. Autonomous damage detection of polymer composites using vision transformer based deep learning model. Explainable artificial intelligence by highlighting region of interest using patch attention. Comparison with the existing state of the art structural health monitoring methods. [ABSTRACT FROM AUTHOR]

Utilizing lightweight composites in aerospace vehicles plays a pivotal role in sustainability by improving fuel efficiency and mitigating emissions. However, due to their low interlaminar strength, delaminations and microcracking degrade their strength and stiffness properties. Through-thickness stitching improves the interlaminar strength, thus increasing the delamination tolerance of composite structures. Therefore, in this study, the influence of repeated periodic stitching patterns, stitched at three different angles (0, 45, and 90°) w.r.t. the transverse direction, on the flexural properties of stitched composites is investigated. The strain distributions of these specimens were obtained using a single continuous optical fiber bonded to the tensile surface of the specimens. The results show that stitching at a 45° angle produced lower strains and higher flexural strength and bending modulus when compared to the stitched and unstitched laminates. An increase of 32.3 and 47.4% in the flexural strength and bending modulus were obtained, respectively, with reference to the unstitched laminates. The failure morphology of specimens was also analyzed using optical microscopy and revealed that the stitch seams arrested delaminations. However, due to the 45° angle, the damage progressed along a longer distance, thus resulting in an increased ultimate failure load. [ABSTRACT FROM AUTHOR]

A sufficiently accurate prediction of mechanics behavior for thin-walled structures has always received much attention in the development of beam theory. This paper proposes a novel modeling approach for thin-walled beams in the framework of the absolute nodal coordinate formulation, in which cross-sectional warping and distortion effects can be explicitly captured by using the Taylor-like polynomials as the description of the kinematics of beam cross-section. Meanwhile, the linear Lagrange interpolation and the cubic Hermite interpolation are respectively adopted for the off-axis vectors of the position coordinates, where it is found that the thin-walled beam elements constructed from the latter have a faster convergence rate. Elastic forces and the Jacobian of the thin-walled composite beams are derived on the basis of nonlinear continuum mechanics, which will therefore contain a strong coupling between various deformations. Furthermore, their efficient calculation scheme is presented by separating the axial and transverse variables of shape functions and by expressing the vector and matrix quantities in terms of their components. By comparison to finite shell element, the accuracy and characteristic features of the new elements are illustrated. [ABSTRACT FROM AUTHOR]

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Wood-based laminated composites with excellent strength and toughness have attracted much attention, but it is a challenge to process fast-growing natural poplar wood with poor mechanical properties into high-performance laminated composites without the use of adhesives. In this study, natural poplar wood was delignified and TEMPO-oxidized by a "top-down" strategy to obtain a wood scaffold with a cellulose content of up to 98%, which was then used as a substrate and impregnated with Ca2+ and PVA to form a large number of hydrogen and ionic bonds within the wood. Finally, under the action of hot pressing, laminated composites with high tensile strength (237 MPa), flexural strength (246 MPa) and impact toughness (50.45 KJ/m2) were obtained, which also displayed excellent thermal stability and water resistance. This work demonstrates that the utilization of renewable fast-growing poplar wood as a substrate and glue-free bonding method can produce low-cost, sustainable and high-performance wood-based laminated composites. [ABSTRACT FROM AUTHOR]

Silicon carbide fiber-reinforced silicon carbide matrix ceramic composites (SiCf/SiC) are extensively utilized in high-temperature resistant materials in the aerospace industry. This study investigated the influence of stacking structure on the performance of SiCf/SiC laminated composite plates with film cooling. Initially, the thermal conductivity of cross-piled SiCf/SiC composites was determined using the laser flash analysis (LFA) method and differential scanning calorimetry (DSC) method. Subsequently, a representative volume element (RVE) model that reflected the stacking structure was established. The anisotropic thermal conductivity of the unidirectional SiCf/SiC layer was calculated using numerical methods and experimental results. Finally, numerical simulations were carried out to assess the film cooling effectiveness of various stacking sequences and layers. The results showed that the thermal conductivity values predicted by the RVE model for the laminated composite aligned well with the experimental results, and the unidirectional SiCf/SiC composite thermal conductivities at different temperatures were obtained. The stacking sequence impacted the temperature distribution near the film hole, with the [0-90-0] structure exhibiting a more pronounced effect on film cooling performance compared with the [0-90] and [0-90-90-0] structures. The performance of the film cooling in the laminated SiCf/SiC composites was consistent across all stacking layers [0-90]1, [0-90]2, and [0-90]3. The maximum difference in overall cooling efficiency was 1.7% between [0-90-0]1 and [0-90]1 and [0-90-90-0]1 [ABSTRACT FROM AUTHOR]

This study addresses the challenges of data scarcity and class imbalance in structural health monitoring (SHM) of composite structures. Data-driven SHM techniques that benefit from non-destructive evaluation (NDE) are used in various composite structures. However, the lack of damaged state data causes data scarcity and class imbalance problems that prevent robust diagnostics of composite structures. This study introduces a novel data-driven multi-class data augmentation method for composite structures, employing a multi-class generative adversarial network (MC-GAN) for the first time to generate synthetic data for multiple classes without the need for excessive experimentation or simulation. Additionally, the MC-GAN model is integrated with the convolutional neural network (CNN) to develop the MC-GAN-CNN model for autonomous data augmentation and delamination detection. The approach has been validated using experimentally obtained vibrational data for laminated composites. The damage detection using manual feature extraction showed overfitting and very high standard deviation during 10-fold cross-validation for various machine learning models. However, the proposed method suggested a more rigorous assessment with a mean accuracy of 99.72 ± 0.08 %. In addition, the proposed framework assists in handling the delamination detection problem autonomously without requiring hand-crafted statistical features with a good generalization capability.

