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At least 901 records · Page 50
All sourcesNASA NTRSDOE OSTI
NASA NTRS1976

Evaluation of hybrid composite materials in cylindrical specimen geometries

Static and fatigue properties of three composite materials and hybrids were examined. The materials investigated were graphite/epoxy, S-glass/epoxy, PRD-49 (Kevlar 49)/epoxy, and hybrids in angle-ply configurations. A new type of edgeless cylindrical specimen was developed. It is a flattened tube with two flat sides connected by curved sections and it is handled much like the standard flat coupon. Special specimen fabrication, tabbing, and tab region reinforcing techniques were developed. Axial modulus, Poisson's ratio, strength, and ultimate strain were obtained under static loading from flattened tube specimens of nine laminate configurations. In the case of graphite/epoxy the tubular specimens appeared to yield somewhat higher strength and ultimate strain values than flat specimens. Tensile fatigue tests were conducted with all nine types of specimens and S-N curves obtained. Specimens surviving 10 million cycles of tensile loading were subsequently tested statically to failure to determine residual properties.

Liber, T.↗
NASA NTRS1988

The 700 F properties of autoclave cured PMR-2 composites

Studies were conducted to develop autoclave processing parameters for graphite reinforced PMR-2 resin composite materials intended for use in applications at temperatures up to 371 degrees (700 F). The effect of resin composition on autoclaveability was investigated. The effect of various graphite fibers and resin composition on 343 C (650 F) and 371 C (700 F) thermo-oxidative stability and mechanical properties was also investigated. The results of the processing studies show that PMR-2 resin composites can be easily fabricated under autoclave conditions. Autoclaved laminates exposed to 1 atm of air at 343 C (650 F) and 371 C (700 F) exhibited less than 5 percent weight loss after 750 hr exposure to 650 F air and 8 percent weight loss during exposure to 700 F air for 500 hr. After 500 hr exposure, autoclaved laminates exhibited greater than 90 percent retention of initial 650 and 700 F flexural and interlaminar shear strengths. The effect of resin formulated molecular weight and postcure conditions on laminate glass transition temperature is also discussed.

Vannucci, Raymond D.↗
NASA NTRS2014

Achieving ICME with Multiscale Modeling: The Effects of Constituent Properties and Processing on the Performance of Laminated Polymer Matrix Composite Structures

Integrated computational materials engineering (ICME) is a useful approach for tailoring the performance of a material. For fiber-reinforced composites, not only do the properties of the constituents of the composite affect the performance, but so does the architecture (or microstructure) of the constituents. The generalized method of cells is demonstrated to be a viable micromechanics tool for determining the effects of the microstructure on the performance of laminates. The micromechanics is used to predict the inputs for a macroscale model for a variety of different fiber volume fractions, and fiber architectures. Using this technique, the material performance can be tailored for specific applications by judicious selection of constituents, volume fraction, and architectural arrangement given a particular manufacturing scenario

computational mechanics↗
NASA NTRS1985

PMR polyimides from solutions containing mixed endcaps

Previous studies have shown that partial substitution of p-aminostyrene (PAS) for the monomethylester of endo-5-norbornene-2, 3-dicarboxylic acid (NE) lowered the cure temperature of PMR polyimides from 316 to 260 C, but the modified PMR polyimides required higher compression-molding pressures than state-of-the-art PMR-15. In this study PMR polyimides are prepared employing three encaps: NE, PAS, and endo-N-phenyl-5-norbornene-2,3-dicarboximide (PN). The effect of PN addition on the processing characteristics and glass transition temperatures of graphite fiber-reinforced PMR composites is studied. The room temperature and short-time 316 C mechanical properties of the composites are determined. The weight loss and mechanical property retention characteristics of the composites after exposure in air at 316 C are also determined.

