Showing papers on "Composite laminates published in 1994"
491 citations
TL;DR: In this paper, the effect of void content on the static strength and fatigue life of composite laminates under flexural loading was investigated. And the authors proposed a fracture criterion correlating the ultrasonic attenuation to the strength of composite laminate and showed that voids have a strong detrimental effect on the fatigue life.
255 citations
TL;DR: In this paper, a diamond-impregnated tubular drill tool was designed and tested, which resulted in a much smaller thrust and much better hole quality as compared with the standard twist drills.
Abstract: Composite laminates in significant numbers are rendered unacceptable due to delamination that occurs during the drilling operation. Thrust generated during the drilling operation is identified as responsible for delamination. Expressions developed for critical thrusts and critical feed rates, by modeling the delamination zone as an elliptical plate in unidirectional laminates, appear to be fairly accurate. It has been demonstrated that the critical thrusts and feed rates obtained for unidirectional laminates can be conservatively used for multi-directional laminates. With regard to the tool geometry, the chisel edge width appears to be the single most important factor contributing to the thrust force and hence delamination. A diamond-impregnated tubular drill tool was designed and tested. This tool resulted in a much smaller thrust and much better hole quality as compared with the standard twist drills.
169 citations
TL;DR: In this paper, failure modes of Spectra polyethylene fiber-reinforced composites were examined under ballistic impact loading, and they were found to exhibit sequential delamination, cut-out of a plug induced by through-the-thickness shear, and combined modes of shear and tensile failure offibers in the cases of glass and graphite fiber composites.
Abstract: Failure modes of Spectra polyethylene fiber-reinforced composites were examined under ballistic impact loading. Both woven fabric-reinforced laminates and angle-plied unidirectional fiber-reinforced laminates were found to exhibit sequential delamination, cut-out of a plug induced by through-the-thickness shear, and combined modes of shear and tensile failure offibers as obserxed in the cases of glass and graphite fiber composites. At low areal density, both laminates demonstrated similar ballistic limits. However, as areal density increased, differences in ballistic limit became more apparent, with angle-plied composite laminates showing higher values. When subjected to the repeated impact of a constant striking velocity below the ballistic limit, a progressive growth of local delamination was observed until gross failure of composites occurred. The use of lower striking velocity of the projectile led to the increase in cumulative numbers of impacts for full penetration defining an impact fatigue lifetim...
132 citations
Abstract: A new higher order plate theory for modeling delamination buckling and postbuckling of composite laminates is developed Delaminations between layers of composite plates are modeled by jump discontinuity conditions, in both lower and higher order terms of displacements, at the delaminated interfaces Some higher order terms are identified at the beginning of the formulation by using the conditions that shear stresses vanish at all free surfaces including the delaminated interfaces Therefore, all boundary conditions for displacements and stresses are satisfied in the present theory Geometric nonlinearity is included in computing layer buckling The general governing equations, along with all boundary and continuity conditions of plates, are derived for predicting the delamination buckling and postbuckling behavior The associated delamination growth problem is also examined by the use of Griffith-type fracture criterion A numerical example is presented to validate the theory The results are also compared with experimentally obtained data
127 citations
TL;DR: In this paper, a micromechanics model is presented to predict thermoelastic properties of composites reinforced with plain weave fabrics, where a representative volume element is chosen for analysis and the fiber architecture is described by a few simple functions.
Abstract: A micromechanics model is presented to predict thermoelastic properties of composites reinforced with plain weave fabrics. A representative volume element is chosen for analysis and the fiber architecture is described by a few simple functions. Equations are developed to calculate various phase fractions from geometric parameters that can be measured on a cross section. Effective elastic moduli and effective thermal expansion coefficients are determined under the assumption of uniform strain inside the representative volume element. The resulting model is similar to the classical laminated theory, and hence is easier to use than other models available in the literature. An experimental correlation is provided for a number of Nicalon SiC/CVI SiC and Graphite/CVI SiC composite laminates.
113 citations
TL;DR: In this article, a micromechanistic deformation model is proposed where loading direction and weave parameters are allowed to vary and the model provides improved estimates for the linear elastic stiffness.
