SEARCH · Search NASA

Results for “Graphite/Epoxy”

Search indexed NASA NTRS and DOE OSTI research on propulsion, heat transfer, battery materials and energy systems. Follow report and document links to the original sources.

SourceResearch connectionFrom yearThrough year

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 595 records · Page 33

All sources NASA NTRS DOE OSTI

NASA NTRS1987

Gain-Compensating Circuit For NDE and Ultrasonics

High-frequency gain-compensating circuit designed for general use in nondestructive evaluation and ultrasonic measurements. Controls gain of ultrasonic receiver as function of time to aid in measuring attenuation of samples with high losses; for example, human skin and graphite/epoxy composites. Features high signal-to-noise ratio, large signal bandwidth and large dynamic range. Control bandwidth of 5 MHz ensures accuracy of control signal. Currently being used for retrieval of more information from ultrasonic signals sent through composite materials that have high losses, and to measure skin-burn depth in humans.

Kushnick, Peter W.↗

NASA NTRS1987

Dielectric Monitoring of Curing Composites

Report describes preliminary attempts at dielectric monitoring of curing of graphite/epoxy and carbon/phenolic composites. Objective is to develop dielectric monitoring for optimizing curing process and reduce incidence of failures of produced composite structures.

Goldberg, Benjamin E.↗

NASA NTRS1987

Measuring the Interlaminar Shear Strengths of Composites

Acousto-ultrasonic technique utilizing computer and waveform digitizer developed for nondestructive evaluation (NDE) of composite materials. Technique employed on filament-wound composite (FWC) specimens cut from sample segments of graphite/epoxy cylinders. Developed for use on large composite structures to verify integrity and assure reusability. Similar applications of technique anticipated for variety of composite structures, such as pipelines and storage tanks.

Kautz, Harold E.↗

NASA NTRS1987

Thermally Insulating Support for Cryogenic Tanks

Passive alternate-load-path support scheme keeps weight low while conserving cryogenic liquid. Method of supporting inner vessel of large Dewar container minimizes heat conductance and weight but ensures high strength and impact resistance. Accommodates thermal expansion and contraction of vessel while introducing minimal stresses in structure. Inner vessel hangs from struts in outer vessel. Thin wall graphite/epoxy tube protected from high loads by close tolerance stops.

Parmley, Richard T.↗

NASA NTRS1986

Flight service evaluation of composite helicopter components

This report presents an assessment of composite helicopter tail rotor spars and horizontal stabilizers, exposed to the effects of the environment, after up to five and a half years of commercial service. This evaluation is supported by test results of helicopter components and panels which have been exposed to outdoor environmental effects since September 1979. Full scale static and fatigue tests have been conducted on graphite/epoxy and Kevlar/epoxy composite components obtained from Sikorsky Model S-76 helicopters in commercial operations in the Gulf Coast region of Louisiana. Small scale static and fatigue tests are being conducted on coupons obtained from panels under exposure to outdoor conditions in Stratford, Connecticut and West Palm, Florida. The panel layups are representative of the S-76 components. Additionally, this report discusses the results of moisture absorption evaluations and strength tests on the S-76 components and composite panels with up to five years of outdoor exposure.

Mardoian, G. H.↗

NASA NTRS1986

Factors influencing elastic stresses in double cantilever beam specimens

An elastic stress analysis was conducted for a double cantilever beam (DCB) specimen using finite-element methods. The purpose of this study was to identify the important parameters that influence stresses ahead of the delamination front. The study focused on an aluminum DCB specimen, typical of adhesively-bonded joints, and on a graphite/epoxy specimen representing a cocured composite. Opening mode sigma sub y stresses ahead of the crack tip were calculated and compared with those for a monolithic reference specimen. Beyond the singularity-dominated region very near the crack tip, the sigma sub y distribution was elevated compared to the monolithic case. Both the adhesive thickness and the adherend transverse (thickness-direction) stiffness were found to influence the elevation of sigma sub y. In contrast, adherend thickness and longitudinal stiffness has very little effect on this stress distribution. Estimates for adhesive yielding beyond the aluminum DCB crack tip showed that both the area and height of the plastic zone increased to a peak value for increasing adhesive thicknesses. Results from this study would provide insight for comparing data from different DCB specimens and for designing new DCB specimens.

Crews, J. H., Jr.↗

NASA NTRS1986

Flight service evaluation of advanced composite ailerons on the L-1011 transport aircraft

This report covers flight evaluation of composite inboard ailerons on the L-1011 under Contract NAS 1-15069 for a period of five years. This is the fourth annual report of the maintenance evaluation program, and covers the period from May 1985 when the third yearly inspections were completed, through July 1986. Four shipsets of graphite/epoxy composite inboard ailerons were installed on L-1011 aircraft for this maintenance evaluation program. These include two Delta aircraft and two TWA aircraft. A fifth shipset of composite ailerons was installed in 1980 on Lockheed's flight test L-1011. One instance of minor damage was observed on one of the composite ailerons and was repaired. No other maintenance actions have occurred on any of the composite parts except for repainting of areas with paint loss. Flight hours on the airline components at the time of inspection ranged from 12,051]en1] to 14,046 hours, after approximately 4 years of service.