Delvigs, P.↗
NASA NTRS1989

An evaluation of the interfacial bond properties between carbon phenolic and glass phenolic composites

The effects of moisture and surface finish on the mechanical and physical properties of the interfacial bond between the carbon/phenolic (C/P) and glass/phenolic (G/P) composite materials are presented. Four flat panel laminates were fabricated using the C/P and G/P materials. Of the four laminates, one panel was fabricated in which the C/P and G/P materials were cured simultaneously. It was identified as the cocure. The remaining laminates were processed with an initial simultaneous cure of the three C/P billets. Two surface finishes, one on each half, were applied to the top surface. Prior to the application and cure of the G/P material to the machined surface of the three C/P panels, each was subjected to the specific environmental conditioning. Types of conditioning included: (1) nominal fabrication environment, (2) a prescribed drying cycle, and (3) a total immersion in water at 160 F. Physical property tests were performed on specimens removed from the C/P materials of each laminate for determination of the specific gravity, residual volatiles and and resin content. Comparisons of results with shuttle solid rocket motor (SRM) nozzle material specifications verified that the materials used in fabricating the laminates met acceptance criteria and were representative of SRM nozzle materials. Mechanical property tests were performed at room temperature on specimens removed from the G/P, the C/P and the interface between the two materials for each laminate. The double-notched shear strength test was used to determine the ultimate interlaminar shear strength. Results indicate no appreciable difference in the C/P material of the four laminates with the exception of the cocure laminate, where 20 percent reduction in the strength was observed. The most significant effect and the ultimate strength was significantly reduced in the wet material. No appreciable variation was noted between the surface finishes in the wet laminate.

Jordan, Kelvin↗
NASA NTRS1991

Evaluation of the interfacial bond properties between carbon phenolic and glass phenolic composites

The effects of moisture and surface finish on the mechanical and physical properties of the interfacial bond between carbon/phenolic (C/P) and glass/phenolic (G/P) composite materials have been studied. Test results indicate that moisture substantially degrades the integrity of the interfacial bond between C/P and G/P materials. The apparent effect of the autoclave curing of the C/P material reduces the ultimate interlaminar shear length of the C/P material by 20 percent compared to the hydroclave curing of the C/P material. The variation in applied surface finishes is found to have no appreciable effect on the ultimate interlaminar shear strength of the interface in the wet laminate.

Jordan, K.↗
NASA NTRS1994

Continuous unidirectional fiber reinforced composites: Fabrication and testing

The study of the anisotropic mechanical properties of an inexpensively fabricated composite with continuous unidirectional fibers and a clear matrix was investigated. A method has been developed to fabricate these composites with aluminum fibers and a polymer matrix. These composites clearly demonstrate the properties of unidirectional composites and cost less than five dollars each to fabricate.

Weber, M. D.↗
NASA NTRS1983

Dynamic Mechanical Properties of N-Phenylnadimide Modified PMR Polyimide Composites

The rheological behavior of newly developd Celion 6000/N-phenylnadimide modified PMR polyimide and PMR-15 composites was investigated. The dynamic mechanical properties were correlated with the structure of N-phenylnadimide modified PMR polyimides. The storage modulus (G'), loss modulus (G''), and loss tangent (tan delta) of four composite systems were measured over a temperature range from -150 to 400 C. Three well defined peaks were seen in the regions of 360, 100, and -120 C, corresponding to the alpha, beta, and gamma relaxations, respectively, of the matrix resins. The activation energies of the alpha, beta, and gamma relaxations were estimated to be 232, 60, and 14 kcal/mole, respectively, for PMR-15. Addition of N-phenylnadimide to the PMR-15 composition lowered the glass transition temperature and the activation energies of PMR-15 polyimide. The dynamic mechanical data appear to be consistent with the formation of a copolymer from N-phenylnadimide and a PMR-15 prepolymer.

