Showing papers on "Composite laminates published in 2004"
TL;DR: In this article, a critical review has been performed of the published experimental research concerning delamination onset and growth in composite laminate interfaces of different lay-ups under single-mode loadings, and it was found that the traditional fracture toughness characterization by unidirectionally reinforced composite tests can lead to marked under- or overestimation of material resistance to crack growth.
170 citations
TL;DR: In this paper, the authors present supplementary conclusions from an international exercise to establish the current status of failure prediction theories for polymer composite laminates and compare the performance of the new theories with that of the other fifteen theories using an identical methodology.
170 citations
TL;DR: In this paper, a Lamb wave-based quantitative identification technique for delamination in CF/EP composite structures was established, where the propagation of Lamb waves in a series of composite laminates, individually bearing a delamination, was evaluated using dynamic FEM analyses.
166 citations
TL;DR: In this article, foam filled 3D integrated core sandwich composite laminates with and without additional face sheets were fabricated using vacuum assisted resin infusion molding process in multiple steps, and three samples were tested at each energy level.
147 citations
TL;DR: In this article, a constituent stress-based failure criterion is used to construct a nonlinear progressive failure algorithm for investigating the material failure strengths of composite laminates. But, the proposed failure analysis methodology was used to simulate the nonlinear laminate behavior and progressive damage of selected lamates under both uniaxial and biaxia load conditions up to their ultimate strength.
143 citations
TL;DR: In this article, the response of stitched/unstitched woven fabric carbon/epoxy composite laminates subjected to high velocity impact loading is discussed and the ensuing damage was characterized through ultrasonic NDE.
138 citations
TL;DR: In this paper, the damping properties of carbon fiber-reinforced interleaved epoxy composites were evaluated by the mechanical impedance method and the effects of the lay-up arrangements of the carbon-fiber prepregs on the dampness properties of the interleaving laminates were examined.
133 citations
TL;DR: In this article, a prediction procedure is described to simulate the progressive failure strength of a composite laminate subjected to multiaxial loading in an incremental form, the stress increments exerted on each lamina in the laminate can be determined based on the instantaneous stiffness matrix of the lamina.
126 citations
TL;DR: In this paper, the authors present a simple closed-form method for the analysis of the stress fields in the vicinity of free laminate corners with arbitrary layup, based on adequate stress shape assumption.
Abstract: Stress concentration phenomena in composite laminates are technically important situations. A well-known problem of this class is the free-edge effect in composite laminates or as a superordinated example the stress concentrations in the vicinity of free laminate corners (so-called free-corner effect). The present work is split into two parts. In the present contribution, after a short introduction to the given stress concentration problems in general we will survey relevant selected literature on the classical free-edge effect dating from 1967 until today. Beside accentuation on approximate closed-form analytic methods for the stress analysis in the free-edge effect situation, numerous references on numerical methods and investigations on the occurring stress singularities are also cited. In a subsequent paper we will present a simple closed-form method for the analysis of the stress fields in the vicinity of free laminate corners with arbitrary layup. The method is based on adequate stress shape assumpt...
125 citations
TL;DR: In this article, the impact analysis of composite laminates using the modified Hertzian contact law and the experimental static indentation law was investigated and the difference between the analytical results obtained using the two laws was also investigated.
124 citations
TL;DR: In this article, a method for predicting the nonlinear stress/strain response and failure behavior of composite laminates is described, based on an incremental formulation of a well-established three-dimensional laminated media analysis coupled with a progressive-ply failure methodology.
TL;DR: In this article, the impact response of composite laminate and shell structures is proportional to the impactor velocity, and the effects of various parameters, such as shell curvature, clamped or simple supported boundary conditions, are examined through the parametric study.
TL;DR: In this paper, a linear elastic and progressive damage approach was used to predict the strength of unnotched and notched laminate laminates in tension and compression conditions, and the results showed that the linear elastic model either significantly underestimated (first-ply failure approach) or overestimated (last-plummer failure approach).
01 Apr 2004
TL;DR: In this article, an active excitation control circuit was designed and instrumented with an online damage diagnosis system, by which the desired fundamental symmetric Lamb mode, shear mode and antisymmetric mode can be selectively stimulated.
Abstract: Techniques for the generation of Lamb waves with purpose of non-destructive inspection (NDI) were briefly reviewed. An active excitation control circuit was designed and instrumented with an online damage diagnosis system, by which the desired fundamental symmetric Lamb mode, shear mode and antisymmetric mode can be selectively stimulated. A signal processing and identification algorithm in the time-scale domain, using spectrographic analyses based on the wavelet transform technique, was developed to assist the wave signal interpretation. The proposed excitation methodology was applied to the study of the dispersion and propagation characteristics of Lamb waves in quasi-isotropic CF/EP composite laminates with delamination. For validation, numerical simulations were conducted in parallel with experimental investigations.