Stone, R. H.↗

NASA NTRS1987

Long-term environmental effects and flight service evaluation of composite materials

Results of a NASA-Langley sponsored research program to establish the long term effects of realistic flight environments and ground based exposure on advanced composite materials are presented. The effects of moisture, ultraviolet radiation, aircraft fuels and fluids, sustained stress, and fatigue loading are reported. Residual strength and stiffness as a function of exposure time and exposure location are reported for seven different material systems after 10 years of worldwide outdoor exposure. Flight service results of over 300 composite components installed on rotorcraft and transport aircraft are included. Over 4 million total component flight hours were accumulated on various aircraft since initiation of flight service in 1973. Service performance, maintenance characteristics, and residual strength of numerous composite components installed on commercial and military aircraft are reported as a function of flight hours and years in service. Residual strength test results of graphite/epoxy spoilers with 10 years of worldwide service and over 28,000 flight hours are reported.

Dexter, H. Benson↗

NASA NTRS1987

Protective coatings for composite tubes in space applications

Protective coatings for graphite/epoxy (Gr/Ep) tubular structures for a Manned Space Station truss structure were evaluated. The success of the composite tube truss structure depends on its stability to long-term exposure to the Low Earth Orbit (LEO) environment with particular emphasis placed on atomic oxygen. Concepts for protectively coating Gr/Ep tubes include use of inorganic coated metal foils and electroplating. These coatings were applied to Gr/Ep tubes and then subjected to simulated LEO environmnet to evaluate survivability of coatings and coated tubes. Evaluation included: atomic oxygen resistance, changes in optical properties and adhesion, abrasion resistancem surface preparation required, coating uniformity, and formation of microcracks in the Gr/Ep tubes caused by thermal cycling. Program results demonstrated that both phosphoric and chromic acid anodized Al foil provided excellent adhesion to Gr/Ep tubes and exhibited stable optical properties when subjected to simulated LEO environment. The SiO2/Al coatings speuttered onto Al foils also resulted in an excellent protective coating. Electroplated Ni exhibited unaccepatble adhesion loss to Gr/Ep tubes during atomic oxygen exposure.

Dursch, Harry W.↗

NASA NTRS1984

Development of laminar flow control wing surface composite structures

The dramatic increases in fuel costs and the potential for periods of limited fuel availability provided the impetus to explore technologies to reduce transport aircraft fuel consumption. NASA sponsored the Aircraft Energy Efficiency (ACEE) program beginning in 1976 to develop technologies to improve fuel efficiency. This report documents the Lockheed-Georgia Company accomplishments under NAS1-16235 LFC Laminar-Flow-Control Wing Panel Structural Design And Development (WSSD); Design, manufacturing, and testing activities. An in-depth preliminary design of the baseline 1993 LFC wing was accomplished. A surface panel using the Lockheed graphite/epoxy integrated LFC wing box structural concept was designed. The concept was shown by analysis to be structurally efficient and cost effective. Critical details of the surface and surface joints were demonstrated by fabricating and testing complex, concept selection specimens. Cost of the baseline LFC aircraft was estimated and compared to the turbulent aircraft. The mission fuel weight was 21.7 percent lower for the LFC aircraft. The calculation shows that the lower fuel costs for LFC offset the higher incremental costs of LFC in less than six months.

Lineberger, L. B.↗

NASA NTRS1986

Unstalled flutter stability predictions and comparisons to test data for a composite prop-fan model

The aeroelastic stability analyses for three graphite/epoxy composite Prop-Fan designs and post-test stability analysis for one of the designs, the SR-3C-X2 are presented. It was shown that Prop-Fan stability can be effectively analyzed using the F203 modal aeroelastic stability analysis developed at Hamilton Standard and that first mode torsion-bending coupling has a direct effect on blade stability. Positive first mode torsion-bending coupling is a destabilizing factor and the minimization of this parameter will increase Prop-Fan stability. It was also shown that Prop-Fan stability analysis using F203 is sensitive to the blade modal data used as input. Calculated blade modal properties varied significantly with the structural analysis used, and these variations are reflected in the F203 calculations.

Turnberg, J. E.↗

NASA NTRS1986

Dynamic response and stability of a composite prop-fan model

Results are presented for blade response and stability during wind tunnel tests of a 62.2 cm diameter model of a prop-fan, advanced turboprop, with swept graphite/epoxy composite blades. Measurements of dynamic response were made with the rotor mounted on an isolated nacelle, with varying tilt for nonuniform inflow, at flow speeds from 0.36 to 0.9 Mach number. The blade displayed no instabilities over the operating range tested, up to 0.9 Mach number and 10,000 RPM. Measurements are compared with those for other prop-fan models of both solid metal and graphite composite construction. The swept composite blade had less response than an unswept composite blade. Composite blades had more response than metal blades. Measurements are compared with theoretically based predictions. The 1-P blade response was significantly overpredicted using unimproved methods and somewhat overpredicted using improved methods. Unexpectedly high 2-P strain levels were measured and suggest the presence of nonlinear effects on blade response.

