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Showing papers on "Composite laminates published in 2000"


Journal ArticleDOI
TL;DR: The most widely applied methods for the production of composite materials and composite parts are based on casting techniques such as the squeeze casting of porous ceramic preforms with liquid metal alloys and powder metallurgy methods.

836 citations


Journal ArticleDOI
TL;DR: In this paper, the authors investigate the low velocity impact load level at which a composite laminate will delaminate and find that a sudden load drop occurs due to specimen stiffness loss as a result of laminate level damage.
Abstract: An investigation of the low velocity impact load level at which a composite laminate will delaminate is presented. The delamination threshold load is described as the load level, obtained from the load–time history or load–displacement plot, at which a sudden load drop occurs due to specimen stiffness loss as a result of laminate level damage. Approximately 500 low velocity impact load–time histories from the Air Force Research Laboratory (AFRL) Low Velocity Impact Database are used to investigate the delamination threshold load. The database contains laminate impact test data for graphite/epoxy (AS4/3501-6), graphite/PEEK (AS4/APC-2), and graphite/BMI (IM7/5260) material systems. The delamination threshold load observations are compared to C-scan damage measurements of impacted specimens to determine if the sudden load drop corresponds to delamination development.

477 citations


Journal ArticleDOI
TL;DR: In this paper, an overview of the fracture behavior and failure mechanisms of composite laminates containing woven fabrics in mode I and mode II delamination and under impact loading is presented, where potential advantages of using woven fabrics as opposed to cross-ply unidirectional prepreg tapes are discussed from the viewpoint of the microstructure/property relationship.

324 citations


Journal ArticleDOI
TL;DR: In this article, the authors derived a criterion for small-mass (wave controlled) impact response of orthotropic plates and showed that the response type is governed by the impactor-plate mass ratio and not by impact velocity.
Abstract: Impact duration strongly influences the impact response of plates. Long impacts cause a quasi-static response influenced by the plate size and boundary conditions. Short impacts cause a response governed by wave propagation unaffected of plate size and boundary conditions. This paper shows that the response type is governed by the impactor–plate mass ratio and not by impact velocity and derives a criterion for small-mass (wave controlled) impact response of orthotropic plates. Published criteria for large-mass (quasi-static) impact are discussed. Small-mass impacts on composite laminates are shown to be more critical than large-mass impacts of the same energy. Use of mass criteria for selecting analytical response models and considerations for sandwich plates are also discussed.

297 citations


Journal ArticleDOI
TL;DR: In this article, a review is made on the different methods used for the estimation of transverse/interlaminar stresses in laminated composite plates and shells both analytical and numerical methods are considered In numerical methods, while the emphasis is given on finite element methods, other methods like the finite difference method is also briefly discussed Aspects considered are: effects of variation in geometric and material parameters, transverse shear and normal deformation, interface stress continuity and the interfacial bonding on the accuracy of prediction of cross-sectional and interlinear stresses.

297 citations


Journal ArticleDOI
TL;DR: In this paper, the authors examined delaminations and matrix cracking caused by low-energy impacts on quasi-isotropic carbon/PEEK laminated plates by means of different pulse-echo techniques.
Abstract: Conventional ultrasonic inspection methods are largely used for detection of delaminations in composite materials while only recently new techniques have been proposed to identify matrix cracks in simple tension loaded coupon specimens. In this study delaminations and matrix cracking caused by low-energy impacts on quasi-isotropic carbon/PEEK laminated plates are examined by means of different pulse-echo techniques: conventional time-of-flight and amplitude C-scans at normal incidence are used to check for the presence of delaminations, while backscattering C-scans (in which the transducer is set at an angle to the laminate plane) allow the detection of matrix cracks through the laminate thickness. Selected results from full waveform ultrasonic analysis of impacted carbon/PEEK laminates are discussed and compared with X-ray data in order to demonstrate the efficiency of the proposed inspection technique.

209 citations


Journal ArticleDOI
TL;DR: The basic aspects of a material mesomodel dedicated to composite laminates and capable of simulating complete fracture phenomena are discussed and the description of localisation phenomena is described.