The low ductility of titanium aluminide at room temperature has been one of the factors that severely limit its applications. In this study, Ti–6Al–4V (Ti64) alloys were combined with Ti–47Al–2Cr–2Nb (TiAl) alloys to make micro-laminated composites with optimal ply configurations to eliminate crack formation in TiAl and improve the ductility. A dual-material laser powder bed fusion (LPBF) system was used to fabricate the TiAl/Ti64 micro-laminate samples. The presence of cracks, elemental composition and mechanical properties were experimentally characterised and analysed to understand the effect of ply configuration and the mechanism of eliminating cracks. It was found that smaller TiAl ply thickness and lower TiAl volume fraction result in fewer cracks formed in the micro-laminates. Elemental composition analysis reveals that the Al content in the first two powder layers (i.e., 200 μm thick in total) of a TiAl ply is reduced to 10%–35% due to the partial mixture of the TiAl ply and the proceeding Ti64 ply in the LPBF. The reduced Al content leads to combined α-Ti, β-Ti and α2-Ti3Al phases instead of γ-TiAl phases, thus eliminating the formation of cracks within the first 200 μm thick region of the TiAl ply. This study demonstrates that crack-free and dense TiAl/Ti6 micro-laminated composites can be produced with the TiAl ply thickness reduced to 200 μm and the TiAl volume fraction reduced to 25% (Ti64 ply thickness 400 μm). Ductility of the crack-free micro-laminates at room temperature is comparable to or even exceeds the properties of TiAl/Ti64-type laminates made by other manufacturing processes, which may imply good machinability. Note that further research is required to investigate the properties and applications of the micro-laminates at elevated temperatures.

AbstractThe study explores the propagation of symmetric and antisymmetric fundamental Lamb waves in laminated composite strips, employing multi-field piezo-elastic plate models. The findings indicate the necessity of employing higher-order kinematic models to enhance the accuracy of wave propagation assessments. To further optimize computational efficiency, node-dependent kinematic models are utilized. The research delves into the tradeoff between reducing computational costs and maintaining result accuracy demonstrating a reduction of up to 60% in computational expenses in simple models while keeping the error below 1%. Two-dimensional wave propagation in laminated composite plates was further considered, expanding the scope due to material orthotropy. [ABSTRACT FROM AUTHOR]

Structural optimization has been shown to be an invaluable tool for solving large-scale challenging design problems, and this work concerns such optimization of a state-of-the-art laminated composite wind turbine blade root section. For laminated composites structures, the key design parameters are material choice, fiber orientation, stacking sequence, and layer thickness, however a framework for treating these simultaneously in optimization, on the current wind turbine blade scale, has not been demonstrated. Thus, the motivation and novelty of the present work is providing and demonstrating a general gradient-based approach applicable to wind turbine blades, where the key design parameters and structural criteria, i.e., buckling, static strength, and fatigue damage, are considered for multiple design load cases. The optimization framework is based on a variation of the Discrete Material and Thickness Optimization approach, where the thickness is directly parametrized, allowing for appropriately treating the sandwich parts of the blade. It is demonstrated how optimization leads to a design consisting of complex variable-thickness laminates, a good overall distribution of the structural criteria in the model, and a significant reduction in mass compared to the initial design. [ABSTRACT FROM AUTHOR]

The Mg-intermetallic laminated composites were fabricated using Mg sheets and Cu foils. The final microstructure of the composites consisted of alternating layers of unreacted magnesium and intermetallics. The mechanical response of the fabricated composites and pure magnesium was investigated under different loading directions by tensile and three-point bending tests at 20, 100, 150, 200 and 250°C. The fracture surfaces of the specimens after tensile and three-point bending tests were jagged, and cracks were spread mainly perpendicular to the layers of intermetallics. No cracks were observed along the Mg/intermetallic interfaces in any of the composites tested at any temperature. All composites tested at room temperature and elevated temperatures had higher yield strength, higher tensile strength, and higher flexural strength than pure magnesium tested under the same conditions. The laminated Mg-intermetallic composites could be an interesting alternative to the currently used magnesium alloys applied at elevated temperatures. [ABSTRACT FROM AUTHOR]

Flexoelectric effect is strengthened in dielectrics at nanoscale so that it could not be neglected. In this work, a laminated composite plate with flexoelectric core and two coverings of CNTRCs is modeled. The variational principles of the plate with generalized supporting conditions are derived considering both the flexoelectricity of the piezoelectric core and the reinforcement of the CNTRCs. According to it, the governing equation and boundary conditions with any supporting types are obtained. Then the analytical solutions to the displacements and resonant frequencies of the plate with two different boundary conditions for free vibration are given. The numerical results prove that the flexoelectric effect relies on the scale seriously. Moreover, the CNTRCs coverings can improve the bending stiffness of the whole plate. Therefore, the bending responses such as resonant frequency and bending deflection can be adjusted and optimized by changing the ratio of the CNTs to the matrix. It’s hopeful to provide the theoretical basis of numerical calculation of electronic devices with laminated structures at nanoscale. [ABSTRACT FROM AUTHOR]

