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Inspired by the cross-laminated hierarchical structure and flexible interface of high toughness Strombus gigas shell, the "fiber-metal-polymer" laminated composites with different laying modes including cross-laminated structure and interfacial properties were designed, and the corresponding damage and toughening mechanisms were investigated. It shows that the cross-laminated structure, accompanying soft interface modification by metal ultra-thin strip and polymer can optimize the full-field stress distribution and failure behavior, then achieve maximize energy absorption and ensure good strength (ultimate strain and toughness increased to 352% and 127.5%, respectively compared to unidirectional laminated material), which may provide optimization strategies for the design of lightweight composites. [ABSTRACT FROM AUTHOR]

A nonlinear finite element dynamic instability analysis of laminated composite stiffened plates subjected to in-plane harmonic edge loading is presented in this article along with the linear and nonlinear dynamic response study. The eight-noded isoparametric degenerated shell element and a compatible three-noded curved beam element are used to model the stiffened plates. Bolotin method is applied to analyze the dynamic instability regions in linear case. Incremental Harmonic Balance (IHB) method is applied to solve the nonlinear frequency response equations and Newmark-β method is used to solve the linear and nonlinear time history response equations. [ABSTRACT FROM AUTHOR]

This study analyses the bending of helicoidal laminated composite plates, inspired by biological helicoids. The analysis employed Navier solution-based shear deformation theory. Five helicoidal schemes—recursive, exponential, semi-circular, linear, and Fibonacci—were studied. Plate thickness stress distribution investigations have been done. The helicoidal distribution parameter greatly affects stress variation. Helicoidal designs have homogeneous stress distribution across the thickness of the plate, unlike quasi-isotropic schemes. Helicoidal lamination designs also eliminate stress channeling caused by cross-ply and quasi-isotropic systems. Also, the helicoidal schemes exhibited the lowest value for the transverse shear stresses ( σ ¯ yz ). HIGHLIGHTS: Bending analysis of bio-inspired helicoidal laminated composite (BILC) plates. Kinematics in framework of parabolic shear deformation theory. Stress distribution across thickness of BILC plates for first time are analyzed. BILC plates are effective compared to quasi-isotropic laminates. The study can be used to construct pressure vessels, domes, automobiles, and aerospace structures. [ABSTRACT FROM AUTHOR]

AbstractLaminates experience three-dimensional singular stress near their free edges due to elastic mismatches between layers, which can cause delamination. This paper critically evaluates methods for predicting free edge delamination and highlights the limitations of conventional strength-of-materials and fracture mechanics approaches. The Theory of Critical Distances (TCD) uses a material-dependent critical distance parameter, while Finite Fracture Mechanics (FFM) employs a combined stress-energy criterion without needing a predefined length parameter. This review compares TCD and FFM, also discussing Cohesive Zone Models and Phase-Field Models, and aims to guide the selection of appropriate methods for analyzing free edge delamination. [ABSTRACT FROM AUTHOR]

A simple modeling is proposed to estimate the elastic-plastic behavior of two-phase isotropic composites made of interpenetrated co-continuous phases. This nonlinear modeling, without equivalent so far, is based on the extension of an explicit Laminate System (LS) scheme proposed previously for linear elastic behavior of such co-continuous composites. Considering monotonic radial loadings, the effective nonlinear stiffness of bi-continuous elastic-plastic composites is estimated from stepwise linearizing the composite overall and phase behaviors using a classical secant linearization procedure. The efficiency of this proposed modeling is checked on some comparisons with rare experimental literature data and with other classical analytical homogenization estimate schemes. [ABSTRACT FROM AUTHOR]

In this article, wave propagation in a one-dimensional (1-D) composite periodic frame structure is analyzed using spectral finite elements (SFE) method together with Bloch's theorem. Each element in the periodic frame structure is modeled as a first-order shear deformation theory (FSDT) beam element and wave equations for the beam elements are derived using FSDT considering axial, flexural, and shear deformations. Next, these equations are solved using the frequency domain SFE method to obtain an elemental dynamic stiffness matrix which on assembly gives the dynamic stiffness matrix for the unit cell of the periodic structure. A polynomial eigenvalue problem is formulated thereafter using Bloch's theorem to evaluate the dispersion coefficients and wave amplitude ratios. Finally, the entire periodic frame is modeled as homogenized two-noded elements capturing the wave response of the PS with a drastic reduction in computational cost. The results obtained using the present method are validated with finite element simulation using ANSYS mechanical Ansys Parametric Design Language (APDL). The frequency band gaps observed in the frequency domain responses are investigated and corroborated with those predicted by the dispersion relations. This is followed by a detailed parametric study on the influence of different parameters on the band gap characteristics. The present method provides a scheme of wave propagation analysis of composite periodic frames with substantial computational efficiency. [ABSTRACT FROM AUTHOR]

This paper presents the time-domain viscoelastic formulation based on the Carrera unified formulation (CUF) to obtain the response of composite structures submitted to bending loads. The governing equations are obtained through a modified form of the principle of virtual displacement (PVD) for a viscoelastic analysis. The problem is solved using the Laplace transform instead of direct integration to reduce the computational cost. The results demonstrate the strong capability of the time-domain viscoelastic formulation. Overall, the proposed methodology allows the direct implementation of new optimized high order deformation theories including the thickness stretching effect that may be implemented in futures works. [ABSTRACT FROM AUTHOR]