183 citations


Journal ArticleDOI
TL;DR: In this paper, an experimental program was conducted using graphite/epoxy AS4/3501-6 material to validate the fatigue progressive damage model, developed in the first part of this paper, and an extensive experimental program, by using standard experimental techniques, was performed for this purpose.
Abstract: To validate the fatigue progressive damage model, developed in the first part of this paper, an experimental program was conducted using graphite/epoxy AS4/3501-6 material. As the input for the model, the material properties (residual stiffness, residual strength and fatigue life) of unidirectional AS4/3501-6 graphite/epoxy material are fully characterized under tension and compression, for fiber and matrix directions, and under in-plane and out-of-plane shear in static and fatigue loading conditions. An extensive experimental program, by using standard experimental techniques, is performed for this purpose. Some of the existing standard testing methods are necessarily modified and improved. To evaluate the progressive fatigue damage model, fatigue behaviour of pin/bolt-loaded composite laminates is simulated as a complicated example. The model is validated by conducting an experimental program on pin/bolt-loaded composite laminates and by comparison with experimental results from other authors. Different...

182 citations


Journal ArticleDOI
TL;DR: In this article, the wavelet transform using the Gabor wavelet is applied to the time-frequency analysis of dispersive plate waves, and it is shown that the peaks of the magnitude of WT in the timefrequency domain are related to the arrival times of group velocity.

182 citations


Journal ArticleDOI
TL;DR: In this article, a set of fundamental dynamic equations of a two-dimensional higher-order theory for thick rectangular laminates subjected to in-plane stresses is derived through Hamilton's principle.

181 citations


Journal ArticleDOI
TL;DR: In this article, a finite-element model is developed to predict the response of pin-loaded composite plates, taking into account contact at the pinhole interface, progressive damage, large deformation theory, and a non-linear shear stress-strain relationship.

Journal ArticleDOI
TL;DR: In this paper, composite sandwich beams were fabricated by bonding unidirectional carbon/epoxy face sheets (laminates) to aluminum honeycomb cores with an adhesive film, and they were tested under four-point and three-point bending.

Journal ArticleDOI
TL;DR: In this article, the impact behavior of carbon fiber/epoxy composite laminates reinforced by short fibres and other interleaving materials was investigated, and the trade-off between impact resistance and residual strength was minimized for composites reinforced by Zylon fibres.
Abstract: Low-velocity impact tests were performed to investigate the impact behaviour of carbon fibre/epoxy composite laminates reinforced by short fibres and other interleaving materials. Characterisation techniques, such as cross-sectional fractography and scanning acoustic microscopy, were employed quantitatively to assess the internal damage of some composite laminates at the sub-surface under impact. Scanning electron microscopy was used to observe impact fractures and damage modes at the fracture surfaces of the laminate specimens. The results show that composite laminates experience various types of fracture; delamination, intra-ply cracking, matrix cracking, fibre breakage and damage depending on the interlayer materials. The trade-off between impact resistance and residual strength is minimised for composites reinforced by Zylon fibres, while that for composites interleaved by poly(ethylene-co-acrylic acid) (PEEA) film is substantial because of deteriorating residual strength, even though the damaged area is significantly reduced. Damages produced on the front and back surfaces of impact were also observed and compared for some laminates.

Journal ArticleDOI
TL;DR: In this article, a shell/3D modeling technique was developed for which a local solid finite element model is used only in the immediate vicinity of the delamination front, and the results were in good agreement with mixed mode strain energy release rate distributions obtained from computations where the entire specimen had been modeled with solid elements.
Abstract: A shell/3D modeling technique was developed for which a local solid finite element model is used only in the immediate vicinity of the delamination front. The goal was to combine the accuracy of the full three-dimensional solution with the computational efficiency of a shell finite element model. Multi-point constraints provided a kinematically compatible interface between the local 3D model and the global structural model which has been meshed with shell finite elements. Double Cantilever Beam, End Notched Flexure, and Single Leg Bending specimens were analyzed first using full 3D finite element models to obtain reference solutions. Mixed mode strain energy release rate distributions were computed using the virtual crack closure technique. The analyses were repeated using the shell/3D technique to study the feasibility for pure mode I, mode II and mixed mode I/II cases. Specimens with a unidirectional layup and with a multidirectional layup were simulated. For a local 3D model, extending to a minimum of about three specimen thicknesses on either side of the delamination front, the results were in good agreement with mixed mode strain energy release rates obtained from computations where the entire specimen had been modeled with solid elements. For large built-up composite structures the shell/3D modeling technique offers a great potential for reducing the model size, since only a relatively small section in the vicinity of the delamination front needs to be modeled with solid elements.

