Laminate Orientation Research Articles

Laminated Nb/Nb3Al composites: effect of layer thickness on fatigue and fracture behavior

Abstract Fracture and fatigue crack growth properties of coarse scale Nb/Nb 3 Al laminated composites are examined, and their performance is contrasted with similarly reinforced in situ particulate and microlaminate composites. It is found that laminate orientation has a larger effect on fatigue crack growth resistance than on fracture toughness; properties are optimal in the crack arrester as compared with the crack divider orientation. In addition, thicker Nb layers yield improved fracture and fatigue crack growth properties; and the effect is more prominent in the divider orientation. Mechanisms underlying this behavior are briefly described.

The effect of laminate orientations on friction and wear mechanisms of glass reinforced polyester composite

Friction and wear properties of polyester composite reinforced with laminated glass fibres are experimentally examined in three different orientations, namely, cross-laminar CL, and inter-laminar (normal, NL and parallel, PL). The rubbing experiments of the composite specimens are carried out against abrasive paper (silicon carbide, P600) under various sliding speed and loading conditions. Experimental results show that PL orientation gives the highest value of friction coefficients followed by NL and CL. Microscopic investigations of the worn surfaces are conducted to identify the operating wear mechanism. They reveal that the weaving configuration in CL orientation inhibits an easy detachment of fibres during the wear process. Therefore, intermediate values of wear resistance between PL and NL orientation are obtained. Furthermore, entrapped soft components of matrix resin between laminates in CL orientation play an important role in reducing the friction coefficient. In NL orientation, the individual fibres within the laminates do not get mutual support as in PL orientation. As a result, fibres suffer bending at their ends, leading to an easy shear mechanism.

Vibration control of laminated composite plate with piezoelectric sensor/actuator: active and passive control methods

Vibration of a laminated composite plate is controlled by passive and active control methods. Stiffness change in composite structures by changes in laminate orientation is used as an example of a passive control method, negative velocity feedback control with the piezoelectric sensor/actuator is used as an example of an active control method. The effect of passive and active controls are investigated by changing the layer angles of a laminated composite plate or the location and number of the sensor/actuator pairs. Classical lamination theory with the induced strain actuation and Hamilton's principle are used to formulate the equations of motion of the system. The system equations are discretised by the finite element method. Using numerical simulation, a design strategy for a laminated composite plate with piezoelectric sensor/actuator is suggested.

Effect of Laminate Orientation on the Thermomechanical Fatigue Behavior of a Titanium Matrix Composite

Thermomechanical fatigue (TMF) tests were conducted on the silicon carbide fiber and titanium alloy matrix composite, SCS-6/TIMETAL®21S. Three different laminate orientations were considered: [0]4, [0/90]s, and [0/±45/90]s. Both in-phase and out-of-phase stress-controlled tests were conducted under a temperature cycle of 150° to 650°C and a stress ratio of 0.1. The fatigue lives for these different orientations can be consolidated within a factor of 3 by normalizing the maximum applied stress (Smax) by the ultimate tensile strength at the Smax temperature of the TMF cycle. For all laminate orientations, the maximum and minimum strain increase during in-phase cycling, whereas only maximum strain increases during out-of-phase cycling. Damage accumulation under inphase cycling is attributed to a combination of the increasing stress carried by the [0] fibers due to cyclic matrix stress relaxation and the gradual breakage of [0] fibers. The damage during out-of-phase cycling is attributed to matrix cracks which initiate at the surface with the aid of the environment and/or initiate internally at the transverse fibers in [0/90]s and [0/±45/90]s composites. A simple model to compute cyclic strain accumulation based on the proposed mechanisms successfully captures the experimentally observed behavior. TMF life is shown to be sensitive to fiber volume fraction under inphase cycling, but not under out-of-phase cycling. TMF conditions are shown to be more severe than isothermal fatigue.

Scaling of Energy Absorbing Composite Plates

The energy absorption response and crushing characteristics of geometrically scaled graphite-Kevlar epoxy composite plates were investigated. Two different trigger mechanisms including notch, and steeple geometries were incorporated into the plate specimens to initiate crushing. Sustained crushing was achieved with a new test fixture which provided lateral support to prevent global buckling. Values of specific sustained crushing stress (SSCS) were obtained which were lower than values reported for tube specimens from previously published data. Two sizes of hybrid plates were fabricated; a baseline or model plate, and a full-scale plate with inplane dimensions scaled by a factor of two. The thickness dimension of the full-scale plates was increased using two different techniques: the ply-level method in which each ply orientation in the baseline laminate stacking sequence is doubled, and the sublaminate technique in which the baseline laminate stacking sequence is repeated as a group. Results indicated that the SSCS has a small dependence on trigger mechanism geometry. However, a reduction in the SSCS of 10-25% was observed for the full-scale plates as compared with the baseline specimens, indicating a scaling effect in the crushing response.

