Showing papers in "Journal of Composite Materials in 1981"
TL;DR: In this paper, the cured shape of thin unsymmetric laminates does not conform to the predictions of classical lamination theory and the curvature directions of the cylindrical shapes are predictable.
Abstract: This paper discusses the fact that the cured shape of thin unsymmetric laminates do not conform to the predictions of classical lamination theory. Rather than being saddle shaped, as predicted by the classical theory, the paper shows that thin unsymmetric laminates cure into a shape of a right circular cylinder. This anomalous behavior has been observed by many but the paper serves to quantify the effect and to inspire investigators to begin thinking about using the phenomenon to advantage. The paper indicates that the anomalous behavior is repeatable and that thicker laminates con form to the predictions of the classical theory. Laminates of the [0/902 /θ ]T, [02 /θ2 ] T and [04 /θ4 ] T families are investigated for this be havior and it is shown the principal curvature directions of the cylindrical shapes are predictable.
447 citations
TL;DR: In this paper, a theory explaining the characteristics of the cured shapes of unsymmetric laminates is presented, based on an extension of classical lamination theory which accounts for geometric nonlinearities.
Abstract: A theory explaining the characteristics of the cured shapes of unsymmetric laminates is presented. The theory is based on an extension of classical lamination theory which accounts for geometric nonlinearities. A Rayleigh-Ritz approach to minimizing the total potential energy is used to obtain quantitative information regarding the room temperature shapes of square T300/5208 (0(2)/90(2))T and (0(4)/90(4))T graphite-epoxy laminates. It is shown that, depending on the thickness of the laminate and the length of the side the square, the saddle shape configuration is actually unstable. For values of length and thickness that render the saddle shape unstable, it is shown that two stable cylindrical shapes exist. The predictions of the theory are compared with existing experimental data.
380 citations
TL;DR: In this paper, the plane strain of adhesively bonded structures which consist of two different orthotropic adherents is considered and the problem is reduced to a system of differential equations for the adhesive stresses which is solved in closed form.
Abstract: The plane strain of adhesively bonded structures which consist of two different orthotropic adherents is considered. Assuming that the thicknesses of the adherends are constant and are small in relation to the lateral dimensions of the bonded region, the adherends are treated as plates. The transverse shear effects in the adherends and the in-plane normal strain in the adhesive are taken into account. The problem is reduced to a system of differential equations for the adhesive stresses which is solved in closed form. A single lap joint and a stiffened plate under various loading conditions are considered as examples. To verify the basic trend of the solutions obtained from the plate theory a sample problem is solved by using the finite element method and by treating the adherends and the adhesive as elastic continua. The plate theory not only predicts the correct trend for the adhesive stresses but also gives rather surprisingly accurate results.
216 citations
TL;DR: In this paper, a parametric analysis of postbuckled through-width delaminations in laminated coupons was performed, where a finite element analysis was developed to analyze the coupons as a combination of linear and geometrically nonlinear components.
Abstract: A parametric study of postbuckled through-width delaminations in laminated coupons was performed. A finite element analysis was developed to analyze the coupons as a combination of linear and geometrically nonlinear components. Because most of the coupon configuration studied behaves linearly, the mixed linear and nonlinear analysis greatly reduced computational costs. The analysis was verified by comparing numerical with exact solutions for simple hypothetical problems. In addition, measured lateral deflections of postbuckled through-width delaminations in laminated coupons were compared with predicted deflections. In the parametric study, stress distributions and strain-energy release rates were calculated for various delamination lengths, delamination depths, applied loads, and lateral deflections. Also, a small number of coupons with through-width delaminations were fatigue tested to obtain delamination growth data. Calculated strain-energy release rates were compared with the observed growth rates to determine the relative importance of the Mode 1 and Mode 2 components of energy release. Growth process was dominated by G sub I.
187 citations
TL;DR: In this article, three types of glass epoxy composites have been studied and water diffu sion leading to saturation has been shown to occur under humid conditions for two of them, the third composite was seen to de
Abstract: Three types of glass epoxy composites have been studied and water diffu sion leading to saturation has been shown to occur under humid conditions for two of them, the third composite was seen to de
181 citations
TL;DR: In this paper, a finite difference analysis describing the transient thermal response of fiber-reinforced organic matrix composte plates subjected to intense surface heating is presented, and a one-dimensional finite difference analyzer is presented.