Journal ArticleDOI
TL;DR: This paper explores the development of suitable models for machining of composites and for coupling the models to intelligent control strategies and proposes an intelligent machining scheme as the basis for the design of a new machine tool.
Abstract: Composite laminates exhibit very high in-plane strengths but are plagued by delamination damage when subjected to machining. This is due to their poor transverse strengths and low delamination fracture toughness. In drilling, delamination is initiated when the thrust force exceeds a threshold value, particularly at the critical entry and exit locations of the drill bit. To minimize damage, therefore, it is important to monitor process variables such as the machining forces and the position of the tool relative to the workpiece. The availability of a suitable model coupled with an intelligent control scheme would be a large advancement in the machining of composite laminates. This paper explores the development of such models for machining of composites and for coupling the models to intelligent control strategies. Using a machining center, a series of drilling experiments were conducted on carbon fiber-reinforced composite laminates to determine key process parameters for various cutting conditions. An intelligent machining scheme is proposed as the basis for the design of a new machine tool.

Journal ArticleDOI
TL;DR: In this article, the thermal response of laminated glass fiber reinforced panels to severe fire conditions has been investigated by furnace fire testing and thermal modelling, and excellent fire resistance has been demonstrated for several matrix materials and the materials response has been modelled to a high degree of accuracy.
Abstract: The thermal response of laminated glass fibre reinforced panels to severe fire conditions has been investigated by furnace fire testing and thermal modelling. Excellent fire resistance has been demonstrated for several matrix materials and the materials response has been modelled to a high degree of accuracy. The thermal resistance properties are due to a combination of low thermal conductivity, good structural integrity and significantly, the endothermic decomposition of the matrix, which slows down the heat transmission through the laminate.

Journal ArticleDOI
TL;DR: In this paper, a general solution is obtained to consider an arbitrary shape of hole and arbitrarily oriented uniaxial, biaxia, and shear stresses at infinity as well as uniform tangential force, and uniform pressure around the hole.

Journal ArticleDOI
TL;DR: In this article, the authors evaluated the changes in the mechanical properties, mass and coefficient of thermal expansion of composites in space, graphite/epoxy composite specimens were exposed to simulated low earth orbit (LEO) environmental conditions including ultraviolet radiation, thermal cycling and high vacuum.
Abstract: In order to evaluate the changes in the mechanical properties, mass and coefficient of thermal expansion of composites in space, graphite/epoxy composite specimens were exposed to simulated low earth orbit (LEO) environmental conditions including ultraviolet radiation, thermal cycling and high vacuum. Surface morphology was investigated by using a scanning electron microscope, and outgassed products were analyzed with a quadrupole mass spectrometer. The failure cycle of composite laminates exposed to the attack of LEO environmental factors was predicted by using four modified failure criteria. The modified failure criteria were expressed as a function of stresses as well as thermal cycles.

Journal ArticleDOI
TL;DR: In this paper, a finite element model for predicting shear and normal stresses in the adhesive layer of plated reinforced concrete beams has been developed and the numerical results carried out agree with those obtained in previous studies by other authors.
Abstract: In this paper a finite element model for predicting shear and normal stresses in the adhesive layer of plated reinforced concrete beams has been developed. The numerical results carried out agree with those obtained in previous studies by other authors. It is found that shear stresses and high concentrations of peeling forces are present at the ends of the plates when the composite beam is loaded in flexure. These concentrations can produce premature failure of the strengthened beam because of debonding of the plate or cracking of the concrete cover along the level of internal steel reinforcement. The numerical simulation captures the actual interfacial stresses and, in particular, the maximum values of shear and normal stresses.

Journal ArticleDOI
TL;DR: In this paper, a comprehensive experimental program was conducted to measure and characterize the development of damage in the vicinity of fastener holes in graphite/epoxy composite laminates.

Journal ArticleDOI
H.A. Whitworth1
TL;DR: In this article, the residual strength degradation in graphite/epoxy composite laminates is evaluated and a model proposed relating residual strength to the applied fatigue cycles and the maximum applied stress.

Journal ArticleDOI
TL;DR: In this paper, the steering of composite tows within composite laminates has been investigated as a means of producing composite structures with increased strength, and a manufacturing technique for the steered plies has been proposed.
Abstract: Trajectorial fibre steering of composite tows within composite laminates has been investigated as a means of producing composite structures with increased strength. Strategies to design the fibre trajectories in laminates have included aligning the fibres with principal stress vectors and a newly developed concept of load paths. In the laminate, the steered plies were inter-mingled with unidirectional or fabric plies. A manufacturing technique for the steered plies has been proposed. Applications include a specimen containing an open hole and a specimen with a pin-loaded hole. Specific strength increases of 62 and 85%, respectively, were achieved.