Pater, R. H.↗
NASA NTRS1982

Long-term thermal degradation and alloying constituent effects on five boron/aluminum composites

Thermal exposure effects on the properties of five boron/aluminum composite systems were experimentally investigated. The composite systems were 49 volume percent boron fibers (203 micron diameter) in aluminum-alloy matrices 1100 Al, 2024 Al, 3003 Al, 5052 Al, and 6061 Al. Specimens were thermally exposed up to 10,000 hours at 500 K and 590 K, up to 500 hours at 730 K, and up to 10,000 hours at 500 K and 590 K, up to 500 hours at 730 K, and up to 2000 thermal cycles between 200 K and 590 K. Composite longitudinal and transverse tensile strengths, longitudinal compression strength, and in-plane shear strength were determined. None of the systems was severely degraded by exposure at 590 K. The best performing system was B-2024 Al. Effects of matrix alloys on degradation mechanisms were experimentally investigated. Composite specimens and individual fibers were metallurgically analyzed with a scanning electron microscope and an electron microprobe to determine failure characteristics, chemical element distribution, and reaction layer morphology. Alloying constituents were found to be affect the composite degradation mechanisms as follows: alloys containing iron, but without manganese as a stabilizer, caused increased low-temperature degradation; alloys containing magnesium, iron, or manganese caused increased degradation; and alloys containing copper caused increased fiber strength.

Olsen, G. C.↗
NASA NTRS1982

Thermodynamic and transport combustion properties of hydrocarbons with air. Part 1: Properties in SI units

Thermodynamic and transport combustion properties were calculated for a wide range of conditions for the reaction of hydrocarbons with air. Three hydrogen-carbon atom ratios (H/C = 1.7, 2.0, 2.1) were selected to represent the range of aircraft fuels. For each of these H/C ratios, combustion properties were calculated for the following conditions: Equivalence ratio: 0, 0.25, 0.5, 0.75, 1.0, 1.25 Water - dry air mass ratio: 0, 0.03 Pressure, kPa: 1.01325, 10.1325, 101.325, 1013.25, 5066.25 (or in atm: 0.01, 0.1, 1, 10, 50) Temperature, K: every 10 degrees from 200 to 900 K; every 50 degrees from 900 to 3000 K Temperature, R: every 20 degrees from 360 to 1600 R; very 100 degrees from 1600 to 5400 R. The properties presented are composition, density, molecular weight, enthalphy, entropy, specific heat at constant pressure, volume derivatives, isentropic exponent, velocity of sound, viscosity, thermal conductivity, and Prandtl number. Property tables are based on composites that were calculated by assuming both: (1) chemical equilibrium (for both homogeneous and heterogeneous phases) and (2) constant compositions for all temperatures. Properties in SI units are presented in this report for the Kelvin temperature schedules.

Gordon, S.↗
NASA NTRS1983

Interlaminar shear properties of graphite fiber, high-performance resin composites

Short beam testing was used to determine the shear properties of laminates consisting of T-300 and Celion 3000 and 6000 graphite fibers, in epoxy, hot melt and solvent bismaleimide, polyimide and polystyrylpyridine (PSP). Epoxy, composites showed the highest interlaminar shear strength, with values for all other resins being substantially lower. The dependence of interlaminar shear properties on the fiber-resin interfacial bond and on resin wetting characteristics and mechanical properties is investigated, and it is determined that the lower shear strength of the tested composites, by comparison with epoxy resin matrix composites, is due to their correspondingly lower interfacial bond strengths. An investigation of the effect of the wettability of carbon fiber tow on shear strength shows wetting variations among resins that are too small to account for the large shear strength property differences observed.

Needles, H. L.↗
NASA NTRS1983

Role of fiber/matrix interphase in carbon fiber-epoxy composite impact toughness

Experimental results were obtained which show the effect of the interphase on composite performance. Various finish variants were formulated, based on different chemical and mechanical properties and applied to Celion 6000 carbon fiber. Inerfacial bond strength and failure mechanisms were studied by single-filament critical length determination. Composite properties at room and elevated temperatures, both wet and dry, were measured. Impact toughness was evaluated with a Dynatup drop dart instrumented impact tester. A significant 30 percent increase in maximum penetration load was obtained by 'Interphase-tailoring' without significant loss in both conditioned and unconditioned composite properties.