Laminated composite structures suffer from delamination, the detachment of the layers due to the rupture of the fiber-matrix interface, as their principal mode of failure. In contrast to other damages, such as cracks, delaminations are often not visible on the surface, causing late detection and leading to sudden failures. To ensure that laminated composite structures operate flawlessly, precise monitoring methods are required. This work proposes a damage index composed of coefficients obtained from applying a Discrete Wavelet Transform to the mode shapes of a laminated composite beam with the purpose of identifying delaminations. Numerical damages were induced by reducing the stiffness in specific locations in order to simulate different damage cases and then providing data for the coefficient optimization in the damage index. After promising results for identifying damage in numerical cases, the damage index's efficiency was tested with real carbon fiber-reinforced polymer beams. The experimental specimens were manufactured with delaminations induced by embedding non-sticking films between the layers. Again, high quality results in identifying damage were achieved. The damage index proved efficient at locating damage in almost all positions along the beam, just having issues at the free end due to the discontinuity of the signal. The same specimens were subjected to tensile stress below the yield point to obtain the strain fields of the structure through the Digital Image Correlation technique. A Discrete Wavelet Transform was applied to the strain fields, aiming to identify the delaminations. It is important to emphasize that the proposed damage index is a no-baseline method, a method that does not require information about the pristine structure. [ABSTRACT FROM AUTHOR]

A thermo-mechanical progressive analysis model is proposed for predicting fatigue-driven delamination in composite laminated plates. The delamination is simulated based on extended layerwise method (XLWM). The traction-separation law is employed to the heat flux transfer and mechanical load transfer across the delamination front. A thermo-mechanical cohesive zone model (TM-CZM) is developed by Peerlings damage law to simulate the fatigue characteristic of delamination front. In the numerical examples, the effects of mesh lengths, acceleration multipliers, interface strengths, and cyclic temperature load magnitudes on the delamination expansion process are investigated, and the temperature-life curves of composite laminates are determined as well. [ABSTRACT FROM AUTHOR]

A modified higher-order zigzag theory (HOZT) is proposed for static analysis of laminated composites/sandwich shells, which accounts for transverse shear and normal strain. In-plane displacement fields are assumed to vary as a combination of globally cubic and locally zigzag linearly varying fields in this model. The transverse displacement field varies quadratically. The extended thickness criteria is utilized in this formulation. The inter-laminar shear stress continuity requirement at the interface, and zero transverse shear stress condition at the free surfaces are fulfilled. The accuracy of the model is proved by comparison with the 3D-elasticity solution and other relevant literature results. [ABSTRACT FROM AUTHOR]

Due to the high vibration sensitivity, the flexible composite structure is prone to vibration and structural deformation, thus it is necessary to study active vibration control to improve its performance. Based on the idea of the PID control and LQR control, a PID-LQR hybrid controller is proposed in this article. It is proved that the hybrid controller has better control performance by simulating the structural vibration response under various excitation conditions. Finally, the effectiveness of the hybrid controller is verified by the active control experiment, and the vibration response is reduced by about 31.55% after control. [ABSTRACT FROM AUTHOR]

It is well-known that the concentrated force develops high-stress concentration at the point of application which is one of the important parameters to be considered while designing the laminated composite structures under the action of concentrated force. The literature available shows that the study on static deformation of laminated sandwich shallow arches under the action of the concentrated force is limited. In the present study, static deformation of laminated sandwich arches under the action of concentrated loading is investigated using higher-order arch theory considering the effects of transverse normal strain. An exponential type higher-order arch theory is developed in this study which satisfies the traction-free boundary conditions at the top and the bottom surfaces of the arch using constitutive relations. Governing equations are derived within the framework of the principle of virtual work. An analytical solution for the static deformation of simply supported laminated and sandwich shallow arches are obtained using Navier's technique. The effects of the lamination scheme, radius of curvature and aspect ratio on the deflection, and stresses of shallow arches are evaluated. The present results are compared with previously published results wherever possible for the verification of the present theory. [ABSTRACT FROM AUTHOR]

The vibration energy of the track slab can be converted into electric energy for wireless sensors by piezoelectric energy harvesters. A track laminated circular plate harvester (TLCP harvester) is designed in this paper based on foundation excitation. The central frequency of the harvester is 222 Hz, which is matched with the 222.8 Hz of the track slab. The stiffness curve, damping, equivalent capacitance, and electromechanical coupling coefficient of the harvester are obtained through the experiment. The harmonic balance method and Runge–Kutta's voltage results are consistent with the experimental results. The frequency responses verify the jump phenomenon and soft characteristics. The experiment results show that the maximum output power is 8.07 mW under 7 kΩ load resistance, and the maximum RMS power is 0.3804 mW under 5 kΩ load resistance. This paper develops a safe and high-efficiency piezoelectric energy harvester for track slabs. [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]

