Showing papers on "Composite laminates published in 1998"
TL;DR: In this article, the authors present a description of the laminates provided to all participants in an exercise to predict the strength of composite Laminates, including the elastic constants and the stress/strain curves for four unidirectional laminae.
790 citations
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21 Dec 1998
TL;DR: In this paper, the authors present an analysis of the mechanical behavior of composite material structures, including the bending of Laminate and Sandwich Beams, as well as the effect of stacking sequence.
Abstract: Preface.- Translators Preface.- Part I: Composite Materials. Basic Features of Composite Materials. The Constituents of a Composite Material. Molding processes and Architecture of Composite Materials.- Part II: Basic Concepts of the Mechanical Behavior of Materials. Mathematical Basics. Stresses. Strains. The Elastic Behavior of Materials. The Mechanics of Deformable Solids.- Part III: Mechanical Behavior of Composite Materials. Elastic Behavior of Unidirectional Composite Materials. Elastic Behavior of an Orthotropic Composite. Off-Axis Behavior of Composite Materials. Fracture Mechanisms and Damage of Composite Materials.- Part IV: Modeling the Mechanical Behavior of Laminates and Sandwich Plates. Basics of Laminate Theory. Classical Laminate Theory. Effect of the Stacking Sequence. Mat and Cloth Reinforced Materials. Governing Equations and Energy Formulation of Classical Laminate Theory. Including Transverse Shear Deformation in Laminate Theory. Theory of Sandwich Plates.- Part V: Analysis of the Mechanical Behavior of Composite Material Structures. Cylindrical bending. Bending of Laminate and Sandwich Beams. Bending of Orthotropic Laminate Plates. Bending of Plates.
357 citations
TL;DR: In this paper, a methodology is presented to predict the displacements of flat unsymmetric epoxy-matrix composite laminates as they are cooled from their elevated cure temperature.
293 citations
TL;DR: In this paper, a 3D finite element model of bolted composite joints was developed to determine non-uniform stress distributions through the thickness of composite laminates in the vicinity of a bolt hole.
223 citations
TL;DR: In this article, changes in electrical resistance during static and fatigue loading of unidirectional and cross-ply carbon fiber reinforced polymer composites have been studied and it was found that the initial linear portion of the resistance increase on static testing was reversible and could be attributed to reversible elastic strains in the fibres; later non-linear changes were a consequence of fibre fracture and were irreversible.
Abstract: Changes in electrical resistance during static and fatigue loading of unidirectional and cross ply carbon fibre reinforced polymer composites have been studied. The carbon fibres in the study were T300 and the matrix resins were Hexcel 914 and 920. It was found that changes in resistance during static tensile testing were about three per cent of the original resistance of the samples, while fatigue testing caused resistance changes of up to 10% of the original resistance, immediately prior to final failure. The initial linear portion of the resistance increase on static testing was reversible and could be attributed to reversible elastic strains in the fibres; later non-linear changes were a consequence of fibre fracture and were irreversible. Changes in resistance during fatigue also contained both reversible and non-reversible components. It was found that during fatigue testing the initial changes in resistance caused by the first few thousand cycles could be correlated with the eventual life. Samples with large initial resistance change had reduced lives compared with those with small changes in resistance. Fatigue lives of composite laminates may thus be predicted from monitoring of initial resistance changes. Many of the results could be explained via the parallel resistance model of conduction in composite laminates.
208 citations
TL;DR: In this paper, the meso-scale damage model of composite laminates is used to identify precisely the interlaminar interface model for ±θ interfaces, with θ = 0 °, 22.5 ° and 45 ° being the relative directions of the fibres of adjacent plies.
168 citations
TL;DR: In this paper, a series of impact and compression after impact tests were carried out on composite laminates made of carbon fibre reinforced epoxy resin matrix, and four stacking sequences of two different epoxy resins in carbon fibres representative of four different elastic behaviours and with a different number of interfaces were used.
155 citations
TL;DR: In this article, the authors investigated the rate dependence of interlaminar fracture behavior in unidirectional carbon-fibre/epoxy composite laminates over a wide range of loading rates from quasi-static (displacement rate, δ = 0.01-500 mm min−1) to impact (δ = 5-20 mm see−1).
