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We present a method for evaluating the damage in and failure of fiber reinforced composite materials. The method is based on dissipated energy and has three major components: (i) a relationship between the strain in the material and the magnitude of the dissipated energy density, (ii) a model that relates the dissipated energy density to matrix damage and fiber failure inside the material, and, accordingly, reduces the elastic properties of the material, and (iii) a nonlinear finite element code for calculating the strain at each point in the material taking into account the degradation of the stiffness as damage occurs. The method provides the parameters of interest, namely, the regions of matrix damage and fiber failure, the load-displacement curve, the failure load, and the failure displacement. Tensile, shear, and four point bend tests were performed with S-glass/epoxy solid coupons as well as with coupons containing a central hole. The load-displacement curves, failure loads, and failure displacements were measured and compared to the results computed by the method. The data and the results of the method are in good agreement. [ABSTRACT FROM AUTHOR]

Tests were conducted with continuous glass fiber reinforced epoxy matrix composites that had different types of fiber reinforcements. Composites reinforced with either unidirectional, triaxial or random fibers were tested. The tensile and compressive strengths and moduli, the Iosipescu shear moduli, the short beam shear strengths, the mode I critical strain energy release rates, and the damage introduced by impact were measured. The results demonstrate the influence of fiber form on these properties and provide design guides for the use of different fiber forms. [ABSTRACT FROM PUBLISHER]

Tests were performed to evaluate the effects of moisture and temperature on the com pressive and short beam shear properties of Fiberite T300/976 fabric. The maximum mois ture content was measured as a function of relative humidity and temperature. The diffusivity was determined as a function of temperature. The compressive and short beam shear strengths and moduli of dry and moisturized specimens were measured at 70, 250, and 350°F. The changes in these mechanical properties caused by drying after moisturiza tion and by subsequent remoisturization were also assessed. [ABSTRACT FROM PUBLISHER]

The effects of moisture on the compressive and interlaminar shear strengths of aramid fiber reinforced epoxy matrix composites were investigated. The compressive strengths were measured with a Celanese fixture, the interlaminar shear strengths were inferred from the results of three point bend tests. The influence of fiber surface treatment on the compressive and interlaminar shear strengths were also assessed by testing composites containing fibers with their surfaces treated and with fibers without surface treatment. [ABSTRACT FROM PUBLISHER]

Tests were conducted measuring the changes in weight of aramid fiber reinforced epoxy matrix composites during exposure to humid air. Composites containing surface treated fibers and composites containing fibers without surface treatment were tested. In addition, for the purpose of comparison, the weight changes of glass fiber reinforced epoxy com posites and pure epoxy were measured. From the weight change data the values of the maximum moisture contents and diffusivities were determined. The effects of fiber surface treatment on the moisture absorption characteristics of the aramid fiber reinforced com posite were assessed. An expression was developed for estimating the transverse diffu sivities of composites from the known resin and fiber properties when fibers absorb a sig nificant amount of moisture. [ABSTRACT FROM PUBLISHER]

Tests were performed to evaluate the effects of crystallinity on the mechanical properties of PEEK 150P polymer and APC-2 graphite/PEEK composite. The tensile strengths, ten sile moduli and fracture toughnesses of the polymer, and the mixed mode I and mode II fracture toughnesses of the composite were measured at crystallinities ranging from 27 to 43 percent by weight. The results show that, in the crystallinity range studied, the tensile properties are not affected significantly by changes in crystallinity, while the fracture toughness depends strongly on the crystallinity. A model is also described which can be used to calculate the crystallinity from the known applied cooling rate. The validity of the model was verified by tests performed with PEEK 150P polymer. [ABSTRACT FROM PUBLISHER]

Procedures are described for calculating the in-plane deformations and curvature changes of sandwich panels caused by nonuniform temperature and moisture distribu tions. The procedures apply to panels consisting of a honeycomb core covered by fiber reinforced, composite face sheets. Results are presented in tables and charts, which can be used to estimate the deformations and curvature changes of panels made of dif ferent, commonly used, composites. [ABSTRACT FROM PUBLISHER]

