Showing papers in "Journal of Composite Materials in 1975"
TL;DR: In this paper, a method based on total stress-strain-temperature relations is formulated and applied to determine the curing stresses in boron/epoxy composite laminates.
Abstract: Analysis of curing stresses in resin matrix composite laminates involves a temperature range over which variation of elastic moduli is appreciable. A method based on total stress-strain-temperature relations is formulated and applied to determine the curing stresses in boron/epoxy composite laminates. This method is shown to be preferable to the incremental method because the former requires the thermal strains and the stress-strain relations only at the final temperature of interest. The use of incremental constitutive equations is also discussed, and it is shown that proper care must be exercised to insure inclusion of interaction terms that have no counterparts in linear theories.
232 citations
TL;DR: In this article, a unique relationship between the static strength and time to rupture is demonstrated for a unidirectional glass/epoxy composite subjected to static fatigue, and the maximum significance level at which a Weibull distribution is applicable to represent scatter is 35% for the static strongness and 61% for fatigue life.
Abstract: The paper presents a concept of proof testing for composite materials. A unique relationship between the static strength and time to rupture is demonstrated for a unidirectional glass/epoxy composite subjected to static fatigue. The maximum significance level at which a Weibull distribution is applicable to represent scatter is 35% for the static strength and 61% for the fatigue life. Limitations and variations of the strength degradation model for the life prediction are discussed.
185 citations
TL;DR: In this paper, an approximate solution in the form of a polynomial is presented for the normal stress distribution adjacent to a circular hole in an infinite orthotropic plate, and a comparison of the approximate solut...
Abstract: An approximate solution in the form of a polynomial is presented for the normal stress distribution adjacent to a circular hole in an infinite orthotropic plate. Comparison of the approximate solut...
171 citations
TL;DR: In this paper, experimental investigation of failure of balanced angle-ply laminates under symmetric uniaxial tension revealed three distinct failure modes for reinforcement angles smaller than ±45°.
Abstract: Experimental investigation of failure of balanced angle-ply laminates under symmetric uniaxial tension revealed three distinct failure modes. The three different modes were observed for reinforcement angles smaller than ±45°, for the ±45° angle ply and for angles larger than ±45°. Comparison of experimental failure loads with theoretical failure loads based on first laminate failure criteria showed good agreement for certain ranges of reinforcement angle and disagreement for others.
119 citations
TL;DR: Using boundary layer theory for laminated composites, a complete analytical solution was obtained for all the interlaminar shear stresses as well as the normal or "peel" stress of a finite strip in unidirec tional extension.
Abstract: Using a newly developed boundary layer theory for laminated compos ites, a complete analytical solution is obtained for all the interlaminar shear stresses as well as the normal or "peel" stress of a finite strip in unidirec tional extension. Results obtained by the present analysis are compared to the finite-difference solution of Pipes and Pagano, and to the analytical solution of Puppo and Evensen.
114 citations
TL;DR: In this article, the composites have a relatively high density (1.70 g/cm3), a crystallite size LC = 150 A and an interlayer spacing d002 = 3.35 A.
Abstract: Composites of boron nitride (BN) have been made by the chemical vapor deposition (CVD) of a BN matrix on a BN felt fiber substrate. Reactant gases were boron trifluoride and ammonia. The composites have a relatively high density (1.70 g/cm3), a crystallite size LC = 150 A and an interlayer spacing d002 = 3.35 A. Measurements of elastic modulus and thermal conductivity and expansion showed some anisotropy as a result of the preferred fiber orientation of the substrate.
88 citations
TL;DR: In this paper, the size and character of the damage zone at the tip of sharp notches in fiber reinforced plastic laminates have been investigated, and a strong dependence of damage zone size and fracture toughness on ply thickness, fiber orientation, and fiber properties is demonstrated and discussed.
Abstract: The size and character of the damage zone at the tip of sharp notches in fiber reinforced plastic laminates have been investigated The variables studied were the stress intensity factor, specimen size, laminate thickness, ply thickness, ply orientation, and fiber properties The damage zone consists of subcracks parallel to the fibers of each ply, in some cases accompanied by delamination between plies The damage zone is found to increase in extent approximately in proportion to K2I up to fracture for notch-sensitive laminates For notch-insensitive laminates, a point is reached where the zone spreads rapidly across the entire specimen prior to fracture A strong dependence of damage zone size and fracture toughness on ply thickness, fiber orientation, and fiber properties is demonstrated and discussed
84 citations
TL;DR: In this article, a series of tensile tests were performed to characterize the response of this composite and define the variation of the mechanical properties with changes in the volume fraction of glass.
