Search NASA⌕ Search

SEARCH · Search NASA

Results for “Modulus”

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.

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

At least 505 records · Page 28
All sourcesNASA NTRSDOE OSTI
NASA NTRS1992

Mechanical properties of brittle materials

Brittle materials are difficult to tensile test because of gripping problems. They either crack in conventional grips or they are crushed. Furthermore, they may be difficult to make into tensile specimens having, for example, threated ends or donut shapes. To overcome the problem, simple rectangular shapes can be used in bending (i.e., a simple beam) in order to obtain the modulus of rupture and the elastic modulus. The equipment necessary consists of a fixture for supporting the specimens horizontally at two points, these points contact points being rollers which are free to rotate. The force necessary to bend the specimen is produced by a tup attached to the crosshead of an Instron machine. Here, the experimental procedure is explained.

Cornwell, L. R.↗
NASA NTRS1992

Probabilistic assessment of space trusses subjected to combined mechanical and thermal loads

A three-bay, space, cantilever truss is probabilistically evaluated to quantify the range of uncertainties of buckling loads and member forces due to nonuniform thermal loads, applied loads and moments (mechanical loads), and combination of both. The truss members are assumed to be made from Aluminum tubes or high modulus graphite-fiber/intermediate modulus epoxy-matrix composite tubes. Cumulative distribution function results show that certain combinations of thermal loads with mechanical loads reduce the probabilistic buckling loads and increase the magnitude of the member axial forces for the aluminum truss. The same trend is observed for the composite truss as well, as however, the thermal effects on the probabilistic buckling loads and member axial forces are not as substantial as that for an aluminum truss. This can be attributed to the large differences in the values of coefficient of thermal expansion. Finally, the sensitivities associated with the uncertainties in the structural, material, and load variables (primitive variables) are investigated. They show that buckling loads and member axial forces are most sensitive to the uncertainties in spacial (geometry) variables.

Pai, Shantaram S.↗
NASA NTRS1991

Polymer blends for LDB applications

A series of LCP/PE blends have been studied to determine the potential of such systems to produce a high modulus balloon film material which retains the balloon fabrication and low temperature flight advantages of the current PE films. Blown films of blends of 5 and 15 percent LCP in PE have been produced which show a 28 percent enhancement in modulus over the neat PE matrix. These results are substantially lower than anticipated and are explained in terms of the LCP reinforcement aspect ratio and fibril diameter.

Lichkus, Andrew M.↗
NASA NTRS1992

Environmental effects on the compressive properties - Thermosetting vs. thermoplastic composites

The influence of moisture and temperature on the compressive properties of graphite/epoxy and APC-2 materials systems was investigated to assess the viability of using APC-2 instead of graphite/epoxy. Data obtained indicate that the moisture absorption rate of T-300/epoxy is higher than that of APC-2. Thick plate with smaller surface area absorbs less moisture than thin plate with larger surface area. The compressive strength and modulus of APC-2 are higher than those of T-300/epoxy composite, and APC-2 sustains higher compressive strength in the presence of moisture. The compressive strength and modulus decrease with the increase of temperature in the range of 23-100 C. The compression failure was in the form of delamination, interlaminar shear, and end brooming.

Haque, A.↗
NASA NTRS1992

Anodized aluminum coatings for thermal control. II - Environmental effects and cracking

The environmental effects of thermal cycling and humidity on coating cracking are examined. Experimental measurements of thermal deflection were used to calculate values for the thermal expansion coefficient and the in situ elastic modulus of an anodized aluminum. The thermal expansion coefficient is found to be approximately the same as for alumina in bulk form. The modulus in atmospheres with less than 100 ppm water is about 12,500 ksi. Two sets of experiments are used to study cracking directly during thermal excursions: one determines the minimum temperature (Tc) at which cracks first appear during a single heating cycle and the other involves rapid thermal cycling (RTC) between fixed T max and T min values. Fatigue models for describing initiation of the first crack and the development of multiple cracking are presented, which can be used as the basis for prediction of LEO cracking.