Abstract: A micromechanistic deformation model, that could realistically be incorporated into structural finite element codes, is proposed where loading direction and weave parameters are allowed to vary. Comparisons are made to previous models and experimental results for woven materials, indicating that the proposed model provides improved estimates for the linear elastic stiffness. The model further provides predictions for internal stresses in the longitudinal, transverse, and interlace regions of the woven laminate which qualitatively correspond to the experimentally observed failure mechanisms
108 citations
Journal Article•
TL;DR: In this article, the possibility of using Lamb waves for the long range NDE evaluation of composite laminates has been investigated and three different possible testing strategies using the S[sub 0] Lamb mode were described and evaluated.
Abstract: The possibility of using Lamb waves for the long range nondestructive evaluation (NDE) of composite laminates has been investigated. Three different possible testing strategies using the S[sub 0] Lamb mode--S[sub 0] mode transmission, S[sub 0] mode conversion to A[sub 0], and S[sub 0] mode reflection--are described and evaluated. It is shown that the S[sub 0] mode reflection technique is the most promising method for long range inspection, 10--20 mm diameter delamination being detectable at a range of at least 500 mm. The time taken to test along a line using this technique is similar to that required to test at a point in conventional ultrasonic inspection, so considerable savings in testing time may be obtained.
102 citations
TL;DR: In this paper, a geometrically and physically nonlinear finite element approach is presented for the analysis of mode-I and mixed-mode free edge delamination in composite laminates which properly accounts for the effects of initial thermal and hygroscopic stresses.
92 citations
TL;DR: In this paper, the authors show that extensive fibre bridging, pull-out and fracture of the chopped Kevlar fibres have occurred during delamination, which is a very beneficial side effect and an important factor for the toughness improvement.
92 citations
TL;DR: In this article, a Lamb wave immersion tomography technique was used to image damaged regions in two polymer composite plate samples, which had been previously loaded in a biaxial test method until failure.
TL;DR: In this article, the authors compared different models based on variational analysis with respect to the thermo-elastic properties of cross-ply laminates with transverse cracks in the 90°-layer.
Abstract: Different models based on variational analysis are compared with respect to the thermo-elastic properties of cross-ply laminates with transverse cracks in the 90°-layer. This approach, pioneered by Hashin, applies the principle of minimum complementary energy to describe the stress state in a cross-ply laminate with transverse cracks. Apart from material data, only laminate geometry data and stress distribution assumptions are required. The model developed in the present study contains stress distribution assumptions that are closer to reality than previous models. Non-uniform stress distributions are included through-the-thickness of both the 0°- and the 90°-layers. An importan result is the improved agreement with stiffness reduction data. As expected from the nature of the model, predictions generally provide lower bounds to the stifness of the cracked laminate. However, at high crack densities, this is not the case. This additional stiffness reduction at high crack densities indicates the presence of new damage types, such as branched cracks and local delamination.
TL;DR: In this article, it was shown that mechanical compression behavior in the fiber direction for laminated carbon/epoxy structure can be predicted with an elastic non-linear model, and a specific bending test has been developed.
TL;DR: In this paper, the ballistic limit of plain woven glass/epoxy composite laminates struck by a 14.9 gm bullet-like rigid projectile with a tip radius of 5 mm was predicted.
TL;DR: In order to simulate the long-term exposure of composite laminates in space, various graphite/epoxy laminate specimens have been subjected to electron radiation combined with thermal cycling, or to oxygen atom fluxes as discussed by the authors.
TL;DR: In this paper, a simple and approximate approach is proposed for the prediction of progressive stiffness loss, matrix-crack density, and delamination area in terms of tension-tension fatigue load and number of cycles for general composite laminates containing 0° plies.
TL;DR: In this paper, an analytical method for the identification of force histories on a rectangular laminated plate when it is struck by foreign objects at multiple locations has been presented, where the modal superposition method is employed to obtain Green's function in a transformed time domain.