Abstract: T WAS THE intent of this investigation to produce a birefringent solid, suitable Ifor holographic and photoelastic analysis, which had variable mechanical properties [1]. For this purpose a mechanically and optically homogeneous, isotropic material was needed. A material of this nature was obtained by fabrication of a composite system composed of solid glass microspheres embedded in a polyester matrix. A series of tensile tests was performed to characterize the response of this composite and define the variation of the mechanical properties with changes in the volume fraction of glass. The results of these tests are compared to’ existing theories which predict the influence of reinforcement on the overall composite response. Four different theories for the prediction of the mechanical behavior of particulate filled composites were studied. Each theory is employed to produce an analytical definition of the variation of the elastic modulus and Poisson’s ratio for this material as a function of glass content.
79 citations
TL;DR: The boundary layer theory of plane stress in isotropic elasticity developped by Reiss and Locke is extended here to the laminated composites, in the boundary layer region, equations are separated into two problems, i.e., torsion problem and plane strain problem as mentioned in this paper.
Abstract: The boundary layer theory of plane stress in isotropic elasticity devel oped by Reiss and Locke is extended here to the laminated composites, In the boundary layer region, equations are separated into two problems, i.e., torsion problem and plane strain problem. These two problems are coupled through the compatibility equations as well as the continuity condition at the interfaces of the laminates. This formulation provides a tool to obtain analytical solutions to predict the two interlaminar shear stresses as well as the normal or "peel" stress.
78 citations
TL;DR: In this article, the authors evaluated whether aircraft flight conditions change moisture absorption behavior in graphite-epoxy composites and found that both the amount and rate of moisture absorption were significantly increased.
Abstract: Tests were conducted to determine whether aircraft flight conditions change moisture absorption behavior in graphite-epoxy composites. Flight temperature profiles were simulated for a subsonic mission, -65°F (-54°C) for 90 minutes, and for a flight involving a subsonic segment with a supersonic dash. The simulated dash involved rapid heating to a peak of 300°F (149°C) followed by rapid cooling. These simulated dashes or thermal spikes caused small, temporary drying effects. However, they also caused permanent changes in the subsequent moisture diffusion behavior of the graphite-epoxy. Both the amount and rate of moisture absorption were significantly increased. Subsonic temperatures, however, caused no detectable change in diffusion behavior.
78 citations
TL;DR: In this article, the crack growth resistance curves (R-curves) for epoxy and polyester composites have been developed to study the total fracture behavior of these composites.
Abstract: Crack growth resistance of a random glass fiber composite has been studied by applying the concepts of Linear Elastic Fracture Mechanics. The crack growth resistance curves (R-curves) for epoxy and polyester composites have been developed to study the total fracture behavior of these composites. It is shown that the R-curve approach is suitable for these type of materials. An attempt has been made to use the information from the R-curves to predict the fracture strength of plate specimens with a hole at the center and subjected to tensile loading.
TL;DR: In this article, the mixed mode fracture of unidirectional composites is investigated by application of the strain energy density theory, and two analytical models are used: the first assumes that the composite is an ideal homogeneous anisotropic body, and the second assumes that failure takes place in a layer of matrix material whose edges are bonded to two orthotropic plates.
Abstract: The mixed mode fracture of unidirectional composites is investigated by application of the strain energy density theory. Two analytical models are used. The first assumes that the composite is an ideal homogeneous anisotropic body, and the second assumes that failure takes place in a layer of matrix material whose edges are bonded to two orthotropic plates. The expressions for the strain energy density factor, S, are derived for both models, and brittle fracture is assumed to occur when the S-factor in an element of material ahead of the crack reaches a critical value, Sc. Results are presented for E-glass fiber reinforced plastics, stainless steel fiber reinforced aluminum and graphite fiber epoxy materials and compared with available experimental data. The latter model is preferred as it accounts for the effect of nonhomogeneity that is inherent in the filament-reinforced composites.
TL;DR: In this article, a new model for the deformation behavior of ATJ-S graphite, a non linear transversely isotropic material, under initial loading is described, which is based on a new deformation theory of ortho tropic plasticity.
