Showing papers on "Composite laminates published in 1995"
TL;DR: In this article, a refined theory of laminated composite plates with piezoelectric laminae is developed using an energy principle, which includes coupling between mechanical deformations and the charge equations of electrostatics.
360 citations
TL;DR: In this article, the Iosipescu shear test was used to evaluate the inplane shear strength of fiber angle test specimens and a model for predicting the cutting forces and the dependence of cutting direction on machinability requirements was presented.
Abstract: With the increasing use of fiber reinforced plastic (FRP) composites outside the defense, space and aerospace industries, namely, civilian industries, machining of these materials is assuming a significant role. Unit cost rather than solely performance at any cost will be the consideration for the implementation of FRP composites to consumer industries. The current knowledge of machining FRP composites, unfortunately, is inadequate for its optimum utilization in many applications. This paper presents some observations made on the orthogonal machining of unidirectional carbon fiber reinforced plastic (UD-CFRP) laminates with different fiber orientations. Iosipescu shear test was adopted to evaluate the inplane shear strength of varied fiber angle test specimens. A model for predicting the cutting forces and the dependence of cutting direction on machinability requirements is presented.
306 citations
TL;DR: In this article, a damage meso-modeling of composite laminates is proposed to analyze delamination specimens within the framework of a damage-mosahedron model.
304 citations
TL;DR: In this article, the authors developed unified mechanics with the capability to model both sensory and active composite laminates with embedded piezoelectric layers with two discretelayer (or layerwise) formulations enable analysis of both global and local electromechanical response.
Abstract: Unified mechanics are developed with the capability to model both sensory and active composite laminates with embedded piezoelectric layers. Two discretelayer (or layerwise) formulations enable analysis of both global and local electromechanical response. The first assumes constant through-the-thickness displacement, while the second permits piecewise continuous variation. The mechanics include the contributions from elastic, piezoelectric and dielectric components. The incorporation of electric potential into the state variables permits representation of general electromechanical boundary conditions. Approximate finite element solutions for the static and freevibration analysis of beams are presented. Applications on composite beams demonstrate the capability to represent either sensory or active structures, and to model the complicated stressstrain fields, the interactions between passive/active layers and interfacial phenomena between sensors and composite plies. The capability to predict the dynamic c...
219 citations
TL;DR: In this paper, a micromechanics model that includes the effects of the fibre-matrix interface is used in a simple cumulative damage scheme to predict the tensile fatigue behavior of composite laminates.
133 citations
01 Mar 1995
TL;DR: In this article, a micromechanical theory for the thermoelastic response of functionally graded composites with non-uniform fiber spacing in the through-thickness direction is further extended to enable analysis of material architectures characterized by arbitrarily nonuniform fibre spacing in two directions.
Abstract: A recently developed micromechanical theory for the thermoelastic response of functionally graded composites with nonuniform fiber spacing in the through-thickness direction is further extended to enable analysis of material architectures characterized by arbitrarily nonuniform fiber spacing in two directions. In contrast to currently employed micromechanical approaches applied to functionally graded materials, which decouple the local and global effects by assuming the existence of a representative volume element at every point within the composite, the new theory explicitly couples the local and global effects. The analytical development is based on volumetric averaging of the various field quantities, together with imposition of boundary and interfacial conditions in an average sense. Results are presented that illustrate the capability of the derived theory to capture local stress gradients at the free edge of a laminated composite plate due to the application of a uniform temperature change. It is further shown that it is possible to reduce the magnitude of these stress concentrations by a proper management of the microstructure of the composite plies near the free edge. Thus by an appropriate tailoring of the microstructure it is possible to reduce or prevent the likelihood of delamination at free edges of standard composite laminates.
124 citations
105 citations
TL;DR: In this article, a technique is described for replicating impact damage artificially by including PTFE film delaminants and cut plies during lay-up and compared with real and artificially reproduced damage.
100 citations
TL;DR: In this article, the authors developed a multiple transform technique coupled with a numerical evaluation scheme to calculate the resulting double integral expressions for the displacements and stresses produced in a composite laminate subjected to dynamic loads.
90 citations
TL;DR: In this article, an analytic method for the prediction of the compressive strength of composite laminates containing impact damage has been developed using the characteristics of the impact damage detected by the ultrasonic time-of-flight C-scan technique, the state of the damage is modelled by an elliptical soft inclusion.
87 citations
TL;DR: In this article, the effect of stitching on Mode II delamination toughness is analyzed by using two specimen geometries, namely, the end-notch flexure (ENF) specimen geometry and the endnotch cantilever (ENC) geometry, and identical closed form analytical expressions are obtained for the potential energy release rate, GIIR(Δa), required for crack propagation.
TL;DR: Schlecht et al. as mentioned in this paper used the finite element analysis (FEA) for the calculation of the room-temperature shapes of unsymmetric cross-ply laminates.
