Search NASA⌕ Search

SEARCH · Search NASA

Results for “MA”

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 217 records · Page 12
All sourcesNASA NTRSDOE OSTI
NASA NTRS1981

Creep and residual mechanical properties of cast superalloys and oxide dispersion strengthened alloys

Tensile, stress-rupture, creep, and residual tensile properties after creep testing were determined for two typical cast superalloys and four advanced oxide dispersion strengthened (ODS) alloys. The superalloys examined included the nickel-base alloy B-1900 and the cobalt-base alloy MAR-M509. The nickel-base ODS MA-757 (Ni-16CR-4Al-0.6Y2O3 and the iron-base ODS alloy MA-956 (Fe-20Cr-5Al-0.8Y2O3) were extensively studied, while limited testing was conducted on the ODS nickel-base alloys STCA (Ni-16Cr-4.5Al-2Y2O3) with a without Ta and YD-NiCrAl (Ni-16Cr-5Al-2Y2O3). Elevated temperature testing was conducted from 114 to 1477 K except for STCA and YD-NiCrAl alloys, which were only tested at 1366 K. The residual tensile properties of B-1900 and MAR-M509 are not reduced by prior creep testing (strains at least up to 1 percent), while the room temperature tensile properties of ODS nickel-base alloys can be reduced by small amounts of prior creep strain (less than 0.5 percent). The iron-base ODS alloy MA-956 does not appear to be susceptible to creep degradation at least up to strains of about 0.25 percent. However, MA-956 exhibits unusual creep behavior which apparently involves crack nucleation and growth.

Whittenberger, J. D.↗
NASA NTRS1979

Development program on a cold cathode electron gun

A prototype electron gun with a field emitter cathode capable of producing 95 mA in a 1/4 mm diameter beam at 12 kV was produced. Achievement of this goal required supporting studies in cathode fabrication, cathode performance, gun design, cathode mounting and gun fabrication. A series of empirical investigations advanced fabrication technology: More stable emitters were produced and multiple cone failure caused by chain reaction discharges were reduced. The cathode is capable of producing well over 95 mA, but a substantial collector development effort was required to demonstrate emission levels in the 100 mA region. Space charge problems made these levels difficult to achieve. Recommendations are made for future process and materials investigation. Electron gun designs were modeled and tested. A pair of two-electrode gun structures were fabricated and tested; one gun was delivered to NASA. Cathodes were pretested up to 100 mA at SRI and delivered to NASA for test in the gun structure.

Spindt, C. A.↗
NASA NTRS1981

Advanced oxide dispersion strengthened sheet alloys for improved combustor durability

Burner design modifications that will take advantage of the improved creep and cyclic oxidation resistance of oxide dispersion strengthened (ODS) alloys while accommodating the reduced fatigue properties of these materials were evaluated based on preliminary analysis and life predictions, on construction and repair feasibility, and on maintenance and direct operating costs. Two designs - the film cooled, segmented louver and the transpiration cooled, segmented twin Wall - were selected for low cycle fatigue (LCF) component testing. Detailed thermal and structural analysis of these designs established the strain range and temprature at critical locations resulting in predicted lives of 10,000 cycles for MA 956 alloy. The ODs alloys, MA 956 and HDA 8077, demonstrated a 167 C (300 F) temperature advantage over Hastelloy X alloy in creep strength and oxidation resistance. The MA 956 alloy was selected for mechanical property and component test evaluations. The MA 956 alloy was superior to Hastelloy X in LCF component testing of the film cooled, segmented louver design.

Henricks, R. J.↗
NASA NTRS1982

Development of powder metallurgy Al alloys for high temperature aircraft structural applications, phase 2

In this continuing study, the development of mechanically alloyed heat resistant aluminum alloys for aircraft were studied to develop higher strength targets and higher service temperatures. The use of higher alloy additions to MA Al-Fe-Co alloys, employment of prealloyed starting materials, and higher extrusion temperatures were investigated. While the MA Al-Fe-Co alloys exhibited good retention of strength and ductility properties at elevated temperatures and excellent stability of properties after 1000 hour exposure at elevated temperatures, a sensitivity of this system to low extrusion strain rates adversely affected the level of strength achieved. MA alloys in the Al-Li family showed excellent notched toughness and property stability after long time exposures at elevated temperatures. A loss of Li during processing and the higher extrusion temperature 482 K (900 F) resulted in low mechanical strengths. Subsequent hot and cold working of the MA Al-Li had only a mild influence on properties.

