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At least 1,315 records · Page 73
All sourcesNASA NTRSDOE OSTI
NASA NTRS1983

Galvanic coupling between D6AC steel, 6061-T6 aluminum, Inconel 718 and graphite-epoxy composite material: Corrosion occurrence and prevention

The effects of galvanic coupling between D6AC steel, 6061-T6 aluminum, Inconel 718, and graphite-epoxy composite material (G/E) in 3.5% NaCl were studied. Measurements of corrosion potentials, galvanic currents and corrosion rates of the bare metals using weight-loss methods served to establish the need for corrosion protection in cases where D6AC steel and 6061-T6 aluminum are galvanically coupled to G/E in salt water while Inconel 718 was shown to be compatible with G/E. Six tests were made to study corrosion protective methods for eliminating galvanic corrosion in the cases of D6AC steel and 6061-T6 aluminum coupled to G/E. These results indicate that, when the G/E is completely coated with paint or a paint/polyurethane resin combination, satisfactory protection of the D6AC steel is achieved with either a coat of zinc-rich primer or a primer/topcoat combination. Likewise, satisfactory corrosion protection of the aluminum is achieved by coating it with an epoxy coating system.

Danford, M. D.↗
NASA NTRS1984

Non-destructive evaluation of composite materials using ultrasound

Investigation of the nondestructive evaluation of advanced composite-laminates is summarized. Indices derived from the measurement of fundamental acoustic parameters are used in order to quantitatively estimate the local material properties of the laminate. The following sections describe ongoing studies of phase insensitive attenuation measurements, and discuss several phenomena which influences the previously reported technique of polar backscatter. A simple and effective programmable gate circuit designed for use in estimating attenuation from backscatter is described.

Miller, J. G.↗
NASA NTRS1984

Investigating compression failure mechanisms in composite laminates with a transparent fiberglass-epoxy birefringent materials

The response and failure of a + or - 45s class laminate was studied by transparent fiberglass epoxy composite birefringent material. The birefringency property allows the laminate stress distribution to be observed during the test and also after the test if permanent residual stresses occur. The location of initial laminate failure and of the subsequent failure propagation are observed through its transparency characteristics. Experimental results are presented.

Shuart, M. J.↗
NASA NTRS1985

Investigation of the effects of NaOH dopant level on the physical and mechanical properties of carbon/phenolic composite material

The near-catastrophic erosion of the STS-8A solid rocket booster nozzle was the instigating factor in the recent, and on-going, intensive investigation of carbon/phenolic composite materials. Much of this effort has been focused on the effect of sodium contamination on the carbon fibers. It is known that sodium acts as a catalyst in the oxidation of the fibers at elevated temperatures. A study was undertaken to determine what changes were caused by variation in sodium content. Investigations were conducted in three areas: (1) phenolic resin; (2) carbon/phenolic prepreg; and (3) cured laminates. Due to the exploratory nature of the studies, a variety of tests in addition to those normally run in production facilities were considered. The experimental methodologies and results of these experiments are discussed, and recommendations for improving techniques and extending the research program are presented.

Clinton, R. G., Jr.↗
NASA NTRS1985

NASA/aircraft industry standard specification for graphite fiber toughened thermoset resin composite material

A standard specification for a selected class of graphite fiber/toughened thermoset resin matrix material was developed through joint NASA/Aircraft Industry effort. This specification was compiled to provide uniform requirements and tests for qualifying prepreg systems and for acceptance of prepreg batches. The specification applies specifically to a class of composite prepreg consisting of unidirectional graphite fibers impregnated with a toughened thermoset resin that produce laminates with service temperatures from -65 F to 200 F when cured at temperatures below or equal to 350 F. The specified prepreg has a fiber areal weight of 145 g sq m. The specified tests are limited to those required to set minimum standards for the uncured prepreg and cured laminates, and are not intended to provide design allowable properties.

Source record↗
NASA NTRS1985

Long-term thermal aging of Celion/V378A composite materials

Celion 6000/V378A graphite/bismaleimide composite materials were aged in air at temperatures of 177, 204, 232 and 260 deg C for various times up to 15,000 hours. Three unidirectional specimen types were aged: short beam shear (SBS), flexure, and 153 mm square panels. Aged specimens of V378A laminates exhibited excellent thermal stability. Extensive cracking was observed during aging on the 0 deg edges of the unidirectional laminates. These cracks penetrated as deep as 12 mm from the edge. The cracking appeared to have little or no effect on the observed properties of the laminates. The study indicates that the useful life of unrestrained unidirectional graphite/V378A laminates is 10,000 hours or greater at 177 C to 232 C and 2,000 to 2,000 hour at 260 C.

Nelson, J. B.↗
NASA NTRS1986

Factors influencing the ultrasonic stress wave factor evaluation of composite material structures

To demonstrate that the finite-element model can be used to investigate some of the factors influencing the ultrasonic stress wave evaluation of materials, a hypothetical case was studied in which classical vibration theory was used. Vibration analysis and experiments for the undamaged case were conducted on an isotropic aluminum plate and a unidirectional graphite-epoxy plate, using a point source to excite the plates. The finite-element solution correlated within eight percent with the exact method. The frequencies predicted by the finite-element model were observed in the experiments in both plates, although in the composite plate, additional frequencies were observed which could not be accounted for. Damaged isotropic plates were also considered. The effects of increasing damage severity with constant damage area, and increasing damage area with constant severity on the resonant frequencies were analyzed.

