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Composite laminates have become increasingly popular in industries like aerospace and shipbuilding. In practical applications, the creation of notches in composite laminates is often necessary to enable assembly and modifications. This rise in the use of notched composite laminates highlights the need for reliable methods to predict potential failures in these components. With these predictions, the safety and reliability of composite structures can be ensured by preventing catastrophic failures. The present paper investigates the use of the Virtual Isotropic Material Concept (VIMC) combined with the Finite Fracture Mechanics (FFM) criterion to predict the Last Ply Failure (LPF) load in keyhole notched composite laminates and under mode I loading conditions. Experimental tests were conducted to measure the LPF load of E-glass/Epoxy keyhole notched specimens, and the results were compared with the predicted results using the VIMC-FFM criterion. The paper also derives an expression for the Stress Intensity Factor (SIF) function for a crack that emanates from the keyhole notch tip under mode I loading conditions. The derived equation matches very well with numerical data and have a mean absolute error about 2% in the studied domain. The study shows that the VIMC-FFM criterion predicts the LPF load of keyhole notched composite laminates with acceptable accuracy and in a simple and low-cost manner. [ABSTRACT FROM AUTHOR]

A large number of experiments show that composite materials usually show different modulus properties in tension and compression (bi-modulus). However, for actual composite engineering structures, especially complex models, the numerical simulation calculation is usually based on a single modulus. In order to consider the different modulus characteristics of composite materials in tension and compression, researchers put forward simplified constitutive models of dual-modulus materials. However, these constitutive models have not been verified by a large number of experiments, especially by complex models. In this paper, the GWFMM model is simplified and used to analyze complex structures with different modulus in tension and compression. The experimental results of stiffened plate show that the improved GWFMM model can be used to analyze different modulus of tension and compression of complex stiffened structures. In addition, the influence of elastic modulus ratio in tension and compression under different experimental load conditions is further explored, and the influence law of bending and torsion on structures with bi-modulus is discussed. The relevant conclusions provide reference for the design and optimization of full-scale composite structures in marine engineering. [ABSTRACT FROM AUTHOR]

In this paper, the free-edge effects which play an important role in the failure analysis of composite laminates are studied. Pure temperature change and its combination with biaxial tension are investigated for a composite plate with a centric circular hole that is adequately small in comparison to the dimension of the plate. Moreover, the laminate is assumed to be thin, the temperature change of all points of the plate is identical and the biaxial tensile load is applied far from the center of the hole. For this purpose, a semi-analytical method based on a two-dimensional thermoelastic boundary layer theory and a minimum potential energy principle is proposed. It is shown that the present method predicts the interlaminar peeling and shear stresses surrounding the hole with good agreement compared to the results obtained by FEM analysis. [ABSTRACT FROM AUTHOR]

Numerical and experimental research programs have been carried out to investigate the effect of scaling on the tensile strength of notched composites. This paper presents a computational study of scaled open-hole tensile tests using the Discrete Ply Model (DPM) method. This finite element model is discrete, and only a small number of parameters are required from experimental characterization tests. Experimental and numerical strength values are compared here, and reveal that DPM simulations tend to slightly overestimate strength values, with an average discrepancy of 9.7%. However, DPM Results show that such modeling simulates both the reduction in strength when specimen size is increased for sublaminate level scaled specimens, where failure is fiber dominated, and the increase in strength when specimen size is increased for ply level scaled specimens, where failure is delamination dominated. In all cases, increasing the total thickness of the specimen leads to a decrease in strength and this effect is dominant over the effect of increasing hole diameter. As well as the variation in strength, three distinct failure mechanisms are observed: fiber failure with extensive matrix damage (pull-out failure), fiber failure with little or no matrix damage (brittle failure) and delamination failure. Comparisons with experiments demonstrate that tensile strengths, damage propagation scenarios and failure patterns are predicted with acceptable accuracy. [ABSTRACT FROM AUTHOR]

Out-of-plane waviness is one of the most common defects which degenerates the strength, stiffness, and fatigue life of hybrid glass–carbon fiber–reinforced polymer composites (FRPs). An accurate and high-speed non-destructive testing method is highly desired for large composite structures in industries. Ultrasonic phased array is a great candidate for such application. This paper applies the wavenumber algorithm to image the waviness in hybrid FRP plates which are a multi-layered medium. The central frequency of 5 MHZ is chosen in order to maximize the ply resonance. Transducers are migrated virtually to each interface between glass and carbon plies in order to overcome the difficulty of wave propagation analysis in such multi-layered system. The wavenumber algorithm demonstrates a better computational performance compared to that of the traditional total focusing method (TFM) in time domain up to 6 times. The glass ply depth and waviness angle can be more accurately presented with relative errors less than 1.5% and 14.8%, respectively. In addition, the resin-rich defect characterization is also achievable with a maximum error of 14.4%. [ABSTRACT FROM AUTHOR]

In this paper, the dynamic and aeroelastic analysis of variable fiber spacing composite (VFSC) laminated plates are carried out. The effects and benefits of changing the fiber distribution pattern on natural frequency and mode shape are explored taking various boundary conditions. Taking cantilever boundary condition flutter characteristics of VFSC plate with different fiber distribution patterns are compared. Further stochasticity of flutter velocity due to randomness in material properties that could arise due to complex manufacturing and fabrication process of VFSC laminates is investigated. The perturbation technique is implemented to perform the stochastic as well as reliability analysis. Various parametric studies are conducted to check the accuracy and efficiency of perturbation technique, by comparing the results with that of Monte Carlo simulation and the first-order reliability method. [ABSTRACT FROM AUTHOR]