Chellman, D. J.↗
NASA NTRS1984

Fabrication development for ODS-superalloy, air-cooled turbine blades

MA-600 is a gamma prime and oxide dispersion strengthened superalloy made by mechanical alloying. At the initiation of this program, MA-6000 was available as an experimental alloy only and did not go into production until late in the program. The objective of this program was to develop a thermal-mechanical-processing approach which would yield the necessary elongated grain structure and desirable mechanical properties after conventional press forging. Forging evaluations were performed to select optimum thermal-mechanical-processing conditions. These forging evaluations indicated that MA-6000 was extremely sensitive to die chilling. In order to conventionally hot forge the alloy, an adherent cladding, either the original extrusion can or a thick plating, was required to prevent cracking of the workpiece. Die design must reflect the requirement of cladding. MA-6000 was found to be sensitive to the forging temperature. The correct temperature required to obtain the proper grain structure after recrystallization was found to be between 1010-1065 C (1850-1950 F). The deformation level did not affect subsequent crystallization; however, sharp transition areas in tooling designs should be avoided in forming a blade shape because of the potential for grain structure discontinuities. Starting material to be used for forging should be processed so that it is capable of being zone annealed to a coarse elongated grain structure as bar stock. This conclusion means that standard processed bar materials can be used.

Moracz, D. J.↗
NASA NTRS1985

Heat flow increase following the rise of mantle isotherms and crustal thinning

Heat flow measurements in the western United States define a zone of high heat flow which coincides with the Basin and Range Province where extension has taken place recently. In this region, the average reduced heat flow is approx 30 mW sq. meters higher than in stable continental provinces; locally (e.g., Battle Mountain High), the heat flow anomaly can be more than 100 mW/sq meters above average. Estimates of the amount of extension range between 30% and 100% for the past 30 Ma. In the Colorado Plateau, which has been uplifted without major tectonic deformation, the heat flow is only slightly above average. Analytical calculations show that an abrupt change in heat flow at the base of the lithosphere 30 Ma ago would not affect the surface significantly. Uplift would proceed at a slow rate. A thermal perturbation at the base of a 40 km thick crust, however, would reach the surface faster and, after 30 Ma, the increase in surface heat flow would be about 75% of the amplitude of the heat flow anomaly. The number of volcanic rocks in the Basin and Range suggests that magma intrusions may provide an effective heat transfer mechanism. It can be show that if the source of the intrusions is at the base of the lithosphere, the response time will be much longer than 30 Ma, and most ot the heat transferred from the asthenosphere will be absorbed in the lithosphere.

Mareschal, J. C.↗
NASA NTRS1986

Trends of Sr and Nd isotopes through time near the Japan Sea in northeastern Japan

Nd and Sr isotopic analyses were performed on selected volcanic rocks of 27-6 Ma age in the Green Tuff region of northeastern Japan, in adjacent areas, and in two ultramafic inclusions from Ichinomegata. The isotopic data plot generally along the region of the mantle array, and the volcanic rocks vary in epsilon(Nd) from -0.9 to 5.7, and in epsilon(Sr) from 14.1 to -16.3. It is found that the volcanic rocks are part of an evolutionary pattern over a time period of 27 Ma, and that the pattern goes from an initially enriched source to that of a very depleted source. A greater-than-15-Ma preopening stage, characterized by an enriched isotopic signature, and a less-than-15-Ma postopening stage, characterized by a depleted signature, are identified. It is suggested that the degree of continental crust involvement is high during the preopening stages of a back-arc basin when it is associated with a rifted continental mass.

Nohda, S.↗
NASA NTRS1987

Boundary effects on Marangoni-Rayleigh and morphological instabilities

Effects of boundaries (vertical sides) on the Marangoni-Rayleigh problem are reviewed. Spectral crowding and a dimensional singularity when Rayleigh effects are neglected are discussed. In the unbounded case, there is a unique Ma with unique eigenfunction for fixed Ra but infinite Ra for fixed Ma. These infinite values of Ra correspond to vertical cellular modes. In the bounded case, there is infinite Ma for a fixed Ra. The stress free side wall case gives double infinite of Ra for fixed Ma and wave number. Clearly, a dimensional singularity occurs for the Marangoni problem when the side walls go to infinity and a fixed Ra is considered. There is no direct analogy regarding this singularity in the morphological instability problem. Results on the behavior of Mac, Rac with boundary conditions also show only marginal connection to the morphological stability problem.