This article proposes a framework for the damage assessment of and effect of temperature variations in laminated composites using Lamb waves and unsupervised autonomous features. A network of piezoelectric transducers is employed to generate data for 18 health states of a laminated composite plate. The data is processed with sparse autoencoder (SAE) for unsupervised autonomous features. The discriminative capabilities of the extracted features are confirmed by processing the feature space in the supervised and unsupervised frameworks of machine learning. The confusion matrices of supervised learning provided physical insights into the problem. The feature space was also visualized in two dimensions in an unsupervised manner through principal component analysis (PCA), which revealed physically consistent results for the effect of temperature variations, damage of different severity levels, and the undamaged paths between the actuator and sensors. The healthy state data and information on the paths between the actuator and sensors was processed via SAE for damage localization. The proposed approach can be employed for the autonomous assessment of composite structures for the presence of damage and variations of operating temperatures while using both supervised and unsupervised machine learning algorithms. [ABSTRACT FROM AUTHOR]

Metallic glass-reinforced metal matrix composites (MMCs) are in the focus of attention of many research groups due to the outstanding properties provided by a combination of ductile crystalline matrix and high-strength glassy phase. To date, many fabrication techniques have been used to form such composites. Most of them are based on pressure-assisted sintering of glassy and crystalline components. However, the selection of the heating temperature and holding time is challenging due to the low thermal stability of the metallic glasses (MGs). In this study, a solid-state magnetic pulse welding (MPW) technique was used for manufacturing laminated Ti-based composites with Zr-based MG reinforcement. The structure of the interfaces between Ti and MG layers was studied using light microscopy (LM), scanning electron microscopy (SEM), and synchrotron X-ray diffraction (SXRD). The experimental study was supplemented with smoothed-particle hydrodynamics (SPH) numerical simulations. The Ti-MG-Ti composite obtained by MPW possessed high quality of joint and had no macroscopic defects such as cracks or lack of fusion. The formation of a firm joint was provided by the plastic flow of titanium. Deformation processes in the titanium plates developed mainly in the interfacial zones, while the MG ribbons subjected to deformation by shear mechanism through the entire thickness. Due to the short-term thermal impact and high cooling rates, MPW retained a disordered structure of MG, despite local melting occurring at the interfaces and in shear bands. Tensile tests of composites containing 5 vol. % and 13 vol. % of MG phase showed that their strength follows the rule of mixtures. [ABSTRACT FROM AUTHOR]

AbstractThe industrial applications of singly curved shells significantly increased in modern engineering structures and several of those have non-uniform boundary conditions. A detailed relative performance study for the non-uniformly restricted shells can popularize their use further among practicing engineers. The literature review confirms that there is dearth of research studies in this area. This paper aims to fill up that void. A finite element code of C0 continuity combining von-Karman strains, first order shear deformation theory and eight noded curved elements is proposed. Wide variety of shell problems are solved for different boundary conditions, laminations, radii of curvatures, thickness, and plan dimensions. Relative nondimensional deflections and fundamental frequencies are studied for varying boundaries. It is concluded that although the performances of shells are comparable for different boundaries, the shells with CCCC edges offer better performances. These shells should have longer span along the arch direction, a symmetric 16°/-16°/-16°/16° laminate, side/thickness = 100, and radius of curvature/plan = 0.75 to achieve minimum deflection and maximum fundamental frequency. [ABSTRACT FROM AUTHOR]

Researchers have been challenged to improve the protective performance of composite armor materials. Herein, pure Al and Cu foils were used as raw materials and composited concurrently using ultrasonic additive manufacturing technology to study their microstructure and properties. A scanning electron microscope and universal testing machine were used to systematically study the microstructure and tensile properties of the material. Furthermore, the dynamic mechanical properties were investigated using Hopkinson rods, and the propagation law of shock waves in laminated composites was explored based on the theory of propagation of one-dimensional elastic waves in cyclic layered media. The results showed that ultrasonic solidification of the Al/Cu stacked composite interface between the generation revealed no new phases, and the mechanical bonding in the tensile experiment exhibited a maximum tensile strength of 167 MPa for the Al/Cu stacked composites. In the dynamic impact experiment, with the increase of air pressure, the strength of the material also increases, and its compressive strength can reach up to 813 MPa, while the energy absorption efficiency decreases, and the energy absorption efficiency can reach up to 80%. Analysis of the attenuation process of the shock wave in the laminated composites revealed that reaching five cyclic layers of the Al/Cu laminated composites reduced the intensity attenuation ratio can reach 63% of the total number of circulating layers, and the energy attenuation ratio can reach 77% of the total number of circulating layers, thus reaching an overall optimum material performance.