Mcclung, R. C.↗
NASA NTRS1991

Tension, Compression, and Bend Properties for Sic/RBSN Composites

The room-temperature tension, compression, and bend properties of unidirectional SiC fiber-reinforced reaction-bonded silicon nitride composites (SiC/RBSN) have been investigated. The effects of fiber content on the modulus, first matrix cracking strength, and ultimate strength properties were determined. In tension, composites with greater than 8-percent fiber content showed strain capability beyond matrix fracture and fiber-dominated ultimate strength. In compression, the composites displayed essentially elastic behavior, and matrix-dominated ultimate strength. For both deformation modes, most mechanical properties increased with fiber content. In bend, the modulus, strength properties, and failure modes of the composites were influenced by span-to-thickness ratio.

Bhatt, Ramakrishna T.↗
NASA NTRS1992

Compression failure mechanisms of single-ply, unidirectional, carbon-fiber composites

A single-ply composite compression test was used to study compression failure mechanisms as a function of fiber type, matrix type, and interfacial strength. Composites made with low- and intermediate-modulus fibers (Hercules AS4 and IM7) in either an epoxy (Hercules 3501-6) or a thermoplastic (ULTEM and LARC-TPI) matrix failed by kink banding and out-of-plane slip. The failures proceeded by rapid and catastrophic damage propagation across the specimen width. Composites made with high-modulus fibers (Hercules HMS4/3501-6) had a much lower compression strength. Their failures were characterized by kink banding and longitudinal splitting. The damage propagated slowly across the specimen width. Composites made with fibers treated to give low interfacial strength had low compression strength. These composites typically failed near the specimen ends and had long kink bands.

Ha, Jong-Bae↗
NASA NTRS1992

Nonuniform thermal environmental effects on space truss structural reliability

A three-bay, space, cantilever truss is probabilistically evaluated to quantify the range of uncertainties of buckling loads and member forces due to nonuniform thermal loads, applied loads and moments (mechanical loads), and combination of both. The truss members are assumed to be made from (1) aluminum tubes or (2) high modulus graphite-fiber/intermediate modulus epoxy-matrix composite tubes. Cumulative distribution function results show that certain combinations of thermal loads with mechanical loads reduce the probabilistic buckling loads and increase the magnitude of the member axial forces for aluminum truss. However, the reverse is true for composite truss due to very low coefficient of thermal expansion and higher stiffness of the composite. Finally, the sensitivities associated with the uncertainties in the structural, material, and load variables (primitive variables) are investigated. They show that buckling loads and member axial forces are most sensitive to the uncertainties in spacial (geometry) variables.

Pai, Shantaram S.↗
NASA NTRS1992

Map-based trigonometric parallaxes of open clusters. II - The Hyades: 51 Tauri

The trigonometric parallax, mass, and mass ratio of 51 Tauri, a binary member of the Hyades star cluster, are determined. The parallax solution, 19.4 mas with a standard error of 1.1 mas, is slightly greater than its generally accepted value and yields a cluster distance of 4.30 +/-2.0 pc or a distance modulus equivalent of 3.16 +/- 0.10 mag, in excellent agreement with recent photographic parallax results. The weighted mean of all trigonometric parallax determinations of the cluster is now 22.9 +/-0.6 mas or a modulus of 3.20 +/- 0.06 mag. The total mass of the 51 Tauri system was found to be 2.56 +/- 0.44 solar masses. Adopting a magnitude difference in line with the spectral types of the components yields individual masses of 1.61 +/- 0.28 and 0.95 +/- 0.18 solar masses. This result places the mass of both the A8 V primary and the G0 secondary stars within the errors of the measurement of the mass-luminosity relation established for solar-neighborhood main-sequence stars.

Gatewood, George↗
NASA NTRS1992

Mechanical properties of 3C silicon carbide

The residual stress and Young's modulus of 3C silicon carbide (SiC) epitaxial films deposited on silicon substrates were measured by load-deflection measurements using suspended SiC diaphragms fabricated with silicon micromachining techniques. The film's residual stress was tensile and averaged 274 MPa while the in-plane Young's modulus averaged 394 GPa. In addition, the bending moment due to the residual stress variation through the thickness of the film was determined by measuring the deflection of free-standing 3C-SiC cantilever beams. The bending moment was in the range of 2.6 x 10 exp -8 -4.2 x 10 exp-8 N m.