Abstract: A new model for the deformation behavior of ATJ-S graphite, a non linear transversely isotropic material, under initial loading is described. This material model, which is based on a new deformation theory of ortho tropic plasticity, has excellent potential for description of the biaxial softening phenomenon found in ATJ-S graphite. Biaxial softening is char acterized by the development of larger strains in biaxial tension than in uniaxial tension, in contradiction to conventional Poisson effects. The new model is examined for sensitivity to (1) a nonsymmetric compliance matrix, (2) how the material model constants are obtained, and (3) varia tions in material properties. Comparisons are made between strain values obtained with the material model incorporated in a finite element com puter analysis and strain values from biaxial test results.
TL;DR: In this article, the assumption of the constancy of the Weibull distribution parameters with variations in gauge length was tested for SiC-on-carbon and sapphire filaments.
Abstract: The assumption of the constancy of the Weibull distribution parameters with variations in gauge length was tested for SiC-on-carbon and sapphire filaments. Surface damage was superimposed on the ga...
TL;DR: In this article, a heat-treated, polyacrylonitrile (PAN)-based carbon felt, rough laminar carbon matrix composite has a superior thermal shock figure-of-merit based on these results.
Abstract: Properties of carbon-felt, pyrolytic carbon-matrix composites have been measured as a function of fiber precursor [rayon and polyacrylonitrile (PAN)] and matrix microstructure (smooth laminar, rough laminar, and isotropic). The primary matrix effect is caused by the graphitic nature of the heat-treated rough laminar matrix which yields a high composite thermal conductivity. The increased modulus of the PAN-based fibers results in increased composite strength and modulus and a significantly reduced thermal expansion. A heat-treated, PAN-based carbon felt, rough laminar carbon matrix composite has a superior thermal shock figure-of-merit based on these results.
TL;DR: In this paper, the progressive nature of fatigue damage due to cyclic loading on glass fiber reinforced plastics was studied and the residual strength of the specimens subjected to fluctuating tension with a given number of cycles was measured, and the number of cracks developed in the samples were counted by means of a microscope.
Abstract: The progressive nature of fatigue damage due to cyclic loading on glass fiber reinforced plastics was studied. The residual strength of the specimens subjected to fluctuating tension with a given number of cycles was measured, and the number of cracks developed in the samples were counted by means of a microscope. From our test results, the progression process of fatigue damage in the composite materials can be divided into three stages.
TL;DR: In this article, the early fatigue damage detection in composite materials by nondestructive inspection (NDI) techniques has been demonstrated for ±45° Glass/Epoxy, and ± 45°/0° Graphite/Glass/ Epoxy.
Abstract: Detection of early fatigue damage in composite materials by nondestructive inspection (NDI) techniques has been demonstrated for ±45° Glass/Epoxy, and ±45°/0° Graphite/Glass/Epoxy. Dynamic axial mo...
TL;DR: In this article, it was shown that the combination of the gradual failure model and the rule of mixtures for modulus leads to the rule-of-mixtures for the strength of random fiber composite.
Abstract: It is shown that the combination of the gradual failure model and the rule of mixtures for modulus leads to the rule of mixtures for the strength of random fiber composite. For analysis purposes, the random composite is replaced by a laminate consisting of unidirectional plies in every direction in the plane of the laminate. When the maximum stress criterion is employed, the strength of the random composite is given in terms of the uniaxial strengths of the unidirectional composite through a simple relation. Although the method is intended for discontinuous fiber composites, it is as well applicable to some of continuous fiber composites. Other possible modes of failure are also discussed and the corresponding equations for prediction of strengths are given.
TL;DR: In this paper, a statistical approach based on Weibull distribution was applied to account for the difference between tensile and flexural test results, and the experimental scatter for elastic modulus and its effect on strength were shown not to be negligible.
Abstract: Experimental results for tests of strength and elastic modulus of a randomly-distributed short fiber composite are reported in this paper. Three different tests were employed: tension, 3-point flexure, and 4-point flexure. A statistical approach based on Weibull distribution was applied to account for the difference between tensile and flexural test results. Mate rial variation, as exhibited in the experimental scatter for elastic modulus, and its effect on strength were shown not to be negligible. Test results also showed wider experimental scatter than observed with continuous fiber composites. Consequently considerable penalty had to be paid by reducing the design strength in order to assure the same level of confidence and reliability.
