Showing papers on "Composite laminates published in 1988"
TL;DR: In this article, a satisfactory theory for cross-ply laminates which have been damaged by transverse matrix cracking under monotonic loading has attracted a substantial number of investigators.
Abstract: HE DEVELOPMENT OF a satisfactory theory for cross-ply laminates which have been damaged by transverse matrix cracking under monotonic loading has attracted a substantial number of investigators. The formulation of a shear lag model appears to have been first proposed in a series of papers by Bailey and his co-workers [1,2,3,4,5,6]. This work, in turn, relies on some studies of unidirectional composites by Aveston and Kelly [6]. Subsequent contributions to the theory have geen given by Wang [7], Highsmith and Reifsnider [8], Flaggs and Kural [9], Nuismer and Tan [10], Manders, Chou, Jones and Rock [11], Fukunaga, Chou, Peters and Schulte [12], Flaggs [13], Ohira [14] and Ogin, Smith and Beaumont [15,16]. Doubtless a diligent search of the literature would disclose other related work.
338 citations
TL;DR: In this article, the problem of edge delamination at the -35/90 interfaces of an 8-ply composite laminate subjected to uniform axial strain was studied and the results showed that the imaginary part of the singularity is the cause of the nonconvergent behavior of the individual components.
328 citations
TL;DR: In this article, the residual stresses in APC-2 cross-ply laminates have been investigated and predictions based on classical laminate theory are compared to measured levels of residual stress obtained from a number of experimen tal techniques.
Abstract: Residual stresses in composite laminates depend on thermoelastic properties of the material and processing temperatures. Their distribution in the various laminae is a func tion of stacking sequence and ply orientation. In this work residual stresses in APC-2 cross-ply laminates have been investigated. Predictions based on classical laminate theory are compared to measured levels of residual stress obtained from a number of experimen tal techniques. The analysis of the results shows that accurate predictions can be made pro vided that the changes in thermoelastic properties of the materials with temperature are taken into account.
212 citations
TL;DR: In this article, a matrix method is presented for the solution of wave propagation problems in multilayered anisotropic media subjected to time harmonic disturbances, which leads to stable numerical schemes for the evaluation of the displacement and stress fields within the laminate.
196 citations
TL;DR: In this paper, the effect of matrix strength and ductility on the onset and growth of delamination in composite laminates has been investigated and a strength criterion for the onset of delaminatoin is proposed and an assessment made of the impact of matrix properties on delamination onset.
176 citations
TL;DR: Failure in quasi-isotropic (π/4 and π/3) laminates with free edges under on-axis and off-axis loads has been studied experimentally and analytically as discussed by the authors.
Abstract: Failure in quasi-isotropic (π/4 and π/3) laminates with free edges under on-axis and off-axis loads has been studied experimentally and analytically. Although these laminates are isotropic in stiff...
110 citations
TL;DR: In this paper, the application of scaling laws to fiber composite laminates is discussed and a particular emphasis is placed on the case of impact loading, where scaling difficulties and conflicts are identified and illustrated in an experimental program based on impacted carbon-fiber composite beams.
Abstract: The application of scaling laws to fiber composite laminates is discussed Particular emphasis is placed on the case of impact loading Scaling difficulties and conflicts are identified and illustrated in an experimental program based on impacted carbon-fiber composite beams It is shown that the lay-up of laminates is important in assessing the likely validity of scale-model tests for such composites It is also observed that significant size effects may dominate strength modeling
100 citations
01 Jan 1988
TL;DR: In this paper, an analytical and experimental investigation of the failure of selected compression-loaded composite laminates is described, and a general nonlinear theory is presented for predicting a laminate's compressive strength and failure mode.
Abstract: An analytical and experimental investigation of the failure of selected compression-loaded composite laminates is described. A general nonlinear theory is presented for predicting a laminate's compressive strength and failure mode. The theory includes the effects of out-of-plane ply waviness, inplane fiber waviness, and fiber scissoring. A simple compressive test technique is used to obtain the experimental data. The analytical and experimental results show good agreement for theta less than 45 deg and show excellent agreement for theta not less than 45 deg. The dominant compression failure modes for the laminates in this study were found to be interlaminar shearing, inplane matrix shearing, and matrix compression.