The design of the next generation of aeronautical vehicles is driven by the vastly increased cost of fuel and the resultant imperative for greater fuel efficiency. Carbon fiber composites have been used in aeronautical structures to lower weight due to their superior stiffness and strength-to-weight properties. However, carbon composite material behavior under dynamic ballistic impact and blast loading conditions is relatively unknown. For aviation safety consideration, a computational constitutive model has been used to characterize the progressive failure behavior of carbon laminated composite plates subjected to ballistic impact and blast loading conditions. Using a meso-mechanics approach, a laminated composite is represented by a collection of selected numbers of representative unidirectional layers with proper layup configurations. The damage progression in a unidirectional layer is assumed to be governed by the strain-rate-dependent layer progressive failure model using the continuum damage mechanics approach. The composite failure model has been successfully implemented within LS-DYNA® as a user-defined material subroutine. In this paper, the ballistic limit velocity (V50) was first established for a series of laminates by ballistic impact testing. Correlation of the predicted and measured V50 values has been conducted to validate the accuracy of the ballistic modeling approach for the selected carbon composite material. A series of close-in shock hole blast tests on carbon composite panels were then tested and simulated using the LS-DYNA® Arbitrary-Lagrangian-Eulerian (ALE) method integrated with the Army Research Laboratory (ARL) progressive failure composite model. The computational constitutive model has been validated to characterize the progressive failure behavior in carbon laminates subjected to close-in blast loading conditions with reasonable accuracy. The availability of this modeling tool will greatly facilitate the development of carbon composite structures with enhanced ballistic impact and blast survivability. [ABSTRACT FROM AUTHOR]

Mechanical and thermodynamical properties and thus machinability of carbon fibre reinforced polymer composites significantly depend on the fibre orientation relative to the load direction. However, the orientations of the fibre groups in polymer composites reinforced by chopped carbon fibres are stochastic; therefore, the properties and machinability of such composites are challenging to plan, predict and optimise. We developed four different and novel approaches for fibre detection in polymer composites reinforced by chopped carbon fibres: (i) detecting the fibres through naked eye supported manual drawing, (ii) digital image processing of optical images, (iii) machine learning-based fibre detection, and (iv) rectangle fitting on the outputs of the automated processes using the Chaudhuri and Samal method. The applicability of the novel approaches was tested through optically captured images of polymer composites reinforced by chopped carbon fibres. The developed methods are each capable of detecting fibre groups at the top and bottom of the composite plate with certain limitations. The rectangle fitting approaches performed the best from the point of view of correctly identifying of fibre groups, followed by the machine learning-based and the conventional digital image processed, respectively. As a result of this study, the machining process planning and condition monitoring of polymer composites reinforced by chopped carbon fibres is more deeply supported. [ABSTRACT FROM AUTHOR]

This paper gives a method of obtaining the three-dimensional elastic constants of a completely free orthotropic plate from experimental plate vibration data, using an optimized three-mode Rayleigh formulation that incorporates through-the-thickness shear and rotatory inertia. The author believes this is the first reported attempt employing this formulation for obtaining the frequencies of thick plates with the incorporation of these two phenomena. The primary purpose of this paper is to develop the basic theory and method for this class of plates. The author had earlier utilized the classical lamination theory (which does not include these two effects) with both three and six optimized modes. The forward problem of computing plate vibration frequencies from given elastic constants by the Rayleigh method is solved for three thickness ratios (.075, .1, .125) for an isotropic (aluminum) and an orthotropic (graphite/epoxy) material. The inverse method for extracting the elastic constants from experimental vibration data is then applied to two thick plates fabricated from these materials. The results suggest that the proposed method is potentially useful for rapid, inexpensive extraction of in situ elastic constants of composite plates. The major original contribution of this paper is the novel approach for formulating and solving both the forward and inverse problems for thick plates. [ABSTRACT FROM PUBLISHER]

In this paper, the low-energy impact behavior of a fully biobased composite made of bio-sourced polyamide 11 resin reinforced with flax fibers was investigated. Different composite laminates were studied in order to determine the stacking sequence effects on the impact behavior of these composites. Four stacking sequences were manufactured: unidirectional [0°]8, cross-ply [0°/90°]2s, sandwich-like [02°/902°]s and quasi-isotropic [45°/0/−45°/90°]s. A low impact energy of 3.6 J was applied on these laminates by means of a drop weight impact tower. The impact properties of these lay-ups were ascertained by analysing the impact load history, the maximal displacement of the impactor and the absorbed energy. Damage after impact was further assessed by visual inspections, topographic measurements, C-scan and X-ray micro-tomography observations. The results show that impact damage of composite plates is highly influenced by fiber orientation. The impact test data are in good agreement with damage analysis after impact and indicate that stacking plies in the same orientation lead to a larger induced damage, which is responsible for energy dissipation. The quasi-isotropic composite has the smallest induced damage and the highest peak load. Otherwise, the sandwich-like sequence shows the lowest peak load, the highest energy absorption and significant induced damage. Therefore, it is necessary to choose the most suitable lay-up, in terms of impact behavior, for each considered industrial application. [ABSTRACT FROM AUTHOR]

In this paper, the static and fatigue behavior of flax fiber-reinforced composites with and without an interleaved natural viscoelastic layer are investigated. Viscoelastic composite plates consist of a soft natural viscoelastic layer which is confined between two identical flax fiber reinforced composites. Different stacking sequences of specimens are tested with uniaxial tensile loading until failure. The mechanical behavior and the acoustic activity of damage sources in various configurations with and without a viscoelastic layer are compared. The analysis of acoustic emission signals and the macroscopic and microscopic observations led to the identification of the main acoustic signatures of different damage modes dominant in each type of composites (with and without a viscoelastic layer). These results allow better identification of the influence of the impact of a viscoelastic layer on the mechanical behavior of different composites. In addition, static and fatigue flexural behavior of unidirectional composites with and without viscoelastic layer are characterized in 3-point bending tests. The effects of viscoelastic layer on the stiffness, hysteresis loops, and loss factor are studied for various numbers of cycles during cyclic fatigue. [ABSTRACT FROM AUTHOR]