Smith, A. F.↗

NASA NTRS1986

Dynamic response of two composite prop-fan models on a nacelle/wing/fuselage half model

Results are presented for blade response wind tunnel tests of two 62.2 cm diameter Prop-Fan (advanced turboprop) models with swept and unswept graphite/epoxy composite blades. Measurements of dynamic response were made with the rotors mounted on a simulated nacelle/wing/fuselage model, with varying tilt, at flow speeds up to 0.85 Mach number. The presence of the wing, downstream of the rotor, induced 1-P responses that were about twice those previously measured for an isolated nacelle installation. The swept blade had less 1-P response than the unswept (straight) blade. The 2-P response was significant for both blades, and was closely correlated to wing lift. Higher order response was not important for the straight blade, but possibly important for the swept blade near critical speeds, due to the proximity of the blade tips to the wing leading edge. Measurements are compared with theoretically based prediction. Correlations between calculated and measured 1-P response were good for the straight blade, and fair for the swept blade. Improvements to the calculation method were identified and implemented.

Smith, Arthur F.↗

NASA NTRS1987

Flight service evaluation of advanced composite ailerons on the L-1011 transport aircraft

This report covers flight service evaluation of composite inboard ailerons on the L-1011 under contract NAS1-15069 for a period of five years. This is the fifth and final annual report of the maintenance evaluation program, and covers the period from July 1986 when the fourth yearly inspections were completed, through May 1987. Four shipsets of graphite/epoxy composite inboard ailerons were installed on L-1011 aircraft for this maintenance evaluation program. These include two Delta and two TWA aircraft. A fifth shipset of composite ailerons was installed in 1980 on Lockheed's flight test L-1011. The previous four annual inspections had been visual exterior inspections only. For this final inspection, the lower covers were removed for access and both interior and exterior surfaces, spars and ribs, and fastener holes were inspected. No damage or defects were observed on any of the composite ailerons, and no maintenance actions had occurred except for repainting of areas with paint loss. Flight hours on the airline components at the time of inspection ranged from 14,597 to 17,180 hours, after approximately 5 years of service.

Stone, R. H.↗

NASA NTRS1987

Method for machining holes in composite materials

A method for boring well defined holes in a composite material such as graphite/epoxy is discussed. A slurry of silicon carbide powder and water is projected onto a work area of the composite material in which a hole is to be bored with a conventional drill bit. The silicon carbide powder and water slurry allow the drill bit, while experiencing only normal wear, to bore smooth, cylindrical holes in the composite material.

Daniels, Julia G.↗

NASA NTRS1986

Hidden impact damage in thick composites

NASA is developing light-weight graphite/epoxy filament-wound cases (FWC) for the solid rocket motors of the Space Shuttle. The 12-foot-diameter FWC's are about 1.4 inches or more thick. Tests were conducted to determine the tension strength of an FWC after low-velocity impact. Impactors of various kinetic energies, masses, and shapes were used. The conditions that give minimum visual evidence of damage were emphasized. The capability to characterize impact damage with radiography and ultrasonic attenuation was also evaluated. After impact, the specimens were loaded uniaxially in tension to determine residual strengths.

Poe, C. C., Jr.↗

NASA NTRS1986

The role of fiber and matrix in crash energy absorption of composite materials

Static crushing tests were conducted on tube specimens fabricated from graphite/epoxy, Kevlar/epoxy and hybrid combinations of graphite-Kevlar/epoxy to examine the influence the fiber and matrix constitutive properties and laminate architecture have on energy absorption. Fiber and matrix ultimate failure strain were determined to significantly effect energy absorption. The energy absorption capability of high ultimate failure strain materials (AS-6/F185 and AS-6/HST-7) was less than materials having lower ultimate failure strain. Lamina stacking sequence had up to a 300 percent change in energy absorption for the materials tested. Hybridizing with graphite and Kevlar reinforcements resulted in materials with high energy absorption capabilities that have postcrushing integrity.

Farley, G. L.↗

NASA NTRS1986

Criterion for mixed mode fracture in composite bonded joints

A study was undertaken to characterize the debond growth mechanism of adhesively bonded composite joints under mode I, mixed mode I-II, and mode II static loadings. The bonded system consisted of graphite/epoxy (T300/5208) composite adherends bonded with a toughened epoxy (EC 3445) adhesive. The mode I, mode II and mixed-mode I-II fracture energies of the tested adhesive were found to be equal to each other. Furthermore, the criterion for mixed mode fracture in composite bonded joints was determined.

Mall, S.↗