Showing papers on "Composite laminates published in 1989"

Application of fracture mechanics to composite materials

Abstract: I. General Aspects. 1. Fracture mechanics of anisotropic materials (J.G. Williams). 2. Statistical concepts in the study of fracture properties of fibres and composites (H.D. Wagner). II. Fracture of Polymer Composites. IIA. Interlaminar Fracture Studies. 3. Interlaminar mode I-fracture testing (P. Davies, M.L. Benzeggagh). 4. Mode II - Interlaminar fracture of composites (L.A. Carlsson, J.W. Gillespie Jr.). 5. Relationship of matrix toughness to interlaminar fracture toughness (W.L. Bradley). IIB. Fracture of Short Fiber Reinforced Thermoplastics. 6. Microstructure and fracture mechanical performance of short fiber reinforced thermoplastics (J. Karger-Koscis). 7. The Crack layer approach to polymers and composites (A. Dolgopolsky, J. Botsis). IIC. Complex Fracture in Composite Laminates. 8. Damage mechanisms, including edge effects, in carbon fiber reinforced composite materials (K. Schulte, W.W. Stinchcomb). 9. Fracture mechanics of notched carbon/epoxy laminates (K. Kageyama). 10. Environmental effects on fracture mechanical properties of polymer composites (G. Marom). 11. Fractographic analysis of polymer composites (K. Friedrich). III. Fracture of Metallic, Ceramic and Natural Composites. 12. Fracture mechanical approach to metal matrix composites (S. Ochiai). 13. The mechanical properties and fracture behaviour of ceramic matrix composites (CMC) reinforced with continuous fibres (R.W. Davidge). 14. Fracture of whisker reinforced ceramics (R. Warren, V.K. Sarin). 15. Fracture toughness of natural composites with reference to cortical bone (W. Bonfield, J.C. Behiri). IV. Concluding Remarks. 16. Concluding remarks on the application of fracture mechanics to composite materials (F.X. de Charentenay).

On refined computational models of composite laminates

Abstract: Finite element models of the continuum-based theories and two-dimensional plate/shell theories used in the analysis of composite laminates are reviewed. The classical and shear deformation theories up to the third-order are presented in a single theory. Results of linear and non-linear bending, natural vibration and stability of composite laminates are presented for various boundary conditions and lamination schemes. Computational modelling issues related to composite laminates, such as locking, symmetry considerations, boundary conditions, and geometric non-linearity effects on displacements, buckling loads and frequencies are discussed. It is shown that the use of quarter plate models can introduce significant errors into the solution of certain laminates, the non-linear effects are important even at small ratio of the transverse deflection to the thickness of antisymmetric laminates with pinned edges, and that the conventional eigenvalue approach for the determination of buckling loads of composite laminates can be overly conservative.

Effect of Delamination on the Natural Frequencies of Composite Laminates

Abstract: This paper presents the results of a study on the effect of prescribed delamination on the natural frequencies of laminated beam specimens. Experimental modal analysis was used to measure the effect of delamination length on the first four fre quencies of the simply supported test specimens. The experimental results were cor roborated with detailed finite element models as well as with simplified beam theory models. The presence of a delamination degraded the even numbered vibration modes much more rapidly than the odd numbered modes for a delamination centered at the speci men midspan. Delaminations which covered 1/3 of the specimen length had no more than a 20% effect on any of the first four frequencies.

Buckling and vibration of laminated composite plates using various plate theories

Abstract: Analytical and finite-element solutions of the classical, first-order, and third-order laminate theories are developed to study the buckling and free-vibration behavior of cross-ply rectangular composite laminates under various boundary conditions

A theory for progressive matrix cracking in composite laminates

Abstract: The progressive matrix cracking of composite laminates that contain a cracked 90° ply and subject to uniaxial tensile or shear loading is modeled using a fracture mechanics approach and an elastici...