AbstractAs known, ceramics possess desirable strength, hardness and low density, which have been extensively applied in engineering fields. However, the inherent brittleness makes the ceramics present poor toughness and consequently impact resistance as well. In recent decades, some ingenious architectures of biomaterials employed to improve the mechanical properties of brittle bulk materials, such as laminate and brick-mud, have become increasingly popular. Here, in order to further enhance the impact resistance of ceramics, a kind of hybrid ceramic-based composite structure is designed according to the gradient feature in dactyl club of mantis shrimp. The impact resistance performances of bulk, laminate, brick-mud and hybrid structures are investigated by finite element simulation. The results show that the hybrid structure can effectively avoid catastrophic failure, thereby having large scope of deformation area to store energy. Moreover, the damage mass of impactor for the hybrid plate is the largest due to the beginning hard collision between impactor and target plate and long cumulative damaging time of impactor. As a result, with the highest internal energy and eroding kinetic energy of impactor simultaneously, the hybrid structure dissipates the most energy of impactor. Further, under extreme working conditions of oblique and high velocity impact, the hybrid structure still exhibits optical impact resistance performance. [ABSTRACT FROM AUTHOR]

AbstractThis study investigates the influence of moisture and Thermo-hygroscopic influence on bio-inspired helicoidally laminated composite plates (BHLC) for strengthening damaged reinforced concrete (RC) beams. Borrowing inspiration from nature’s design principles, BHLC plates represent a novel approach to rehabilitation. An analytical approach based on deformation compatibility is employed, assuming constant shear and normal stresses across the adhesive layer within the framework of linear elasticity. BHLC plates are implemented to restrict crack propagation within the RC beam. The analytical methodology considers equilibrium and deformation compatibility across all components: the concrete beam, BHLC plate, and adhesive layer. A parametric study explores the sensitivity of interfacial stresses to parameters such as laminate and adhesive stiffness, plate thickness, and helicoidal layup configuration. The results reveal a significant influence of these factors on the magnitude of maximum interfacial shear and normal stresses. This study establishes a foundation for future analyses of damaged RC beams strengthened with BHLC plates, potentially leading to advancements in rehabilitation methodologies and improved crack propagation modeling in RC beams. [ABSTRACT FROM AUTHOR]

This study presents a meshless modeling approach to design variable-stiffness laminates considering manufacturing constraints. The governing equations are derived using lamination parameters and first-order shear deformation theory. The solution approach uses Chebyshev polynomials and Galerkin's method to obtain the discretized equations of motion. The developed framework was used to maximize the fundamental frequency of composite plates. The variable-stiffness designs provided up to 28.4% higher frequencies compared to optimum constant-stiffness laminates, although the actual level of improvement depends on the number of layers. Finally, manufacturable fiber paths were obtained considering the allowed fiber curvature, which can also reduce the frequency values. [ABSTRACT FROM AUTHOR]

In this paper, for reducing the number of independent generalized displacements of the traditional piecewise model to decrease the number of vibration equations, a refined piecewise shear deformation model considering the effect of rotary inertias and shear deformation for vibration analysis of laminated composite and sandwich plates is presented. Unlike the conventional piecewise model, the significant novelty of the proposed theory is that the new proposed piecewise theory reduces the number of independent generalized displacements from 9 to 8. Some relevant assumptions, dividing the transverse displacement into bending and shear parts, are introduced into the traditional piecewise model, and the displacement fields of the refined piecewise shear deformation theory are obtained. Next, the governing equations are derived by employing Hamilton's principle and solved by the closed-form Navier method. Then, the present solutions are compared with those available in the previous literature for confirming their validity. Finally, the variations of frequencies and loss factors with system parameters are evaluated and presented graphically. [ABSTRACT FROM AUTHOR]

AbstractVariable angle tow (VAT) composite laminated structures are produced by automated tow-placement technology which can take advantage of the designability of composites to meet the aerospace industry’s need for dynamic properties. Complex production techniques inevitably lead to uncertainties in material properties due to manufacturing defects. The aim of this work is to present an efficient computational method for estimating the dynamical properties of VAT composite laminated plates due to multiscale hybrid uncertainties. This method consists of perturbation stochastic finite element method and particle swarm optimization combined with Mori-Tanaka homogenization. The degree of influence of the multiscale parameters on the dynamic properties of VAT composites with different structural forms has been obtained by sensitivity analyses of the frequency and mode. The method is applied to investigate variations in natural frequency and mode of a variety of VAT composite laminated plates with different fiber tow paths, layers, and boundary conditions. The results indicate that variations in natural frequencies and mode shapes are strongly linked to fiber tow paths and boundary conditions. The frequency and modes of the VAT show a nonlinear variation with angle. This method can quickly obtain the probability distribution intervals of the frequency, which is of great significance for assessing the reliability of VAT composites laminated plates dynamic designs. [ABSTRACT FROM AUTHOR]