127 citations
TL;DR: In this paper, the use of the original and truncated versions of the maximum-strain failure criterion for fiber/polymer composites is illustrated by sample solutions of specific problems provided by the organizers of the exercise.
111 citations
TL;DR: In this article, failure envelopes for unidirectional composites and multi-layered composite laminates have been predicted by linear laminate theory using the ply-by-ply discount method with parallel spring stiffness reduction model.
111 citations
TL;DR: In this paper, a coupled deformation/failure model for multilayered hybrid composites in a state of plane stress is presented, which is capable of predicting both stress/strain curves and failure envelopes under a variety of loading conditions.
TL;DR: In this article, it is shown that interlaminar shear failure actually consists of tension failures in the resin rich layers between plies followed by the coalescence of ligaments created by these failures and not the sliding of two planes relative to one another that is assumed in fracture mechanics theory.
Abstract: The concept of G2c as a measure of the interlaminar shear fracture toughness of a composite material is critically examined. In particular, it is argued that the apparent G2c as typically measured is inconsistent with the original definition of shear fracture. It is shown that interlaminar shear failure actually consists of tension failures in the resin rich layers between plies followed by the coalescence of ligaments created by these failures and not the sliding of two planes relative to one another that is assumed in fracture mechanics theory. Several strain energy release rate solutions are reviewed for delamination in composite laminates and structural components where failures have been experimentally documented. Failures typically occur at a location where the mode 1 component accounts for at least one half of the total G at failure. Hence, it is the mode I and mixed-mode interlaminar fracture toughness data that will be most useful in predicting delamination failure in composite components in service. Although apparent G2c measurements may prove useful for completeness of generating mixed-mode criteria, the accuracy of these measurements may have very little influence on the prediction of mixed-mode failures in most structural components.
TL;DR: In this article, a finite element model using linear, quasi-static analysis was developed to analyse the internal stress state in the laminate and predict delamination damage, which is capable of predicting the relative damage trends with respect to changes in stacking sequence.
TL;DR: In this article, an experimental investigation in interlaminar fracture behavior and toughness of multi-directional composite laminates was conducted, and ENF-like specimens were used for three-point-bending tests firs.
Abstract: An experimental investigation in interlaminar fracture behavior and toughness of multi-directional composite laminates was conducted. ENF-like specimens were used for three-point-bending tests firs...
TL;DR: In this paper, an investigation on the prediction of first-ply failure and fracture in selected composite laminates is described, which is made from glass fibers and graphite fibers in epoxy matrices.
TL;DR: In this article, the impact response of composite laminates was investigated and the impact characteristics (peak force, contact duration and absorbed energy) and mechanical properties degradation (residual compressive maximum force and residual compressive absorbed energy).
TL;DR: In this article, the effects of embedding piezoelectric lead zirconate-titanate (PZT) sensors on the tensile strength and fatigue behavior of a quasi-isotropic graphite/epoxy laminate as well as the embedded sensor's voltage degradation under these loading conditions were investigated.
Abstract: This study investigated the effects of embedding piezoelectric lead zirconate-titanate (PZT) sensors on the tensile strength and fatigue behavior of a quasi-isotropic graphite/epoxy laminate as well as the embedded sensor's voltage degradation under these loading conditions. For this, AS4/3501-6 laminates were fabricated with a lay-up where PZT was inserted into a cut-out area in the two middle plies. Monotonic tensile tests showed that both the average ultimate strength and Young's modulus of the tested laminate with or without PZT were within 4% of each other. The fatigue lives with and without PZT were very close to each other as well. Overall, the sequence of damage in this study agreed with previous investigations of the damage mechanisms for quasi-isotropic laminates. The ranges of modulus reduction in both cases, with and without PZT, were within 5 to 15% of each other during fatigue loading. Delamination growths in both cases during most of the fatigue life were also very comparable to each other. Further, this study showed that the embedded PZT would maintain a steady voltage output indefinitely when mechanically cycled within its operational strain limit. It thus appears that the embedment of PZTs in a cut-out area of plies of quasi-isotropic graphite/epoxy laminates would not affect their monotonic tensile and fatigue behavior.