80 citations
TL;DR: In this paper, resistance welding of preconsolidated unidirectional graphite (AS4) rein forced polyetheretherketone (PEEK) composite laminates (I.C.2) is investigated experimentally.
Abstract: Resistance welding of preconsolidated unidirectional graphite (AS4) rein forced polyetheretherketone (PEEK) composite laminates (I.C.I. APC-2) is investigated experimentally. An apparatus is developed to conduct experiments to identify important process variables governing the efficiency of the welding process. Experiments were con ducted under displacement control and prescribed initial consolidation pressure. Heating elements consisted of a single ply of APC-2 with adjacent layers of neat film to minimize current leakage into the laminates to be welded. Temperature at the weld interface and consolidation pressure versus time were monitored and provided insight into the welding process. A strong correlation between the extent of welded surface area and process parameters such as power, energy and time in the melt were demonstrated. The quality and extent of the welded surface is quantified using ultrasonic nondestructive evaluation techniques. Experimental results indicate that superior welds exhibiting ...
72 citations
TL;DR: In this paper, three models for the ultimate strength prediction of multidirectional unnotched and notched composite laminates are proposed for graphite/epoxy materials system.
Abstract: Three models are proposed for the ultimate strength prediction of multidirectional unnotched and notched composite laminates. These models utilize a characteristic length and a proposed failure criterion that requires the longitudinal strength parameters and stress distribution of a lamina within a laminate. The characteristic length for the second model: effective average stress model is independent of the opening shape and that for the third model: minimum strength model can be related in a simple form. Comparisons show that the ultimate strength predictions for unnotched and notched laminates both agree very well with experimental data for graphite/epoxy materials system. A direct relation between the fracture toughness and the unnotched laminate strength (determined analytically) is also obtained.
65 citations
Book•
01 Jan 1988
TL;DR: In this paper, the authors proposed an Acousto-ultraltrasonic approach for measuring the strength of composite material Adhesive Joints using the backscattering mechanism in fiber-reinforced composites.
Abstract: Keynote.- The Acousto-Ultrasonic Approach.- Theory - Wave Propagation for Acousto-Ultrasound.- Interaction of Ultrasonic Waves with Layered Media.- Diffuse Waves for Materials NDE.- Low Frequency Flexural Wave Propagation in Laminated Composite Plates.- Preliminary Evaluation of Non-Contact Acousto-Ultrasonic Displacement Fields in Polymeric Matrix Composite.- Utilization of Oblique Incidence in Acousto-Ultrasonics.- Data Interpretation.- Ultrasonic Velocity Studies of Composite and Heterogeneous Materials.- Acousto-Ultrasonic Wave Propagation in Composite Laminates.- Ray Propagation Path Analysis of Acousto-Ultrasonic Signals in Composites.- Nondestructive Evaluation of Composite Material Using Ultrasound.- Experimental and Theoretical Analysis of Backscattering Mechanisms in Fiber-Reinforced Composites.- Statistical Evaluation of Quality in Composites Using the Stress Wave Factor Technique.- Application of Acousto-Ultrasonics to Quality Control and Damage Assessment of Composites.- Predicting Damage Development in Composite Materials Based on Acousto-Ultrasonic Evaluation.- Sources/Detectors.- Laser Generated Ultrasound.- Electromagnetic Transducers for Generation and Detection of Ultrasonic Waves.- Applications and Advantages of Dry Coupling Ultrasonic Transducers for Materials Characterization and Inspection.- Fiber Waveguide Sensors of Stress Waves in Solids.- Calibration and Method Implementation.- Considerations for Developing Calibration Standards for Acousto-Ultrasonic Inspection.- Test Conditions in Stress Wave Factor Measurements for Fiber Reinforced Composites and Laminates.- Measurement of the Energy Content in Acousto-Ultrasonic Signals.- Applications - General.- Acousto-Ultrasonics: Applications to Wire Rope, Wood Fiber Hardboard, and Adhesion.- An Acousto-Ultrasonic Method for Evaluating Wood Products.- Acousto-Ultrasonic Characterization of Physical Properties of Human Bones.- Applications - Composite Materials.- Multi-Parameter, Multi-Frequency Acousto-Ultrasonic for Detecting Impact Damage in Composites.- Trans-Ply Crack Density Detection by Acousto-Ultrasonics.- Application of Acousto-Ultrasonics for Predicting Hygrothermal Degradation of Unidirectional Glass-Fiber Composites.- Applications - Bonding.- Bond Quality Evaluation of Bimetallic Strips: Acousto-Ultrasonic Approach.- Acousto-Ultrasonic Evaluation of the Strength of Composite Material Adhesive Joints.