Abstract: A one-dimensional finite difference analysis describing the transient ther mal response of fiber-reinforced organic matrix composte plates subjected to intense surface heating is presented The eff
142 citations
TL;DR: In this paper, the influence of the coefficient of mutal influence, Poisson's ratio and coefficients of thermal and moisture expansion on delamination was studied and the results can be used for design of composite laminates.
Abstract: The influence of the coefficient of mutal influence, Poisson's ratio and coefficients of thermal and moisture expansion on delamination is studied. Engineering theories are compared to finite element and experimental results. It is shown that the mismatch in coefficients of mutual influence can have a strong influence on delamination with fiber angles in the 10-15 degree range being critical for adjacent layer combinations. The mismatch in coefficient of mutual influence is reduced by a factor of two and the interlaminar shear stress is reduced significantly when the + or - adjacent layers are interspersed between 0 and 90 degree layers. It is shown how the results can be used for design of composite laminates.
111 citations
TL;DR: In this article, the authors measured degree radation in various in-plane stiffnesses (Exx, Byy, Gxy) using a combination of uniaxial tension, rail shear, and flexure tests.
Abstract: Stiffness reductions, resulting from fatigue damage, were measured for unnotched [±45]s, [0/90] s, and [0/90/ ±45 ] s boron/epoxy laminates. Deg radation in the various in-plane stiffnesses (Exx, Byy, Gxy) were measured using a combination of uniaxial tension, rail shear, and flexure tests. An attempt was made to predict stiffness loss at failure from a secant modulus criterion. Damage growth and stiffness loss were load-history dependent, hence, the secant modulus criterion is not a valid criterion for general application.
110 citations
TL;DR: In this paper, the authors developed an analysis for predicting the stress distribution in unidirectional discontinuous fiber composites, where the basic approach is based upon the shear-lag analysis, the load transfer at fiber ends is taken into consideration.
Abstract: This paper develops an analysis for predicting the stress distribution in unidirectional discontinuous fiber composites. Although the basic ap proach is based upon the shear-lag analysis, the load transfer at fiber ends is taken into consideration. This consideration becomes important if the bonding between the fiber and matrix at the fiber end is perfect such as the cases often observed in metal matrix composites, as well as during the early stage of loading of polymeric matrix composites. The present analysis in cludes the ordinary shear-lag analysis as a special case.
108 citations
TL;DR: In this paper, a finite element analysis of bolted joints in fiber reinforced plastic is presented, and some correspondence is demonstrated between the calculated strains and experimental data from tests on glass fibre reinforced epoxy resin.
Abstract: The results are presented of a finite element analysis of bolted joints in fibre reinforced plastic. Although the finite element model uses only two- dimensional elements, through-thickness stresses being ignored, some cor respondence is demonstrated between the calculated strains and experimental data from tests on glass fibre reinforced epoxy resin.
76 citations
TL;DR: In this article, the linear viscoelastic response of polymeric matrix laminated composites to hygrothermal exposure is investigated within the framework of lamination theory, and the effect of residual thermal stress relaxation upon creep in laminated composite plates under mechanically applied loads is shown.
Abstract: The linear viscoelastic response of polymeric matrix laminated com posites to hygrothermal exposure is investigated within the framework of lamination theory. Experimentally measured curvature changes in non- symmetric GY70/339 composite laminates during long term exposures to elevated hygrothermal conditions are shown to be accurately predicted by the linear viscoelastic analysis. Application of the analysis is made to prob lems involving 1) dimensional stability and alteration of residual stresses, 2) the strain rate dependence of tensile response, and 3) the effect of residual thermal stress relaxation upon creep in laminated composite plates under mechanically applied loads.
TL;DR: In this paper, the effective coefficient of thermal expansion for fiber composites in two-dimensional quasi-isotropic form and three-dimensional isotropic form was derived for constructions that have fibers ran domly oriented in a plane and in three dimensions.