Abstract\nHIGHLIGHTSThis study explores the flexural behavior and free vibration analysis of sandwich plates including natural fiber-reinforced polymer composite faces and Polyethylene Terephthalate (PET) foam cores under a range of edge situations. ABAQUS is used to do numerical simulations with three-dimensional solid elements (C3D8R). To ascertain the natural frequencies of the plates, experimental procedures such as impact hammer testing and Fast Fourier Transform (FFT) analysis are carried out. The inference of different geometrical parameters on the natural frequencies is investigated through numerical simulation in ABAQUS. The study gives brief outlines regarding the sandwich plates for different engineering applications.Free vibration analysis of the Polyethylene Terephthalate (PET) foam and different natural fiber-reinforced polymer laminate composite faces-based sandwich plates under different edge conditions.The uniaxial tensile test and compression test are performed in the Universal Testing Machine (UTM) Instron 5967 is used to determine the elastic constants of the different natural fiber-reinforced laminated composite face layers and PET foam core.The obtained elastic properties from the tensile test and compression test of the face layers and PET foam core layer are used in the finite element software ABAQUS for the numerical simulation of the natural frequency of the sandwich plates.A set of experiments is conducted on different sandwich plates to capture the natural frequencies through an impact hammer test and Fast Fourier Transform (FFT) in the PulseLab software. The obtained natural frequency from the experimental technique and numerical simulation are compared and found to be highly consistence. [ABSTRACT FROM AUTHOR]

This research aims to study the non-linear parametric vibration of laminated composite shallow (LCS) shells with the optimal fiber angles exposed to external and parametric excitations, including primary and 1:2 internal resonances. In this regard, optimal fiber angles are found with implementations of the P-T method for the objective functions and utilization of the particle swarm optimization (PSO). Also, the non-linear model of the shallow shells is established based on the stress function and the first-order shear deformation theory (FSDT). According to FSDT, Hooke's law, von-Kármán equation, Hamilton's principle, and Galerkin method, two-degree-of-freedom non-linear ordinary differential governing equations are discretized. [ABSTRACT FROM AUTHOR]

This study investigates the vibration energy flow transmission behavior of laminated composite plate structures coupled with a line hinge. The time-averaged vibration energy transfer is determined using the substructure-based power flow analysis (SPFA) method. The effects of the fiber orientation, boundary conditions and the position of the coupling hinge on the vibration transmission path and its level are examined. It is demonstrated that the fiber orientations can be used to modify substantially the power flow transmission path and locations of energy sinks. Enhancement of vibration suppression of the coupled structure can be achieved by tailor designing the fiber angles. [ABSTRACT FROM AUTHOR]

Needled composites have stronger interlaminar properties compared to two-dimensional fiber composite structures due to the introduction of z-directional fibers in the fiber composite layup. An effective multi-scale finite element model is developed in this paper for the complex structure of needle-punched composites. Three scales, namely fRVE, pRVE, and lRVE, are modeled from the fiber scale, the delamination scale, and the laminate scale. using ABAQUS, periodic boundary conditions are applied to the RVEs at different scales to obtain the effective mechanical properties of various RVEs. Meanwhile, the effect of needling density on the needled composites is predicted by applying the above multi-scale model. The increase of needling density can enhance the out-of-plane effective mechanical properties of the composites, but it also weakens the in-plane effective mechanical properties. The maximum error of the elastic modulus calculation is 17.68% with that of the reference, thus verifying the rationality of the multi-scale model. [ABSTRACT FROM AUTHOR]

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]

AbstractThis present work investigates the buckling load optimization of the laminated composite plates with the elliptical hole under different non-uniform edge loads. The design objective is the maximization of the critical buckling load by determining the optimum fiber orientations in the layers. The stability equations are derived based on the first-order shear deformation theory (FSDT) of the laminated plates. The critical buckling loads are calculated using the finite element method with the nine noded rectangular element having five degrees of freedom per node. The bonobo optimizer (BO) algorithm is employed to optimize the laminated composite plates with the elliptical hole. The computer programming is developed in the MATLAB environment. Besides, the parametric studies are conducted for different types of the non-uniform edge loads, boundary conditions, cutout radius ratio and aspect ratios and the obtained numerical results are compared. Finally, the optimum results show that these factors play an imperative role in the optimum pattern and stacking sequence of the laminated composite plates with hole. The new significant findings can aid the designers in the structural design, and other industrial applications. [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]

Abstract\nHIGHLIGHTSThis numerical study represents an effort to characterize the dynamic behavior of distinct armor-grade steel plates and fiber metal laminates (FMLs) of the same masses under blast loads. The blast resistance of finite element models of square steel plates and FMLs is evaluated by applying conventional weapon effects program air-blast loading ranging from 1 to 3 kg of trinitrotoluene (TNT) at a fixed stand-off distance (SoD) of 0.1 m. A user-defined subroutine is used to implement a failure criterion to determine realistic failures in the composite. A variation of kinetic energy, radial deflection, and energy absorptions of the steel plates and FMLs are determined to discover their blast mitigation performance. The deformation modes and equivalent plastic strain of both the steel plate and FMLs are also compared. The obtained results show that the armor-grade AISI 4340 steel has up to 50.5% smaller peak deflection than the other armor-grade steels. The use of FML with multi-thin layers of composite laminate and steel sheets instead of equivalent AISI 4340 steel plate significantly reduces the peak deflection up to 23.9% under similar blast loading conditions. The findings of steel plates and FMLs also represent their applicability for making complex protective structures.AISI 4340 armor-grade steel provides the highest blast resistance.AISI 4340 steel has 50.5% higher deflection resistance than Q235 steel.Incorporation of CFRP improves the blast resistance of AISI 4340 steel. [ABSTRACT FROM AUTHOR]