TL;DR: Adhesive layers were included along the interfaces of a baseline graphite/epoxy [0 5 /90 5 /0 5 ] laminate for impact study as discussed by the authors, which resulted in the following effects: delamination was effectively suppressed up to very high impact velocities; matrix cracking in the upper lamina was greatly reduced; and the contact area appreciably increased thereby reducing the stress concentration effect.
Abstract: Adhesive layers were included along the interfaces of a baseline graphite/epoxy [0 5 /90 5 /0 5 ] laminate for impact study. Impacted specimens were sectioned longitudinally and transversely for observation of the damage modes. The existence of adhesive layers resulted in the following effects: delamination was effectively suppressed up to very high impact velocities; matrix cracking in the upper lamina was greatly reduced; and the contact area appreciably increased thereby reducing the stress concentration effect. An apparent disadvantage in using adhesive layers was found; that is, the bending crack in the bottom lamina which could branch out into delamination cracks when adhesive layers Were absent tended to penetrate the middle lamina and break fibers.
TL;DR: In this article, a nonlinear method to analyze composite panels with elliptical delaminations under compressive loads is presented, based on solving the fully coupled partial differential equations for anisotropic elasticity using infinite series.
TL;DR: In this article, the von Karman plate theory was used to analyze composite laminates under in-plane and transverse loadings, and the governing equations were reduced to linear differentia with nonlinear boundary conditions yielding a simple solution procedure.
Abstract: Linear laminated plate theory is shown to be inadequate for analysis of asymmetric composite laminates, even in the small deflection range. The von Karman plate theory was used to analyze composite laminates under in-plane and transverse loadings. For cylindrical bending problems, the governing equations were reduced to linear differentia} equations with nonlinear boundary conditions yielding a simple solution procedure. Cross-plied laminates were used as examples.
TL;DR: In this paper, an analytical methodology was developed capable of describing interrelations between thermal processing and polymer structure for thermoplastic based composite laminates, which was used to describe experimental results generated with a specially designed match die quench mold by processing both neat PEEK polymer and carbon fiber reinforced laminate samples at different cooling rates.
Abstract: An analytical methodology was developed capable of describing interrelations between thermal processing and polymer structure for thermoplastic based composite laminates. Specifically, this modeling methodology was used to describe experimental results generated with a specially designed match die quench mold by processing both neat PEEK polymer and carbon fiber reinforced laminate samples at different cooling rates. The developed model accurately predicted temperature profiles for PEEK laminates of different thicknesses, under normal as well as extreme quenching conditions of 114°C/s. surface cooling rates that are possible to generate with the quench mold. In general, the modeling methodology is capable of predicting a part's thermal profile during processing in terms of the composite's microscopic intrinsic properties (fiber and matrix), composition, and lamina orientation. Furthermore, by coupling to the thermal profile description, a previously developed crystallization kinetics model for PEEK polymer and its carbon reinforced composite, a quantitative description of structural development during processing was obtained. Thus, with this analytical methodology, a skin-core crystallinity profile, where the crystallinity varies with part-thickness as a result of uneven cooling experienced during processing, was predicted both for the neat PEEK polymer and its carbon reinforced laminate forms. Finally, the developed methodology clearly established the interplay of both microscopic heat transfer and kinetics of crystallization/solidification of the matrix that must be accounted for in predicting the final structure of a carbon fiber reinforced laminate that will, in turn, govern microscopic and macroscopic performance.
TL;DR: In this paper, two different methods of solution are used to study the effects of transverse cracks in cross-ply composite laminates, and the results of an approximate analytical solution are compared with those obtained using a finite element analysis in order to analyze the degradation of elastic and thermal coefficients as well as stress distributions.