Abstract: This paper presents an analytical method for the identification of force histories on a rectangular laminated plate when it is struck by foreign objects at multiple locations. The governing equations of motion of the plate are constructed by using the classical lamination theory and the Rayleigh-Ritz method. The modal superposition method is then employed to obtain Green's function in a transformed time domain. To obtain the impact force histories exerted at multiple locations on the laminate, a constrained optimization method has been employed. The method has been verified using both randomly generated numerical signals with a signal-to-noise ratio of 1.0 and experimental data. The agreement is satisfactory in all of the comparisons. The method is then applied to further identify the actual impact points among several locations on a laminate that may be hit. With minor modifications, this method is also applied to reconstruct the strain histories, a portion of which are accidently lost in an impact event. ECAUSE of the tendency for invisible damage to occur inside structures made of advanced composite materials, study of the low-velocity-impact response of composite laminates has attracted the attention of many researchers during recent decades. Most of the work has involved analyzing the responses of a laminated structure when the initial configurations of the structure and the impactor are known.1 To obtain the relationship between the impactor movement and the plate motion at the impact location, the force-indentation relationship has been frequently applied. This relationship may be obtained by experiment,1'2 by Hertz contact law,3 or by more rigor- ously theoretical derivations.4'5 In addition, the laminates analyzed may be subjected to in-plane prestressed loading,6 large deflection,7 or various types of damage.8 On the other hand, experimental results have been reported for the investigation of the responses of lami- nated structures subjected to single1'2'8 or repeated2'9 impact load- ing at low striking velocities. The relationship between a laminated plate subjected to low-velocity impact and to quasistatic contact was also reported.2'10 When the initial striking velocity of the projectile was higher, the focus was on investigation of the ballistic resistance capability of the composite materials.11'12 An alternate approach to understanding the impact behavior of a composite structure is to use the inverse method. When the impact duration is short such that wave motion dominates the impact re- sponse, the generalized ray theory is frequently employed.13'14 As the impact duration becomes longer, such as in low-velocity impact by a foreign object, the generalized ray theory becomes not applica- ble because stress waves are reflected many times from the bound- aries of a structure. To overcome this problem, Doyle has proposed a frequency domain method using a complicated filtering procedure to suppress the effect of this wave reflection and has successfully identified the impact force of a duration longer than 1 ms.15'16 Another method for identifying the impact force history with a du- ration on the order of 1 ms is to use the modal superposition method. Hollandsworth and Busby17 have identified the impact force exerted on a cantilever beam using the response recorded by an accelero- meter as the input data. For a circular plate struck at its center, Wu et al.18 have constructed Green's functions from a series of Bessel functions. An optimization method was employed to search for the optimal impact force history. In the same paper, they also proposed an experimental method, by which the impact force history could be identified through a simple deconvolution process. This empirical method can thus be applied to structures with complicated material properties or boundary conditions. However, responses of a structure to impact of foreign objects acting simultaneously at multiple loca- tions have not been addressed by any of the aforementioned studies. In this paper, an analytical method has been developed to iden- tify the force histories of a composite laminate when it is struck by foreign objects at multiple locations. This situation may be encoun- tered when a flying vehicle is passing through a region with rain, dust, or hail. In other situations, multiple dents may be found on the surface of a laminated structure such that it is hard to determine whether single or multiple impact occurred. For all of these situa- tions, the method developed in this paper can be used to identify the impact force histories from the recorded strain histories. Further, this method can be extended to reconstruct the strain histories when a portion of the strains are not recorded due either to an improper trig- gering setting or to unexpectedly large signals occurring in an impact event. To develop this analytical method, a rectangular composite laminated plate will be modeled by using the classical lamination theory, and the Rayleigh-Ritz method will be employed to form the governing equations of motion of the plate. The modal superposition method will then be applied to construct Green's functions, which will be used to relate the forces exerted at multiple locations to the responses of the plate. Meanwhile, the gradient projection method will be applied to search for the optimal impact force histories. Both numerical data with a signal-to-noise ratio of 1.0 and experimental data will then be used to verify the proposed method.
TL;DR: In this article, a simple C0 isoparametric finite element formulation based on a higher-order displacement model for the analysis of symmetric and unsymmetric, composite, and sandwich laminates subjected to a thermal gradient across the thickness is presented.