Tong, Lijun↗
NASA NTRS1992

Characterization of unnotched SCS-6/Ti-15-3 metal matrix composites at 650 C

Ti-15-3 reinforced with SCS-6 silicon carbide fibers, in five different layups, was tested at 650 C to determine monotonic and fatigue strengths, basic mechanical properties, and damage initiation and progression. The elevated temperature results were compared to those obtained at room temperature. Analytical predictions were made of the monotonic stress-strain response as well as cyclic stress-strain hysteresis. The fiber reinforcement was found to significantly increase the static and fatigue strengths of the laminates over that of the matrix material at elevated temperature while the increase was insignificant at room temperature. Initial damage, in either the fibers or the matrix, was partitioned as a function of the life and applied strain range in the constituents. High strains and short lives resulted in multiple fiber failure with no signs of matrix fatigue cracking. Low strains and long lives resulted in extensive matrix cracking and no fiber breaks away from the fracture surface. At 650 C the matrix was too weak to cause fiber-matrix interface failure prior to matrix yielding. Laminate fatigue lives were hypothesized to be a function of the 0 deg fiber stress. More scatter was found in the 0 deg fiber stress vs. high temperature fatigue life data than for the room temperature data. An initial unloading modulus that was greater than the initial loading modulus was observed in the elevated temperature fatigue tests.

Pollock, William D.↗
NASA NTRS1992

RR Lyrae stars in Local Group galaxies. IV - IC 1613

Deep charge-coupled device images of a field in IC 1613 away from the star forming central regions were taken with the '4-shooter' on the Hale 5 m telescope, and processed to find photometrically measure variable stars. Fifteen RR Lyrae stars were found, and periods, light curves, and finding charts for them are presented. The mean magnitude of RR Lyrae stars in this galaxy is deduced to be 24.90 mag. Assuming the absolute g magnitude for RR Lyraes to be Mg = 0.73 mag, and using extinction Ag = 0.07 mag, a distance modulus of 24.10 +/- 0.27 mag is derived. The finding of RR Lyrae stars indicates the unambiguous presence of an old population. The distance modulus derived from them is smaller than that derived from the Cepheids by an amount which is dependent upon the RR Lyrae zero-point calibration adopted, and may be as large as 0.3 mag. The difference has the same sense and magnitude as the discrepancy in the LMC. The probable sources of the problem are discussed.

Saha, A.↗
NASA NTRS1992

Physical properties of concrete made with Apollo 16 lunar soil sample

This paper describes the first phase of the long-term investigation for the construction of concrete lunar bases. In this phase, petrographic and scanning electron microscope examinations showed that the morphology and elemental composition of the lunar soil made it suitable for use as a fine aggregate for concrete. Based on this finding, calcium aluminate cement and distilled water were mixed with the lunar soil to fabricate test specimens. The test specimens consisted of a 1-in cube, a 1/2-in cube, and three 0.12 x 0.58 x 3.15-in beam specimens. Tests were performed on these specimens to determine compressive strength, modulus of rupture, modulus of elasticity, and thermal coefficient of expansion. Based on examination of the material and test results, it is concluded that lunar soil can be used as a fine aggregate for concrete.

Lin, T. D.↗
NASA NTRS1988

The development of new, low-cost perfluoroalkylether fluids with excellent low and high-temperature properties

A series of perfluoroalkylether (PFAE) fluids were synthesized by direct fluorination. Viscosity-temperature properties, oxidation stabilities, oxidation-corrosion properties, and lubricity were determined. The fluids were tested in the presence of common elastomers to check for compatibility. The bulk modulus of each was measured to determine if any could be used as nonflammable aircraft hydraulic fluid. It was determined that as the carbon to oxygen ratio decreases, the viscometric properties improve, the fluids may become poor lubricants, the bulk modulus increases, the surface tension increases, and the fluid density increases. The presence of difluoromethylene oxide units in the polymer does not seriously lower the oxidation and oxidation-corrosion stabilities as long as the difluoromethylene oxide units are separated by other units.