The effects of the environment on adhesive bonded single lap joints formed using XMC-3 and SMC-R50 composites were investigated. Tests were performed at temperatures of 23C and 93C with test coupons immersed in air, water, and 5% NaCl water mixture. The weight changes of both bonded joints (XMC-3 to SMC-R50 and SMC-R50 to SMC-R50) and unbonded materials were measured. Data were also ob tained showing the effects of moisture, temperature, and applied load on changes in weight, on creep deformation, lap shear strength, and separation modes of the joints. [ABSTRACT FROM PUBLISHER]

A model is presented for predicting the changes in the mechanical properties of organic matrix composites exposed to elevated temperatures. The model can be used to calculate changes in the tensile, compressive and shear strengths and moduli as func tions of exposure time. The model also provides the decrease in the stress ratio with time and the time of failure. [ABSTRACT FROM PUBLISHER]

A summary is given on the effects of moisture and temperature on the properties of chopped fiber reinforced sheet molding compounds. The properties surveyed include tensile strength and modulus, compression strength and modulus, shear strength and modulus, flexural strength and modulus, fatigue, creep, vibration damping, moisture absorption characteristics, and thermal expansion. [ABSTRACT FROM PUBLISHER]

A model was developed for calculating the motion of dilute suspensions of rigid, slender particles in a uniformly sheared viscous liquid, taking into ac count interactions between particles. The model was applied to the plane Couette flow problem in which particles are suspended in a liquid moving parallel to a plane with a uniform, shearing motion. The results of the model were compared to existing data, and good agreement was found between the calculated and experimental results. Using the model, results were also ob tained which illustrate the major effects of particle-particle interactions on the angular motion of the particles. [ABSTRACT FROM PUBLISHER]

Tests were conducted to validate the thermoplastic manufacturing process models described by Mantell and Springer. In the tests, APC-2 graphite/PEEK plates were fabricated both in a press and with a specially constructed tape laying apparatus. The tem perature, intimate contact and bonding inside the plates were measured. The data agreed well with the results of the model. [ABSTRACT FROM PUBLISHER]

Tests were conducted to validate the model and the CHAR computer code previously developed for calculating the thermomechanical behavior of carbon-phenolic and carbon-carbon composites exposed to high temperatures. Temperature distributions in and damage of rapidly heated carbon-phenolic composites were measured. The data com pared well to the results calculated by the code. Parametric studies were also performed, the results of which yield physical insights into the ply-lift phenomenon observed in solid rocket motor exit cone linings, and provide a guide in the design of parts made of carbon- phenolic and carbon-carbon composites. [ABSTRACT FROM PUBLISHER]

Tests were performed measuring the temperature, ionic conductivity, and compaction in 16 to 200 ply thick graphite-epoxy laminates made of either Fiberite T300/976 (tape or fabric) or Hercules AS/3501-6 (tape). The data were compared to results calculated by the Loos-Springer CURE model. Good agreement was found between the model results and the data indicating that the model can be used to select the cure cycle. It is also shown that the cure cycle recommended by the manufacturer may result in ex cessive temperatures and in incomplete compaction and cannot be used to manufacture "thick" or even moderately thick composites. [ABSTRACT FROM PUBLISHER]

Models are presented for describing the time dependent viscoelastic and viscoplastic stress-strain relationships of unidirectional fiber reinforced thermoset matrix composites exposed to elevated temperatures. For Fiberite T300/976 graphite-epoxy com posite the constants in the stress-strain relationships were determined from data obtained in four point bend tests over the range 75 to 350°F. A procedure is also described which, together with the stress-strain models developed in this study, can be used to calculate the stresses and strains in loaded multidirectional laminates at high temperatures. Strains in loaded multidirectional Fiberite T300/976 laminates were measured as a function of time at temperatures varying from 75 to 350°F. Strains calculated by the models were compared to these data, and good agreements were found between the analytical and experimental results. [ABSTRACT FROM PUBLISHER]