Abstract: The effective coefficient of thermal expansion is derived for fiber com posites in two dimensional quasi-isotropic form and three-dimensional isotropic form. These systems represent constructions that have fibers ran domly oriented in a plane and in three dimensions. The effective coeffi cients of thermal expansion are related to the thermal-mechanical proper ties of individual fiber and matrix phases. These results are put into asymp totic forms appropriate to very stiff fiber systems. The asymptotic predic tions are evaluated against the complete forms, and both results are com pared with an experimental result.
TL;DR: The NALCOM (Nonlinear Analysis of Laminated Composites) computer program as mentioned in this paper uses a fully three dimensional isoparametric finite element with 24 nodes and 72 degrees of freedom.
Abstract: Formulations of the inelastic response of laminated composites to thermal and mechanical loading are used as the basis for development of the computer NALCOM (Nonlinear Analysis of Laminated Composites) computer program which uses a fully three dimensional isoparametric finite element with 24 nodes and 72 degrees of freedom. An incremental solution is performed with nonlinearities introduced as pseudoloads computed for initial strains. Equilibrium iteration may be performed at every step. Elastic and elastic-plastic response of boron/epoxy and graphite/epoxy graphite/epoxy and problems of curing 0/90 sub s Gr/Ep laminates with and without circular holes are analyzed. Mechanical loading of + or - 45sub s Gr/Ep laminates is modeled and symmetry conditions which exist in angle-ply laminates are discussed. Results are compared to experiments and other analytical models when possible. All models are seen to agree reasonably well with experimetnal results for off-axis tensile coupons. The laminate analyses show the three dimensional effects which are present near holes and free corners.
TL;DR: In this article, a theoretical analysis has been performed to evaluate the dynamic stress concentration factor in hybrid composites composed of low elongation and high elongation (HE) fibers, and the authors concluded that hybrid effect always exists in a beneficial manner and the case of the parent LE fiber composite provides the upper bound for the dynamic stressed concen tration factor in hybrids.
Abstract: A theoretical analysis has been performed to evaluate the dynamic stress concentration factor in hybrid composites composed of low elongation (LE) and high elongation (HE) fibers. At a fracture of a fiber, the present model predicts two stress waves propagating along each fiber in the hybrid. The phase difference of the dynamic responses contributed by these waves at the middle section of a fiber immediately adjacent to a fiber breakage is controll ed by the fiber mass per unit length. The magnitude of the dynamic responses is determined by the fiber extensional stiffness. The study concludes that hybrid effect always exists in a beneficial manner and the case of the parent LE fiber composite provides the upper bound for the dynamic stress concen tration factor in hybrids. The validity of the approximations made in the derivations has been examined.
TL;DR: In this paper, the stress state in the bonded joint region of a laminated composite tube subjected to torsional and hygrothermal loadings is analyzed and a finite-element solution technique is utilized.
Abstract: The stress state in the bonded joint region of a laminated composite tube subjected to torsional and hygrothermal loadings is analyzed. A finite ele ment solution technique is utilized. The composi...
TL;DR: In this paper, the effects of moisture and temperature on the flexural response of Kevlar 49 fabric-reinforced epoxy laminates were examined and failure was not catastrophic, but was characterized by a loss in load carry ing capacity.
Abstract: This study examines the effects of moisture and temperature on the flexural response of [0/90] Kevlar 49 fabric-reinforced epoxy laminates. Two high temperature (190°C) cure commercially available epoxies, Narmco 5208 and Ferro CE-9000, were used as matrix materials. Results indicate that the mechanical properties of Kevlar 49/epoxy laminates are temperature dependent over the range -55°C to 150°C. The addition of moisture magnifies temperature sensitivity. At 150°C and near saturation moisture content (5 weight percent), a strength loss of 60-70 percent and an effective stiffness loss of 40 percent from dry, room temperature values are measured. At 21°C, saturated specimens are found to be 35-40 per cent weaker than dry material. At low temperature (-55°C), strengths increase with the addition of moisture. Over the range of conditions tested, failure was not catastrophic, but was characterized by a loss in load carry ing capacity. Microscopic examination of failure modes indicates that flexural strength ...
TL;DR: In this article, a variant on an approximative solution indicated by Lekhnitskii was used to deal with stresses around rectangular and square openings with rounded corners in orthotropic plates.