Bierschenk, Thomas R.↗
NASA NTRS1993

Internal strain analysis of ceramics using scanning laser acoustic microscopy

Quantitative studies of material behavior characteristics are essential for predicting the functionality of a material under its operating conditions. A nonintrusive methodology for measuring the in situ strain of small dimeter (to 11 microns) ceramic fibers under uniaxial tensile loading and the local internal strains of ceramics and ceramic composites under flexural loading is introduced. The strain measurements and experimentally observed mechanical behavior are analyzed in terms of the microstructural development and fracture behavior of each test specimen evaluated. Measurement and analysis of Nicalon silicon carbide (SiC) fiber (15 microns diameter) indicate that the mean elastic modulus of the individual fiber is 185.3 GPa. Deviations observed in the experimentally determined elastic modulus values between specimens were attributed to microstructural variations which occur during processing. Corresponding variations in the fracture surface morphology were also observed. The observed local mechanical behavior of a lithium alumino-silicate (LAS) glass ceramic, a LAS/SiC monofilament composite, and a calcium alumino-silicate (CAS)/SiC fully reinforced composite exhibits nonlinearities and apparent hysteresis due to the subcritical mechanical loading. Local hysteresis in the LAS matrices coincided with the occurrence of multiple fracture initiation sites, localized microcracking, and secondary cracking. The observed microcracking phenomenon was attributed to stress relaxation of residual stresses developed during processing, and local interaction of the crack front with the microstructure. The relaxation strain and stress predicted on apparent mechanical hysteresis effects were defined and correlated with the magnitude of the measured fracture stress for each specimen studied. This quantitative correlation indicated a repeatable measure of the stress at which matrix microcracking occurred for stress relief of each material system. Stress relaxation occurred prior to the onset of steady state cracking conditions. The relaxation stress occurred at 18.5 percent of the fracture stress in LAS and 11.0 percent of the yield stress in CAS/SiC. The relaxation stress ratio was dependent upon the dominant fracture mode of the LAS/SiC specimens. Relaxation stress ratios greater than 0.30 were observed for specimens which fractured due to shear at the fiber matrix interface; specimens which fracture due to tensile cracking had relaxation stress ratios less than 0.30. The stress relaxation ratio appeared to be a specific characteristic of the glass ceramic material. The measured stress relaxation for LAS indicated a measure of the inherent residual stresses in the material due to processing and suggested localized toughening mechanisms for brittle material structures.

Kent, Renee M.↗
NASA NTRS1993

Dynamic Hardness Tester and Cure Meter

The Shore hardness tester is used extensively throughout industry to determine the static modulus of materials. The new apparatus described here extends the capability of an indentor-type tester into the dynamic regime, and provides a measurement of the dynamic shear or Young's modulus and loss factor as a function of frequency. The instrument, model and data of typical rubber samples are given and compared to other dynamic measurements.

Madigosky, Walter M.↗
NASA NTRS1991

Combined micromechanical and fabrication process optimization for metal-matrix composites

A method is presented to minimize the residual matrix stresses in metal matrix composites. Fabrication parameters such as temperature and consolidation pressure are optimized concurrently with the characteristics (i.e., modulus, coefficient of thermal expansion, strength, and interphase thickness) of a fiber-matrix interphase. By including the interphase properties in the fabrication process, lower residual stresses are achievable. Results for an ultra-high modulus graphite (P100)/copper composite show a reduction of 21 percent for the maximum matrix microstress when optimizing the fabrication process alone. Concurrent optimization of the fabrication process and interphase properties show a 41 percent decrease in the maximum microstress. Therefore, this optimization method demonstrates the capability of reducing residual microstresses by altering the temperature and consolidation pressure histories and tailoring the interphase properties for an improved composite material. In addition, the results indicate that the consolidation pressures are the most important fabrication parameters, and the coefficient of thermal expansion is the most critical interphase property.

Morel, M.↗
NASA NTRS1993

Multichannel astrometric photometer parallax studies in the regions of Groombridge 1618, Zeta Bootis, and Sigma Draconis

Improved trigonometric parallaxes are reported for stars in the regions of Groombridge 1618, Zeta Bootis, and Sigma Draconis which differ from generally accepted parallaxes by two to five standard deviations. The weighted mean parallax of Groombridge 1618 becomes 0.2079 +/- 0.0013 arcsec, indicating a distance modulus of -1.59 +/- 0.014 and yielding an absolute magnitude of this K7 V star of 8.20 +/- 0.017. The parallax determined for the visual binary Zeta Bootis is 0.0202 +/- 0.0010 arcsec and implies an average absolute visual magnitude of 1.067 +/- 0.12 for the spectroscopically similar components. The weighted mean parallax of Sigma Draconis becomes 0.1747 +/- 0.0010 arcsec, indicating a distance modulus of -1.210 +/- 0.012 and yielding an absolute visual magnitude of 5.90 +/- 0.012 for this K0 V star. The absolute visual magnitudes of the high velocity star Roman 336 and of the subdwarf star AO 1187 are found to be + 4.0 +/- 0.13 and + 5.9 +/- 0.17, respectively.

Gatewood, George↗