Models are presented for describing the stress-strain relationships and the strengths of a thermoset matrix composite exposed to elevated temperature. The models take into account the nonlinear elastic characteristics of the material. For Fiberite 976 resin and for unidirectional Fiberite T300/976 composite the constants required in the models were determined by measuring the tensile, compressive, and shear properties, and Poisson ratios at 75, 250, 300, and 350°F. The strengths, initial (stress → 0) moduli, and initial Poisson's ratios of the unidirectional composite were calculated from the known resin and fiber properties using micromechanics equations. A procedure is also described which, together with the stress-strain-strength models developed in this study, can be used to calculate the deformations and strengths of loaded multidirectional laminates at high temperatures. To evaluate the accuracies of the models and the calculation procedure deformations and strengths of multidirectional Fiberite T300/976 laminates were calculated. These results were compared to data obtained at temperatures ranging from 75 to 350°F. The calculated results agreed well with the data. [ABSTRACT FROM PUBLISHER]

Tests were conducted to determine the moisture absorption characteristics of PEEK 150P polymer and APC-2 composite exposed to humid air, and to evaluate the effects of moisture content and crystallinity on the fracture toughness. Tests were con ducted with PEEK 150P specimens having 30, 34, and 43 percent crystallinities and with APC-2 specimens having 17 and 21 percent crystallinities. The weight gains of these speci mens were measured during exposure to air kept at relative humidities ranging from 60 to 100 percent and temperatures ranging from 140 to 200°F. The values of the maximum moisture content and diffusivity were deduced from the weight gain data. Empirical cor relations were established for the maximum moisture content and for the diffusivity. The room temperature fracture toughnesses of PEEK 150P and APC-2 were measured. For the conditions of the tests the fracture toughness was found to be unaffected by crystallinity and by moisture content. [ABSTRACT FROM PUBLISHER]

A model was developed which describes heating of filament wound composite cylinders by applying voltage across the fibers. Two situations were examined: power applied both during and after the wind, and power applied only after completion of the wind. Electrical connections in series and in parallel were modeled.The model yields temperature and cure profiles within the laminate as functions of time during and after the filament wind process. Sample calculations were performed showing the effects of geometry and power applied on the temperature, degree of cure, and manufacture time of the cylinder. The temperature, degree of cure, and manufacture time were also calculated for a filament wound cylinder cured conventionally in an oven. Assessments were made on the merits of electrothermal curing versus curing in an oven. [ABSTRACT FROM PUBLISHER]

Tests were performed to evaluate the effects of cure on the mechanical properties of composite laminates. The longitudinal and transverse tensile and compressive moduli and strengths and the longitudinal shear moduli and strengths of Fiberite T300/976 laminates were measured, with laminates cured to different degrees of cure ranging from 0.6 to 0.96. The laminate moduli and strengths were also calculated from the known values of the resin and fiber properties using the rule of mixture, Tsai-Hahn, Chamis, and Halpin-Tsai formu las. Comparisons were made between the measured and calculated laminate properties and the applicabilities of these formulas were assessed. [ABSTRACT FROM PUBLISHER]

Tests were performed to evaluate the effects of cure and moisture on the moisture ab sorption characteristics and on the mechanical properties of Fiberite 976 resin. The maxi mum moisture content Mm was determined as a function of degree of cure, temperature, and relative humidity. The diffusivity D was determined as a function of degree of cure and temperature. Empirical correlations were established for the maximum moisture con tent and for the diffusivity. The tensile, compressive, and shear strengths and moduli, and the fracture toughness of dry resin were measured at different degrees of cure ranging from 0.6 to 0.95. The tensile, compressive, and shear properties were also measured at dif ferent degrees of cure with resins containing 0 to 4 percent moisture. These data indicate the individual effects of cure as well as the combined effects of cure and moisture on the mechanical properties. [ABSTRACT FROM PUBLISHER]