Abstract: A simple C0 isoparametric finite element formulation based on a higher-order displacement model for the analysis of symmetric and unsymmetric, composite, and sandwich laminates subjected to a thermal gradient across the thickness is presented. The displacement model accounts for the nonlinear distribution of in-plane displacement components through the plate thickness, and the theory requires no shear correction coefficients. The nine-noded quadratic Lagrangian two-dimensional element is used with five and nine degrees of freedom per node. The accuracy of the formulation is verified by analyzing sample problems available in literature. Numerical results are presented in nondimensional form for symmetric, antisymmetric, and cross-ply laminates, both thick and thin.
01 Jan 1994
TL;DR: The effective laminate constitutive equations as discussed by the authors define the geometric response caused by loads exerted on the laminate, as distinguished from the conventional implication of an elastic constitutive equation, namely the stress-strain relationship of an infinitesimal material element.
Abstract: One of the most important aspects of the analysis of the response of composite materials is related to the studies of the overall behavior of laminates composed of anisotropic layers. In this phase of the analysis, we are concerned with the relationship between forces and moments per unit length and the deformations which they produce. These relations may be termed the “effective” laminate constitutive equations since they define the geometric response caused by loads exerted on the laminate, as distinguished from the conventional implication of an elastic constitutive equation, namely the stress-strain relationship of an infinitesimal material element. Once the effective constitutive law is formulated, theories can be developed based upon consideration of the laminate as a unit, rather than resorting to a layer by layer elasticity analysis. Once a particular boundary value problem is solved, however, one can determine the detailed stress distribution throughout the laminate. Another motivation for the study of effective laminate moduli is the popular use of the laminate as a model for the behavior of complex heterogeneous materials, such as composites reinforced with three-dimensional networks of fibers (Halpin and Pagano, 1969; Berkowitz and Cohen, 1970; Halpin et al., 1971). Finally, proper interpretation of data from even the most routine experiments involving composite laminates requires appreciation of an effective constitutive relation.
TL;DR: In this article, an analytical model was proposed for determining the response of the laminates containing a matrix crack-induced delamination and subjected to a concentrated load through a spherical indenter.
Abstract: An investigation was performed to study the mechanics of delamination growth in fiber-reinforced laminated composites resulting from transverse concentrated loads. The effect of matrix cracking on delamination propagation was the primary focus of the study. For simplicity's sake, only cross-ply laminates were investigated. An analytical model was proposed for determining the response of the laminates containing a matrix crack-induced delamination and subjected to a concentrated load through a spherical indenter. Two types of matrix cracks were considered in the model: a surfacebending crack and an internal shear crack. The model consists of three parts: a stress analysis, a contact analysis, and a failure analysis. A nonlinear three-dimensional finite element model based on an updated Lagrange formulation was developed for calculating stresses and strains in composites. An augmented Lagrangian method was utilized to simulate the interfacial contact condition of the embedded delamination and the indentatio...
TL;DR: In this paper, the total strain energy release rate associated with delaminations that initiate from a matrix crack in a symmetric composite laminate is calculated using the potential energy approach in elastic fracture mechanics and a two-dimensional finite element analysis.
TL;DR: In this paper, a solution method is derived for determining the free-edge stresses in composite laminates based on expanding stress functions in terms of a harmonic series in the thickness direction.
TL;DR: In this article, the impact response analysis using the finite element method incorporated with the modified Hertzian contact law was used to predict the impact force history on composite laminates subjected to low-velocity impact.
Abstract: A new method for simple prediction of the impact force history on composite laminates subjected to low-velocity impact is proposed. First, the impact force history is calculated from the impact response analysis using the finite element method incorporated with the modified Hertzian contact law. Frequency characteristics of the numerical impact force history are investigated from modal analysis and compared with the natural frequencies of the system in which the mass of an impactor is lumped with the plate. The present method can be efficiently applied to isotropic or orthotropic plates with unknown contact laws as well as composite laminates with no restraint on the material properties and the geometrical shape
TL;DR: In this article, a three-dimensional finite element analysis treating the nonlinear viscoelastic response of laminated composites is presented, where individual plies in the laminate are modeled using 20-node isoparametric solid elements.
Abstract: A three-dimensional finite element analysis treating the nonlinear viscoelastic response of laminated composites is presented. The individual plies in the laminate are modeled using 20-node isoparametric solid elements. The transient creep compliance in the viscoelastic model is represented as an exponential series plus a steady-flow term, which allows for a simplification of the numerical procedure for handling hereditary effects. Time-dependent stress and strain distributions are calculated for unnotched and notched laminates subjected to tensile loading or bending.