Rebello, C. J.↗
NASA NTRS1986

A three dimensional calculation of elastic equilibrium for composite materials

A compact scheme is applied to three-dimensional elasticity problems for composite materials, involving simple geometries. The mathematical aspects of this approach are discussed, in particular the iteration method. A vector processor code implementing the compact scheme is presented, and several numerical experiments are summarized.

Lustman, Liviu R.↗
NASA NTRS1987

Contribution to the study of composite materials and their damage

Chapter 1 describes the homogenization techniques used for defining the overall behavior of composite materials for conventional cases of linear and perfectly glued elastic constituents. Chapters 2 and 3 focus on solving the problems inherent in two types of degenerated situations: elastic media with microcavities, and elastic media containing rigid inclusions. Through suitable definitions of deformation concepts and macroscopic stresses it is shown that conventional theory results apply naturally to these limits.

Lene, F.↗
NASA NTRS1987

The role of damage-softened material behavior in the fracture of composites and adhesives

The failure mechanism of polymer composites and adhesives with high strain in the zone near and ahead of the crack tip is investigated analytically, summarizing the findings of Ungsuwarungsri (1986). A double-cantilever-beam specimen with the nonlinear material confined to a thin strip between two wedge-loaded elastic beams is modeled as a beam on a nonlinear foundation; the two-point boundary-value problem for stationary and propagating cracks is solved numerically; and an FEM approach is applied to study the behavior of the nonlinear strip in detail. Typical results are presented in extensive graphs, and the accuracy and efficiency of the present method are shown to be superior to those of the Berry (1963) procedure.

Ungsuwarungsri, T.↗
NASA NTRS1988

A three dimensional calculation of elastic equilibrium for composite materials

A compact scheme is applied to three-dimensional elasticity problems for composite materials, involving simple geometries. The mathematical aspects of this approach are discussed, in particular the iteration method. A vector processor code implementing the compact scheme is presented, and several numerical experiments are summarized.

Lustman, Liviu R.↗
NASA NTRS1988

The strength of laminated composite materials under repeated impact loading

When low velocity and energy impact is exerted on a laminated composite material, in a perpendicular direction to the plane of the laminate, invisible damage may develop. It is shown analytically and experimentally that the invisible damage occurs during the first stage of contact between the impactor and the laminate and is a result of the contact stresses. However, the residual flexural strength changes only slightly, because it depends mainly on the outer layers, and these remain undamaged. Repeated impact intensifies the damage inside the laminate and causes larger bending under equivalent impact load. Finally, when the damage is most severe, even though it is still invisible, the laminate fails because of bending on the tension side. If the repeated impact is halted before final fracture occurs the residual strength and modulus would decrease by a certain amount.

Rotem, Assa↗
NASA NTRS1989

Optical properties of sputtered aluminum on graphite/epoxy composite material

Solar absorptance, emittance, and coating thickness were measured for a range of coating thicknesses from about 400 A to 2500 A. The coatings were sputtered from an aluminum target onto 1-inch-diameter substrates of T300/5209 graphite/epoxy composite material with two different surface textures. Solar absorptance and emittance values for the specimens with the smooth surface finish were lower than those for the specimens with the rough surface finish. The ratio of solar absorptance to emittance was higher for the smooth specimens, increasing from 2 to 4 over the coating thickness range, than for the rough ones, which had a constant ratio of about 1. The solar absorptance and emittance values were dependent on the thickness of the sputtered coating.

Witte, William G., Jr.↗
NASA NTRS1988

Nondestructive evaluation/characterization of composite materials and structures using the acousto-ultrasonic techniques

This paper introduces the nature and the underlying rational of the acousto-ultrasonic stress wave factor technique and some of its applications to composite materials and structures. Furthermore, two examples of successful application of the acousto-ultrasonic technique are presented in detail. In the first example, the acousto-ultrasonic technique is used to evaluate the adhesive bond strength between rubber layers and steel plates, and in the seocnd example the tehcnique is used to monitor progressive damage in wire rope.

Dos Reis, H. L. M.↗
NASA NTRS1989

Techniques for measurement of the thermal expansion of advanced composite materials

Techniques available to measure small thermal displacements in flat laminates and structural tubular elements of advanced composite materials are described. Emphasis is placed on laser interferometry and the laser interferometric dilatometer system used at the National Aeronautics and Space Administration (NASA) Langley Research Center. Thermal expansion data are presented for graphite-fiber reinforced 6061 and 2024 aluminum laminates and for graphite fiber reinforced AZ91 C and QH21 A magnesium laminates before and after processing to minimize or eliminate thermal strain hysteresis. Data are also presented on the effects of reinforcement volume content on thermal expansion of silicon-carbide whisker and particulate reinforced aluminum.

Tompkins, Stephen S.↗