The mechanical properties of PEEK 150P polymer and APC-2 graphite/PEEK com posite were measured at different crystallinities, from 0 to 40 weight percent. For PEEK 150P the tensile, compressive, and shear properties and the fracture toughness were measured. For APC-2 the mode I and mode II fracture toughnesses and fracture energies as well as the mixed mode stress intensity factors were determined. Expressions are pre sented relating the mechanical properties to crystallinity. Finally, data are given which compare the mechanical properties of materials in which the same crystallinity was estab lished by different thermal processes. [ABSTRACT FROM PUBLISHER]

A model is presented of the steps involved in the manufacturing process of semicrystal line thermoplastic matrix composites. The model relates the temperature and pressure ap plied during processing to a) the flow of the matrix into the fiber tow, b) the formation of contact and bond between adjacent plies, and c) the crystallinity. The results of the model were verified by tests performed with PEEK 150P polymer and APC-2 graphite/PEEK composite. [ABSTRACT FROM PUBLISHER]

The effects of cure pressure on resin flow, compaction, void content, and mechanical properties of fiber reinforced composites were investigated. Tests were performed on lami nates made of Fiberite T300/976 and T300/934 unidirectional prepreg tape. Data are pre sented on compaction, resin flow, and void content which lend support to the validity of the Springer-Loos model. Data are also given showing the effects of cure pressure on void content and on the compressive strength and short-beam shear strength and modulus. [ABSTRACT FROM PUBLISHER]

Using data generated by a differential scanning calorimeter, the heat of reaction, the rate of cure, and the degree of cure of Fiberite 976 resin were determined at the constant temperatures of 413, 423, 433, and 443°K (isothermal scanning). The ultimate heat of reaction was also measured at the constant heating rate of 2°K/min (dynamic scanning). Using a disc and plate type viscometer, the viscosity was measured as a function of time at the temperatures of 413, 423, 433, and 443°K. Expressions were also developed which represent the rate of cure, the degree of cure, and the viscosity data. [ABSTRACT FROM PUBLISHER]

A procedure is presented for accelerated environmental testing of composites, which yields the test conditions required to achieve a desired moisture content in the shortest time. Charts are presented from which the appropriate test conditions can readily be deter mined. The use of the charts is illustrated by an example. Tests were also performed to assess the validity and accuracy of the proposed procedure. Data, obtained with Fiberite T300/976 fabric, show that the moisture contents and the mechanical properties of the material are nearly the same after "regular" and "accelerated" environmental conditioning. [ABSTRACT FROM PUBLISHER]

Experiments were performed to evaluate the effects of cure and sizing on the bond strength between graphite fiber bundles and epoxy resins. Fiberite 976 and 934 resins and Thornel T300 (3K) fibers were used in the tests. The fibers were either uncoated (no siz ing) or coated with different types of sizing. Pure resin specimens and resin specimens containing a single coated or uncoated fiber bundle were prepared by curing in a mold at different temperatures. The specimens were subjected to three-point bending, and the load versus deflection curves were recorded. Photomicrographs of fiber bundles em bedded in the resin were also taken. The data show the influence of the cure temperature (and the corresponding degree of cure) on the fracture strain and on the stiffness of the pure resins. The data also indicate the effects of cure temperature and sizing on the fiber bundle-resin bond strength (as manifested by the specimen's fracture strain), and the effect of sizing on the geometry of the bundle and on the fiber density inside the bundle. [ABSTRACT FROM PUBLISHER]

This paper presents an analysis for the preliminary design of boxbeams made of fiber-reinforced composites. The analysis provides deflections, bending and torsional stiffnesses, stresses, and the conditions for buckling and first-ply failure. Use of the analysis is illustrated through the example of a single cell, three bay, cantilevered box beam. This example demonstrates a design procedure for selecting the configuration which results in the required strength and stiffness at a minimum weight. [ABSTRACT FROM PUBLISHER]

An analysis is presented for calculating the stresses and strains in bends made of fiber reinforced composites and for estimating the strengths of bends. The stress field is calculated by a finite element method. The strength is predicted using the Tsai-Hill criterion for inplane failure and the Chang-Springer criterion for out of plane failure. Results are presented which illustrate the effects of geometry and ply orientation on the strength and on the mode of failure. [ABSTRACT FROM PUBLISHER]