This paper addresses the effects of different stacking sequences and seawater on the buckling behavior of hybrid composite plates. For the buckling tests, 12-layered hybrid composite plates were produced using different combinations of carbon, E-glass and aramid fibers, with an epoxy resin system as the matrix (Araldite LY1564/Aradur 3486). The hybrid composite plates were designed at the symmetric orientation angles of [(0/90)3]s, [(30/−60)3]s, [(45/−45)3]s and an anti-symmetric orientation angle of [(0/90)3]2. The hybrid composite samples were divided into groups and were subjected to buckling tests after being kept in different settings for varying periods of time (room temperature for 90 days, Black Sea water for 90 days, Mediterranean Sea water for 90 days, Mediterranean Sea water for 150 days). In light of the data obtained from the tests, the buckling behaviors of the layered hybrid composite plates were examined. The highest critical buckling load occurred in the carbon/aramid/glass (CAG) hybrid samples with the stacking sequence of [(0/90)3]s, whereas the lowest critical buckling load occurred in the carbon/aramid/glass (CAG45) hybrid samples with the stacking sequence of [(45/−45)3]s. It was observed that the critical buckling loads of the samples immersed in seawater decreased when compared to the critical buckling loads of the samples kept at room temperature. It was also found that the critical buckling loads of the hybrid samples immersed in the Mediterranean Sea water, which has high salinity, were lower than the critical buckling loads of the hybrid samples immersed in the Black Sea water, which has lower salinity. [ABSTRACT FROM AUTHOR]

This study presents a novel approach for optimizing the critical buckling load of the stiffened piezolaminated composite plates using a self-adaptive special relativity search (SASRS) algorithm. The fiber orientations in the layers are considered as design variables. The stability equations are first derived based on the classical laminated plate theory (CLPT) with von Karman nonlinearity. The optimization problem is implemented in MATLAB. The optimization results are obtained to indicate the effecs of various boundary conditions, applied voltages, grid shapes, angles of diagonal ribs, and plate aspect ratios on the optimal design. Numerical investigations are carried out for 10-ply symmetrical stiffened piezolaminated plates. The robustness and efficiency of the proposed SASRS algorithm in maximizing the critical buckling load of the stiffened piezolaminated plates are demonstrated by comparing the optimized results from the standard special relativity search (SRS) algorithm. It is found that the proposed optimization method has better performance than the SRS algorithm. [ABSTRACT FROM AUTHOR]

This study examines how structural discontinuities created during production affect glass fiber-reinforced composite plates. Due to geometrical constraints, the composite microstructure's discontinuities can be categorized as inter-ply and intra-ply. Material testing was conducted at the coupon level as an initial step to ascertain material characteristics. Two full-scale models of intra-ply composite samples were manufactured by employing layers of glass fiber-reinforced prepregs. Discontinuities were generated in the samples using a computer numeric control cutter and then manually applied. The discontinuities' impact on the composite laminate's mechanical properties was assessed through full-scale pieces using three-point bending quasi-static tests. Servo-hydraulic actuators were used to conduct tests on the items. The experimental test results were compared with CAE analysis predictions by evaluating sectional fiber volume fraction. The characteristics of local discontinuities were analyzed using a microscope to enhance the findings of the CAE model. This comprehensive approach offers insights into the intricate connection between internal structural inconsistencies and the mechanical properties of continuous glass fiber-reinforced materials. It supports optimizing composite manufacturing processes and improves composite parts' structural reliability. Dislocation areas were found to result in the formation of resin-rich zones in this investigation. The exothermic curing process in the component's zones results in elevated temperatures, leading to a color change in the resin from clear to yellow. The yellow areas are easily recognizable and show decreased mechanical durability. [ABSTRACT FROM AUTHOR]

The significance of bi-axial testing is increasing with the use of composites in more complex applications and the advent of new manufacturing techniques (Ash and Welsh. Collection of Technical Papers - AIAA/ASME/ASCE/AHS/ASC Structures, Structural Dynamics and Materials Conference, 2004, vol. 2, pp.1402–1412). Existing failure theories have not been proven to be accurate for predicting failure for laminated composites and very limited test data are available for woven composites (Ash and Welsh. Collection of Technical Papers – AIAA/ASME/ASCE/AHS/ASC Structures, Structural Dynamics and Materials Conference, 2004, vol 2, pp.1402–1412). It is believed that the fabrication process used to make composite bi-axial specimens induces initial damage into the specimen (Smits. Exp Anal Nano Eng Mater Struct 2007; 35: 933–934). Two different methods were developed to reduce the amount of damage induced into a bi-axial tests specimen. In addition, the effect of stress concentration due to a center hole added to a composite bi-axial specimen is studied. [ABSTRACT FROM AUTHOR]

This paper presents an experimental and numerical investigation on low velocity impact response of S2 glass/epoxy and aramid/epoxy composite plates. Two different impact energy levels, 20 J and 30 J, were considered for impact tests. The commercial software called LS-DYNA was used in order to perform numerical simulations. The experimental and numerical results were found to be in good agreement. [ABSTRACT FROM AUTHOR]

Discontinuities such as cutouts always cause stress concentration in the structure, which increases the local stress. Understanding the effective parameters on stress concentration and proper selection of these parameters enables the designer to achieve a reliable design. In this paper, the optimum values of the effective parameters on stress distribution around the cutout are determined by genetic algorithm. The fitness function for a genetic algorithm is defined by generalization of the analytical solution based on Lekhnitskii method for different cutouts. The finite element method is used to check the validity of the obtained fitness function. Also, the genetic algorithm was able to predict the optimal value of each effective parameter on stress distribution while keeping constant the values of the other parameters. The results showed that material properties, geometry of cutout and angle load have much effect on stress concentration. [ABSTRACT FROM AUTHOR]