Narayanan, R.↗
NASA NTRS1988

Late-Archaean crustal growth in the Lewisian Complex of Northwest Scotland: Diachroneity in magmatic accretion and implications for models of crustal growth

The Lewisian Complex of northwestern Scotland is an Archaean basement terrain that was reworked during the Proterozoic. Previous geochronological studies have established that the complex represents an entirely new crustal addition during late-Archaean times, and the difference between a Sm-Nd accretion date of 2920 + or - 50 Ma and a Pb/Pb metamorphic date of 2680 + or - 70 Ma was interpreted as indicating a crustal accretion-differentiation superevent (CADS) lasting 240 + or - 110 Ma. A combined Rb-Sr, Pb/Pb, and Sm-Nd isotopic study reported was applied to the Lewisian CADS to attempt to address the problem of whether this comprised a short regional scale magmatic accretion event followed approximately 200 Ma later by regional high-grade metamorphism, or a long period of episodic or semi-continuous magmatic accretion prior to high-grade metamorphism.

Whitehouse, M. J.↗
NASA NTRS1992

Ar-40 to Ar-39 ages of the large impact structures Kara and Manicouagan and their relevance to the Cretaceous-Tertiary and the Triassic-Jurassic boundary

Since the discovery of the Ir enrichment in Cretaceous-Tertiary boundary clays in 1980, the effects of a 10-km asteroid impacting on the Earth 65 Ma ago have been discussed as the possible reason for the mass extinction--including the extinction of the dinosaurs--at the end of the Cretaceous. But up to now no crater of this age that is large enough (ca. 200 km in diameter) has been found. One candidate is the Kara Crater in northern Siberia. Kolesnikov et al. determined a K-Ar isochron of 65.6 +/- 0.5 Ma, indistinguishable from the age of the K-T boundary and interpreted this as confirmation of earlier proposals that the Kara bolide would have been at least one of the K-T impactors. Koeberl et al. determined Ar-40 to Ar-39 ages ranging from 70 to 82 Ma and suggested an association to the Campanian-Maastrichtian boundary, another important extinction horizon 73 Ma ago. We dated four impact melts, KA2-306, KA2-305, SA1-302, and AN9-182. Results from the investigation are discussed.

Trieloff, M.↗
NASA NTRS1991

Estimation of optimal Kalman filter gain from non-optimal filter residuals

This paper presents a novel method of estimating the optimal steady state Kalman filter gain of a linear discrete time-invariant system from a non-optimal Kalman filter residual sequence. The relation between the optimal residual sequence and a signal derived from the non-optimal residual sequence is described by a Moving Average (MA) model whose coefficients are expressed in terms of the state space parameters and the optimal steady state Kalman filter gain. In order to identify the MA model, a whitening filter of the derived signal, which corresponds to an AutoRegressive (AR) model of the signal, is first identified using the least-squares method. Then the inverse filter of the whitening filter, which corresponds to the MA model, is calculated. From the coefficients of the identified MA model, the optimal steady state Kalman filter gain can be obtained. Numerical example is provided to illustrate the feasibility of this approach.

Chen, Chung-Wen↗
NASA NTRS1993

Cenozoic crustal rotations in the Mojave Desert from paleomagnetic studies around Barstow, California