TL;DR: In this paper, the authors investigated the mode II delamination toughness of z-pin reinforced composite laminates using finite element (FE) method and showed that z-pins can significantly increase the delamination strength of composite laminate.
TL;DR: In this article, an empirical model for the stress ratio effect on the fatigue delamination growth rate in composite laminates under single-mode loading is proposed, which is based on heuristic considerations of damage accumulation ahead of the crack.
TL;DR: In this article, a new inspection technique using Lamb waves to detect impact-induced delamination in composite laminates is proposed, which consists of two line scans, which are as follows: the first scan measures the arrival times of the transmitted S0 mode along the 0° direction to detect delamination and evaluate its size.
01 Jan 2004
TL;DR: In this paper, the authors presented nonlinear stress-strain data and elastic constants for linear elastic analysis and discussed a wide range of practical biaxial loading conditions, which produce a variety of modes of failure.
Abstract: Publisher Summary
This chapter provides the details of the input data and a description of the laminates provided to all participants in an exercise to predict the strength of composite laminates. The input data include the elastic constants and the stress strain curves for four unidirectional laminae and their constituents. Six types of laminates, chosen for the analysis are selected and described to represent a wide range of parameters. These parameters include the type of composite material (fiber and matrix), the type of laminate lay-up (unidirectional, angle ply, cross ply, and quasi-isotropic), and the loading conditions. The chapter explains the schematic diagrams showing the loading directions, layer and laminate dimensions, and stacking sequence of the laminates. The six laminates chosen for analysis by the participants are considered to be the representative of a wide range of composite laminates encountered in practical use in a variety of industries. The materials selected have been widely used in practical applications and their properties are well characterized. The chapter presents nonlinear stress–strain data and elastic constants for linear elastic analysis and discusses a wide range of practical biaxial loading conditions, which produce a variety of modes of failure. In some cases, a succession of failures may occur before the laminate can no longer carry load. In some cases, the stress–strain behavior of the laminates is expected to be linear and in some other cases, highly nonlinear.
TL;DR: In this article, the effect of an embedded optical fiber in unidirectional composite laminates was evaluated and failure initiation was hypothesized as due to transverse stress concentration, and the results showed that the embedded optical sensor had practically no loss of tensile modulus and about 10% loss in tensile strength while compression strength reduction was as large as 40%.
Abstract: Embedding fiber optic sensor (FOS) in fiber reinforced composites caused resin pockets and geometric disturbance of the reinforcing fibers around the optical fiber. The disturbance angle varied from 6.2 to 8.2 and the resin pocket area varied from 7 to 10 times the cross-sectional area of the sensor. These two act like defects and cause premature failure initiation. Failure initiation was hypothesized as due to transverse stress concentration. A static experimental study was conducted to evaluate the effect of an embedded optical fiber in unidirectional composite laminates. Inclination of FOS with respect to reinforcing fiber (loading direction) varied from 0 to 90 and the laminate thickness varied from 8 to 20 plies. The embedment had practically no loss of tensile modulus and about 10% loss of tensile strength while compression strength reduction was as large as 40%.
TL;DR: In this article, a finite element model is proposed to quantify the material damage, which has been experimentally validated by means of nondestructive dye-penetrant testing, and good agreement is observed for laminates with fiber orientations up to 60°.
Abstract: Machining of fiber reinforced plastic (FRP) components is often needed in spite of the fact that most FRP structures can be made to near net shape. The material removal mechanism of FRP is very difficult as compared with metals due to their inherent inhomogeneity and anisotropy. This results in frequent fiber pullout, delamination, matrix burning, and other damages leading to poor cut surface quality. A finite element model is proposed to quantify the material damage, which has been experimentally validated by means of nondestructive dye-penetrant testing. Good agreement is observed for laminates with fiber orientations up to 60°. Divergence is noticed for higher fiber orientations, and the discrepancies increase with increasing fiber orientation. Proper interfacial properties vis-a-vis machining of FRP materials are considered to be the main reasons for the divergence.
TL;DR: A modified Iosipescu test fixture has been designed and manufactured to investigate the in-plane shear properties of cross-ply composite laminates with different off-axis angles.
TL;DR: In this article, a three-dimensional fatigue progressive damage model (FPDM) was used to assess fatigue damage accumulation and residual strength of carbon-fibre reinforced plastic (CFRP) laminates under fully reversed cyclic loading (R=σmin/σmax=−1).
TL;DR: In this article, the specific damping capacity (SDC) of composite beams in flexure is measured and analyzed for the detection of initial damage in woven fabric composites and the damage mechanisms and location of the damage in the woven laminates are deduced from comparison of dynamic results with the dynamic response from the cross-ply Laminates containing well characterized damage.