Ying, L.↗
NASA NTRS1988

Future directions in meteorite research

Information presently available on meteorite composition and history and the areas in meteorite research that should be covered in future in order to shed additional light on the earliest history of the solar system are discussed. Attention is given to the work needed in the classification schemes for chondrites, the question of the identification of parent bodies of the major meteorite and chondrite types, the igneous differentiation of certain asteroids, the effects of irradiation, the solar-system chronology, and issues concerning the early solar system. Other important areas discussed include the elemental composition of chondrites, the magnetic properties of meteorites, the composition and the petrology of chondrules, the properties of primitive material surviving in chondrites, the micrometeorites, the nebula, the presolar material in meteorites, the nucleosynthesis, and the nucleocosmochronology.

Anders, E.↗
NASA NTRS2016

Multifunctional Hybrid Carbon Nanotube/Carbon Fiber Polymer Composites

For aircraft primary structures, carbon fiber reinforced polymer (CFRP) composites possess many advantages over conventional aluminum alloys due to their light weight, higher strengthand stiffness-to-weight ratio, and low life-cycle maintenance costs. However, the relatively low electrical and thermal conductivities of CFRP composites fail to provide structural safety in certain operational conditions such as lightning strikes. Despite several attempts to solve these issues with the addition of carbon nanotubes (CNT) into polymer matrices, and/or by interleaving CNT sheets between conventional carbon fiber (CF) composite layers, there are still interfacial problems that exist between CNTs (or CF) and the resin. In this study, hybrid CNT/CF polymer composites were fabricated by interleaving layers of CNT sheets with Hexcel® IM7/8852 prepreg. Resin concentrations from 1 wt% to 50 wt% were used to infuse the CNT sheets prior to composite fabrication. The interlaminar properties of the resulting hybrid composites were characterized by mode I and II fracture toughness testing (double cantilever beam and end-notched flexure test). Fractographical analysis was performed to study the effect of resin concentration. In addition, multi-directional physical properties like thermal conductivity of the orthotropic hybrid polymer composite were evaluated. Interleaving CNT sheets significantly improved the in-plane (axial and perpendicular direction of CF alignment) thermal conductivity of the hybrid composite laminates by 50 - 400%.

Kang, Jin Ho↗
NASA NTRS1971

Thermodynamic properties and theoretical rocket performance of hydrogen to 100,000 K and 1.01325 x 10 to the 8th power N/sq m

The composition and thermodynamic properties were calculated for 100 to 110,000 K and 1.01325 x 10 to the 2nd power to 1.01325 x 10 to the 8th power N/sq m for chemical equilibrium in the Debye-Huckel and ideal-gas approximations. Quantities obtained were the concentrations of hydrogen atoms, protons, free electrons, hydrogen molecules, negative hydrogen ions, hydrogen diatomic molecular ions, and hydrogen triatomic molecular ions, and the enthalpy, entropy, average molecular weight, specific heat at constant pressure, density, and isentropic exponent. Electronically excited states of H and H2 were included. Choked, isentropic, one-dimensional nozzle flow with shifting chemical equilibrium was calculated to the Debye-Huckel and ideal-gas approximations for stagnation temperatures from 2500 to 100,000 K. The mass flow per unit throat area and the sonic flow factor were obtained. The pressure ratio, temperature, velocity, and ideal and vacuum specific impulses at the throat and for pressure ratios as low as 0.000001 downstream were found. For high temperatures at pressures approaching 1.01325 x 10 to the 8th power N/sq m, the ideal-gas approximation was found to be inadequate for calculations of composition, precise thermodynamic properties, and precise nozzle flow. The greatest discrepancy in nozzle flow occurred in the exit temperature, which was as much as 21 percent higher when the Debye-Huckel approximation was used.

Patch, R. W.↗