A mesoscopic, time-dependent finite element model for the simulation of dynamic fracture in laminated composite plates is presented. The computational model allows for the simulation of mesh-objective multiple matrix cracking and delamination in laminated composite plates. The analyses are performed with an emphasis on the quantification of the effect of the loading rate on interacting damage mechanisms, i.e. matrix cracking and delamination. In particular, rate effects on damage initiation, propagation, and interaction between matrix cracking and delamination under low and high velocity impact are studied. Moreover, the paper addresses computational issues related to time continuity in stress/strain and velocity fields, during dynamic simulation, at the time of incorporation of new degrees of freedom in a mesh-objective crack modeling approach. Illustrative numerical examples are presented to show the performance of the model. The model is validated with a fast crack growth simulation in a unidirectional laminate. An impact test on a cross-ply laminated plate is performed in order to study the rate effects on structural response and damage mechanics. [ABSTRACT FROM AUTHOR]

The use of micromechanical models to study composite material's behavior leads to save time and cost. In this paper, bridging micromechanical models have been used in order to observe the behavior of unidirectional laminate composite under fatigue loading. In order to study the fatigue behavior, stiffness degradation has been studied as well as the strength degradation and a driftnet model has been proposed for each of them. The strength degradation has only been studied for the unidirectional fiber, while the stiffness degradation has been studied for the fibers with different fiber angle. The results are compared with macro-mechanical models and other methods in literature. [ABSTRACT FROM AUTHOR]

The effectiveness of variable fiber spacing composite (VFSC) laminates subjected to thermal loading is compared with uniformly distributed fiber composite (UDFC) laminates. The higher-order shear deformation theory (HSDT) is adopted to develop a FE model for estimating critical thermal buckling load. Three types of fiber distribution patterns are considered to study the effect of the non-uniform spacing distribution of fiber on thermal buckling, and the results are compared with UDFC. Further, a surrogate model based on the radial basis function network (RBFN) is developed to examine the impact of composite properties uncertainty on the critical buckling response of UDFC and VFSC laminates under thermal loading. The RBFN model is found to be highly efficient and possesses a close match with Monte Carlo simulation (MCS). Though the VFSC laminates possess a large deviation (standard deviation) in the buckling temperature, the stochastic effect (standard deviation/mean) shows relatively minimal variation in VFSC and UDFC laminates. The effect of each composite property is investigated for different lamination sequences and boundary conditions. From the sensitivity analysis, the thermal expansion coefficient of matrix (α m) is found to be the most sensitive property for all the investigated cases. Lastly, the RBFN model is utilized to quantify reliability parameters for multiple stochasticity levels. [ABSTRACT FROM AUTHOR]

We propose an asymptotic framework that may be used as a platform to model general thin microstructural plates, and our initiative is twofold. First, it provides an explanation to why so many tailored plate theories have been introduced for modelling plates bearing microstructures. In hypotheses-based plate theories, the microstructural details within each ply are usually smeared out. But it is shown that with such in-ply details properly taken into account, one manages to address, even only with leading-order terms, several key issues, such as transverse shear strain effects, shear locking, etc., whose rationalisation is believed to necessitate higher-order terms. To a certain degree, the proposed formulation can be used as a target for tailoring kinematic shape functions in both Reissner-Mindlin types of plate theories and zig-zag theories. Second, being slender in nature, a microstructural plate should accommodate a stress state that is close to the state of plane stress. This agrees with our findings that the (leading-order) mechanical units of a microstructural plate should be two-dimensional slices parameterised with the thickness coordinate, distinguishing the proposed framework from other plate theories based on asymptotic analysis. To demonstrate what the present framework can predict beyond existing theories, the effects on the behaviour of fibrous laminates due to manufacturing uncertainties are investigated. [ABSTRACT FROM AUTHOR]

Natural Bouligand structure is a special class of hierarchical architectures, which have proven to be effective in enhancing its mechanical properties. In this work, we demonstrate that the thermal buckling capacity of Carbon Fibre Reinforced Plastics can also be improved by mimicking bio-inspired Bouligand architectures. A finite element approach using commercial software ABAQUS is developed to predict the critical buckling temperature of the Bouligand inspired laminated plates under thermal loading. Numerical predictions show a good agreement with analytical results obtained from the literature. The effectiveness of Bouligand-type composite laminates in enhancing thermal buckling behavior is first confirmed by comparing with unidirectional, cross-ply and quasi-isotropic laminates. We then present the effects of pitch angle and ply thickness on the thermal buckling temperature of bio-inspired Bouligand-type laminates. Finally, we conclude that the improved mechanical and thermal properties can be simultaneously achieved by the Bouligand structure of laminates as the pitch angle is increased. The present study highlights the high thermal buckling behavior of biomimetic Bouligand structure, offering a possibility in developing biomimetic composites with good trade-off between mechanical properties and thermal performance. [ABSTRACT FROM AUTHOR]

A Levi-type analytical solution procedure is developed to characterize static and dynamic deformation response of smart laminated simply-supported composite rectangular plates induced by inclined piezoelectric actuators under (1) constant electrical voltage and (2) time-dependent electrical voltage with excitation frequency. The key to development of this analytical solution is to employ higher order finite integral transform and discretized higher order partial differential unit step function equations. Unlike earlier studies, this research aims to investigate the effect of inclination angle of piezoelectric actuators on static and dynamic deformation response of laminated composite plates under both static and dynamic conditions. The developed analytical solution procedure is implemented computationally through Matlab-based computer code. Its accuracy is initially investigated through convergence study and results comparison with the published literature for a particular case when inclination angle is θ = 0°, which is only limited to bending deformation response. Since there is no published benchmark data for twisting deformation response analysis caused by inclination angle of piezoelectric actuators (θ ≠ 0°), a set of robust and realistic numerical analysis using Abaqus finite element analysis (FEA) is conducted. Good agreement between the analytical and numerical results is observed. Unlike applied electrical voltage, inclination angle of a piezoelectric actuator does not have a significant impact on twisting deformation response during static mode; whereas, both the excitation frequency and inclination angle can significantly influence maximum amplitude of vibration. [ABSTRACT FROM AUTHOR]