Carbon fiber reinforced polymer (CFRP) composites have been continuously replacing conventional metallic materials due to their excellent material properties. The orthotropic nature of CFRP composites makes them vulnerable to various types of damage. Among these, delamination stands out as the most common and severe form of damage. Therefore, deep learning based structural health monitoring (SHM) which performs autonomous health monitoring from sensor data have gained wide attention for delamination detection of CFRP composites. However, limited training data often restricts the application of these models for autonomous health monitoring. Therefore, the present research proposes convolutional neural network (CNN)-based pre-trained transfer learning method using ResNetV2 (RNV2) model to solve the data scarcity problem. The use of RNV2 model eliminated the need for developing the model from scratch and only required fine-tuning on the target composites dataset. The target dataset contained multi-class wavelet-transformed vibrational data obtained from CFRP specimens. The efficacy of the proposed approach is determined using various evaluation metrics on unseen dataset. The results of the validation demonstrated that the pre-trained RNV2 model can effectively perform SHM of CFRP composites even under limited data conditions.

SHPB simulation of TC4/2024AL/TC4, TC4/TA2/TC4, and TC4/Al3Ti/TC4 laminated composites under different impact velocities of strike bar was carried out by ANSYS/LS-DYNA. Then stress distribution of the laminated composites under impact loading was theoretically analyzed according to the one-dimensional stress wave theory. Influencing factors of stress distribution and energy attenuation were emphatically analyzed, including impact velocities of the strike bar, wave impedance of interlayer, and plastic deformation. The results show that, when the impact velocity is determined, impact resistance is negatively correlated with the impedance of the interlayer. Under certain conditions, impact resistance is negatively correlated with impedance of interlayer, and positively correlated with impact velocity. In addition, the accumulation of plastic deformation could make residual stress distribution along the position coordinate axis shows a trend of gradual increase from both sides to the middle position. [ABSTRACT FROM AUTHOR]

The progressive fatigue damage (PFD) model is a comprehensive method to simulate the fatigue damage behavior of laminated composites under multiaxial cyclic stress. The generalized material property degradation (GMD) technique is a component of the PFD model. Also, the fatigue life modeling of a UD ply under a uniaxial state of stress is a subcomponent of the GMD technique. The present article compares and evaluates the results achieved by using different fatigue life models within the GMD technique. For this purpose, three commonly used fatigue life models (the normalized fatigue life model, the Luders fatigue life model, and the unified fatigue life model) were considered. Based on the capabilities of these models in predicting the fatigue life of unidirectional plies, a combined fatigue life model is developed and integrated into the progressive fatigue damage model. The results demonstrate that using the combined fatigue life model improves the prediction accuracy of the PFD model. [ABSTRACT FROM AUTHOR]

In the present work, nonlinear mechanical response of laminated composite structures is investigated by a constitutive numerical model based on damage mechanics. A numerical method is included in progressive damage analysis to simulate the damage accumulation and failure response of composite structures under service load conditions. This model is capable of predicting the residual strength and residual stiffness of laminate with arbitrary lay-up and geometry. The state-of-the-art progressive damage model exploits a set of stress-based Hashin-type criteria and a set of appropriate degradation rule of ply discount. The constitutive model is developed wherein the damage initiation criteria are based on Hashin failure criterion for damage evolution. The proposed progressive damage model involves the steps of stress analysis, failure analysis, and material properties degradation. This work involves a comprehensive study of quasi-isotropic elliptical hole specimen to develop the failure model. Overall, the results of the exercise aid in design applications to predict the impact of progressive damage in aircraft composite structures under service loads. [ABSTRACT FROM AUTHOR]

This paper deals with an innovative nondestructive technique for composites (local-IET), which is based on the Impulse Excitation Technique (IET) and, in the presence of damage, assesses the degradation of the elastic properties of a local region of the laminate by reversibly clamping its boundaries. In this paper, a numerical analysis of the sensitivity of the local-IET to the delamination damage mechanism is conducted. Firstly, a Finite Element (FE) model of the local-IET test is determined through experimental investigations on undamaged composite laminates, which cover a wide range and are made of glass or carbon fibers, through resin infusion or pre-preg consolidation and with unidirectional or fabric textures. The vibrational response of a glass fiber composite with local delamination is then assessed with the local-IET. By modeling the delamination in the simulation environment, the effectiveness of the FE model in replicating the vibrational response, even in the presence of delamination, is shown through a comparison with the experimental results. Finally, the FE model is exploited to perform a sensitivity analysis, showing that the technique is able to detect the presence of delamination. [ABSTRACT FROM AUTHOR]

The main aim of this paper was to make rivet joints of metal-composites without drilling the laminated composites. Experimental and numerical approaches were used to show the efficiency of this manufacturing method and its effects on the energy absorption of the metal-composites joint under bending loading. In this research, E-glass/epoxy laminated composites were joined to Al 6061-T6 and ASTM A283 St Grade C. Various number of rivets, i.e., 1, 2 and 4, and two arrangements, i.e., square and diamond, were embedded in the laminated composites. Then, the single lap joints were tested under flexural loading. A 3D finite element (FE) analysis at the meso-scale was performed to compare the response of woven E-glass/epoxy composites with and without drilling. Since the meso-scale model could not be applied to simulate the considered single lap joint, a refined micro-blocks model was also proposed for the regions affected by the riveting process. The experimental results showed that the embedding method significantly improves the energy absorption of the joints. This improvement was around 15% and 28–62% for the Al/composites and St/composites samples, respectively. Besides, the samples with the diamond arrangement have the best flexural properties. The FE analysis demonstrated that the results obtained by the refined micro-blocks model compare well with the experimental data. [ABSTRACT FROM AUTHOR]