The Seismic Reflection Process in Anisotropic Media

A study of the seismic reflection process in anisotropic media showed a number of results which have direct consequences in an exploration context. Using laminated blocks of an anisotropic material to simulate shale-type layering, the seismic wave propagation was observed to be dependent upon the lamination orientation and, hence, on the shale layering orientation in an exploration sense. The seismic waves were demonstrated to travel at a faster velocity in the direction parallel to the layering orientation. Stacks of conventionally recorded seismic lines parallel and across the layering resulted in a two-way travel time mis-tie at their tie-point. Time to depth conversion indicated that a severe depth mis-tie would occur. The implication for exploration is that mis-ties in 2-D land and marine data may indicate the presence of anisotropy, while 3-D land and marine data do not. 2-D recording is therefore a necessary requirement to indicate the presence of anisotropy prior to 3-D recording. Numerical modelling of equivalent seismic data showed that commercially available numerical modelling software is inadequate for modelling the effects of anisotropy.

Plane-wave shielding characteristics of anisotropic laminated composites

The EM plane-wave shielding properties of anisotropic laminated composites are analyzed, based on a model that treats each lamina as a homogeneous and anisotropic sheet and then uses a method that cascades the wave-transmission matrices in the computation, Numerical results are presented for graphite/epoxy laminates. In particular, the parameters that influence the shielding effectiveness, such as material properties, laminate thickness, fiber orientation and anisotropy of laminates, and angle and polarization of incident wave, are investigated in detail. For design purposes, empirical formulas are also proposed to estimate the shielding effectiveness of the laminated composites in the lower frequency range.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Some strength studies on FRP laminates

The usage of fibre reinforced plastics can lead to a significant reduction in the weight of structural elements. The most important design variables in laminate design are the fibre orientation angle, ply thickness and fibre volume fraction. The first ply failure strength for [0/90/ ± 45] s laminate with different material systems and the corresponding first ply failure envelopes are presented for different in-plane loading conditions and ply orientations. The optimum biaxial stress ratio gives the highest value of the major failure load. At equal biaxial loading, all the plies of the laminate fail simultaneously in tension as well as compression for all values of laminate orientation angle.

Laminate Orientation and Thickness Effects on An Scs-6/Ti-24ai-11 Nb Composite Under Thermal Fatigue

ABSTRACTA SiC/Ti-24AI-11 Nb (at. %) composite (30–35 vol. %) was thermally cycled in air and an inert environment between 150 °C and 815 °C for various cycle counts. Various hold times at maximum temperature were employed to determine timedependent effects on composite integrity. Laminate orientations investigated included: [0]4, [0]8, [90]4, [90]8 and [0/90]2S. Acoustic emission produced during thermal fatigue of selected specimens was employed to monitor damage progression. Post-cycling room temperature tension tests as well as optical and scanning electron microscopy were used to document damage, which was particularly acute when hold times at temperature were employed on tests performed in air. The roles of the environment, composite thickness, and off-axis fibers during thermal fatigue on the composite strength and integrity are discussed.

Micromechanics Analysis of Space Simulated Thermal Stresses in Composites. Part II: Multidirectional Laminates and Failure Predictions

A finite element micromechanics approach was used to predict thermally induced stresses in fiber reinforced polymer matrix composites at temperatures typical of spacecraft operating environments. The influence of laminate orientation was investigated with a simple global/local formulation. Thermal stress calculations were used to predict probable damage initiation locations, and the results were compared to experimentally observed damage in several epoxy matrix composites. Multidirectional [O2/ ±θ]s laminates had larger predicted matrix stresses than unidirectional [0] laminates. The stresses in creased with increasing lamination angle θ, and resulted in large tensile radial stresses at the fiber/matrix interface, that were not present in unidirectional laminates. Thermally in duced matrix failure predictions, using a failure criterion based on the maximum radial in terfacial stress and the ultimate radial interfacial strength, were in excellent agreement with experimental data. This criterion was able to accurately account for the influence of both laminate configuration and constituent properties. Predictions based on the bulk matrix tensile strength or on lamina stresses (computed from laminated plate theory) and strengths were in poor agreement with experimental data.

Optimal fibre orientation of antisymmetric hybrid laminates for maximum fundamental frequency and frequency separation

Optimal fibre orientations of antisymmetric, angle-ply laminates are determined with the objective of maximizing their vibration characteristics. The design problems involve the maximization of the fundamental frequency and the frequency separations subject to a mass constraint. The laminated plate is constructed as a sandwich hybrid structure with outer layers of a high-stiffness material and inner layers of a low-stiffness material. The numerical results are given for laminates made of a boron/glass material combination. Cost and frequency implications of hybrid construction are discussed. Comparative studies of hybrid and non-hybrid optimal laminates of equal mass are presented in graphical form. The optimal fibre orientations are found to display several jump discontinuities when plotted against the aspect ratio. It is observed that the results for hybrid laminates do not always fall in between those for non-hybrid laminates. Furthermore, the vibration characteristics of optimal hybrid laminates are found to be better than those of non-hybrid ones of high-stiffness material for certain ranges of problem parameters.

