SEARCH · Search NASA

Results for “compositional”

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 1,585 records · Page 88

All sources NASA NTRS DOE OSTI

NASA NTRS1985

Graphite/PMR polyimide composites with improved toughness

The toughness of composites made with modified PMR (Polymerization of monomer reactants) polyimides and Celion 6000 graphite fibers was studied. Various types/levels of monomer reactants containing flexible links were incorporated into PMR resin compositions used to prepare composites. The composites were evaluated for toughness using instrumented drop weight and 10 deg off axis tensile tests at room temperature, and for strength using flexure and short beam shear tests at room temperature and at elevated temperature. The effect of resin composition on composite processability, thermo-oxidative stability, toughness and mechanical properties are discussed.

Vannucci, R. D.↗

NASA NTRS1985

Composites in today's and tomorrow's U.S. airliners

The research conducted by NASA's Aircraft Energy Efficiency Composites program in developing essential technologies for the efficient utilization of composites in the airframe structures of transport aircraft is described. Current activities, present state-of-the-art, production trends in the U.S., and the outlook for major use of composites in primary structures are examined. Special attention is given to application of composites in transport wing and fuselage structures. The projections for the Advanced Tactical Fighter of the late eighties suggest application of composites in the airframe structures to the extent of 50 percent, an all-composite transport could become a reality in the mid-nineties.

Bohon, H. L.↗

NASA NTRS1984

Advanced composite combustor structural concepts program

An analytical study was conducted to assess the feasibility of and benefits derived from the use of high temperature composite materials in aircraft turbine engine combustor liners. The study included a survey and screening of the properties of three candidate composite materials including tungsten reinforced superalloys, carbon-carbon and silicon carbide (SiC) fibers reinforcing a ceramic matrix of lithium aluminosilicate (LAS). The SiC-LAS material was selected as offering the greatest near term potential primarily on the basis of high temperature capability. A limited experimental investigation was conducted to quantify some of the more critical mechanical properties of the SiC-LAS composite having a multidirection 0/45/-45/90 deg fiber orientation favored for the combustor linear application. Rigorous cyclic thermal tests demonstrated that SiC-LAS was extremely resistant to the thermal fatigue mechanisms that usually limit the life of metallic combustor liners. A thermal design study led to the definition of a composite liner concept that incorporated film cooled SiC-LAS shingles mounted on a Hastelloy X shell. With coolant fluxes consistent with the most advanced metallic liner technology, the calculated hot surface temperatures of the shingles were within the apparent near term capability of the material. Structural analyses indicated that the stresses in the composite panels were low, primarily because of the low coefficient of expansion of the material and it was concluded that the dominant failure mode of the liner would be an as yet unidentified deterioration of the composite from prolonged exposure to high temperature. An economic study, based on a medium thrust size commercial aircraft engine, indicated that the SiC-LAS combustor liner would weigh 22.8N (11.27 lb) less and cost less to manufacture than advanced metallic liner concepts intended for use in the late 1980's.

Sattar, M. A.↗

NASA NTRS1987

Mechanical and electrical properties of graphite fiber-epoxy composites made from pristine and bromine intercalated fibers

The mechanical and electrical properties of pristine and bromine intercalated graphite fiber-epoxy composites were compared. The two types of composite were similar in terms of tensile modulus, tensile strength, and Poisson's Ratio. However, the interlaminar shear strength of the brominated composite was 18 percent greater than its pristine counterpart. Only slight differences were observed in flexural properties. A five-fold decrease was observed in the electrical resistivity of the brominated composite parallel to the axis of the fibers, resulting in a unidirectional resistivity of about 90 microOmega/cm. Transverse resistivity was unaffected. Both types of composite were subjected to a simulated lightning strike of 10 KJ (at a peak current of 150 kA), and the composite with the intercalated graphite exhibited less damage.

Jaworske, Donald A.↗

NASA NTRS1986

Mechanical properties of SiC fiber-reinforced reaction-bonded Si3N4 composites

The room temperature mechanical and physical properties of silicon carbide fiber reinforced reaction-bonded silicon nitride composites (SiC/RBSN) have been evaluated. The composites contained 23 and 40 volume fraction of aligned 140 micro m diameter chemically vapor deposited SiC fibers. Preliminary results for composite tensile and bend strengths and fracture strain indicate that the composites displayed excellent properties when compared with unreinforced RBSN of comparable porosity. Fiber volume fraction showed little influence on matrix first cracking strain but did influence the stressed required for matrix first cracking and for ultimate composite fracture strength. It is suggested that by reducing matrix porosity and by increasing the volume fraction of the large diameter SiC fiber, it should be possible to further improve the composite stress at which the matrix first cracks.