In this work, a firefly algorithm was implemented and used to optimise composite structures in the postbuckling regime. In the first case studied, the goal was to maximise the post-buckling load of a rectangular plate subjected, independently, to shear load and uniaxial compression. The orientations of the layers served as design variables, while a maximal transverse displacement was considered as a constraint. Next, a reinforced flat panel was studied, with the goal of maximising the shear load in the post-buckling regime while constrained by the Tsai-Wu criterion. The design variables were the positions of the stiffeners and the orientations of the layers of the laminate. The degree of improvement in the maximum post-buckling load depended on the specific problem and ranged from 2.5 to 36 % compared to baseline designs. The selection of the structures chosen for the analyses ensured that the firefly algorithm was tested with progressively more challenging optimisation problems. The results suggested that the firefly algorithm could be used in the design of laminated composite structures. [ABSTRACT FROM AUTHOR]

In this work, Ti/Al3Ti laminated composites were prepared by "explosive welding + heat treatment". On this basis, the microstructure and the fracture failure process of the laminated composites were analyzed using SEM and the in situ tensile test. The results show that no pure aluminum remains in the laminate composites and the bonding interfaces of the laminate composites still exhibit wavy-like bonding. When the Ti/Al3Ti laminated composites are subjected to continuous horizontal stress, cracks appear in the brittle layers first, and cracks begin to appear in the ductile layers after all the brittle layers fail. And the cracks generated in the brittle Al3Ti layers are diverse, making the Al3Ti layers absorb more horizontal stress. Cracks in the ductile layers will constantly propagate and deflect, thus increasing the toughness of the material. Therefore, the fracture failure mechanism of Ti/Al3Ti laminated composites is the combined action of brittle Al3Ti layers and ductile Ti layers. [ABSTRACT FROM AUTHOR]

Buckling behavior of laminated composites are entirely depends on the geometry and stacking sequence of layers. The different fiber paths as a result of the stacking sequence can affect the buckling properties of laminates. The aim of this paper is to determine the effect of fiber path on the buckling behavior of laminated composites using Yarn Interlacing Matrix (YIM). Different fiber paths were implemented by making hybrid/uniform laminates. Glass woven fabrics with different yarn architectures and epoxy resin were used to fabricate the 8-plies laminated composites in 25 × 25 cm2 with 25 × 8.5 cm2 aluminum sheet in middle layer by vacuum infusion process (VIP). The buckling test was carried out on the prepared samples using DARTEC testing machine with five replicates. In addition, the buckling behavior of laminates was simulated using ABAQUS software. The novelty of this study is to use the YIM in theoretical model and investigate the critical buckling load of hybrid laminate composite in pattern of weave and understand the effect of geometrical hybridization on critical buckling load. It showed that the critical buckling load for hybrid samples are larger than the uniform ones. Comparison between theoretical and experimental results of the critical buckling load showed a maximum error of 16% in predicting the critical buckling loads. Also, comparison between theoretical and experimental results of the critical buckling load showed a maximum error of 59.7% in predicting the critical buckling loads. The main outcome of this research is that the fiber path has a greater effect on the buckling behavior than the elastic modulus of the laminates; so that despite the lower elastic modulus, the critical buckling load of laminates with hybrid reinforcement is higher than that of laminates with uniform reinforcements. [ABSTRACT FROM AUTHOR]

Purpose: In comparison to traditional, constant stiffness laminates, variable stiffness composite laminates (VSCL) with curvilinear fibres represent an extra analysis effort. It is the purpose of this work to present and test a relatively simple optimisation procedure, in order to find the maximum fundamental frequency of vibration in bending and in in-plane vibrations. It is also intended to explain why certain fibre paths lead to higher frequencies. Methods: The optimisation is performed using a genetic algorithm (GA), which is described in detail. The bending and the in-plane plate models are based on the p-version Finite Element Method. Each model requires a small number of degrees of freedom, an important feature because applying the GA involves the solution of a large number of eigenvalue problems. In order to support the physical interpretation of the optimal designs, mode shapes and stress fields corresponding to some optimal solutions are illustrated. Results: Single- and multi-layer plates with different boundary conditions and fibre path types are studied. Fibre paths that lead to maximum fundamental frequencies are found and justified. The consequences that maximising the first frequency has on the higher-order modes of vibration are studied. Conclusion: The proposed optimisation and modelling methods are effective. Curvilinear fibres with the characteristics considered led to the maximum first natural frequency of vibration in a few cases, but not all. Particularly in in-plane vibrations, curvilinear fibres can provide major gains in comparison to straight fibres. The increase in the vibration frequency is accompanied by, overall, larger stresses. [ABSTRACT FROM AUTHOR]

The accuracy of a wavelet depends on the choice of the mother wavelet adopted. The present work aims to predict the free vibration behavior of laminated sandwich plates using wavelet finite element (WFE). Different kinds of mother wavelets, namely, B-spline wavelet on the interval (BSWI), Gaussian, Haar, Daubechies 6 (db6), Biorthogonal 3.7 (bior3.7), Coiflet5 (coif5), Symlets (sym8), Morlet, Mexican hat (Mh), and Meyer mother wavelets, are employed in WFE for predicting the frequencies. Both symmetric and unsymmetric laminates are studied using the proposed approaches. A wide range of problems, including the influence of the geometric and material properties and end conditions on the free vibration behavior of the laminated sandwich plates, are solved. The effectiveness of the WFE over the conventional finite element method in terms of computational efficiency is discussed. In conclusion, BSWI-based WFE method (WFEM) is found to be the most accurate and computationally efficient in predicting the free vibration behavior of laminated sandwich plates. The accuracy of the WFEM depends widely on the type of mother wavelet adopted. [ABSTRACT FROM AUTHOR]