Analysis of interlaminar stresses in viscoelastic composites

The viscoelastic response of laminated composites under the influence of mechanical and hygrothermal loads is studied analytically. A finite element formulation is developed for the thermo-viscoelastic solution of free edge stresses in composite laminates. Numerical results are obtained to verify the present finite element approach and to demonstrate the viscoelastic effect in graphite epoxy composites. In addition, the effect of laminate orientations and environmental conditions on the interlaminar stress distributions and histories is presented.

複合材料の疲労寿命推定法 引張モードを基にした場合

In this paper, a fatigue life prediction method based on linear fracture mechanics is proposed to composite materials. In order to evaluate this method, the cyclic loading tests of graphite/epoxy composites plates with [±30]s, [±45]s and [±60]s laminate orientations were carried out.It was revealed that the computational result was satisfactory agreement with the experimental ones except long life region [±30]s laminate orientations. The fracture mode was the combination of tension and shear modes when the angle between loading direction and fiber orientation became small. Therefore, it is recognized that the long life prediction of these materials has to require fracture mechanics base on the combined mode which is not dealt with in this paper.Furthermore, the effects of material properties on fatigue life were investigated as an application of the proposed model to material design. As a result, it became clear that the fatigue life is affected by the ultimate tensile and shear strengths of the matrix and depends strongly on the influence of initial crack length that is calculated from the size of voids or defects.

Strength of quasi-isotropic laminates under off-axis loading

An experimental investigation was carried out to determine the failure properties of quasi-isotropic AS4/3501-6 carbon/epoxy laminates under conditions where the loading axis did not coincide with the fiber axis. A tubular specimen subjected to combinations of pressure and axial tension was used to determine the response under various tension-tension biaxial stress states. The results showed no loss of strength with rotation of the laminate orientation with respect to the loading axes at angles including 22·5°,the maximum possible for the laminate used. Maximum fiber direction strains at failure were essentially independent of the rotation of the laminate as well as the biaxial stress state.

On the validity of the reduced bending stiffness method for laminated composite plate analysis

The ‘reduced bending stiffness’ (RBS) method has been used on occasions in the past as a means of simplifying the analysis of the flexural behavior of unsymmetrically laminated composite plates. However, the validity of the method has never been established. This paper makes direct comparisons between relatively simple, exact solutions for the static deflections, buckling loads and vibration frequencies of simply-supported plates and those arising from the RBS method. Extensive calculations are made for wide ranges of the physical parameters involved (aspect ratio, moduli ratio, lamination orientation angle, numbers of plies). The RBS method is found to yield sufficient accuracy for cross-ply plates, but errors up to 29% are obtained for angle-ply plates constructed with materials currently under development.

The influence of fiber length and fiber orientation on damping and stiffness of polymer composite materials

This paper describes the theoretical analysis, the experimental results and the curve-fitting of the analytical model to the experimental results on the influence of fiber length and fiber orientation on damping and stiffness of polymer-composite materials. The experimental results show that, as predicted, very low fiber aspect ratios are required to produce significant improvements in damping. Measurements and predictions also indicate that the control of lamina orientation in a continuous fiber-reinforced laminate may be a better approach to the improvement of damping than the control of the fiber aspect ratio.

Influence of lamination orientation and stacking on magnetic characteristics of grain-oriented silicon steel laminations

Analytical and experimental investigations have been carried out upon the behaviour of flux in laminations, where the rolling directions of adjacent sheets are reversed. The paper clarifies the mechanism of the greatly different magnetic characteristics between such laminations and usual ones, where the rolling directions of adjacent sheets are coincident.

Analysis and Performance of Fiber Composites

Analysis and Performance of Fiber Composites

Early Detection of Fatigue Damage in Composite Materials

Early detection of fatigue damage in composite materials by nondestructive inspection (NDI) techniques has been demonstrated for glass/epoxy, graphite/glass/epoxy, and graphite/epoxy composites. Modulus and temperature were monitored and a correlation between them observed. Axial modulus and torsional modulus changes were a function of the laminate orientation. Torsional modulus measurements and coin tap tests were performed at 0, 1 million, 5 million, and 10 million cycles, on axial fatigue specimens. Three distinct regions were noted. In the primary region a small but rapid change in stiffness was noted in the first few thousand cycles. This was followed by a secondary region of little or no stiffness change. The tertiary region was characterized by an increasing rate of stiffness change leading to fracture. NDI procedures including holographic interferometry, ultrasonics, penetrant, and X-ray radiography were evaluated for fatigue damage detection.

Applicability of Linear Elastic Fracture Mechanics to 5.6-mil Boron/6061 Aluminum

A coordinated experimental and analytical program was directed toward assessing the applicability of linear elastic fracture mechanics to 5.6-mil boron/6061 aluminum subjected to Mode I loading. Fifty-nine standard ASTM three-point bend and center-notched specimens were tested. The effects of laminate orientation, specimen thickness, crack length, specimen configuration, and heat treat condition on laminate fracture toughness are reported. A technique of predicting the fracture toughness of an arbitrary (0/±a/90) laminate from critical strain energy release rate data for 0-, =fc«-, and 90° specimens was evaluated for (0/±45) boron/aluminum.