TL;DR: In this paper, a Maxwell rotating beam apparatus was used to measure the dynamic mechanical properties as well as the fatigue life of nylon 6 filled with glass beads or fine silica powder, a nylon 66 filled with calcined clay, an epoxy filled withglass beads, and high-impact polystyrene.
Abstract: A Maxwell rotating beam apparatus was used to measure the dynamic mechanical properties as well as the fatigue life of nylon 6 filled with glass beads or fine silica powder, a nylon 66 filled with calcined clay, an epoxy filled with glass beads, and high-impact polystyrene Attempts to monitor damage by changes in the dynamic mechanical properties failed; the properties remained essentially constant until only a relatively few cycles before failure occurred The decrease in modulus and increase in damping with increasing maximum cyclic stress were due mostly to heat build-up rather than to any permanent damage The fatigue life can be drastically decreased by small surface scratches
TL;DR: In this article, the SiC-on-carbon filaments were tested at a strain rate of 0.033 min-l in the TM-SM Instron testing machine and the thermal treatments were performed in the Instron with a 10&dquo; split tube furnace having a 2&dqo; hot zone.
Abstract: HE CONTINUOUS SILICON carbide (SiC) filament currently being considered T for reinforcement in high temperature metal matrices [1] is manufactured by chemical vapor deposition (CVD) from reactant gases onto a heated tungsten substrate [2]. Recently, investigators at AVCO Systems Division’ reported the development of a silicon carbide filament manufactured by CVD on a carbon monofilament [2]. It has been shown previously that the reaction of the tungsten core with the SiC coincides with the loss of strength at high temperature [3]. This investigation of the high temperature strength of the SiC-on-carbon filaments was conducted to determine if the absence of this strength degradation mechanism results in higher strengths at the temperatures where the SiC-W reaction becomes appreciable. A model TM-SM Instron testing machine was used to tensile test the filaments employing the hypodermic needle/pivot bearing grips described elsewhere [4]. The thermal treatments were performed in the Instron with a 10&dquo; split tube furnace having a 2&dquo; hot zone. The 12&dquo; long filaments were tested at a strain rate of 0.033 min-l. The SiC-on-carbon filaments supplied by Avco consisted of a 0.001&dquo; diameter monofilament carbon substrate coated with ==0.0001&dquo; layer of pyrolytic graphite upon which the SiC was deposited to form an overall diameter of 0.004&dquo;. In the final stages of deposition excess carbon is added to form a carbon rich layer which is more abrasion resistant than stoichiometric SiC as witnessed by the fact that the strength of the pristine filaments is not degraded by self-abrasion. Scanning electron microscopic examination of fractures surfaces of the filaments revealed that fracture always seems to initiate at the carbon/SiC interface or in the carbon core as illustrated in Figure 1. 1 AVCO Systems Division, Lowell Industrial Park, Lowell, MA
TL;DR: Filament wound/CVD (Chemical Vapor Deposition) carbon-carbon composites have received considerable attention and application within the past few years because of their desirable characteristics as mentioned in this paper.
Abstract: Filament wound/CVD (Chemical Vapor Deposition) carbon-carbon composites have received considerable attention and application within the past few years because of their desirable characteristics suc...
TL;DR: In this article, the preparation and evaluation of a CVD/PAN carbon/carbon frustum was described, and the thermal gradient infiltration technique has successfully yielded a matrix composed primarily of the desired rough laminar microstructure.
Abstract: The preparation and evaluation of a CVD/PAN carbon/carbon frustum are described. The thermal gradient infiltration technique has successfully yielded a matrix composed primarily of the desired rough laminar microstructure. Characterization of the composite includes thermal and mechanical properties as functions of temperature, as well as room temperature crystallographic parameters.
TL;DR: In this paper, the theory of maximum work was used as the strength criterion for the symmetric laminated cylindrical shells under combined loadings and a modified golden section method was employed for the optimization.
Abstract: Optimum fiber orientations in symmetrically laminated cylindrical shells under combined loadings are investigated. The theory of maximum work is used as the strength criterion. A modified golden section method is employed for the optimization. The glass-epoxy composite is taken for numerical examples.