TL;DR: In this paper, an axisymmetric concentric cylinder model and a flat laminate model, each based on Reissner's variational principle with equilibrium stress fields, are compared and the results for the elastic stress fields and energy release rates in composite laminates with free edge and/or internal delaminations and transverse cracking are presented.
TL;DR: In this paper, a general approach that avoids the abovementioned problems of nonconvexity when ply-angles are used as design variables is proposed, which is based upon the fact that the design space for an optimization problem formulated in lamination parameters is proven to be convex, because the laminate stiffnesses are expressed linearly in terms of the lamin parameters.
Abstract: This paper deals with optimization of laminated composite structures in which the ply angles are taken as design variables. One of the major problems when using ply-angles as design variables, is the lack of convexity of the objective function and thus the existence of local optima, which implies that usual gradient based optimization procedures may not be effective. Therefore, a new general approach that avoids the abovementioned problems of nonconvexity when ply-angles are used as design variables is proposed. The methodology is based upon the fact that the design space for an optimization problem formulated in lamination parameters [introduced by Tsai and Pagano (1968)] is proven to be convex, because the laminate stiffnesses are expressed linearly in terms of the lamination parameters. However, lamination parameters have at least two major shortcomings: as yet, for the general case involving membrane-bending coupling, the constraints between the lamination parameters are not completely defined; also, for a prescribed set of lamination parameters physically realizable composite laminates (e.g. laminates with equal thickness plies) may not exist. The approach here, uses both lamination parameters and ply-angles and thereby uses the advantages of both and eliminates the shortcomings of both. In order to illustrate this approach, several stiffness optimization examples are provided.
TL;DR: In this article, the authors compare the independent predictions for these same problems made by several originators of composite failure models and, simultaneously, compare the predictions with test data with the intent of this exercise.
TL;DR: In this paper, the effect of tool-plate on the cured shape of unsymmetric composite laminates has been investigated and a dimensionless slippage coefficient was introduced to predict curvatures of general lamination layup configurations.
Abstract: The room-temperature shapes of cured unsymmetric composite laminates have out-of-plane warping after autoclave processing. In addition, they exhibit two stable room-temperature configurations due to snap-through phenomena when the side length of laminates exceed a critical value. The cured shape of unsymmetric laminates are influenced by many factors. Experiments show that the effect of tool-plate cannot be ignored and has significant influence on the cured shape.This study examines slippage effects resulting from the interaction between the laminates and the tool-plate which are ignored in the previous researches. By introducing a dimensionless slippage coefficient and correlating the corresponding value with experimental results, the influence of processing parameters is investigated. Modeling is extended to predict curvatures of general lamination layup configurations.
TL;DR: In this article, a piecewise cubic spline interpolation scheme has been used to represent the basic material properties along the lamina material axes and a laminated plate theory that includes an iterative incremental constitutive law to account for the non-linear behavior of the lamine is combined with a strain-energy based failure criterion for orthotropic materials.
TL;DR: In this article, a numerical procedure to predict long-term laminate properties of fiber reinforced composite materials was developed, which extended the classical laminate theory to include time related response of composite materials for membrane and flexural loading.
Abstract: A numerical procedure to predict long-term laminate properties of fibre reinforced composite materials was developed. In the procedure, we extended the classical laminate theory to include time related response of composite materials for membrane and flexural loading. The material response, dependent on the stress history, was modelled using the Schapery single integral equation. The integrals were handled by an approximate method that uses the Prony's series and only requires the storing of the current stress and some internal strain components. An efficient semi-direct time-integration scheme, providing a stable integration process, was derived to be included in the numerical procedure. Comparisons of theoretical results were made with experiments conducted on composite materials under creep-creep recovery, relaxation and ramp loading.
20 Apr 1998
TL;DR: In this paper, the effects of overlap and gap presence on laminate compression strength were assessed using specimens containing defects of defined size and location, and it was shown that failure was most likely driven by interaction of in-plane compression and interlaminar shear stresses in the wavy 0° plies.