This work presents an experimental investigation of the post-fire flexural strength of Filament-wound Glass Fiber Reinforced Polymer (GFRP) tubes manufactured by CTRA Company. These tubes are assembled according to both the NFT57-900 and DIN-16966 standards' recommendations. To this end, flexural tests have been carried out on butt-to-butt assembled tubes, before and after fire endurance tests. To gain a better insight into fire-induced damage mechanisms, thermal analysis (DSC and TGA), FTIR analysis tests, as well as Scanning Electron Microscope (SEM) observations have been conducted. The experimental results revealed that a water leakage was observed prior to the recommended threshold time by the International Maritime Organization (IMO) resolution. It has been also confirmed that flexural properties of the GFRP tube are degraded after the fire tests. Furthermore, a quantitative comparison for both filament tubes assembled according to the NFT and DIN standards confirms that the NFT ones depict higher resistance. Finally, damage investigation reveals that the main observed forms of damage occurring during this experiments are delamination and matrix cracking phenomena. The main novelties of this work are (a) extending the classic analysis carried out on simple composite plate to cover water-filled GFRP assembled tubes subject to fire endurance test, and (b) the experimental investigation of DIN and NFT butt welded joined pipes under three point loading prior and post fire endurance test. [ABSTRACT FROM AUTHOR]

In the present study, the stress distribution and first ply failure strength of hybrid laminated composites subjected to uniaxial tensile and compression loads are predicted using Isogeometric analysis (IGA) based on non-uniform rational B-splines technology, commonly referred to as non-uniform rational B-splines (NURBS) technology. The obtained results were compared to finite element method results (ANSYS) published in the literature and analytical results using Autodesk Helius Composite software. Graphite-glass/epoxy hybrid composite plates are analyzed for different lamination orientations and used to calculate first ply failure strength. Non-interactive theories such as maximum stress, maximum strain, and fully interactive criteria such as Tsai-Wu, Tsai-Hill and Hoffman are used to predict the failure strength of different laminates. The failure envelopes of the hybrid composites are developed using the same failure criteria used for the graphite-glass/epoxy hybrid composite. The effects of IGA refinement and plate's dimension on the present analysis were also established. The IGA results showed good accuracy, robustness and good convergence speed with the analytical software results and the finite element method (FEM) reference value. [ABSTRACT FROM AUTHOR]

The influence of the drilling parameters and the stacking sequence of flax/epoxy composite laminate on the cutting force and the damage induced were studied experimentally and numerically. Drilling tests were carried out based on full experimental design and the delamination at the entry and exit of the hole were quantified using an optical microscopy. Moreover, the damages at the wall of the hole were analyzed using scanning electron microscopy. Based on the experimental results, it was observed that the drilling forces and the machining quality are influenced on the one side by the spindle speed and feed and on the other side by the stacking sequence composite plate. In fact, the cutting forces recorded when drilling a composite plate with [90/0/90/0]2s is 30% higher to the one recorded when drilling a composite made with quasi-isotropic stacking sequence. A numerical model was developed in ABAQUS/Explicit using Hashin's failure criteria in order to predict the cutting forces and the defects induced by the interaction of the drill and composite as a function of the machining parameters. The developed model has been validated at the macro-scale (thrust force) and the meso-scale (delamination at the entry and exit of the hole). [ABSTRACT FROM AUTHOR]

In the present study, the viscoelastic analysis is investigated for composite laminated plates using a smoothed finite element method called cell/element based smoothed discrete shear gap method. Moreover, the hygrothermal effects is considered on the viscoelastic responses of composite laminated plates. The first-order shear deformation theory is employed due to its simplicity and accuracy. With the help of the convolution theorem in Laplace transformation, the complex stress-strain relationship in integral form is simplified to linear in transformed domain. Therefore, all computing procedures are performed in the transformed domain and then, using inverse techniques (Fast Fourier Transform) to converted back to the real-time domain. The study provides an effective computational tool to analyze the viscoelastic response of laminated composite taking into account the influence of the time and hygrothermal effects. [ABSTRACT FROM AUTHOR]

The analytical solution for static analysis of laminated composite plate integrated with piezoelectric fiber reinforced composite actuator is obtained using a recently developed Trigonometric Zigzag theory. The kinematic field consists of five independent field variables accommodating non-linear variation of transverse shear strains through the thickness of the laminated composite plate. The principle of minimum potential energy is adopted to derive the governing equations of equilibrium. Navier's solution technique is employed to convert the system of coupled partial differential equations into a system of algebraic equations. The electric potential is assumed to vary linearly through the thickness of the piezoelectric layer. The analytical formulation also does not include voltage as an additional primary variable. The response in the form of deflection and stresses are obtained for smart composite plates subjected to electro-mechanical loads and compared with the elasticity solutions and available results reported by other researchers in the existing literature. The transverse shear stresses are accurately determined by an efficient post-processing technique of integrating the equilibrium equations of elasticity. Parametric studies on actuation in the response of the smart composite plate are also presented graphically in order to have a clear understanding of the static behavior. [ABSTRACT FROM AUTHOR]