TL;DR: In this article, the effect of large deflection term becomes pronounced even in the "small deflection" range and the apparent laminate bending rigidity depends on the direction of deflection.
Abstract: Static and dynamic behaviors of unsymmetric cross-ply laminates in cylindrical bending are investigated using von Karman large deflection theory. Due to the presence of bending- extension coupling, the effect of the large deflection term becomes pronounced even in the "small deflection" range. Further, the apparent laminate bending rigidity depends on the direction of deflection. It is also found that in free vibration at small amplitudes, large deflection theory may yield frequencies lower than linear theory.
TL;DR: In this article, a cumulative damage model for the prediction of stiffness loss in graphite/epoxy laminates applies a thermomechanical constitutive theory for elastic composites with distributed damage.
Abstract: The present cumulative damage model for the prediction of stiffness loss in graphite/epoxy laminates applies a thermomechanical constitutive theory for elastic composites with distributed damage. The model proceeds from a continuum mechanics and thermodynamics approach in which the distributed damage is characterized by a set of second-order tensor-valued internal state variables. A set of damage-dependent laminated plate equations is obtained; this is developed by modifying classical Kirchhoff plate theory.
TL;DR: In this article, the effects of cure on the mechanical properties of composite laminates were evaluated and the longitudinal and transverse tensile and compressive moduli and strengths and the longit...
Abstract: Tests were performed to evaluate the effects of cure on the mechanical properties of composite laminates. The longitudinal and transverse tensile and compressive moduli and strengths and the longit...
01 Jan 1988
TL;DR: In this paper, shear deformation and rotary inertia are included in plate theory to determine the dispersion curves for flexural waves propagating in laminated composite plates, and the results of a unidirectional laminate are compared with the elasticity solutions for flexurys traveling in transversely isotropic plates to determine shear correction factors in the low frequency, long wavelength range.
Abstract: Shear deformation and rotary inertia are included in plate theory to determine the dispersion curves for flexural waves propagating in laminated composite plates. The results of a unidirectional laminate are compared with the elasticity solutions for flexural waves traveling in transversely isotropic plates to determine the shear correction factors in the low frequency, long wavelength range. The values of the shear correction factors for the unidirectional composite laminate are in good agreement with the theoretical values calculated from static cylindrical bending. An acousto-ultrasonic technique using narrowband excitation frequencies is used to obtain experimental data for flexural waves. By measuring the phase velocities for different excitation frequencies, dispersion curves are generated. There is excellent agreement between the experimentally determined values and the theoretical results for aluminum and unidirectional composite plates. For symmetric cross-ply and quasi-isotropic laminates, the data definitely have the characteristic of a dispersion curve for flexural waves, although the agreement between analytic and experimental results is not quite as good. The results of the present work indicate that the inclusion of shear deformation and rotary inertia in plate theory improves the prediction of dispersion curves for flexural waves propagating in composite laminates and suggest that the acousto-ultrasonic technique can be used to characterize composite plates with and without damage since each material and stacking sequence gives distinct dispersion curves.
TL;DR: In this article, the effects of fiber preloads on the ply stresses induced within continuous-fiber compos ite laminates are considered and a micromechanics analysis based primarily upon the rule-of-mixtures is used to predict the fiber and matrix stresses within a single prestressed ply.
Abstract: The effects of fiber preloads on the ply stresses induced within continuous-fiber compos ite laminates are considered. A micromechanics analysis based primarily upon the rule-of- mixtures is used to predict the fiber and matrix stresses within a single prestressed ply. These results are integrated with classical lamination theory, allowing calculation of the ply stresses for prestressed composite laminates. The analysis indicates that prestressing will dramatically influence the ply stresses induced within composite laminates.
TL;DR: In this paper, an analytical procedure for the determination of stress concentrations and strength pre diction of finite composite laminates with elliptical holes is proposed, where the Airy stress function expressed i.e.,
Abstract: An analytical procedure for the determination of stress concentrations and strength pre diction of finite composite laminates with elliptical holes is proposed. The Airy stress function expressed i...
18 Apr 1988
TL;DR: In this paper, a stiffness degradation model is proposed to predict the statistical distribution of the residual stiffness of composite laminates subjected to fatigue cycling, and two analytical methods are presented, which are capable of predicting the stiffness degradation of a particular composite specimen under cyclic loading.