Abstract: The detection of damage in composite laminates is a vital step in allowing their wider use in critical applications. Measurement of specific damping capacity (SDC) is a useful potential method for damage detection. The work reported in this paper consists of measurements and analysis of SDC of composite beams in flexure. Beams have been tested before and after the introduction of damage using quasi-static loading or fatigue. The damage mechanisms and location of the damage in the woven laminates is deduced from comparison of dynamic results with the dynamic response from the cross-ply laminates containing well characterized damage. The results indicate that measurement of SDC is a promising technique for detection of initial damage in woven fabric composites.
TL;DR: In this article, the authors described both experimental and analytical programs focused on the torsional strengthening of reinforced concrete spandrel beams using composite laminates, including fiber orientation, composite laminate, and effects of a laminate anchoring system.
Abstract: Research has shown that fiber-reinforced polymer (FRP) composites can increase flexural, axial, and shear capacity of beams, columns, and walls. The present paper describes both experimental and analytical programs focused on the torsional strengthening of reinforced concrete spandrel beams using composite laminates. The variables considered in this study included fiber orientation, composite laminate, and effects of a laminate anchoring system. The study proved that the FRP laminates could increase the torsional capacity of concrete beams by more than 70%. The analytical procedure developed revealed a good comparison between experimental and analytical results.
TL;DR: In this article, it was shown that a square, unsymmetrical 0.90 laminate will tend to form two stable geometries with a snap-through phenomenon between them.
Abstract: The phenomenon of thermally induced distortions in unsymmetrical laminates is well understood, and it may be shown that a square, unsymmetrical 0.90 laminate will tend to form two stable geometries with a snap-through phenomenon between them. This paper discusses laminates in which at each point the lay-up is symmetrical across the laminate mid-plane, but which still exhibit multiple stable geometries. The number of stable geometries can be controlled by the details of the lay-up from the minimum of two to, in principle, an unlimited number. In addition it will be shown how a similar process can be used to generate multiple stable stress states and geometries in unidirectional laminates. This paper represents a very preliminary experimental investigation of the design space available for such composite laminates. Possible applications of composites with multiple stable geometries are noted.
TL;DR: In this paper, the authors proposed mathematical models for drilling-induced damage in terms of the cutting speed and the feed speed of fiber reinforced plastic and the resulting thrust force and torque.
Abstract: Machining of fiber reinforced plastic is a process that is substantially different from metals. The inherent anisotropy in the material system makes the material removal mechanism quite complex. Drilling composite materials is necessary to ascertain the structural integrity of intricate composite products. Drilling of laminated structures results in extensive damage around the drilled hole. This study is an attempt to quantify and propose mathematical models for drilling-induced damage in terms of the cutting speed and the feed speed. Mathematical models have also been proposed for the resulting thrust force and the torque. Four different drill point geometries, namely 4-faceted, 8-faceted, parabolic, and Jodrill, are investigated in this study.
TL;DR: In this article, an energy profiling technique based on instrumented impact tests and the least-squares method is presented to characterize the impact properties and to correlate them with the damage process of the composite laminates.
Abstract: This paper investigates the responses of glass/epoxy composite laminates subjected to impact loading. It presents a new technique to characterize the impact properties and to correlate them with the damage process of the composite laminates. The technique, called the energy profiling technique, is based on instrumented impact tests and the least-squares method. The technique gives specific definitions of the penetration and perforation thresholds of the composite laminates. It also defines the range of the penetration process and quantifies the energy absorption efficiency of the composite laminates. The primary damage modes in the damage process of the composite laminates can also be correlated with the impact properties by using the energy profiling technique. The advantages of using this technique to analyze the experimental data obtained from impact tests are demonstrated by investigating the glass/epoxy composite laminates with various impactor sizes, laminate thicknesses, fiber orientations, and a s...
TL;DR: In this article, the applicability of standard composite mode I interlaminar toughness data reduction schemes for composites reinforced by inserting straight pins in the z-direction is investigated, and a simple model of a z-pinned mode I test is used to generate load, displacement and crack length data.
TL;DR: In this paper, a mesh-free model based on the first-order shear deformation theory is presented for the shape and vibration control of laminated composite plates with integrated piezoelectric sensors and actuators.
Abstract: A meshfree model based on the first-order shear deformation theory is presented for the shape and vibration control of laminated composite plates with integrated piezoelectric sensors and actuators. A point interpolation method using radial basis functions (RPIM) is employed to construct shape functions for mechanical and electrical variables, which possess the delta function property and show linear reproduction behavior. The method shows a high convergence rate equivalent to that of the second-order finite elements approach. Comparing, one sees that a very simple nodal topology can be used for the field representation and no element continuity is required. A constant displacement and velocity feedback control algorithm is used for the active control of the static deflection as well as the dynamic response of plates through closed loop control. Numerical results for the static deformation, vibration modes and dynamic responses are in good agreement with those from the finite element method.
TL;DR: In this paper, a three-dimensional elasticity based layer-wise finite element method (FEM) is employed to study the static, free vibration and buckling responses of general laminated thick composite plates.