Interlaminar response of composite materials

Abstract: 1. Models for Studying Free-Edge Effects (N.J. Pagano, S.R. Soni). Introduction. Effective-modulus theory. Free-edge boundary value problem. Finite-difference solution. Analysis of stacking sequence effect. Primitive delamination model. Elastic plate model for s z . Extended Reissner variational principle for composite laminates (local model). The global-local laminate variational model. Recent work in free-edge models. References. 2. Fracture Analysis of Interlaminar Cracking (A.S.D. Wang). Introduction. Physical characteristics of delamination. The energy method for free-edge delamination. Illustrative examples of free-edge delamination. Summarizing remarks. Appendix. References. 3. Experimental Observations of Free-Edge Delamination (R.Y. Kim). Abstract. Introduction. Initiation of delamination. Experimental determination of interlaminar normal stress. Prediction methodology for onset of delamination. Effect of delamination on stiffness. Delamination control. Summary. References. 4. Experimental Characterization of Delamination Fracture (J.M. Whitney). Introduction. The short-beam shear test. Strain energy release rate. The double cantilever beam test. Mode-I edge-delamination test. The end-notch flexure test. The cracked-lap shear specimen. Off-axis centre-notch tensile test. One-dimensional delamination buckling. Summary. List of symbols. References. Author Index. Subject Index.

Buckling of Laminated Plates with Holes

Abstract: This paper deals with buckling analysis of rectangular composite laminates with circular holes under inplane static loadings. The first-order shear deformation theory and the variational energy method are employed in mathematical formulation, and the nine-node Lagrangian finite element method is used for finding critical loads. The effects on critical load by hole size, plate thickness ratio, material modulus ratio, ply lamination geometry, loading types, and boundary conditions are investigated. Numerical solutions are shown in graphical form where some comparisons are made with those of given litera tures.

A model for the thermal and chemorheological behavior of thermosets. I: Processing of epoxy‐based composites

Abstract: The rheological and thermokinetic aspects of the cure of epoxy based composite laminates are analyzed by means of a computer program developed using the heat transfer and heat generating characteristics of a polymerizable system. In particular, the temperature and degree of cure influence on the resin viscosity have been first considered, then the temperature profiles, calculated according to an appropriate kinetic and heat transfer modeling, have been used to predict the corresponding viscosity profiles. Molecular and thermocalorimetric parameters are used for the prediction of the theoretical chemorheological behavior. Commercial epoxy systems commonly used in the preparation of carbon fiber laminates have been characterized by Differential Scanning Calorimetry (DSC) and dynamic viscosity measurements and the results are compared with the theoretically predicted values.

A damage prediction method for composite structures

Abstract: Damage generally refers to the more or less gradual development of micro-voids and micro-cracks. Damage mechanics is the modelling of these phenomena on a structural analysis scale. In this paper we first recall the non-linear behaviour models we have developed to model composite laminates. Then we present two examples of implementations of such models in a structural analysis code in order to simulate the inner-failure of a structure, or to study delamination initiation.

Thermo-viscoelastic analysis of composite materials

Abstract: The thermo-viscoelastic boundary value problem for anisotropic materials is formulated and a numerical procedure is developed for the efficient analysis of stress and deformation histories in composites. The procedure is based on the finite element method and therefore it is applicable to composite laminates containing geometric discontinuities and complicated boundary conditions. Using the present formulation, the time-dependent stress and strain distributions in both notched and unnotched graphite/epoxy composites have been obtained. The effect of temperature and ply orientation on the creep and relaxation response is also studied.

The failure of fibre composites: An overview

Abstract: Static and cyclic loading, impact, and environmental attack all contribute to the accumulation of damage in composite laminates. The damage can take many forms: delamination and splitting during load cycling, matrix cracking during thermal fatigue, and so on. With this diversity of damage mechanisms, it is no wonder that variability in static strength is significantly enhanced by service in the field. We recognise, therefore, that damage is progressive and is accompanied by a gradual deterioration in strength and stiffness of the laminate. In other words, static strength and life-time are part of the same design phenomenon.One way forward is to identify the broad rules governing fibre composite behaviour. There are two directions: continuum modelling and microscopic modelling. Continuum modelling is useful, but generally demands a formidable experimental programme to determine important design parameters. On a much smaller scale, microscopic modelling provides insight into the damaging mechanisms,...