A method is presented for calculating the failure strengths and failure modes of composite laminates containing a pin loaded hole for materials exhibiting nonlinearly elastic behavior. The analysis follows that proposed by Chang, Scott, and Springer for linearly elastic composites with two notable exceptions: a) the shear stress-shear strain relation in each ply is taken to be nonlinear with the form proposed by Hahn and Tsai, and b) the Yamada-Sun failure criterion is modified to include nonlinear effects. Numerical results, generated using a nonlinear finite element scheme, were compared to data. These comparisons show that for laminates exhibiting nonlinear behavior the present analysis provides the failure strengths and failure modes more accurately than the previous method employing a linear stress-strain analysis. [ABSTRACT FROM PUBLISHER]

A model was developed which describes the microwave curing process of continuous fiber reinforced organic matrix composites. On the basis of the model, a computer code was developed which provides the temperature distribution, the resin viscosity, the degree of cure of the resin, and the resin contents of the composite and the bleeder during microwave curing of flat plate composites. In addition, the computer code gives the void sizes and the residual stresses after the cure. Tests were conducted using a microwave oven measuring the temperature distribution inside Fiberite S2/9134B glass epoxy composites, and the temperature distribution inside and resin flow out of Hercules AS/3501-6 graphite epoxy composites. The data were compared with results calculated with the computer code for the conditions employed in the tests, and good agreements were found between the data and the numerical results. Parametric studies were also performed to illustrate how the model and associated computer code can be used to determine the appropriate microwave cure cycle which results in a composite that is cured uniformly and in the shortest amount of time. [ABSTRACT FROM PUBLISHER]

A model was developed which describes the interaction between linearly polarized transverse electromagnetic waves or isotropic electromagnetic waves and continuous fiber-reinforced organic matrix composites. On the basis of the model, a user-friendly computer code was developed which provides the reflectance, transmittance, total ab sorbed energy, and absorbed energy distribution inside the composite. In order to validate the model, tests were performed using a waveguide measuring the reflectances and transmittances of Fiberite S2/9134B glass epoxy and Hercules AS/3501-6 graphite epoxy composites. The data were compared with the results calculated by the computer code. Good agreements were found between the experimental data and the numerical results. A parametric study was also performed which shows the dependence of the reflectance, transmittance, and absorbed energy on the characteristics of the incident electromagnetic wave, the geometry (composite and coating thicknesses and ply orientation), and the properties of the composite. [ABSTRACT FROM PUBLISHER]

Tests were performed measuring the characteristic lengths in tension and in com pression and the rail shear strength of Fiberite T300/1034-C graphite epoxy com posites. The results show the effects of geometry on the characteristic lengths. The results also indicate the variability of rail shear strength with the volume fraction of zero degree plies in the laminate. [ABSTRACT FROM PUBLISHER]

Methods are presented for sizing composite laminates containing one, two, or several pin loaded holes, the holes being arranged either in a single row or in two parallel rows. It is shown how the design parameters (number of holes, hole diameter, hole positions) can be found, which result in the maximum failure load and in the max imum failure load per unit weight. [ABSTRACT FROM PUBLISHER]

A method is presented for predicting the failure strength and the failure mode of fiber reinforced composite laminates containing one or two pin loaded holes. The method involves two steps. First, the stress distribution in the laminate is calculated by the use of a finite element method. Second, the failure load and failure mode are predicted by means of a proposed failure hypothesis together with the Yamada-Sun failure criterion. A computer code was developed which can be used to calculate the maximum load and the mode of failure of laminates with different ply orientations, different material properties, and different geometries. Tests were also conducted measuring the failure strengths and failure modes of Fiberite T300/1034-C laminates containing a pin-loaded hole or two pin-loaded holes in parallel or in series. Com parisons were made between the data and the results of the model. Good agreement was found between the analytical and the experimental results. [ABSTRACT FROM PUBLISHER]