Bhatt, Ramakrishna T.↗

NASA NTRS1986

Kink band formation in unidirectional composites under compression

The kink band formation in unidirectional composites under compression was studied with the help of optical and scanning electron microscopy. Materials studied included graphite/epoxy, S-2 glass/epoxy, and Kevlar 49/epoxy composites. The kink bands in the graphite/epoxy and glass/epoxy composites were initiated by fiber microbuckling while those in the Kevlar/epoxy composite were triggered by microkinking in the fibers themselves. Fracture surfaces of the graphite/epoxy composites showed fibers broken in bending and fiber segments tilted in the direction of slip. The kink band formation depended not only on the constituent material properties but also on the kinematic constraints imposed. Both primary and secondary kink bands were observed in the graphite/epoxy specimens, but only primary kink bands were present in the other two composites because of higher lateral flexibility of the specimen during testing.

Sohi, M. M.↗

NASA NTRS1986

Mechanical properties characterization of composite sandwich materials intended for space antenna applications

The composite materials proposed for use in the Advanced Communications Technology Satellite (ACTS) Program contains a new, high modulus graphite fiber as the reinforcement. A study was conducted to measure certain mechanical properties of the new fiber-reinforced material as well as of a composite-faced aluminum honeycomb sandwich structure. Properties were measured at -157, 22, and 121 C. Complete characterization of this material was not intended. Longitudinal tensile, picture-frame shear, short-beam shear, and flexural tests were performed on specimens of the composite face-sheet materials. Unidirectional, cross-plied, and quasi-isotropic fiber composite ply layup designs were fabricated and tested. These designs had been studied by using NASA's Integrated Composite Analyzer (ICAN) computer program. Flexural tests were conducted on (+/- 60/0 deg) sub s composite-faced sandwich structure material. Resistance strain gages were used to measure strains in the tensile, picture-frame, and sandwich flexural tests. The sandwich flexural strength was limited by the core strength at -157 and 22 C. The adhesive bond strength was the limiting factor at 121 C. Adhesive mechanical properties are reflected in sandwich structure flexural properties when the span-to-depth ratio is great enough to allow a significant shear effect on the load-deflection behavior of the sandwich beam. Most measured properties agreed satisfactorily with the properties predicted by ICAN.

Bowles, Kenneth J.↗

NASA NTRS1987

Advanced organic composite materials for aircraft structures: Future program

Revolutionary advances in structural materials have been responsible for revolutionary changes in all fields of engineering. These advances have had and are still having a significant impact on aircraft design and performance. Composites are engineered materials. Their properties are tailored through the use of a mix or blend of different constituents to maximize selected properties of strength and/or stiffness at reduced weights. More than 20 years have passed since the potentials of filamentary composite materials were identified. During the 1970s much lower cost carbon filaments became a reality and gradually designers turned from boron to carbon composites. Despite progress in this field, filamentary composites still have significant unfulfilled potential for increasing aircraft productivity; the rendering of advanced organic composite materials into production aircraft structures was disappointingly slow. Why this is and research and technology development actions that will assist in accelerating the application of advanced organic composites to production aircraft is discussed.

Source record↗

NASA NTRS1987

Development of a new generation of high-temperature composite materials

There are ever-increasing demands to develop low-density materials that maintain high strength and stiffness properties at elevated temperatures. Such materials are essential if the requirements for advanced aircraft, space power generation, and space station plans are to be realized. Metal matrix composites and intermetallic matrix composites are currently being investigated at NASA Lewis for such applications because they offer potential increases in strength, stiffness, and use temperature at a lower density than the most advanced single-crystal superalloys presently available. Today's discussion centers around the intermetallic matrix composites proposed by Lewis for meeting advanced aeropropulsion requirements. The fabrication process currently being used at Lewis to produce intermetallic matrix composites will be reviewed, and the properties of one such composite, SiC/Ti3Al+Nb, will be presented. In addition, the direction of future research will be outlined, including plans for enhanced fabrication of aluminide composites by the arc spray technique and fiber development by the floating-zone process.

Brindley, Pamela K.↗

NASA NTRS1987

Composite materials for rail transit systems

The potential is explored for using composite materials in urban mass transit systems. The emphasis was to identify specific advantages of composite materials in order to determine their actual and potential usage for carbody and guideway structure applications. The literature was reviewed, contacts were made with major domestic system operators, designers, and builders, and an analysis was made of potential composite application to railcar construction. Composites were found to be in use throughout the transit industry, usually in secondary or auxiliary applications such as car interior and nonstructural exterior panels. More recently, considerable activity has been initiated in the area of using composites in the load bearing elements of civil engineering structures such as highway bridges. It is believed that new and improved manufacturing refinements in pultrusion and filament winding will permit the production of beam sections which can be used in guideway structures. The inherent corrosion resistance and low maintenance characteristics of composites should result in lowered maintenance costs over a prolonged life of the structure.