Notch sensitivity of thermoset and thermoplastic laminates loaded in tension

Abstract: Inplane tensile fracture of unnotched and notched thermoset graphite-epoxy and thermoplastic graphite-PEEK composite laminates is examined. Both fibre-dominated quasi-isotropic and matrix dominated ±45 angle-ply layups were investigated. Classical lamination theory predictions of elastic and strength properties of unnotched specimens are compared with experiments. Several notched geometries, i.e. centre-notched, double-edge notched and open-hole specimens subjected to tensile loading to fracture were examined. The notched strength of the quasi-isotropic laminates was analysed by a damage zone model, where damage around the notch is represented by an “equivalent crack” with cohesive force acting between the crack surfaces. Good agreement between experimental and calculated strength was observed for the graphite-epoxy laminates which failed in a collinear manner. For the graphite-PEEK laminates discrepancies between predicted and experimental strength are related to observed deviations from collinear crack growth. The angle-ply graphite-PEEK laminates showed larger notch sensitivity than the corresponding graphite-epoxy, probably due to less degree of stress relieving damage formation around the notch.

An Evaluation of Composite Material Compression Test Methods

Abstract: Discrepancies concerning the compressive strength of composite materials exist mainly because of the test method used. An experimental evaluation of three compressive test fixtures, namely, the Illinois Institute of Technology Research Institute (IITRI), modified Celanese, and end-loaded side-supported, selected based on a literature search, was performed. Mechanical testing of glass/epoxy and carbon/epoxy composite materials indicated the IITRI test fixture, currently a ASTM Test Method for Compressive Properties of Unidirectional or Crossply Fiber-Resin Composites, (D 3410) to be a very satisfactory method of composite material compressive properties characterization.

Delamination Resistance of Stitched Thermoplastic Matrix Composite Laminates

Abstract: This paper shows how to improve delamination resistance in composite laminates by the use of thermoplastic matrix resins and by stitching Discussed are fatigue crack growth characteristics in thermoplastic matrix composites as well as the differences between the crack growth processes in thermoplastic and thermosetting matrix composites under cyclic fatigue and monotonically increasing loads Further improvement of delamination resistance achieved by stitching shows a 20 to 30% increase in the critical crack-opening load, a 20 times higher fatigue threshold, and a two-orders-of-magnitude increase in fatigue life Fractography evidence is presented to illustrate the role of the stitching yarns in resisting delamination A fracture model was constructed to simulate delamination crack propagation in the presence of stitching yarns The effects of geometric stitching parameters, as well as intrinsic and extrinsic yarn properties, were simulated with this fracture model Finally, practical issues on the effective and economical application of stitching to composite structures are discussed

Free-Edge Delamination: Laminate Width and Loading Conditions Effects

Abstract: The width and loading conditions effects on free-edge stress fields in composite laminates are investigated using a three-dimensional finite element analysis. This analysis includes a special free-edge region refinement or superelement with progrssive substructuring (mesh refinement) and finite thickness interply layers. The different loading conditions include in-plane and out-of-plane bending, combined axial tension and in-plane shear, twisting, uniform temperature and uniform moisture. Results obtained indicate that: axial tension causes the smallest magnitude of interlaminar free edge stress compared to other loading conditions; free-edge delamination data obtained from laboratory specimens cannot be scaled to structural components; and composite structural components are not likely to delaminate.