Although various simplified models can capture size effects of composite laminated micro beam and plate by combining new modified couple stress theory, there is no benchmark to access the accuracy of predicting size effects in those models. Therefore this paper develops a quasi-3D model based on new modified couple stress as a benchmark for analyzing thermal size effects of composite laminated micro plate, and also proposes two simplified quasi-3D models with assumptions out of computational cost at the same time. By a classical example of simply-supported micro laminated square plate, several conclusions can be got from numerical results. For the present quasi-3D model under non-uniform temperature loading, (i): the model is capable to capture size effects of composite laminated micro plate, (ii): discovering a law to define the boundary size between micro and macro laminated plate, which is important for the engineering applications; For the simplified quasi-3D models under uniform temperature loading, (i): As the material length parameter l decreases, the accuracy of both of models is rising gradually, (ii): The first simplified quasi-3D model may substitute the present quasi-3D model to predict thermal size-dependent behaviors of composite laminated micro plate, whereas the second simplified quasi-3D model is suitable to laminated micro plate for which span-to-thickness ratio is no less than 14. [ABSTRACT FROM AUTHOR]

Thin-plies are generally defined as composites with ply thicknesses below 100 μm. These materials are rapidly gaining interest for high-performance applications, for example, the aerospace sector. Many practical techniques have been proposed to prevent delamination and improve the strength of composite laminates. A recent study has shown that the delamination could be postponed by replacing layers of CFRP with thin-ply in a unidirectional composite laminate, a configuration known as hybrid laminates reinforced with thin-plies. Since fiber orientation is known to be one of the most important parameters in composite laminate design, this study investigates the effect of oriented layers of thin-ply or both thin-ply and conventional CFRP in a hybrid laminate under out-of-plane tensile loading. A numerical Representative Volume Element (RVE) model for CFRP and thin-ply was generated, considering the unidirectional [0], cross-ply [45/−45], and [0/90] in order to better understand the effect of angle-plied hybrid composite laminates. Experimental results show that angle-plied composite laminates present higher failure load under out-of-plane tensile loading compared to the unidirectional ones. This can be attributed to the fact that an initiated crack is faced with a significantly more complex crack path in an angle-plied laminate to advance in the through-the-thickness direction. [ABSTRACT FROM AUTHOR]

AbstractThis paper presents an analytical model for the free vibration of composite laminated plates with arbitrary biaxial symmetric geometry under elastic boundary conditions, applicable to cross-ply fiber-reinforced composites. In this model, the domain segmentation integral method proposed by the authors is extended to the first-order shear deformation theory (FSDT) and the laminated plate theory. The energy integrals pertaining to the FSDT are analytically simplified by segmenting the integration domains and synthesizing orthogonal polynomial displacement functions over the plate domain coordinate intervals. This synthesis is achieved through the amalgamation of the penalty function method and the Gram-Schmidt orthogonalization process. Then, using the Rayleigh-Ritz procedure, a series solution for the free vibration problem of cross-ply fiber-reinforced composite laminated plates is obtained. The model provides an analytical mathematical relationship between the profile curve of composite laminated plates with arbitrary biaxial symmetric geometry and the strain energy, kinetic energy, and boundary potential energy during vibrational processes. The correctness and applicability of the method are validated by comparing the obtained results with those from the literatures. New results for laminated plates, such as hexagonal and astroid-shaped plates, were presented as references for future research. Taking a track shaped plate as an example, the effect of the number of layers on the vibration characteristics of cross-ply fiber-reinforced composite laminated plates with a certain thickness is studied. [ABSTRACT FROM AUTHOR]

Abstract\nThe inherent brittleness of unidirectional fiber-reinforced composites represents a major complication in their broad practical applications. However, exploiting different reinforcement architectures can offer an opportunity for highly desirable ductile fracture nature. This article is aimed at investigating experimentally the tensile behavior of an epoxy laminate reinforced by different layers of plain weft-knitted fabrics. The fabricated laminates were subjected to uniaxial tension in different loading directions, and the corresponding tensile responses were recorded. Basic mechanical properties were characterized and digital image correlation (DIC) was employed to capture surface deformations. Tensile test results demonstrated strong nonlinearity and pseudo-ductility as well as loading-direction dependence in this type of composite laminates. Fracture tests were conducted showing high fracture toughness ranging from 10 to 20 MPa·m1/2. Typical damage modes were characterized using microscopy, which were coupled to a few distinct tensile deformation stages. This work demonstrates that weft-knitted composites are promising in permitting great amounts of pseudo-ductility with clear warning before complete failure. It is also expected to contribute to the understanding of the specific role of weft knit fabrics in composite laminates.Analysis of the deformation process of plain weft-knitted composites and various failure modes by DIC and microscopy.Observation and explanation of pseudo-ductility in the knitted composites subjected to off-axis tension.Translaminar fracture toughness measured by over-height compact tension (OCT) specimens. Flaw insensitive length scale estimated on the order of 10 mm.Yarn loop reorientation permitted by matrix plasticity contributing to identified stiffening in off-axis specimens. [ABSTRACT FROM AUTHOR]