Paleomagnetic data from the Mojave Desert around Barstow, California, suggest 55 to 75 deg of clockwise rotation of this area in earliest Miocene time, followed by 23 deg of counterclockwise rotation in the Early Miocene, and no rotation after 18 Ma. Earliest Miocene clockwise rotation of the Barstow area is suggested by data from nine sites in the Oligocene-Miocene Lane Mountain Quartz Latite and Jackhammer Formation and may be related to oroclinal bending of the southern Sierra Nevada batholith. Data from 13 sites in the Early Miocene Pickhandle Formation indicate counterclockwise rotation, which coincides with Early Miocene E-NE - W-SW extension and detachment faulting in the Mojave Desert. These results suggest that Miocene extension in the Mojave Desert is related to similarly oriented extension in the Colorado River extensional corridor. Early Miocene to Pliocene rocks of the Andesite and Dacite of the Calico Mountains, Barstow Formation, Andesite of Murphy's Well, and Black Mountain Basalt show no evidence for significant rotation of the Barstow area after 18 Ma. Most other paleomagnetic data from elsewhere in the Mojave are consistent with a lack of significant post-18 Ma rotations, suggesting that post-10 Ma right-lateral faulting there has produced relatively little crustal rotation.

Valentine, Michael J.↗
NASA NTRS1993

Exposure history of the lunar meteorite, Elephant Moraine 87521

We report the noble gas concentrations and the Al-26, Be-10, Cl-36, and Ca-41 activities of the Antarctic lunar meteorite Elephant Moraine 87521. Although the actual exposure history of the meteorite may have been more complex, the following model history accounts satisfactorily for the cosmogenic nuclide data: A first stage of lunar irradiation for about 1 Ma at a depth of 1-5 g/sq cm followed, not necessarily directly, by a second one for 26 Ma at about 565 g/sq cm; launch from the moon less than 0.1 Ma ago; and arrival on earth 15-50 ka ago. The small concentration of trapped gases shows that except for some material that may have been introduced at the moment of launch, EET 87521 spent less than 1 Ma at a lunar depth less than 1 g/sq cm. EET 87521 has a K/Ar age in the range 3.0-3.4 Ga, which is typical for lunar mare basalts.

Vogt, S.↗
NASA NTRS1993

An ancient inner lake in Maadim Vallis

The survey of Ma'adim Vallis and crater Gusev area by the new topographic Aeolis southeast map allows to document the hydrodynamics processes which occurred in the valley. The inner Ma'adim Vallis hypsometric and volume deposits analyses point out that Gusev impact was subsequent to the first incision of Ma'adim Vallis in the craterized upland. The study of the deposit distributions as revealed by the topography leads to reconstruct the chronology of three major events in the Aeolis Region : Ma'adim incision, Gusev impact, and Apollinaris Patera/flow interactions.

Cabrol, N. A.↗
NASA NTRS1993

Geochemical evidences for two chondritic-like cometary or asteroidal impacts before and at the K/T boundary

A number of geological and palaeontological evidences support multiple impacts of cometary showers within a short time (approximately 1-3 Ma) and their connection with mass extinctions. Observations include clustered crater ages, stratigraphic horizons of impact ejecta closely spaced in time, and evidence for stepwise mass extinctions spanning intervals of 1-3 Ma. For the K/T boundary, three candidates, Popigai, Manson, and Yucatan, have been proposed as impact craters. Two distinct strata at the K/T boundary in western North America have been interpreted as evidence for two sequential impacts. If multiple impacts occurred within a time span of about 1 Ma then multiple Ir enrichments should be observed. DSDP Hole 577B on the Shatsky Plateau in the northern Pacific at K/T time is the first site. Samples contain approximately greater than 97 percent CaCO3, which exhibit clear chemical signals associated with asteroidal/cometary impact. Ir, Fe, and Cr data are presented. From the Th-normalized data, two satellite peaks below the major peak at 78 cm and 81 cm of 577B-1-4 are clearly shown. The major Ir peak (K/T boundary) is at 72 cm. Fe and Cr, from C1-like impactor ejecta fallout, also show two peaks at the same positions. For hole 738C on the southern Kerguelen Plateau, Ir values reach a peak concentration of 18 ppb in the clay layer at 96.0-96.2 cm in section 20R-5, and gradually tail off. In the sample 115 cm above the boundary, Ir concentrations have still not reached background levels. From the Ir peak downward to the lowermost sample analyzed at 102 cm, the Ir concentration is still as high as 1.7 ppb. From the Th-normalized data, we observe a small Ir/Th peak at 100-101 cm. Though this peak is within the error margin, the trend is clear. Fe and Cr exhibit the same pattern. The third case is Hole 690C on the Queen Maud Ridge. Again, the Ir/Th plot indicates the strong possibility of satellite peaks at approximately 52 cm. The main peak is at 39-40 cm. For the Stevns Klint K/T boundary layers, the stratification of trace elements appears threefold with peak concentrations in sublayers A1, A3, and B2 for different element groups, including Ir. C1 ratios for many siderophile elements found in combined layers III and IV, corresponding to layers A, B, C, and D, strongly support the impact hypothesis. Also, multiple Ir anomalies in the K/T section at Lattengebirge, Bavarian Alps are reported. Recent works on Ni-rich spinels and Ir at the K/T boundaries clearly establish cometary/asteroidal impacts at the K/T boundary. Lastly, cometary showers can explain the enhanced Ir contents over approximately a 1 Ma interval in Gubbio shales.