TL;DR: In this article, the effects of interlaminar bonding condition on the laminate deformation and stress distribution are also presented, and it is concluded from numerical results that the present theory is suitable for analysis of composite laminates with imperfect interfaces.
Abstract: Delamination is a major damage mode in laminated composites since it can cause severe structural degradation. Based on an interlaminar shear stress continuity theory and a linear shear slip theory, a so-called Interlayer Shear Slip Theory was presented in a previous study. This theory was verified to be feasible for shearing-mode delamination analysis. However, in order to account for opening-mode delamination in laminated composites, the continuity of interlaminar normal stress and the modelling of normal separation on the composite interface should also be considered. The present study gives a complete discussion on the Interlaminar Bonding Theory. The effects of interlaminar bonding condition on the laminate deformation and stress distribution are also presented. It is concluded from numerical results that the present theory is suitable for analysis of composite laminates with imperfect interfaces.
TL;DR: In this paper, the influence of ply waviness with nonlinear shear material response on the mechanical performance of composite laminates is studied, and an analytic model based on a three-dimensional laminated media analysis is developed to predict the effective nonlinear laminate behavior associated with plywaviness.
Abstract: The influence of ply waviness with nonlinear shear material response on the mechanical performance of composite laminates is studied. An analytic model, based on a three-dimensional laminated media analysis, is developed to predict the effective nonlinear laminate behavior associated with ply waviness. An undulating [0] ply in a [90/0/90] sublaminate configuration and undulating [±β] plies in a [90/±β/90] sub laminate configuration are two types of ply waviness considered. An incremental loading strategy is employed wherein piece-wise linear solutions are superimposed to obtain the overall nonlinear stress/strain response of composite laminates with wavy plies. The anal ysis also predicts individual ply stress and strain distributions within the wavy ply con figuration. The maximum stress failure criterion is used to predict ply failure in local re gions within the wavy ply configuration and a progressive failure methodology is adopted to permit local load redistribution. Results are presented that offer ...
TL;DR: In this paper, a method for predicting the damped dynamic characteristics of thick composite laminates and plates is presented, which relates the damping of composite plates to constituent properties, fiber volume ratio, fiber orientation, laminate configuration, plate geometry, temperature, and moisture.
Abstract: A method for predicting the damped dynamic characteristics of thick composite laminates and plates is presented. Unified damping mechanics relate the damping of composite plates to constituent properties, fiber volume ratio, fiber orientation, laminate configuration, plate geometry, temperature, and moisture. Discrete layer damping mechanics for thick laminates, entailing piecewise continuous displacement fields and including the effects of interlaminar shear damping, are described. A semi-analytical method for predicting the modal damping and natural frequencies of thick simply-supported specialty composite plates is included. Applications demonstrate the validity, merit, and ranges of applicability of the new theory. The applications further illustrate the significance of interlaminar shear damping, and investigate the effects of lamination, thickness aspect ratio, fiber content, and temperature.
TL;DR: In this paper, the influence of layer waviness on the compression fatigue response of carbon/polysulphone composite laminates was studied and a one and a half decade loss of compression fatigue life was observed for moderate layer wave specimens as compared with the control specimens.
TL;DR: In this article, the effects of the interfacial bond quality on the mechanical response of composite laminates, for example an epoxy matrix reinforced by continuous carbon fibres of varying surface coating, were investigated.
01 Jan 1994
TL;DR: In this article, the influence of in-plane fiber waviness on structural response and its sensitivity on a composite beam was evaluated and the change of deflection and natural frequency of a symmetrically laminated composite beam due to fiber Waviness was also investigated.
Abstract: Fiber waviness is often found to be a failure initiation site in a structural part. The objective of this research is to evaluate the influence of in-plane fiber waviness on structural response and its sensitivity on a composite beam. Explicit forms of lamina and laminate stiffness and their sensitivity analysis due to fiber waviness are formulated. The change of deflection and natural frequency of a symmetrically laminated composite beam due to fiber waviness was also investigated.