In this study, quasi-static punch shear test was conducted on aramid fiber-reinforced composite (AFRC) laminates consisting of different ratios of graphene nanoplatelet (GNP), carboxyl (COOH) functionalized multi-walled carbon nanotube and their hybrid combinations. Two different punch nose geometries (conical and ogival) and two different support span-to-punch ratios (SPR = Ds/Dp = 2 and 4) were employed in the experiments. The results indicate that the ogival punch geometry causes deformation at a higher load while also reaching the maximum load at a lower displacement compared to the conical punch. Moreover, incorporation of nanoparticles increased the energy required for complete penetration compared to non-reinforced AFRC. In particular, the composite containing 0.2% GNP demonstrated the most significant increase in energy required for complete penetration, showing a remarkable 32.30% improvement with the conical punch configuration. Similarly, the 0.1% hybrid composite exhibited a substantial 42.13% increase in complete penetration energy under the ogival punch configuration. Although the energy required for complete penetration is expected to increase as the SPR ratio rises from 2 to 4, this trend is not particularly evident due to embrittlement caused by the nanoadditives. [ABSTRACT FROM AUTHOR]

Computational progressive failure analysis of carbon fiber reinforced polymer composite is of vital importance in the verification and validation process of the structural integrity and damage tolerance of modern lightweight aeronautical structures. Enhanced Schapery theory (EST) has been developed and applied to predict the damage pattern and load-bearing capacity of various composite structures. In this paper, EST is enhanced by a deep neural network (DNN) model, which enables fast and accurate predictions of matrix cracking angles under arbitrary stress states of any composite laminate. The DNN model is trained by TensorFlow based on data generated by a damage initiation criterion, which originates from the Mohr–Coulomb failure theory. The EST-DNN model is applied to open-hole tension/compression problems. The results from the EST-DNN model are obtained with no loss in accuracy. The results presented combine the efficient and accurate predicting capabilities brought by machine learning tools and the robustness and user-friendliness of the EST finite element model. [ABSTRACT FROM AUTHOR]

A new, innovative vibration cast-rolling technology of "electromagnetic stirring + dendrite breaking + asynchronous rolling" was proposed with the adoption of sinusoidal vibration of crystallization roller to prepare Ti/Al laminated composites, and the effect of sinusoidal vibration of crystallization roller on composite microstructure was investigated in detail. The results show that the metallurgical bonding of titanium and aluminum is realized by mesh interweaving and mosaic meshing, instead of transition bonding by forming metal compound layer. The meshing depth between titanium and aluminum layers (6.6 µm) of cast-rolling materials with strong vibration of crystallization roller (amplitude 0.87 mm, vibration frequency 25 Hz) is doubled compared with that of traditional cast-rolling materials (3.1 µm), and the composite interfacial strength (27.0 N/mm) is twice as high as that of traditional cast-rolling materials (14.9 N/mm). This is because with the action of high-speed superposition of strong tension along the rolling direction, strong pressure along the width direction and rolling force, the composite linearity evolves from "straight line" with traditional casting-rolling to "curved line", and the depth and number of cracks in the interface increases greatly compared with those with traditional cast-rolling, which leads to the deep expansion of the meshing area between interfacial layers and promotes the stable enhancement of composite quality. [ABSTRACT FROM AUTHOR]

The literature review on relative performances of laminated composite skewed shells confirms that research reports on bending performances of moderately thin, stiffened, laminated composite skewed cylindrical panels, using the geometrically nonlinear approach, are not available. This paper aims to fill that deficiency and proposes a finite element code combining eight-noded, doubly curved elements with modified Sanders' first approximation theory for thin shells and von Kármán-type nonlinear strains. Correctness of the proposed geometrically nonlinear bending formulation for skewed shells are verified through solutions of benchmark problems. The deflections, force, and moment resultants are reported for different skew angles, laminations, stacking sequences, radius of curvature, plan dimension ratios, and stiffener properties like orientations, numbers, and eccentric positions. The results are discussed critically which reveals that shells having curved edges free and straight edges clamped fabricated using 0°/90°/0° laminate offer the best performances. The biaxial stiffeners, nx = 7, ny = 7, show the minimum deflections and stress resultants. The skewed shells offer greater deflections and hence, must be avoided in industrial practices. [ABSTRACT FROM AUTHOR]