TL;DR: In this article, the in-plane tensile and transverse impact responses of stitched composite laminates were evaluated using a hemispherically tipped impactor, and stitching was found to significantly reduce the delamination crack area, and 3,000 denier threads provided a better resistance to the propagation of these cracks.
Abstract: Experimental results for in-plane tensile and transverse impact responses of stitched composite laminates were presented in this paper. (02/902). E-glass/epoxy laminates of 2.8 mm nominal thickness fabricated by resin transfer molding were used as the specimens. The through-the-thickness reinforcement was provided by untwisted Kevlar-29 ravings of 1,000 and 3,000 denier. In the in-plane tensile test, although the damage mechanism of the stitched laminates was much affected by the loading directions, the stiffness was not significantly affected by the addition of the stitch threads. In the impact test using a hemispherically tipped impactor, stitching was found to significantly reduce the delamination crack area, and the 3,000 denier threads provided a better resistance to the propagation of these cracks. It was also found that, although the stitch step, stitch spacing, as well as the impact location relative to the stitch threads affected the size and the shape of the delamination area during impact, the ...
TL;DR: In this paper, composite micro-structures are studied, which give rise to high stiffness combined with high viscoelastic loss, and it is shown that such properties are most easily achieved if the stiff phase is as stiff as possible.
Abstract: Composite micro-structures are studied, which give rise to high stiffness combined with high viscoelastic loss. We demonstrate that such properties are most easily achieved if the stiff phase is as stiff as possible. Incorporation of a small amount of damping in the stiff phase has little effect on the composite damping. Experimental results are presented for laminates consisting of cadmium and tungsten and of InSn alloy and tungsten. The combination of stiffness and loss (the product E tan δ) exceeds that of well-known materials.
TL;DR: In this paper, a proper definition for the stress intensity factors and energy release rates of bimaterial interface cracks was introduced to study the fracture criterion for delamination, and the test specimen usually used for the unidirectional composites was redesigned to suit for the cases that the delamination lies between two laminae with different fiber orientations.
Abstract: Due to the singularity nature of delamination, the fundamental concept of fracture mechanics was applied. However, the oscillatory characteristics near the delamination tip prohibited the use of conventional definition assuming the crack embedded into a homogeneous solid. A proper definition for the stress intensity factors and energy release rates of bimaterial interface cracks was introduced in this paper to study the fracture criterion for delamination. To measure the delamination fracture toughness, the test specimen usually used for the unidirectional composites was redesigned to suit for the cases that the delamination lies between two laminae with different fiber orientations. The test results show that the double cantilever beam (DCB) test is near to pure Mode I and the end-notched flexural (ENF) test is near to pure Mode II. Therefore, like the cracks in homogeneous materials, the test methods DCB and ENF are useful for the measurement of delamination fracture toughness GC and G11,. Based upon th...
TL;DR: In this article, a progressive failure algorithm is developed where the Generalized Layerwise Plate Theory (GLPT) of Reddy is used for the kinematic description and the material is modeled as a stable progressively fracturing solid.
Abstract: A progressive failure algorithm is developed where the Generalized Layerwise Plate Theory (GLPT) of Reddy is used for the kinematic description and the material is modeled as a stable progressively fracturing solid. The geometric non-linearity is taken into account in the von Karman sense, and the extensibility of transverse normals is included in the finite element formulation. The progressive failure algorithm is used to study the effect of the geometric non-linearity, span-to-depth ratio, lamination sequence and the boundary conditions at the supports on the first-ply and the ultimate failure loads of composite laminates in bending. In addition, a new stiffness reduction scheme is proposed, in which stiffness properties of the failed element is reduced gradually, resulting in partial unloading depending on the amount of damage it accumulates.
TL;DR: In this paper, the physicico-mechanical properties of composite laminates have been evaluated as a function of fibre length, fibre content, sisal/glass fibres and sisal glass/red mud combinations.
TL;DR: In this article, a method is presented to study the nonlinear behaviors and first-ply failure strengths of centrally loaded laminated composite plates with semi-clamped edges, and the failure strength of the composite plate is analyzed.
Abstract: A method is presented to study the nonlinear behaviors and first-ply failure strengths of centrally loaded laminated composite plates with semi-clamped edges. The method which is developed from the...
TL;DR: In this article, the effect of embedded optical fiber sensors on the mechanical properties of composite laminates under the static tensile and the low cycle fatigue load was evaluated to investigate the effect.
TL;DR: In this paper, a number of damage mechanisms have been observed, and their influence on impact behaviour is found to be generally dependent on the impact force or incident kinetic energy (IKE) level.
TL;DR: In this article, a new boundary element formulation for analysis of cracks in anisotropic composite laminates is presented, referred to as the Dual Boundary Element Method, which utilizes displacement and traction boundary integral equations to enable modelling of crack problems in a single region analysis.