Journal ArticleDOI
TL;DR: In this paper, a higher order shear deformation theory is used to investigate the instability associated with composite plates subject to dynamic loads, both transverse shear and rotary inertia effects are taken into account.

Journal ArticleDOI
TL;DR: Fan et al. as discussed by the authors employed the equivalent constraint model of the damaged lamina to evaluate stiffness degradation due to delaminations growing at the 0°/90° interface from the tips of transverse cracks in the 90° plies and splits in the 0m/90n]s laminates.
Abstract: In an effort to evaluate stiffness degradation due to delaminations growing at the 0°/90° interface from the tips of transverse cracks in the 90° plies and splits in the 0° plies of cross-ply [0m/90n]s laminates, a new theoretical approach was developed. It employs the Equivalent Constraint Model of the damaged lamina [Fan J, Zhang J. In-situ damage evolution and micro/macro transition for laminated composites. Composites Science and Technology 1993;47:107–118], which allows one to avoid cumbersome consideration of the repeated laminate element defined by the intersecting pairs of transverse cracks and splits. It also uses an improved 2D shear-lag analysis [Zhang J, Soutis C, Fan J. Strain energy release rate associated with local delamination in cracked composite laminates. Composites 1994;25(9):851–862] to determine the stress fields in the explicitly damaged lamina and the In situ Damage Effective Functions to describe its reduced stiffness properties. Reduced stiffness properties of the damaged lamina are found to depend explicitly upon the crack density and relative delamination area associated with that lamina and implicitly upon two damage parameters associated with the neighbouring lamina. Theoretical predictions reveal that transverse crack tip delaminations cause significant reduction in the shear modulus and Poisson's ratio of cross-ply and symmetric balanced [±θm/90n]s laminates. Dependence of the laminate reduced elastic properties on the orientation angle of the constraining ply is examined. Contribution of each damage mode (transverse cracking, transverse crack tip delaminations, splitting and split tip delaminations) into stiffness loss is established.

Journal ArticleDOI
TL;DR: In this paper, a numerical analysis for predicting the residual compressive strength of delaminated plates is proposed, where the delamination propagation is modelled by using a damage model based on the indirect use of fracture mechanics.

Journal ArticleDOI
TL;DR: In this paper, the impact behavior and damage tolerance properties of Kevlar multiaxial warp-knit fabric composites and woven and unidirectional composite laminates were evaluated.

Journal ArticleDOI
TL;DR: In this article, an iterative method has been applied to analyze free edge interlaminar stresses of composite laminates which are subject to extension, bending, twisting and thermal loads.

Journal ArticleDOI
TL;DR: In this article, three distinct cross-ply laminate models were compared with each other and with finite element analysis (FEA) predictions for the effective moduli of transversely cracked laminates.

Journal ArticleDOI
TL;DR: In this article, two refined higher-order theories, one that neglects and the other that takes into account the effect of transverse normal deformation, are used to develop two discrete finite element models for the thermal buckling analysis of composite laminates and sandwiches.
Abstract: Two refined higher order theories, one that neglects and the other that takes into account the effect of transverse normal deformation, are used to develop two discrete finite element models for the thermal buckling analysis of composite laminates and sandwiches. The two models, one with nine degrees of freedom per node and the other with eleven degrees of freedom, are based on a nine-node Lagrangian isoparametric element. The geometric stiffness matrices are developed by taking into consideration the effects of the higher order terms on the initial in-plane and transverse shear stresses. The accuracy of the present formulations is first evaluated by analyzing sample problems for which analytical three-dimensional solutions exist in the literature. Numerical results are presented for the first time for sandwich plates, demonstrating the importance and accuracy of the higher order theory in comparison to first-order theory. Some new results are also given for sandwich plates with angle-ply composite face s...

Journal ArticleDOI
TL;DR: In this paper, the authors proposed a methodology for fatigue life prediction that utilizes a micromechanics based evaluation of damage evolution in conjunction with a semi-empirical fatigue failure criterion.
Abstract: The current practice, as well as the hitherto proposed models, for assessment of fatigue life of composite laminates rely largely on experimental fatigue life data. In this paper, we propose a methodology for fatigue life prediction that utilizes a micromechanics based evaluation of damage evolution in conjunction with a semi-empirical fatigue failure criterion. The specific case treated is that of cross ply laminates under cyclic tension. The predicted results are compared with experimental data for several glass/epoxy and carbon/epoxy laminates, and good agreement is found.