Abstract: This paper deals with stresses around rectangular and square openings with rounded corners in orthotropic plates. A variant on an approximative solution indicated by Lekhnitskii was used. Numerical results are presented for three different holes in seven different laminates of carbon fiber reinforced plastic.
TL;DR: In this article, the time history of elastic waves in composite laminates has been obtained by using surface and em- bedded strain gages and measured and calculated values of wave speeds agree well.
Abstract: The details of the time history of the elastic waves in ballistically im pacted composite laminates have been obtained by using surface and em bedded strain gages. Records show that a very low-amplitude in-plane tensile wave arrives first followed by a medium-amplitude flexural wave and then a high-amplitude flexural wave. Measured and calculated values of wave speeds agree well.
TL;DR: In this article, an analytical approach for predicting the probabilistic ultimate strength after initial failure of the carbon fiber helical-wound cylinders under internal pressure is presented. But the analysis is limited to the case of a single cylinder.
Abstract: This paper presents an analytical approach for predicting the probabilistic ultimate strength after initial failure of the carbon fiber helical-wound cylinders under internal pressure.First, the in...
TL;DR: In this article, a model study is conducted on the prediction of the stiffness and fracture toughness of an unidirectional short-fiber reinforced composite containing numerous cracks in the matrix.
Abstract: A model study is conducted on the prediction of the stiffness and fracture toughness of an unidirectional short-fiber reinforced composite containing numerous cracks in the matrix. It is assumed in our model that short-fibers are aligned in the uniaxial loading direction and that cracks in the matrix are perpendicular to the loading axis and are penny-shaped. Then the longitudinal Young's modulus of the composite weakened by those cracks and the energy release rate of a representative penny-shaped crack are com puted by a combination of Eshelby's equivalent inclusion method and Mori- Tanaka's back stress analysis. The interaction between fibers and that be tween fibers and cracks are taken into account by Mori-Tanaka's back stress analysis. Hence our results are valid even for a large volume fraction of fiber and crack.
TL;DR: In this paper, a new method for analyzing the free edge stress field in composite laminates is developed based on a perturbation and assumed stress approach, and the convergence of the interlaminar shear stress in angle-ply LAMs is studied.
Abstract: A new method for analyzing the free edge stress field in composite laminates is developed based on a perturbation and assumed stress approach. Convergence of the interlaminar shear stress in angle-ply laminates is studied.
TL;DR: In this article, the distribution of fibers in a cylindrically reinforced pressure vessel of given size and constituent properties is optimized using the criterion of minimum strain energy, and a stress function approach, in conjunction with the modified Rayleigh-Ritz technique, is employed to obtain an approximate solution to the nonlinear optimization problem.
Abstract: The distribution of fibers in a cylindrically reinforced pressure vessel of given size and constituent properties is optimized using the criterion of minimum strain energy. A stress function approach, in conjunction with the modified Rayleigh-Ritz technique, is employed to obtain an approximate solution to the non-linear optimization problem. Constraint conditions in clude specification of the global volume fraction of fibers and satisfaction of stress boundary conditions. Numerical results are presented for reinforced cylinders having various radii, modulus ratios, and global volume fractions. Included is the case of a reinforced concrete cylinder, in which the concrete is assumed to be ineffective in tension. In most cases examined, use of the op timum fiber distribution, rather than a uniform distribution, results in a substantial reduction in the maximum radial displacement and an increase in the failure pressure load.
TL;DR: In this paper, the interlaminar fracture energy of a glass fiber reinforced polyester composite was studied and the fracture energy at liquid nitrogen temperature (77°K) was found to be about 3 times higher than that at room temperature and fracture energy transverse to the fiber direction is slightly higher than in th...
Abstract: This study deals with the interlaminar fracture energy of a glass fiber reinforced polyester composite. Width tapered double cantilever beam (WTDCB) specimens are used for the test. The compliance and fracture behavior of the specimen as well as the effect of specimen geometry on fracture energy are studied. The fracture energy at liquid nitrogen temperature (77°K) is also studied.It is found that the fracture energy obtained decreases with increasing height of specimens, finally reaching a constant value. The minimum height requirement for the fracture test of Extren is one half inch.The fracture energy slightly decreases with a decrease in specimen taper. A load-deflection hysteresis is observed to increase with specimen width. Hysteresis is dependent on the beam volume, i.e., height, taper and crack length.The fracture energy at liquid nitrogen temperature (77°K) is about 3 times higher than that at room temperature and the fracture energy transverse to the fiber direction is slightly higher than in th...