In this study, numerical modeling is used to investigate the performance of a single-sided composite patch with different scale fillers, as reinforcement of a cracked aluminum plate under static tension. The main concerns of previous studies are about the geometry of patches, composite layups, and failure of adhesive. In this research, the effect of patch properties such as size and fiber volume fraction, the thickness of patch, and thickness of adhesive on the overall performance of the cracked aluminum plate are investigated numerically. Indeed, first, a 3 D representative volume element (RVE) is adopted to calculate the mechanical properties of carbon nanotube (CNT)/epoxy and carbon fiber (CF)/epoxy composite patch at each specified volume fraction for investigating the effect of patch properties on the performance of a single-sided patch for crack repairing. In this regard, the cohesive zone model is adopted to analyze the debonding between the epoxy matrix and reinforcement to characterize the mechanical properties of composite patches. Finally, a linear 3 D finite element analysis is performed to calculate the stress intensity factor (SIF) for cracked aluminum plate repaired by a single-sided composite patch at each specified reinforcement volume fraction for different thickness of patch and different thickness of adhesive. The results demonstrated that the stress intensity factor highly depends on the patch properties (patch stiffness) in addition to patch thickness and adhesive thickness. [ABSTRACT FROM AUTHOR]

Composite structure design experience has demonstrated that use of the finite element method during the first stage of the design process is unfounded and that analytical methods to determine the stress–strain state are needed for more accurate calculations. Therefore, an analytical model of the stress–strain state of multilayer composite plates under the influence of temperature, technological, and power loads with different boundary conditions around four boundaries of a rectangular plate was developed. This model enables the solution of more than 240 different boundary value problems with a combination of the following boundary conditions: fixed, moving, hinged, and free edge. In the derivation of this mathematical analytic model, the Kirchhoff hypothesis was applied to the entire body of the anisotropic medium for the interconnected deflection and bending in the plate plane. The resulting equation is an octic linear partial differential equation to express the generalized function of movements. [ABSTRACT FROM AUTHOR]

Free-edge effects in fibre reinforced composites can produce premature damage at the composite edges due to mechanical, geometrical and hygro–thermal effects. Observation of damage on the free-edge of a composite plate is therefore different than what can be observed inside the material. The amount of individually broken fibres in a composite is counted by observing a test specimen with a polished edge and by cutting test specimens to observe damage inside the material. The amount of damage observed on a polished edge is found to greatly exceed that which is observed inside test specimens subjected to the same testing conditions. It is shown that the progression of important damage mechanisms can be observed on polished edges, but also that invalid damage mechanism may be observed using free-edge microscopy. [ABSTRACT FROM AUTHOR]

In the notched structures, to achieve maximum buckling resistance in comparison with structural weight, the optimal design of a stiffener is very important. In this research, after a review of the existing literature, nonlinear buckling behavior of composite plates containing the cutout with three different designs of stringer was investigated. The considered stiffeners are planer, longitudinal, and ring types. The buckling experiments were carried out on the stiffened plates containing a circular notch. Moreover, to achieve an efficient prediction of the buckling in the stiffened laminate with the hole, a finite strip method is developed based on the Airy stress function and von Karman's large deformation equations. Studies show that there is a good agreement between the postbuckling behaviors derived from developed finite strip method with experimental results. Fast convergence of the considered finite strip method compared with the finite element results shows its efficiency for prediction of buckling behavior in laminated composites. The results show that the buckling load-bearing capacities of perforated plates with a longitudinal and planer stiffener are higher compared with the other stiffener, respectively. The detailed parametric study on the effects of thickness of the plate and stiffener and opening diameter on buckling behavior was performed using experiments and modeling. [ABSTRACT FROM AUTHOR]

Although ultrasonic pulse-echo C-scanning is a mature non-destructive evaluation technique for imaging internal damage in composite structures, a major impediment of obtaining a full characterization of the internal damage state is delamination shadowing effects. Specifically, shadowing refers to regions of interest that are behind other delamination planes or discontinuities with respect to the scanning surface. The delamination planes block ultrasonic wave transmission and the regions of interest are thus hidden (i.e. shadowed) from the scan. A methodology has been developed to expand ultrasonic scan data of impacted composites by utilizing damage morphology information that is well established in the composite impact research community, such as matrix cracks bounding delaminations, to estimate shadowed delamination information and matrix cracking. First, impacted flat composite plates were C-scanned by pulse-echo ultrasonic and the results were segmented by depth of damage to establish interface-by-interface delamination information. These delaminations were then fit by bounding lines representing the fiber/matrix crack directions defined by the orientations of plies adjacent to each interface to estimate the shadowed portion of the delamination results. The area inside this boundary was added to the original ultrasonic delamination area to create an estimation of the full delamination state at each shadowed interface. Additionally, because this extension method is based on the interactions between delaminations and matrix cracking, this extension method provides an approximation of the matrix cracking of adjacent plies. Results were compared with X-ray computed tomography scans to assess the effectiveness of the extension method. [ABSTRACT FROM AUTHOR]

The interest in materials having natural, environmentally friendly, renewable and low density/cost is increasing day by day due to sanctions imposed to reduce the emission rates, especially the Kyoto Protocol. In recent years, the use of environmentally friendly composites by using natural fibers such as flax, jute and sisal has increased in engineering applications. Milling operation has frequently been an important method of machining which can achieve the desired dimensions and tolerances for the plate-shaped parts. In this study, the effects of cutting parameters such as cutting speed and feed rate on cutting force, delamination factor and surface roughness in end milling of jute fiber-reinforced polymer composite plates with different orientation angle (0°/90°, 30°/−60° and ±45°) were examined by using the cemented carbide (WC) end mills (two, three and four number of flutes). Cutting force, deformation factor and surface roughness were found to be influenced by the feed rate and cutting speeds. In addition, increasing the number of the flutes of the cutting tools reduced the cutting force, delamination factor and surface roughness. [ABSTRACT FROM AUTHOR]