Abstract: Stiffness reduction in composite laminates is an important measure of fa tigue damage. The determination of fatigue damage and the prediction of fatigue life can be made through the development of a stiffness degradation model. This paper proposes a stiffness degradation model that can be used to predict the statistical distribution of the residual stiffness of composite laminates subjected to fatigue cycling. Based on the pro posed model, two analytical methods are presented, which are capable of predicting the stiffness degradation of a particular composite specimen under cyclic loading. One method is based on the linear regression analysis and the other on the Bayesian approach. Experi ments have been performed on graphite/epoxy [90, +45, —45,0], laminates to generate sta tistically significant data for evaluating the proposed analytical models and for verifying the predicted results. It is shown that theoretical predictions for the stiffness degradation of an individual specimen and for the statistica...
TL;DR: In this paper, the authors constructed a general model for predicting stiffness loss as a function of damage in composite laminates, and the model predictions are compared to experimental results for axial stiffness and finite element results for out-of-plane stiffness, and it is shown that the model is accurate in predicting this stiffness loss due to curved cracks.
Abstract: Experimental evidence has shown that in crossply laminates numerous matrix cracks often become curved with respect to the plane normal to the laminate plane when three or more 90° plies are stacked in succession. This phenomenon produces damage dependent stiffness losses in both the axial and out-of-plane directions which are strongly dependent on the curved crack state. The authors have constructed a general model for predicting stiffness loss as a function of damage in composite laminates, and the current paper seeks to model this stiffness loss. The model predictions are compared to experimental results for axial stiffness and finite element results for out-of-plane stiffness, and it is shown that the model is accurate in predicting this stiffness loss due to curved cracks.
TL;DR: In this article, a new method for computing the reliability of composite laminates is presented, which is distinct in concept and effective computationally for composite and other brittle component structures.
Abstract: Research on the reliability of composite structures is just beginning. Keeping in mind that a composite laminate is anisotropic and a brittle laminated construction, a new method for computing the reliability of composite laminates is presented. The method is distinct in concept and effective computationally for composite and other brittle component structures. It uses the Tsai-Hill criterion as the failure criterion. Illustrative examples concerning reliability of a laminate under various loadings are given, to confirm the effectiveness of the method.
Dissertation•
01 Jan 1988
TL;DR: In this paper, the authors enhance the understanding of instability-related delamination growth in composite laminates containing either an embedded or an edge delamination, which can cause load redistribution and secondary loads, which in turn cause interlaminar stresses and delamin growth.
Abstract: Compressive loads can cause local buckling in composite laminates that have a near surface delamination. This buckling causes load redistribution and secondary loads, which in turn cause interlaminar stresses and delamination growth. The goal of this research was to enhance the understanding of this instability-related delamination growth in laminates containing either an embedded or an edge delamination.
TL;DR: In this article, the analysis and testing of impact damage composite laminates are discussed, and it is shown that uniaxial S-N curves have a generic shape with a pronounced threshold level and that further research is needed to understand the physical reasons for such a threshold value.
TL;DR: In this paper, the analysis and testing of impact damage composite laminates are discussed, and it is shown that uniaxial S−N curves have a generic shape with a pronounced threshold level, and further research is needed to understand the physical reasons for such a threshold value.
TL;DR: In this paper, a significant amount of emission can be generated during fatigue loading not only by damage accumulation (progression) but also by the continuous friction that results from the fracture surfaces grating against each other.
Abstract: Destructive and nondestructive examinations of composite laminates subjected to exter nal loading have indicated that these materials contain a large number of cracks, both on the micro- and macro-scales. Consequently, a significant amount of emission can be generated during fatigue loading not only by damage accumulation (progression) but also by the continuous friction that results from the fracture surfaces grating against each other. Consequently, in order to monitor fatigue damage progression in composite laminates by acoustic emission (AE), the emission caused by the fretting should be distinguished from that generated by actual damage growth.
TL;DR: In this paper, the damage sustained by 16-ply quasi-isotropic carbon/epoxy composite laminates subjected to repeated impact at various energy levels has been quantified.