TL;DR: In this paper, high-speed photography along with the well-known method of caustics were used for the determination of the crack propagation velocity and the K I-stress intensity factor in iron-epoxy particulate composites.
Abstract: In the present investigation high-speed photography along with the well-known method of caustics were used for the determination of the crack-propagation velocity and the K I-stress intensity factor in iron-epoxy particulate composites. Specimens with three different low percentage filler-volume fractions were used; namely, 3%, 5% and 7%. It was found that the mean crack-propagation velocity decreases linearly with increasing filler-volume fraction. In addition, by using the method of caustics, the KI-stress intensity factor was calculated for each one of the composite specimens separately. It was found that the KI-S.I.F. increases by steps with increasing crack-length.
TL;DR: In this article, a closed form expansion method is introduced which offers a systematic way to calculate statistical in formation for a function of several strength variables for a composite material subjected to multiaxial loadings.
Abstract: There are several interactive failure criteria which give strength predic tions for a composite material subjected to multiaxial loadings. However, if only the average directional strengths are used in the failure criterion, the results give no useful statistical information. A closed form expansion method is introduced which offers a systematic way to calculate statistical in formation for a function of several strength variables. The developed expan sion method is applied to the Maximum Distortional Energy (MDE) criterion using an orthotropic composite material. The results show the expansion technique gives equivalent results to a simulation method for the off-axis ten sile test, but with far less computation. In addition, the expansion technique should prove adaptable to higher order theories such as the Tsai-Wu failure criterion.
TL;DR: In this paper, the modes of crack propagation, as well as the fracture surface of carbon Fiber-Reinforced composites were studied by means of a Scanning Electron Microscope (SEM).
Abstract: The modes of crack propagation, as well as the fracture surface of carbon Fiber-Reinforced composites were studied by means of a Scanning Electron Microscope (SEM). The composite specimens used wer...
TL;DR: In this article, a tension failure factor is proposed to determine the failure modes of composite laminates by observing results of experimental program for testing static strength under combined by-pass tension and bolt load.
Abstract: By observing results of experimental program for testing static strength of composite laminates under combined by-pass tension and bolt load, a tension failure factor is proposed herein to determine the failure modes of the composites. Comparison with experimental results shows that the proposed tension failure factor is a reasonable indicator. Possible application for estimating failure loads by interpolation of available data is illustrated with a numerical example.
TL;DR: In this article, acoustic emission data for graphite and glass-epoxy composites were analyzed and it was shown that matrix crazing and combined delamination and fiber breakage occur at lower and higher amplitude, respectively.
Abstract: This paper presents acoustic emission data for graphite- and glass-epoxy, and glass-chopped matt composites. This micro-earthquake-like wave phenomenon resulting from microstructural failure is noted to possess dif ferent characteristics depending upon the composite material being tested. Results of three point bending of specimens and cantilevered specimens with transverse saw cuts under monotonically increasing load indicate that matrix crazing and combined delamination and fiber breakage occur at lower and higher amplitude, respectively. Differences in behavior were also noted be tween these materials as the type of loading was varied.
TL;DR: In this article, the tensile properties of carbon fibers in a form of strand were studied and the three-plates aluminum tab and loaded through pins were clamped with the strand specimens.
Abstract: Clamping methods for evaluating tensile properties of carbon fibers in a form of strand were studied. When clamped with the three-plates aluminum tab and loaded through pins, the strand specimens i...
TL;DR: In this article, the dispersion of harmonic waves propagating in an arbitrary direction in a layered orthotropic elastic composite is studied, and the corresponding twelfth order characteristic determinant is examined.
Abstract: The dispersion of harmonic waves propagating in an arbitrary direction in a layered orthotropic elastic composite is studied The full three-dimensional field equations of elasticity are considered, and the corresponding twelfth order characteristic determinant is examined Numerical results are obtained and compared with the corresponding estimates of the new quotient method of Nemat-Nasser