Griffin, O. Hayden, Jr.↗

NASA NTRS1988

Creep behavior of tungsten/niobium and tungsten/niobium-1 percent zirconium composites

The creep behavior and microstructural stability of tungsten fiber reinforced niobium and niobium 1 percent zirconium was determined at 1400 and 1500 K in order to assess the potential of this material for use in advanced space power systems. The creep behavior of the composite materials could be described by a power law creep equation. A linear relationship was found to exist between the minimum creep rate of the composite and the inverse of the composite creep rupture life. The composite materials had an order of magnitude increase in stress to achieve 1 percent creep strain and in rupture strength at test temperatures of 1400 and 1500 K compared to unreinforced material. The composite materials were also stronger than the unreinforced materials by an order of magnitude when density was taken into consideration. Results obtained on the creep behavior and microstructural stability of the composites show significant potential improvement in high temperature properties and mass reduction for space power system components.

Petrasek, Donald W.↗

NASA NTRS1988

Computational simulation methods for composite fracture mechanics

Structural integrity, durability, and damage tolerance of advanced composites are assessed by studying damage initiation at various scales (micro, macro, and global) and accumulation and growth leading to global failure, quantitatively and qualitatively. In addition, various fracture toughness parameters associated with a typical damage and its growth must be determined. Computational structural analysis codes to aid the composite design engineer in performing these tasks were developed. CODSTRAN (COmposite Durability STRuctural ANalysis) is used to qualitatively and quantitatively assess the progressive damage occurring in composite structures due to mechanical and environmental loads. Next, methods are covered that are currently being developed and used at Lewis to predict interlaminar fracture toughness and related parameters of fiber composites given a prescribed damage. The general purpose finite element code MSC/NASTRAN was used to simulate the interlaminar fracture and the associated individual as well as mixed-mode strain energy release rates in fiber composites.

Murthy, Pappu L. N.↗

NASA NTRS1988

Evaluation of a thermoplastic polyimide (422) for bonding GR/PI composite

A hot-melt processable copolyimide previously studied and characterized as an adhesive for bonding Ti-6Al-4V was used to bond Celion 6000/LARC-160 composite. Comparisons are made for the two adherend systems. A bonding cycle was determined for the composite bonding and lap shear specimens were prepared which were thermally exposed in a forced-air oven for up to 5000 h at 204 C. The lap shear strengths (LSSs) were determined at RT, 177, and 204 C. After thermal exposure at RT, 177, and 204 C the LSS decreased significantly; however, a slight increase was noted for the 204 C tests. Initially the LSS values are higher for the bonded Ti-6Al-4V than for the bonded composite, however, the LSS decreases dramatically between 5000 and 10,000 h of 204 C thermal exposure. Longer periods of thermal exposure up to 20,000 h results in further decreases in the LSSs. Although the bonded composite retained useful strengths for exposures up to 5000 h, based on the poor results of the bonded Ti-6Al-4V beyond 5000 h, the 422 adhesive bonded composites would most likely also produce poor strengths beyond 5000 h exposure. Adhesive bonded composite lap shear specimens exposed to boiling water for 72 h exhibited greatly reduced strengths at all test temperatures. The percent retained after water boil for each test temperature was essentially the same for both systems.

Progar, Donald J.↗

NASA NTRS1988

Thermo-viscoelastic analysis of composite materials, volume 1

Advanced composite materials, especially graphite/epoxy, are being applied to aircraft structures in order to improve performance and save weight. An important consideration in composite design is the residual strength of a structure containing holes, delaminations, or interlaminar damage when subjected to compressive loads. Recent studies have revealed the importance of viscoelastic effects in polymer-based composites. The viscoelastic effect is particularly significant at elevated temperature/moisture conditions since the matrix material is strongly affected by the environment. The solution of viscoelastic problems in composites was limited to special cases which can be solved by classical lamination theory. A finite element procedure is presented for calculating time-dependent stresses and strains in composite structures with general configurations and complicated boundary conditions. Using this procedure the in-plane and interlaminar stress distributions and histories in notched and unnotched composites were obtained for mechanical and thermal loads. Both two-dimensional and three-dimensional viscoelastic problems are analyzed. The effects of layup orientation and load spectrum on creep response and stress relaxation were also studied.