A dynamic model built theoretically and simulated numerically for an unsymmetric bistable laminate is elucidated, elaborating the dynamic regimes. Peak-to-peak amplitude diagrams being amplitude-frequency and amplitude-force response curves are derived. The single-well vibrations, the limit-cycle oscillations, the multiple-period dynamic snap-through, the chaotic dynamic snap-through and the intermittency dynamic snap-through can be detected. The amplitude-frequency response curves exhibit the softening stiffness effect. The dynamic regimes are correlated with the excitation amplitude and the modal frequencies. Deploying the high-level excitation amplitude and the low-level modal frequency leads to the limit-cycle oscillations. Besides, the single-well vibrations are characterized by the period-doubling bifurcation. [ABSTRACT FROM AUTHOR]

The difficulties in establishing an analytical model for plain woven fabric composites (PWFC) and its implementation are well-accepted due to the complexity of yarn architecture, approximations assumed, and lack of experimental validations. In this paper, a practical engineering approach is proposed to predict the tensile properties of PWFC. The approach assumes PWFC as cross-ply, the undulation angle an elliptical shape. The approach tremendously simplifies the calculation keeping a close agreement with the tensile experimental results of PWFC. The approach is remarkably compatible with other theoretical models and experiments that existed in the literature. [ABSTRACT FROM AUTHOR]

This study analyzes the behavior of CFRP tape laminates under high-velocity impact when they are subjected to in-plane tensile preload. Experimental tests were carried out using a gas-gun setup in non-loaded and preloaded laminates. Impact and residual velocities were measured, the ballistic limit and damage area were estimated, and it was observed that the ballistic limit was lower in preloaded specimens. An analytical model was developed and validated. Some differences were observed in terms of energy absorption mechanism distribution between preloaded and non-loaded laminates for impact velocities close to the ballistic limit. The influence on the ballistic limit with the preload level was studied. [ABSTRACT FROM AUTHOR]

As a promising energy absorbing structure, reentrant honeycomb (RH) structures have been focus of interest in recent years. By reasonably adjusting the geometric configuration of the honeycomb cell, advanced structures with unique mechanical properties and deformation behaviors can be designed flexibly and novely. In this work, inspired by the composite laminates, a novel laminated reentrant honeycomb (LRH) structure is developed by controlling the orientations of RH layers for achieving excellent energy absorption capacity. Mechanical and deformation characteristics of the proposed structures under static and dynamic loadings are investigated experimentally and numerically. By comparing with single-layer RH structure with the same thickness, the results demonstrate that LRH structures have better energy absorption capacity. The deformation modes of RH and LRH structures are also discussed and it is noted that the LRH structure with ±30° honeycomb sublayers shows zero Poisson's ratio effect. It is worth emphasizing that LRH with 0° and 90° sublayers presents similar negative Poisson's ratio effect with RH by analyzing the equivalent Poisson's ratio-strain curves. In addition, it is found that the latter structure has the best energy absorption capacity when the thickness of single-layer 0° RH structure equals to 5 mm. This work provides a new and reliable thought to design the advanced protective structures under compression and impact loadings. [ABSTRACT FROM AUTHOR]

A novel damage tolerance design method of discrete interleaved toughening for laminated composite was proposed. In this paper, discrete thermoplastic Polyamide-6,6 (PA 66) films were deployed at between the selected adjected layers, and three toughening dimensions were considered. Besides, three impact positions of specimens were tested under 5 J, 10 J, and 15 J, respectively. The impact behavior and compression after impact (CAI) of specimens were discussed and compared. Experimental results showed that delamination damage was suppressed in the process of propagation outwards across the toughened region, and the path of delamination crack propagation was changed and swerved. Therefore, the delamination damage projected area (DDPA) of all specimens were reduced by 21.09%–62.85%, compared with the non-toughened plate (base plate). In addition, the finding demonstrated that CAI strength is influenced by the delamination position and DDPA. The proposed method could improve the CAI strength by suppressing delamination and swerving the propagation path of delamination. Moreover, the CAI strength of all toughened plates were improved by 16.35%–61.94% in contrast to the related base plates. [ABSTRACT FROM AUTHOR]

Flutter is a typical dynamic instability phenomenon of the wing or rudder structure. Besides, the phenomenon of aerodynamic heating will be quite significant and temperature can rise rapidly with the increase of the flight speed, thermal flutter characteristics should be taken into consideration for the rudder structure of supersonic vehicle. To improve the thermal flutter characteristics of the rudder structure and meet the design requirements of a lightweight structure, this article optimizes the variable stiffness laminates of the skin on the premise of keeping the thickness of the skin unchanged, so as to improve the critical flutter speed of the rudder. A novel intelligent optimization algorithm named BJASCA, which is a hybrid algorithm coupling of Backtracking Search Algorithm, Sine Cosine Algorithm, and JAYA Algorithms is proposed in this article to improve the efficiency of structural optimization and this algorithm shows obvious advantages in searching global optima compared with several other algorithms. The finite element model and aerodynamic model of the rudder are established to calculate the critical flutter speed. The results represent that the rudder structure optimized by the BJASCA algorithm shows better flutter characteristics and the critical flutter speed can be increased by 76.4% compared with the un-optimized structure. [ABSTRACT FROM AUTHOR]