TL;DR: Based on a refined third-order shear deformation plate theory, a three-node, fully conforming, multilayered anisotropic plate element of arbitrary triangular shape is developed in this paper.
Abstract: Based on a refined third-order shear deformation plate theory recently proposed by the author, a three-node, fully conforming, multilayered anisotropic plate element of arbitrary triangular shape is developed in this paper. The element incorporates 10 nodal d.o.f., namely the two in-plane displacements, the two shear rotations, the transverse displacement and its first and second derivatives, thus giving a total of 30 d.o.f. The formulation includes extension, bending and transverse shear deformation states; moreover, it fulfils a priori the geometric and stress continuity conditions at the interfaces, and it requires only five generalized displacements to describe the kinematics of the plate deformation. The formulated plate element is assessed for its performance comparing its predictions either with exact solutions from the plate model or with other approximate two-dimensional solutions.
TL;DR: In this paper, a different approach has been developed using the fundamental Lamb wave (S 0 mode) to detect delaminations in unidirectional fiber composite materials, which is comparable to the delayed pulse echo technique and can be used to complement other techniques.
Abstract: One of the problems faced in ultrasonic nondestructive testing (NDT) of composite laminates is near-surface delaminations which may be due to impact damage. The normal incidence pulse echo technique has difficulty in resolving echoes from this type of defect since they often lie within the length of the transmitted ultrasonic pulse. Although a high frequency probe may be used, it has its limitations and could be problematic in composite materials in which ply reflections may interfere with defect reflections. The use of an acoustic delay, together with a high frequency probe, may improve the detection. In this paper, a different approach has been developed using the fundamental Lamb wave (S 0 mode) to detect delaminations in unidirectional fibre composite materials. It has been found that the Lamb wave amplitude decreases significantly over a delamination region. The decrease in amplitude is strongly dependent upon the depth of the delamination and is most sensitive to the delaminations near to the surface of the laminate. By scanning the transducer over the surface, it is possible to measure the size and depth of this kind of delamination. This technique is comparable to the delayed pulse echo technique and can be used to complement other techniques.
TL;DR: In this paper, a single-step fabrication method was developed for fabricating multiple-nested wavy 0 ° layers into otherwise wave-free thermoset crossply laminates.
TL;DR: In this article, the performance of hybrid titanium composite laminates (HTCL) was evaluated at room and elevated temperatures using an elastic-plastic laminate analysis program for predicting the tensile response from constituent properties.
Abstract: In this study, the mechanical response of hybrid titanium composite laminates (HTCL) was evaluated at room and elevated temperatures. Also, the use of an elastic-plastic laminate analysis program for predicting the tensile response from constituent properties was verified. The improvement in mechanical properties achieved by the laminates was assessed by comparing the results of static strength and constant amplitude fatigue tests to those for monolithic titanium sheet. Two HTCL were fabricated with different fiber volume fractions, resin layer thicknesses, and resins. One panel was thicker and was more poorly bonded in comparison to other. Consequently, the former had a lower tensile strength, while fewer cracks grew in this panel and at a slower rate. Both panels showed an improvement in fatigue life of almost two orders of magnitude. The model predictions were also in good agreement with the experimental results for both HTCL panels.
TL;DR: In this paper, an actuator location with high fault tolerance for static shape control can be obtained by an optimization with actuator failure consideration, based on a three-ring tetrahedral truss example.
Abstract: the simplest failure model is given. The authors explain that the optimization problem of the present study becomes a min-max problem. This analysis is applied to a realistic problem based on a three-ring tetrahedral truss example. So far as investigated here, an actuator location with high fault tolerance for static shape control can be obtained by an optimization with actuator failure consideration.
TL;DR: In this paper, a finite composite plate weakened by an elliptical hole is treated as an anisotropic multiple connected plate, and an analytical solution is obtained with the help of Fabor series expansion and the least squares boundary collocation technique.
TL;DR: In this article, a double-plate model was proposed to simulate a composite laminate with impact-induced delamination, which was first evaluated by using an isotropic double cantilever beam.
TL;DR: In this article, the effect of optical sensors and fibers embedded in host composite materials is reviewed, and it is shown that improperly embedded optical fibers produce local distortions and resin-rich regions in the host composite that cause structural performance degradation.
Abstract: The published literature on the effect of optical sensors and fibers embedded in host composite materials is reviewed. The literature indicates that improperly embedded optical fibers produce local distortions and resin-rich regions in the host composite that cause structural performance degradation. This is especially true for compressive loading of relatively thin composite laminates. Tensile strength is at most only slightly degraded. The available data are inconclusive for fatigue loading.
TL;DR: In this article, a statistical model for the prediction of residual strength and fatigue life of composite laminates has been developed on the basis of the statistical nature of fatigue damage and the concept of a representative volume for damage evolution.