Abstract: Intraply overlap and gap defects can be created during the fabrication of composite laminates using hand-layup and automated processes. The effects of overlap/gap presence upon laminate compression strength were assessed using specimens containing defects of defined size and location. Strength reductions of 5-27% were observed in laminates containing overlaps and gaps at least 0.03" wide; further reductions were not observed when wider defects were present. Unnotched and open hole tests demonstrated that out-of-plane waviness (induced by the defects into adjacent plies) was the primary cause of the strength reductions. Finite element analysis and follow-on experiments determined that failure was most likely driven by interaction of in-plane compression and interlaminar shear stresses in the wavy 0° plies. Shear stress levels produced local to an overlap or gap defect were shown to be proportional to the slope of the out-of-plane waves in the 0° plies.
15 Oct 1998-Philosophical transactions - Royal Society. Mathematical, physical and engineering sciences
TL;DR: The modified damage representation has been modified and significant simplifications have been achieved in defining the damage–related material constants for this particular form of damage in a convenient way, resulting in a new laminate theory which describes the deformation of laminates as well as the development of the damage process in the form of crack multiplication.
Abstract: In this paper, the effects of damage in the form of transverse matrix cracking in fibrereinforced laminates of arbitrary layup are considered in the context of continuum damage mechanics. A complet...
TL;DR: In this paper, the influence of fiber orientation as a function of depth on the indentation response is considered along with the relationship between the indenter force vs. depth, and it is shown that the orientation-graded material is more compliant when subjected to indentation than the conventional cross-ply laminate.
TL;DR: In this article, a variational approach is taken to estimate the stresses in the region between transverse cracks, and these are found to be accurate away from the crack planes when comparison is made with finite element computations.
TL;DR: In this article, the basic mechanics and mechanism concerning compressive stability of composite laminates with multiple circular delaminations is studied analytically and experimentally, and a buckling equation is derived using the Rayleigh-Ritz method based on classical plate theory and solved as an eigenvalue problem.
Abstract: The basic mechanics and mechanism concerning compressive stability of composite laminates with multiple circular delaminations is studied analytically and experimentally. An experimental program, employing two types of quasi-isotropic laminates with a conventional and toughened epoxy resin, is used to evaluate the validity of the mechanistic model and further demonstrate the accuracy of finite element analysis conducted in the associated paper. Embedded delaminations are introduced at regular intervals in the thickness direction. The loading edges are fixed, and the side edges are simply supported. Although the buckling load does not depend on the matrix resin toughness, the strength is affected by the toughness. In the analysis, a buckling equation is derived using the Rayleigh-Ritz method, based on classical plate theory and solved as an eigenvalue problem. This method is chosen due to its efficiency. As the buckling mode of the lowest buckling load becomes physically admissible due to the assumptions of equally spaced delaminations and the classical plate theory, the contact problem does not need to be considered, that is, all of the delaminated portions deform by the same amount and do not overlap one another even without any constraints. The buckling loads analytically obtained agree well with experimental and finite element results described in the associated paper. The effects of size and number of circular delaminations on the buckling and failure load are also discussed in detail.
TL;DR: The stress-based Grant-Sanders method developed at British Aerospace Defence is described in this paper, and applied to a number of examples to produce envelopes of initial and final failure and stress/strain curves.
TL;DR: In this paper, the static response characteristics of graphite/epoxy composite laminates are obtained with the help of Monte Carlo simulation and the Finite Element Method (FEM) for different boundary conditions, thickness ratio, aspect ratios and fiber orientations.
Abstract: Composite materials have a large number of parameters associated with their manufacturing. It is not physically possible to control all these parameters, and hence variation in the material properties result. In this paper, for a better modeling of the material properties, these are treated as random variables. Static response characteristics of graphite/epoxy composite laminates are obtained with the help of Monte Carlo simulation and the Finite Element Method (FEM) for different boundary conditions, thickness ratio, aspect ratios and fiber orientations. The input material property mean and variance are assumed to be known. From the limited analytical study conducted it is observed that a single design curve can predict normalized characteristics for all the parameters considered.