Liu, Y.-G.↗
NASA NTRS1993

Tectonic resurfacing of Venus

Impact crater distributions and morphologies have traditionally played an important role in unraveling the geologic histories of terrestrial objects, and Venus has proved no exception. The key observations are: mean crater retention age about 500 Ma; apparently random spatial distribution; modest proportion (17 percent) of modified craters; and preferential association of modified craters with areas of low crater density. The simplest interpretation of these data alone is that Venus experienced global resurfacing (assumed to be largely volcanic) prior to 500 Ma, after which time resurfacing rates decreased dramatically. This scenario does not totally exclude present geological activity: some resurfacing and crater obliteration is occurring on part of the planet, but at rates much smaller than on Earth. An alternative endmember model holds that resurfacing is also spatially randomly distributed. Resurfacing of about 1 sq km/yr eliminates craters such that a typical portion of the surface has an age of 500 Ma, but actual ages range from zero to about 1000 Ma. Monte Carlo simulation indicates that the typical resurfacing 'patch' cannot exceed about 500 km in diameter without producing a crater distribution more heterogeneous than observed. Volcanic or tectonic processes within these patches must be locally intense to be able to obliterate craters completely and leave few modified. In this abstract, we describe how global geologic mapping may be used to test resurfacing hypotheses. We present preliminary evidence that the dominant mode of resurfacing on Venus is tectonism, not volcanism, and that this process must be ongoing today. Lastly, we outline a conceptual model in which to understand the relationship between global tectonics and crater distribution and preservation.

Malin, Michael C.↗
NASA NTRS1993

Eruption history of the Tharsis shield volcanoes, Mars

The Tharsis Montes volcanoes and Olympus Mons are giant shield volcanoes. Although estimates of their average surface age have been made using crater counts, the length of time required to build the shields has not been considered. Crater counts for the volcanoes indicate the constructs are young; average ages are Amazonian to Hesperian. In relative terms; Arsia Mons is the oldest, Pavonis Mons intermediate, and Ascreaus Mons the youngest of the Tharsis Montes shield; Olympus Mons is the youngest of the group. Depending upon the calibration, absolute ages range from 730 Ma to 3100 Ma for Arsia Mons and 25 Ma to 100 Ma for Olympus Mons. These absolute chronologies are highly model dependent, and indicate only the time surficial volcanism ceased, not the time over which the volcano was built. The problem of estimating the time necessary to build the volcanoes can be attacked in two ways. First, eruption rates from terrestrial and extraterrestrial examples can be used to calculate the required period of time to build the shields. Second, some relation of eruptive activity between the volcanoes can be assumed, such as they all began at a speficic time or they were active sequentially, and calculate the eruptive rate. Volumes of the shield volcanoes were derived from topographic/volume data.

Plescia, J. B.↗
NASA NTRS1993

Analysis of the TDRS multiple access system for possible use as an attitude control system sensor

A member of the constellation of TDR satellites (TDRS) has experienced a failure of its prime earth sensor. Failure of the remaining earth sensor could result in the inability of the satellite to control its attitude and provide user services. Loss of the satellite would be a serious event. The multiple access (MA) antenna array on the TDRS has been proposed for use as a backup sensor for the attitude control system. This paper describes our analysis of the performance of the MA array as an interferometer used for accurate attitude determination. A least squares fit of a plane to the MA phase information appears to represent the TDRS body roll and pitch within about 0.1 deg. This is sufficient for SGL pointing and MA and SSA user services. Analytic improvements that include ionospheric correction may yield sufficient accuracy for KSA user services.

Blevins, Bruce Allyn↗