Inspired by the microstructures of shells, SiC fibers (SiCf) are introduced into Ti layers, creating hybrid layers of SiCf/Ti, which are combined with Ti2AlNb foils to prepare multilayer SiCf/Ti–Ti2AlNb hybrids in a hot-pressed sintering instrument. The solid-phase bonding interface, mainly including the α+β biphasic structures and B2-rich phases, guarantees an ideal interface connection between the SiCf/Ti and Ti2AlNb layers after the sintering. Herein, the SiC fibers-made SiCf/Ti–Ti2AlNb presents a higher tensile strength and elasticity modulus on the tensile instrument of Model No. Byes (2010), compared with Ti/Ti2AlNb. During the tensile process, the brittle fractures of SiCf first occur, and the loads are transferred to the bonding interface of the Ti2AlNb and Ti layers, generating the crack propagation and resulting in SiCf/Ti–Ti2AlNb fracture. This is mainly because the crack is extended in succession to the bonding interface that is composed of brittle phases such as O and α2, as well as ductile phases such as α, β and B2. This produces the ductile and brittle ruptures at the bonding interface, forming the ductile-brittle mixture fractures at the SiCf/Ti and Ti2AlNb interfaces. In the case of vertical fractures related to the fiber length, brittle fractures are observed on the SiC fibers, which produce high forces that affect their bonding interfaces, resulting in axial interstices and transverse fractures. These obtained results demonstrate a novel method for structural design and fabrication of the innovative composite materials.

The possibility of using the universal software ANSYS to study the concentration of interlaminar stresses near the free edges of laminated composites in a two-dimensional finite element formulation is considered. In this case, the cross-section of a rectangular four-layer composite plate of finite width with free side edges subject to uniform axial deformation is simulated. To create it, an original technique is proposed which consists in using thermal stress. The presented calculation results are in good agreement with the results of other authors.

The present paper explores the ballistic performance of B4C/6061Al laminated targets with the typical configurations of double-layer, sandwich and gradient impacted by 7.62 mm API projectile. Damage patterns were characterized and ballistic mechanism of B4C/6061Al laminated targets was revealed by damage analysis combined with finite element simulation. It is found no interlayer delamination occurs in all B4C/6061Al laminated targets even after being penetrated, which leads to a dependable comparison of different configuration without the interruption of delamination. The protection effect of the laminated configurations is better than that of the homogeneous target, except for the hard-soft-hard sandwich configuration. Among them, the gradient configuration is considered as the optimal configuration due to the supreme ballistic resistance. An important design principle of B4C/6061Al laminated composites is proposed to improve the ballistic performance.

Silicon carbide fiber-reinforced silicon carbide matrix ceramic composites (SiCf/SiC) are extensively utilized in high-temperature resistant materials in the aerospace industry. This study investigated the influence of stacking structure on the performance of SiCf/SiC laminated composite plates with film cooling. Initially, the thermal conductivity of cross-piled SiCf/SiC composites was determined using the laser flash analysis (LFA) method and differential scanning calorimetry (DSC) method. Subsequently, a representative volume element (RVE) model that reflected the stacking structure was established. The anisotropic thermal conductivity of the unidirectional SiCf/SiC layer was calculated using numerical methods and experimental results. Finally, numerical simulations were carried out to assess the film cooling effectiveness of various stacking sequences and layers. The results showed that the thermal conductivity values predicted by the RVE model for the laminated composite aligned well with the experimental results, and the unidirectional SiCf/SiC composite thermal conductivities at different temperatures were obtained. The stacking sequence impacted the temperature distribution near the film hole, with the [0-90-0] structure exhibiting a more pronounced effect on film cooling performance compared with the [0-90] and [0-90-90-0] structures. The performance of the film cooling in the laminated SiCf/SiC composites was consistent across all stacking layers [0-90]1, [0-90]2, and [0-90]3. The maximum difference in overall cooling efficiency was 1.7% between [0-90-0]1 and [0-90]1 and [0-90-90-0]1

This paper presents size dependent stability analysis a cantilever micro laminated beam embedded in elastic medium by using the modified coupled stress theory which includes the length scale parameter. The micro beam subjected to compressive load is considered as three composite laminas and embedded in elastic medium which is modelled in the Winkler foundation model. In the obtaining of the governing equations, the energy principle is used. In the solution of the buckling problem, the energy based Ritz method is implemented with algebraic polynomials. In order to accuracy obtained expressions and used method, a comparative study is performed. Many parametric studies are presented in order to investigate the buckling of laminated micro beams. For this purpose, effects of stacking sequence of laminas, geometric parameters, length scale parameter, fiber orientation angle, the parameter of elastic medium on critical buckling loads of laminated micro beams are investigated. [ABSTRACT FROM AUTHOR]

The continuous carbon fiber‐reinforced polyether ether ketone (CCF/PEEK) composites have been widely utilized in aerospace structures due to their excellent properties. However, the main load‐bearing structure in the next‐generation aircraft needs to withstand high temperatures up to 200°C, and the mechanical properties of CCF/PEEK composites show significant time‐/temperature‐dependence due to the viscoelastic nature of the PEEK matrix. Therefore, accurate predictions of the mechanical performance of CCF/PEEK composites under high‐temperature service conditions are the key issue for structural safety and life assessments and have therefore become a recent research focus. To address these challenges, this study established a bottom‐up analysis framework for the CCF/PEEK composites and employed the theoretical model and the finite‐element representative volume element (FE‐RVE) method to investigate the anisotropic viscoelastic properties of CCF/PEEK composites. We first built an anisotropic viscoelastic model of the unidirectional CCF/PEEK composites by integrating the generalized Maxwell into the bridging model. Upon this foundation, we further developed a viscoelastic laminate model capable of accurately predicting the thermoviscoelastic properties of multidirectional laminates. To verify the developed model, different kinds of FE‐RVEs were built and analyzed. Overall, there is good agreement among the model predictions, the FE‐RVE simulations, and the experimental results within a temperature range of 25–250°C. The developed model can be used to design the high‐temperature performance of CCF/PEEK composites with different fiber volume fractions, laminated configurations, or loading directions. Highlights: An anisotropic viscoelastic model of the unidirectional (UD) continuous carbon fiber‐reinforced polyether ether ketone (CCF/PEEK) composites is built.The viscoelastic laminate composite model is developed based on the UD CCF/PEEK composites model.The finite element representative volume element (FE‐RVE) simulation with fibers in a hexagonal or random array has better accuracy compared with the experimental results.The FE‐RVE simulation and the experimental results verified the developed model from 25°C to 250°C. [ABSTRACT FROM AUTHOR]