This paper presents a multiscale progressive fatigue damage model to predict the fatigue life of composite laminates. The multi-level damage model was employed considering the interfacial debonding effect, and effective material properties were calculated through homogenization. Damage variables and damage slopes were defined at the constituent level, and fatigue damage parameters were obtained using the residual stiffness data with the chaotic firefly algorithm. The model was implemented into ABAQUS, then validated with flat-bar and pin-loaded specimens of AS4/3501-6 composite. The numerical results corresponded well with the experimental data and showed the ability to capture the failure propagation of composite laminates. [ABSTRACT FROM AUTHOR]

Piezoelectric quasicrystals have attracted the tremendous attention of researchers for their unique properties. In this paper, the semi-analysis solutions of the functionally graded multilayered two-dimensional decagonal piezoelectric quasicrystal plates are investigated for mixed boundary-value problems. Based on the quasicrystal linear elastic theory, the state-space method is employed to derive the state equations composed of partial differential along the thickness direction. The differential quadrature method is utilized to discretize state variables to satisfy the mixed boundary conditions in the horizontal plane. Different from the conventional propagator matrix, a new propagator relationship is proposed to study numerical instability caused by extensive discrete points. Comprehensive numerical results are shown for the sandwich quasicrystal plate with four different stacking sequences. The numerical results reveal the effect of the functional gradient index factors, and boundary conditions on the electric potential, electric displacements, stresses, and displacements under the mechanical/electric loadings. [ABSTRACT FROM AUTHOR]

Composite laminates are prone to occur delamination. Currently, there is still lacking research on the temperature effect on mode II delamination of laminates, especially the multidirectional ones. Systematically experimental and numerical studies are conducted here. Delamination tests are performed at four temperatures (−50 °C, 23 °C, 80 °C and 130 °C) on aerospace-grade T800/epoxy multidirectional laminates using an end-notched flexure set-up. Pre-cracked and non pre-cracked fracture toughness, and R-curves are measured. The non pre-cracked fracture toughness is affected by temperature. Their values at −50 °C, 23 °C and 80 °C are relatively close to each other while the value at 130 °C is 34.14% lower than that at 23 °C. The pre-cracked fracture toughness exhibits negligible dependence on temperature and is significantly higher than the non pre-cracked one. R-curve phenomena are observed in specimens evaluated at different temperatures, which exhibit a good linear increase with the increase in delamination length. The R-curves measured at −50 °C∼80 °C are similar while significantly higher than that at 130 °C. In addition, the bridging stress is lower when the temperature is between −50 °C and 23 °C, compared to those at high temperatures of 80 °C and 130 °C. Numerical framework for simulating the mode II delamination growth behavior is established based on the cohesive zone model. Predicted results show that the reasonable interfacial strength of cohesive elements first increases and then decreases with the increase in temperature. Temperature effect on the damage area around crack tip is also revealed. [ABSTRACT FROM AUTHOR]

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]

This study investigates the vibration transmission in coupled metal and composite plates with curvilinear fibers from the power flow viewpoint. The time-averaged power flow variables are obtained using a substructure method to assess the levels of vibration transmission of coupled structures with various configurations and fiber angles. It is demonstrated that by adopting tailored curvilinear fiber designs, the vibration transmission through the coupling edge of the plates can be effectively suppressed. Variable fiber angle designs are shown to exert significant effects on the dominant-excited mode and can be exploited to achieve desirable energy transmission paths for low-vibration transmission and effective suppression. [ABSTRACT FROM AUTHOR]

A novel high-temperature resistant carbon fiber/bismaleimide resin composite shell is proposed and its bistable characteristics are studied in megathermal environment. Bistable structures are prepared with epoxy resin composites conventionally, which prone to undergone glass transition at high temperature. The study of high-temperature resistant bistable structure become necessary to suit aerospace field. In this work, the effect of elevated temperatures and different ply angles were investigated on curvatures and snap behaviors of carbon fiber/bismaleimide resin composite bistable shells through experiment and finite element analysis. These results provided significant understanding of morphing behaviors for the carbon fiber/bismaleimide bistable structure in megathermal environment. A novel high-temperature resistant carbon fiber/bismaleimide resin composite shell is proposed and its bistable characteristics in megathermal environment are studied in this paper. Bistable structures are prepared with epoxy resin composites conventionally, which prone to undergone glass transition at high temperature. The study of high-temperature resistant composite bistable structure become necessary to suit the actual working conditions. In this work, the anti-symmetric bistable shells with different ply angles (40°, 45°, 50°) are fabricated using T700/QY8911 prepreg. The effect of elevated temperatures and different ply angles were investigated on the principal curvatures and twisting curvatures of carbon fiber/bismaleimide resin composite bistable shells through experiment and finite element analysis. The snap behaviors of the bistable shells with different ply angles at different temperatures were obtained. Furthermore, a novel two-point tensile loading method was applied to the snap-back processes of carbon fiber/bismaleimide resin composite bistable shells with the subtended angles greater than 180°. It is noticed that the bistable shells have better high-temperature stability than carbon fiber/epoxy bistable shells. These results provided significant understanding of morphing behaviors for the carbon fiber/bismaleimide bistable structure in megathermal environment. [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]