TL;DR: In this article, a model for the deformation behavior of ATJ-S graphite, a nonlinear transversely isotropic granular composite material, under initial loading is extended in two important ways.
Abstract: A model for the deformation behavior of ATJ-S graphite, a nonlinear transversely isotropic granular composite material, under initial loading is extended in two important ways. First, the constants in the model are physically interpreted and their effect on convergence of the iteration procedure is examined. Second, the model is further qualified by comparison of predicted strains with strains measured in uniaxial off-axis loading.
TL;DR: In this article, the authors studied the fracture behavior of a nonlinear coated woven fabric material, and showed that by proper graphical shifting of the experimental data, the fracture behaviour of the monolayered and laminated nonlinear fabric materials can be explained in view of the Hedgepeth [1] linear discrete fracture theory.
Abstract: Fracture behavior of a nonlinear coated woven fabric material is studied. Some Mode 1 crack extension data of monolayered and laminated sheets of this material are presented.It is shown that by proper graphical "shifting" of the experimental data, the fracture behavior of the monolayered and laminated nonlinear fabric materials can be explained in view of the Hedgepeth [1] linear discrete fracture theory.1 A product of Uniroyal Industrial Coated Fabrics, Mishawaka, Indiana.2In the shear test the relative distance of the sliding sides was maintained constant.
TL;DR: In this paper, critical buckling loads for unidirectional and jaminated cylinders subjected to torsion and axial compression were determined by using classical Fourier analysis in conjunction with Flugge's shell equations modified for anisotropic laminated materials.
Abstract: Using dimensions which are typical of current laboratory tubular specimens, critical buckling loads are determined'for unidirectional and Jaminated cylinders subjected to torsion and to axial compression Buckling loads are obtained by using classical Fourier analysis in conjunction with Flugge's shell equations modified for anisotropic laminated materials Comparison of buckling loads to composite strength, as estimated from maximum strain criterion, suggests that buckling is a potential problem in the use of tubular specimens A relatively easy method for estimating buckling loads is also presented
TL;DR: In this paper, the value of elementary bending theory as it applies to thin isotropic elastic Tbeams and slabs has been substantiated by comparisons with experimental data and with results from elasticity theory.
Abstract: T HE VALIDITY OF elementary bending theory as it applies to thin isotropic elastic Tbeams and slabs has been substantiated by comparisons with experimental data and with results from elasticity theory (see for example Reference [1] ). Generally it is taken for granted that the Bernoulli-Euler theory yields acceptable results for members having a length-to-thickness ratio of 10 or more. For shorter, deeper members the effects of shear deformation can be accounted for using a standard strength-of-material’s approach [2] . ,
TL;DR: In this paper, a more precise expression for CT of an orthotropic rectangular section bar is presented and it is shown that use of this equation can account for some of the discrepancies reported in the literature.
Abstract: N RECENT YEARS many studies have been devoted to the determination of the Iprincipal elastic constants of orthotropic composite materials. Generally, rectangular section specimens have been used in the experimental studies because of their ease of fabrication. However, static and dynamic determinations of the principal shear moduli involve the generalized torsional rigidity, CT, of rectangular sections of the material. Because the cross-section warps during twisting, CT is a complicated expression involving all three principal shear moduli. Approximations which do not fully take into account this warping have been used in some recent studies, and, consequently, large apparent discrepancies between observed and calculated shear moduli have been reported. . In this paper, a more precise expression for CT of an orthotropic rectangular section bar is presented and it is shown that use of this equation can account for some of the discrepancies reported in the literature. The expression for CT-is also of importance in the prediction of the resonant frequencies and normal mode shapes of composite components.
TL;DR: In this paper, the authors argue that the term "distortional energy" discussed in the latter references is a complete misnomer and has no physical significance except when used in connection with isotropic material behavior.
Abstract: IT IS THE PURPOSE of this communication to reflect on a quantity idly referred to as “distortional energy” in contemporary composites technology. While the use of this term to generically classify quadratic failure surfaces has become so prevalent that compilation of literature citations is unnecessary, one can cite specific references in which the quantity has been employed in relation to studies of material failure, e.g., [1, 2, 3]. We shall argue that the term “distortional energy” discussed in the latter references is a complete misnomer and has no physical significance except when used in connection with isotropic material behavior. We shall also suggest a more satisfying definition of the distortional energy of an orthotropic medium.