This work is intended to characterize the mechanical behavior of hybrid carbon–glass composite plates under combined loading of bending and torsion, and to determine the optimal ply fiber orientations to minimize the maximum out-of-plane displacement under such loading conditions. Hybrid composite plates were manufactured with 10 plies each and different stacking sequences using hand lay-up, with carbon fiber and glass fiber reinforcements in an epoxy matrix. Two experimental setups (involving two distinct boundary conditions) are here considered to test the composite plates, both simulating combined loading of bending and torsion. Numerical simulations of the experimental tests were performed in ABAQUS® and validated with the experimental data. Using the ply fiber orientations as design variables, the hybrid composite plates were then optimized using global and local optimization using direct search (GLODS). The objective function of minimization of the maximum out-of-plane displacement is carried out through an interactive cycle between GLODS and ABAQUS®. Specimens of three optimized laminates were also manufactured for experimental validation. The optimization process contributed to improve the performance of the hybrid composite plates in more than 30% when compared to some non-optimized plates. [ABSTRACT FROM AUTHOR]

This study deals with the problem of the least-weight design of a composite multilayer plate subject to constraints of different nature (mechanical, geometrical and technological requirements). To face this problem, a multi-scale two-level design methodology is proposed. This approach aims at optimising simultaneously both geometrical and mechanical parameters of the laminate at each characteristic scale (mesoscopic and macroscopic ones). In this background, at the first level (macroscopic scale), the goal is to find the optimum value of geometrical and mechanical design variables minimising the structure mass and satisfying the set of imposed constraints (on first buckling load, membrane stiffness and feasibility constraints). The second-level problem (mesoscopic scale) aims at finding at least one stacking sequence meeting the geometrical and material parameters provided by the first-level problem. The multi-scale two-level optimisation approach is based on the polar formalism to describe the macroscopic behaviour of the composites (in the framework of the equivalent single-layer theories) and on a special genetic algorithm to perform composite calculations. The optimum solutions provided by the multi-scale two-level optimisation strategy are characterised by a weight saving of about 10% with enhanced mechanical properties when compared to conventional symmetric balanced stacks. The effectiveness of the optimum solutions is also proven through an experimental campaign of buckling tests. The experimental results are in excellent agreement with those foreseen by the numerical simulations. [ABSTRACT FROM AUTHOR]

The present study is concerned with static and free vibration analyses of laminated functionally graded carbon nanotube reinforced composite rectangular plates on elastic foundation based on nth-order shear deformation theory. Four types of carbon nanotubes distributions along the plate thickness are considered, which include uniformly distributed and three other functionally graded distributions. Governing differential equations are derived by means of Hamilton's principle. The differential quadrature method is developed to formulate the problem, and rapid convergence is observed in this study. A numerical comparison with available results in the literature is carried out to show the validity of the proposed theory. Furthermore, effects of the carbon nanotubes volume fraction, thickness side ratio, aspect ratio, foundation parameters, different thermal environments, the number of layers, lamination angle, boundary condition, and carbon nanotubes distribution types on the static response of laminated functionally graded carbon nanotube reinforced composite plates are also investigated. [ABSTRACT FROM AUTHOR]

The presence of holes in composite plates subjected to a uniform heat flux induces thermal stresses. Hole geometry is one of the important parameters in the stress distribution in perforated composite plates. In this study, using the two-dimensional thermoelastic theory, and on the basis of the Lekhnitskii' complex variable technique in steady-state condition, stress distribution around holes with different shapes in an infinite composite plate under uniform heat flux is investigated. Using a conformal mapping function, the thermal stress analysis of an infinite plate with a circular hole under a uniform heat flux is developed to analyze the plate containing a noncircular hole. The perforated composite plate is under a uniform heat flux at infinity and Neumann boundary conditions and thermal-insulated condition at the edge of the hole are considered. The rotation angle of the hole, fiber angle, the flux angle, and bluntness are important parameters investigated in the present study. In addition, the optimal values of the effective parameters to achieve the lowest thermal stress around different holes have been reported for several different materials. The obtained results show that these parameters have a significant effect on the stress and displacement distributions around the rectangular hole. [ABSTRACT FROM AUTHOR]

High-frequency-response, semiconductor, strain gages used in various combinations have been embedded in S-2 glass epoxy composite test plates during in-house fabrication using vacuum-assisted resin transfer molding in order to measure the transient strain and its rate during the impingement of the shock wave and subsequent interactions. To validate the techniques systematically, an in-house-developed, split-view time-resolved, stereo digital image correlation system has been used to compare static and time-dependent strain signals on a two-dimensional surface in a shock tube facility. Small size non-encapsulated solid-state gages were cumbersome to handle during the fabrication process, while encapsulated strain gages had very good spatial resolution and overall performance combined with some ease in handling during fabrication. The strain results indicate that embedding sensors is an accurate and inexpensive method to characterize composites under high-rate loading. [ABSTRACT FROM AUTHOR]

This study deals with a micromechanical detection of stiffness degradation occurred by the fiber damage in vibrating laminated composite plates. Five unknown parameters are considered to determine the fiber or matrix damage distribution, which is a modified form of the bivariate Gaussian distribution function. The proposed approach is more feasible than the conventional element-based damage detection method from the computational efficiency because it is independent on the number of divided elements. The micromechanical model is embedded in the reconstruction algorithm using the modified Halpin–Tsai formulation. The numerical examples show that the proposed technique is a feasible and practical method, which can prove the location of a damaged region as well as inspect the distribution of deteriorated stiffness of composites for different fiber angles and layup sequences. [ABSTRACT FROM AUTHOR]