The present study investigated the effect of damage on the free vibration and the aeroelastic response of variable stiffness (VS) composite laminated plates. The ineluctable defects or internal flaws are incorporated into the finite-element coding through anisotropic damage formulation and coupled with MSC.Nastran using Direct Matrix Abstraction Program to generate the aerodynamic forces at discrete values of reduced frequencies for performing aeroelastic analysis. The sensitive location of damage for the free vibration and flutter characteristics is identified. Thereafter, the best placement of piezoelectric patches is determined to enhance the aeroelastic boundary of the damaged VS plates with active feedback control. [ABSTRACT FROM AUTHOR]

Even though the influence of impact energy on the low velocity impact of laminated plate is well reported, the influence of relative mass of the impactor has not been addressed extensively. This work investigates the effect of impactor mass relative to that of target and other associated factors like impactor velocity and the target plate size on the impact response of a GLARE plate. A 3 D finite element analysis incorporating Newmark-β method and Hertzian contact is used considering appropriate contact stiffness to evaluate the contact force. Results show that the impactor mass significantly influences the contact force and interfacial delamination. [ABSTRACT FROM AUTHOR]

The fatigue life of carbon fiber reinforced thermoplastic matrix composites is of great interest for many engineering applications. This work evaluated the influence of poly(etherimide) (PEI) on the fatigue life of laminated thermoplastic composites reinforced with carbon fibers. The mechanical characterization of the carbon/PEI composites was performed by static loading (tensile test) and cyclic fatigue. Tensile strength obtained was used to calculate 5 stress levels for cyclic fatigue testing with R = 0.1 and 12 Hz for 85, 80, 70, 60, and 55%, being this last stress level found as the infinite life. These stress levels allowed plotting a well-described SN curve. Seeking to understand the fracture behavior of carbon/PEI composites, a fractographic study by scanning electron microscopy (SEM) was performed. SEM micrographs confirm the good quality of carbon/PEI laminate with good adhesion between fibers and matrix and also confirmed the nature of fatigue life showing in-plane fracture for high loads and explosive fracture for lower loads. [ABSTRACT FROM AUTHOR]

The existing finite element formulation generally leads to overestimation on the first ply failure (FPF) load. Reasons of this phenomenon have been less cleared in detail. Therefore, it requires to propose an analytical solution to provide an accurate prediction of the FPF with the high efficiency-cost ratio. To this end, the following work has been carried out: (1) Legendre polynomials as local terms are first introduced into Reddy-type higher-order theory, which provide a novel alternative form of global-local displacement field. (2) Compared with the classical first-order and higher-order shear deformation theories, the proposed model can predict transverse shear stresses directly by constitutive equations which is close to the results obtained by the three-dimensional finite element method (3D-FEM). Therefore, the accuracy and efficiency of the FPF analysis can be improved, attributing to the accurate prediction of the quasi-three-dimensional stress field. (3) The static response and the FPF of laminated composite plates are analyzed, which have been compared with the results of selected models in the published literature and 3D-FEM. Influences of different failure theories, transverse loads, stacking sequence on prediction of the FPF loads are also explored. (4) By visualizing full-field displacement, stress and damage variables rather than those obtained from key points, it is easier to find the failure tendency and the failure modes. As a result, it is necessary to propose an analytical solution for predicting the FPF of composite laminated plates, which can provide a reference for other investigators. [ABSTRACT FROM AUTHOR]

This paper explores the aero-thermo-elastic properties of variable stiffness composite laminates (VSCLs) with fibers steered along curved trajectories using a refined 1 D model. High-order solutions are generated by the p-version finite element method in conjunction with the Carrera Unified Formulation (CUF), which is applied to structural modeling by employing the improved hierarchical Legendre expansion (IHLE) in particular. The merit of using such a kind of expansion lies in that both the Equivalent Single Layer (ESL) and Layer-Wise (LW) theories can be formulated in a compact and straightforward manner. The linear piston theory is utilized to model the aerodynamic force, whereas the steady-state temperature field is applied during the flutter analysis. The weak-form governing equations are derived by taking a perturbation of the equilibrium configuration, and divergence and flutter instabilities are determined by solving the related eigenvalue problem. The accuracy of the proposed model has been verified through several test cases involving flutter, thermal buckling, and vibration of symmetric and antisymmetric VSCLs. The obtained results were compared to those obtained using the ABAQUS software and the available literature. Finally, the effect of the kinematic order, shear coefficient, and temperature variation on the critical dynamic pressure of VSCLs is thoroughly investigated. [ABSTRACT FROM AUTHOR]

Jute fibers are commonly used as reinforcement in composite materials manufacture due to its excellent mechanical properties. In this study, alkali (NaOH) and silane coupling agent KH570 treatment were conducted on component jute nonwovens to improve the bonding strength of jute/PLA composite interface. The jute/PLA composites were prepared from treated jute nonwovens and PLA films by molding method. The results show that alkali treatment can significantly improve the tensile, flexural and dynamic thermomechanical properties of jute/PLA composites. The composites treated with 1% NaOH exhibits the maximum tensile strength while the composites treated with 5% NaOH presents the maximum flexural strength and the minimum loss in the dynamic thermo-mechanical process. Moreover, the tensile and flexural strength of the composite treated with the combination of 5% NaOH-5% KH570 is significantly stronger than that when they act alone. This research can provide an optimal treatment strategy for the jute/PLA degradable composites with higher mechanical and thermos-mechanical tolerance. [ABSTRACT FROM AUTHOR]