Laminated composite structures have a distinct inherent potential for optimization due to their tailorability and their associated complex failure mechanisms that makes intuitive design remarkably difficult. Optimization of such is a maturing technology with many criteria and manufacturing constraints having been successfully demonstrated. An approach for high-cycle fatigue is however yet to be developed in a gradient-based context. Thus, the objective of this work is to introduce a novel framework that allows for effective high-cycle fatigue optimization of laminated composite structures.Offset is taken in the Discrete Material and Thickness Optimization parametrization, which allows for simultaneous material and thickness selection for each layer that constitute a laminate. The fatigue analysis approach is based on accumulating damage from all variable-amplitude cycles in an arbitrary spectrum. As high-cycle fatigue behavior is highly nonlinear, it is difficult to handle in optimization. To stabilize the problem, damage is scaled using an inverse P-mean norm formulation that reduces the nonlinearity and provides an accurate measure of the damage. These scaled damages are then aggregated using P-norm functions to reduce the number of constraints. This is convenient, as it allows sensitivities to be efficiently calculated using analytical adjoint design sensitivity analysis. The effectiveness of this approach will be demonstrated on both benchmark examples and a more complicated main spar structure. [ABSTRACT FROM AUTHOR]

This manuscript deals with the static and dynamic buckling of plates with non-rectangular shapes. The plate has an uneven imperfection and is made of natural composite materials. The model is validated with the existing results. The static buckling loads and the first natural period of the plate are first evaluated. Then, the imperfections are incorporated in the form of the first five buckling mode shapes, and the plate is subjected to in-plane loads. The effect of imperfection and inclination of the edges on the behaviour is evaluated. It is observed that due to the difference in the first five buckling mode shapes of the plates, the plates do not show any definite trend in both nonlinear static loading and nonlinear dynamic loading cases. [ABSTRACT FROM AUTHOR]

Composite polymers are widely used in vibrating environments such as the aerospace, automotive, marine, and sports industries. Accordingly, composite materials are exposed to vibration at various periods. In this study, the effect of the vibration cycle on the mechanical properties of composite plates was investigated. The plates were vibrated at different revolutions. The tensile strength of these plates after vibration was examined, and these effects were compared with each other. As the vibration cycle increased, it was observed that tensile damage gradually occurred at different angles, and scanning electron microscopy (SEM) analysis revealed that the fibers were damaged at different angles. Accordingly, it was observed that the increased vibration cycle caused an angular fracture in the composite plates and decreased the tensile strength from 9.7 to 7.9 kN by nearly 23% as well as the elongation from 3.4 to 2.76 mm. [ABSTRACT FROM AUTHOR]

To understand the differences between the microstructure and stress states owing to uncoordinated deformation in different regions of a Cu–Al contact interface, the normal stress distribution at the contact interface of the Cu–Al composites and the Al metal adhesion on the peeling surface of the Cu layer are investigated by performing numerical simulations and experimental studies. The results show that the percentage of Al metal adhered to the Cu side gradually increased from the edge to the central region. This is mainly because the central area of the contact interface bore a larger normal stress than the edge position, and when the interface normal stress exceeded 470 MPa, the pressure threshold value required for the extrusion of virgin metal from the surface-hardened layer on the Al side was satisfied. The effect of the initial Cu:Al thickness ratio on the degree of interfacial coordination is investigated, and the degree of coordination of the contact interface was observed to improve and then worsen with the increase in the initial Cu:Al thickness ratio (from 3:9 to 8:4). For composites with a Cu:Al thickness ratio of 4:8, the interface was well coordinated, and the bond strength reached 6.13 MPa, corresponding to a 173.7% improvement compared with the Cu–Al composite with more severe stress concentration (8:4).

Flexible photonics, characterized by their planar design and integrated features, have surfaced as a promising technology to unlock new possibilities for multifunctionality within fiber reinforced polymer composite materials. A comprehensive review of current progress, challenges, and opportunities associated with flexible photonic integration into carbon and glass fiber reinforced polymers is provided. A systematic examination of the literature has revealed several flexible photonic technologies that have demonstrated potential for integration in composite components to monitor performance in manufacture, service, and reuse. The review highlights the advantages and limitations of the current state-of-the-art in flexible integrated photonics for making assessments of compatibility with carbon and glass fiber reinforced polymer structures. By examining proof-of-concept demonstrations, the improved performance and novel functionalities that can be achieved for industrial applications are identified. The challenges associated with the integration process, such as durability and scalability are discussed in the context of the manufacturing processes required to create composite components. The concept of integrating flexible photonics in composite structures is relatively new, hence the paper closes by highlighting opportunities for further research and development in this field.