A Stiffness-Based Statistical Model for Predicting the Fatigue Life of Graphite/Epoxy Laminates

Abstract: A stiffness-based statistical model is proposed for predicting the fatigue life of composite laminates under constant-amplitude tensile cyclic loadings. The model parameters are determined using measured stiffness degradation data. Experiments have been performed on graphite/epoxy [90, +45, -45,0]s laminates to verify the analytical model. It is demonstrated that the correlation between the experimental results and the theoretical predictions for the fatigue life distribution is very reasonable.

A Detailed Investigation of the Micromechanisms of Compressive Failure in Open Hole Composite Laminates

Abstract: Micromechanisms responsible for compressive failure in open-hole composite laminates were investigated. Specimens containing circular center holes were loaded in compression to failure at a slow rate, and the surface damage development during loading was monitored. Several coupon compression tests were interrupted prior to catastrophic failure to allow for the assessment of fiber shear crippling and/or fiber microbuckling by NDE techniques. From these sectioning studies, the extent and mode of failure were determined, and a three-dimensional schematic of the shear crippling zone was developed. Results show that the majority of the damage in compression-loaded open-hole composite laminates is shear crippled or microbuckled 0-deg fibers; in many cases, however, the shear crippling damage within the 0-deg plies produced shear strains and damage in the adjacent off-axis plies.

Chapter 3 - Experimental Observations of Free-Edge Delamination

Abstract: In this chapter, experimental methods are presented for defining mechanisms, characterization, consequences, and prevention of free-edge delamination. Discussions are limited to the initiation of delamination only. The experimental results on the onset of delamination on a variety of laminates in terms of strain level, including its location and detection by non-destructive test methods, are presented. An experimental method for determining interlaminar normal stress at the mid-plane of laminates by using strain gages is described and compared with an analytical model. An analytical prediction methodology for onset of delamination at an interface due to combined normal and shear stresses using an approach based on stress analysis and a failure theory is described and compared with experiment. The effect of a transverse crack on the onset of delamination is discussed. The consequences of delamination in terms of stiffness and strength observed in many types of composite laminates are presented. In the final section, several methods for suppression of delamination are discussed.

Mechanical behavior and properties of composite materials

Abstract: v. 1. Mechanical behavior and properties of composite materials / Carl Zweben H. Thomas Hahn, Tsu-wei Chou -- v. 2. Micromechanical materials modeling / James M. Whitney, Roy L. McCullough -- v. 3. Processing and fabrication technology / Michael G. Bader ... [et al.] -- v. 4. Failure analysis of composite materials / Peter W.R. Beaumont, Jerold M. Schultz, Klaus Friedric -- v. 5. Design studies / Keith T. Kedward, James M. Whitney -- v. 6. Test methods / R. Byron Pipes ... [et al.].

Fracture Analysis of Interlaminar Cracking

Abstract: This article details a method for treating interlaminar cracking (delamination) in polymer-based fiber-reinforced composite laminates. The method is developed on the basis of observing the physical characteristics of delamination on the phenomenological scale, interpret the visual findings and model the initiation and propagation mechanisms within the concepts of the classical fracture mechanics. The method is then incorporated into a finite-element simulation procedure for actual delamination processes in specific laminate situations. Thus, this article consists of discussions on three main parts: one part on the physical characteristics as they are observed in actual experiments, one part on the logical formulation of the analysis method and one part on the simulation of some specific laminates with numerical results and experimental correlations. The finite-element procedure used in the simulation is discussed in the appendix at the end of this article for ready reference.

Effects of Matrix Toughness on Fatigue Response of Graphite Fiber Composite Laminates

Abstract: The effect of the matrix toughness on the fatigue response of graphite-fiber-composite laminates was investigated by comparing the fatigue-response results, obtained using the test method of Bakis et al (1989), for two graphite-epoxy specimens subjected to constant-amplitude fully-reversed loading, namely, (0/ +45/90/ -45)s4 AS4/PEEK samples with drilled center holes and T300-5208 samples It was found that, although similar matrix damage modes were observed in the two materials, several significant differences occurred in the S-N data and in stiffness data taken over the lives of the two materials, especially at high cyclic stresses