Lin, K. Y.↗

NASA NTRS1988

Properties of silicon carbide fiber-reinforced silicon nitride matrix composites

The mechanical properties of NASA Lewis developed SiC/RBSN composites and their thermal and environmental stability havd been studied. The composites consist of nearly 30 vol pct of aligned 142 micron diameter chemically vapor-deposited SiC fibers in a relatively porous silicon nitride matrix. In the as-fabricated condition, the unidirectional and 2-D composites exhibited metal-like stress-strain behavior, graceful failure, and showed improved properties when compared with unreinforced matrix of comparable density. Furthermore, the measured room temperature tensile properties were relativley independent of tested volume and were unaffected by artifical notches normal to the loading direction or by thermal shocking from temperatures up to 800 C. The four-point bend strength data measured as a function of temperature to 1400 C in air showed that as-fabricated strength was maintained to 1200 C. At 1400 C, however, nearly 15 pct loss in strength was observed. Measurement of room temperature tensile strength after 100 hr exposure at temperatures to 1400 C in a nitrogen environment indicated no loss from the as-fabricated composite strength. On the other hand, after 100 hr exposure in flowing oxygen at 1200 and 1400 C, the composites showed approximately 40 pct loss from their as-fabricated ultimate tensile strength. Those exposed between 400 to 1200 C showed nearly 60 pct strength loss. Oxidation of the fiber/matrix interface as well as internal oxidation of the porous Si3N4 matrix are likely mechanisms for strength degradation. The excellent strength reproducibility, notch insensitivity, and high temperature strength of the composite makes it an ideal candidate for advanced heat engine applications provided coating or densification methods are developed to avoid internal oxidation attack.

Bhatt, Ramakrishna T.↗

NASA NTRS1988

A sintering model for SiC(sub)w/Si3N4 composites

Presented is a model which suggests that it should be possible to pressureless sinter a SiC(sub w)/ Si3N4 composite to theoretical density. Prior failure to achieve complete densification by sintering is attributed to the use of compositions which result in a glass deficit. There is one basic premise for this model. The ratio of glass amount to surface area of nonglass constituents must be the same for both composite and sinterable monolithic Si3N4. This model suggests that whisker and grain sizes and whisker loading influence the glass amount necessary for successful sintering of composites. According to the model, a large glass amount will be necessary for successful sintering of these composites. However, grain boundary thicknesses in the composite will be less than those in the analogous monolithic materials. This suggests that good high temperature strength may still be attained. A recent report supports the predictions of the model.

Freedman, Marc R.↗

NASA NTRS1989

Composite blade structural analyzer (COBSTRAN) user's manual

The installation and use of a computer code, COBSTRAN (COmposite Blade STRuctrual ANalyzer), developed for the design and analysis of composite turbofan and turboprop blades and also for composite wind turbine blades was described. This code combines composite mechanics and laminate theory with an internal data base of fiber and matrix properties. Inputs to the code are constituent fiber and matrix material properties, factors reflecting the fabrication process, composite geometry and blade geometry. COBSTRAN performs the micromechanics, macromechanics and laminate analyses of these fiber composites. COBSTRAN generates a NASTRAN model with equivalent anisotropic homogeneous material properties. Stress output from NASTRAN is used to calculate individual ply stresses, strains, interply stresses, thru-the-thickness stresses and failure margins. Curved panel structures may be modeled providing the curvature of a cross-section is defined by a single value function. COBSTRAN is written in FORTRAN 77.

Aiello, Robert A.↗

NASA NTRS1988

Evaluation of a thermoplastic polyimide (422) for bonding GR/PI composite

A hot-melt processable copolyimide previously studied and characterized as an adhesive for bonding Ti-6Al-4V was used to bond Celion 6000/LARC-160 composite. Comparisons are made for the two adherend systems. A bonding cycle was determined for the composite bonding and lap shear specimens were prepared which were thermally exposed in a forced-air oven for up to 5000 h at 204 C. The lap shear strengths (LSSs) were determined at RT, 177, and 204 C. After thermal exposure at RT, 177, and 204 C the LSS decreased significantly; however, a slight increase was noted for the 204 C tests. Initially the LSS values are higher for the bonded Ti-6Al-4V than for the bonded composite, however, the LSS decreases dramatically between 5000 and 10,000 h of 204 C thermal exposure. Longer periods of thermal exposure up to 20,000 h results in further decreases in the LSSs. Although the bonded composite retained useful strengths for exposures up to 5000 h, based on the por results of the bonded Ti-6Al-4V beyond 5000 h, the 422 adhesive bonded composites would most likely also produce poor strengths beyond 5000 h exposure. Adhesive bonded composite lap shear specimens exposed to boiling water for 72 h exhibited greatly reduced strengths at all test temperatures. The percent retained after water boil for each test temperature was essentially the same for both systems.

Progar, Donald J.↗