Sophisticated analytical solution methods for the stress concentration problem in multilayered composites with interference-fit bolts have been developed on the basis of layer-related solutions. The model is based on a circular or elliptical isotropic bolt integrated in a fibre- or textile-reinforced multilayered composite plate. For the simulation of the interference between bolt and composite plate a modelling strategy has been proposed featuring the application of a defined temperature load to a metallic elastic inclusion. For analysing the stress concentration effects in the surrounding plate, complex-valued displacement functions in combination with the method of conformal mappings for the interface between inclusion and plate and a combination of boundary collocation and least squares method for the outer boundary are used. For the verification of the developed calculation methods, a number of experimental and numerical studies have been carried out and the decay behaviour of the distortions have been compared for different radians. For all combinations of multilayered composite plate and interference-fit bolt investigated so far, a good correlation of the analytically calculated and the numerically determined results can be observed. [ABSTRACT FROM AUTHOR]

The aim of this study is to diagnose and classify the failure modes for two serial fastened sandwich composite plates using data mining techniques. The composite material used in the study was manufactured using glass fiber reinforced layer and aluminum sheets. Obtained results of previous experimental study for sandwich composite plates, which were mechanically fastened with two serial pins or bolts were used for classification of failure modes. Furthermore, experimental data from previous study consists of different geometrical parameters for various applied preload moments as 0 (pinned), 2, 3, 4, and 5 Nm (bolted). In this study, data mining methods were applied by using these geometrical parameters and pinned/bolted joint configurations. Therefore, three geometrical parameters and 100 test data were used for classification by utilizing support vector machine, Naive Bayes, K-Nearest Neighbors, Logistic Regression, and Random Forest methods. According to experiments, Random Forest method achieved better results than others and it was appropriate for diagnosing and classification of the failure modes. Performances of all data mining methods used were discussed in terms of accuracy and error ratios. [ABSTRACT FROM AUTHOR]

In this article, static and dynamic responses of cross-ply bi-stable composite plates were studied. To accurately predict the natural frequencies and snap-through load, a set of higher order shape functions were proposed. In static analysis, the stable configurations, the deflection of corners, and the midpoint of the plate were calculated. For dynamic analysis, Hamilton’s principle is used to provide approximate solutions to the vibration problem under study. The responses of the plate under ramp and harmonic applied forces were determined, the effect of shape functions on the prediction of the first natural frequency of the plate and the required force for snap-through were investigated. A finite element model is also developed to study the static and vibration characteristics of bi-stable composite plate. The qualitative and quantitative comparisons between the finite element method results and those obtained from the present analysis are generally good and satisfactory. The developed analytical model can also be used for parametric study and further design modification. [ABSTRACT FROM AUTHOR]

A multiaxial quasi-brittle failure criterion for notched orthotropic composites is developed with an emphasis on establishment of an analytical formula to predict their anisotropic notched strength for any notch size under any multiaxial proportional loading. It is formulated by replacing the principal unnotched strengths with the principal notched strengths in the framework of the Tsai–Hill static failure criterion for orthotropic composites. The effects of notch size and specimen width on the principal notched strengths are described by means of the Suo-Ho-Gong model that can consider notch ductile-to-brittle transition. From the proposed multiaxial quasi-brittle failure criterion, an analytical formula is derived to predict the notched strength of finite orthotropic composite plates under multiaxial proportional loading at any angle with the principal directions of material anisotropy. The notched strength prediction formula involves a generalized notch sensitivity parameter that can be defined for any multiaxial state of stress. The multiaxial notch sensitivity parameter allows uniquely defining an intrinsic equivalent mode-I fracture toughness that is independent of notch size as well as of specimen width for any multiaxial proportional loading. Furthermore, an anisotropic size effect law for apparent equivalent mode-I fracture toughness that considers not only the effect of notch size but also the effect of specimen width is derived from the failure criterion. Finally, a quasi-brittle failure criterion for notched interface is briefly discussed as a particular case of the proposed quasi-brittle failure criterion for notched orthotropic composites. [ABSTRACT FROM AUTHOR]

In this study, failure analysis was researched in woven glass fiber-reinforced epoxy resin composite plates jointed with two parallel pins under the effect of seawater. The effects of immersion time in seawater and changes in joint geometry on first failure loads were experimentally examined. In addition to this, the experimental results were compared with the results of the finite element analysis and artificial neural network modeling. The specimens were immersed in seawater for periods of 0, 3, and 6 months to observe the effects of seawater. For joint geometry, the parameters of the edge distance-to-upper hole diameter (E/D), the two hole-to-hole center diameter (K/D), the distance from the upper or the lower edge of the specimen to the center of the hole-to-hole diameter (M/D), and the width of the specimen-to-hole diameter (W/D) ratios were selected. In the numerical analysis, the finite elements models of the specimens were realized with the ANSYS 11.0 finite elements modeling and the Tsai-Wu failure criteria were used to predict the first failure loads. The comparison made in this study, results of the experimental, the finite element analysis, and artificial neural network modeling were compared and were found to be in good agreement for the first failure load. [ABSTRACT FROM AUTHOR]

In this study, buckling behavior of adhesively patch repaired composite plates was investigated experimentally and numerically. Unidirectional carbon/epoxy composite plates with circular cutout were repaired with an adhesively bonded patch. Critical buckling loads of composite plates were researched without cutout, circular cutout, single patch-repaired, and double patch-repaired conditions. In addition to circular hole dimensions, patch length and adhesive thickness were used as geometrical parameters. Numerical study was performed in ANSYS finite element software three dimensionally. As a result, the critical buckling loads of single and double patch-repaired composite plates were increased from 96 and 263 ratios higher than circular-cutout composite plates. The percentile errors between experimental and numerical studies were determined from 2 to 11.5. [ABSTRACT FROM PUBLISHER]