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At least 1,153 records · Page 64
All sourcesNASA NTRSDOE OSTI
NASA NTRS2019

Myco-Architecture off Planet: Growing Surface Structures at Destination

Our work focused on filling major select key technical knowledge gaps, and technical aspects to be addressed in a Phase II proposal were identified such as the secretion of glues or plastics by the fungi or bacteria to form biocomposites. Specifically, we raised the technical TRL by assessing the growth of in-house mycelial-producing strains on potential food substrates and analyzed the advantages and disadvantages to their use off planet. Growth of the mycelia on sawdust and powdered nutrients including dried, powdered algae, was used as a baseline. We measured growth as a function of temperature, tested the relevant material properties of the mycelia products produced, and measured the mass of input and output volume for production per volume of material. Mycotecture was produced in a bag simulating the proposed mission implementation. Post-production such as heat treatment (as is done with terrestrial mycotecture)was assessed.The material properties of the dried, frozen and baked mycelial outputs included density, strength,thermal insulation and flame retardation. Tensile/compression testing on biocomposite material specimens was performed to obtain three-dimensional elastic constants, as well as to examine deformation and fracture behavior. These mechanical tests were performed on both dormant and activated samples to understand the evolution of the structural material. In addition, experimental data obtained from the mechanical testing was used to build a failure prediction model that accounts for material anisotropy. This aided in future structural design through a quantitative understanding of the mechanical limits of the material. To examine the texture, defects, fracture surfaces of the material, high-resolution microstructural imaging was utilized before and after the mechanical tests. This microstructural analysis informed us about the macro-structural behavior and influenced structural design. Thermal decomposition analysis was also performed tounderstand the thermal limits.

Biocomposites↗
NASA NTRS2018

Characterizing Material Scalability for Ultralight Lattice Design

Stiff yet ultra-light lattice structures constructed using digital materials have many practical applications as the building block for aircraft and other structures. By furthering our understanding of how material configuration affects the structural properties of an ultralight lattice, we can intelligently design these structures based on their intended function. Here we compare the behavior of ultralight lattice structures when fabricated by different materials. The individual unit cells of the lattice structures are referred to as voxels. The stiffness, elastic modulus, and yield strength of the specimens in compression and tension are determined through mechanical testing. Specimens are tested both as single voxel as well as 4x4x4 voxel constructions on an Instron 5982 Universal Testing System until failure. Each voxel is manufactured in bulk through injection molding, with a unit cell pitch of 76.2 mm. Individual voxels are fastened with machine screws and nuts to create assemblies. Four separate materials are used as voxel compositions in this experiment. These include a homogeneous polymer referred to as Ultem 1000, a glass-fiber reinforced polymer referred to as Ultem 2200, a polymer with chopped carbon fibers as 30% of its fill, and homogenous polypropylene. This work compares mechanical behavior, as well as the convergence behavior of the lattice as the size of the lattice assembly increases for various materials. The goal of this study is to characterize the behavior of homogenous lattices such that heterogenous lattices can be designed with different material voxels to achieve target material properties for ultralight space applications.

Sajjadi, Afsheen↗
NASA NTRS1980

Microstructure and mechanical properties of hip-consolidated Rene 95 powders

The effects of heat-treatments on the microstructure of P/M Rene 95 (a nickel-based powder metal), consolidated by the hot-isostatic pressing (HIP), were examined. The microstructure of as-HIP'd specimen was characterized by highly serrated grain boundaries. Mechanical tests and microstructural observations reveal that the serrated grain boundaries improved ductility at both room and elevated temperatures by retarding crack propagation along grain boundaries.

Shimanuki, Y.↗
NASA NTRSDate not supplied

Using Optical Lightning Detection Data from the 2017 GOES-R Post Launch Test Field Campaign Flights as an Evaluation of Convective Processes

The primary mechanisms for thunderstorm electrification and lightning production are widely understood and allow connections between lightning intensity and occurrence to be used to derive storm strength and forecast the probability of related weather phenomena. However, these assumed relationships between lightning and convective properties were discovered primarily using ground-based lightning sensors and measurements, meaning the true depth of insight from space or air based detections is widely unexplored. In 2017, a field campaign was launched to validate the instrumentation aboard the GOES-16 satellite. It involved flying a NASA-ER2 aircraft over multiple storms across the continental US and it included the Fly’s Eye GLM Simulator (FEGS) as a proxy for the Geostationary Lightning Mapper (GLM). Utilizing the data from this field campaign, one of the main goals of this project is to investigate how attributes of convection impact optical lightning detection and the subsequent assumptions that can be made in relation to convective dynamics and precipitation microphysics. Hydrometeor identification, 3D winds retrieval, and additional radar and LiDAR data analysis will be utilized alongside FEGS and interferometer data in order to observe these relationships. This presentation will be to lay out the initial conclusions from our analysis and to explore any new insights or contradictions within our findings.

Kaitlyn Wheeler↗
NASA NTRSDate not supplied

Dust-Proofing the Future: Materials Challenges for Lunar Exploration

As humanity expands its ventures into lunar exploration, the demand intensifies for materials capable of enduring extreme environmental and service conditions. The Moon’s surface presents numerous challenges, including ultra-high vacuum exposure, temperature extremes and intense radiation. Additionally, lunar regolith threatens component durability and reusability due to its abrasive nature. Lunar dust particles scoring, adhering or embedding into surfaces and within device-confined geometries, such as bearings, drive mechanisms and connectors, can cause premature component wear or failure. Furthermore, the interaction between the rocket plume and surface during vehicle landings and ascents creates severe erosive conditions near critical vehicle components and adjacent infrastructure. A key barrier hindering materials discovery for lunar dust tolerant applications is a lack of standard laboratory methods to evaluate material properties and performance under representative operating conditions. A case will be presented for research activities supporting identification, processing and characterization of candidate materials in conjunction with innovations in standardized testing and qualification. Results will highlight current and emerging test methods for simulating lunar dust exposure and component degradation, paving the way for a new generation of robust materials and coatings for space exploration.

lunar dust↗
NASA NTRS1980

Short beam shear tests of polymeric laminates and unidirectional composites

The application of advanced composite materials in aerospace, ground transportation, and sporting industries are discussed. Failure theories for the design and mechanical behavior of composite materials are emphasized. Methods for detecting specific types of flaws are outlined. The effect of detected flaws on mechanical properties such as stiffness, strength, fatigue lifetime, or residual strength is described.

Stinchcomb, W. W.↗
NASA NTRS1984

Investigation of the relations between neat resin and advanced composite mechanical properties. Volume 1: Results

A detailed evaluation of one untoughened epoxy baseline resin and three toughened epoxy resin systems was performed. The Hercules 3502, 2220-1, and 2220-3, and Ciba-Geigy Fibredux 914 resin systems were supplied in the uncured state by NASA-Langley and cast into thin flat specimens and round dogbone specimens. Tensile and torsional shear measurements were performed at three temperatures and two moisture conditions. Coefficients of thermal expansion and moisture expansion were also measured. Extensive scanning electron microscopic examination of fracture surfaces was performed, to permit the correlation of observed failure modes with the environmental conditions under which the various specimens were tested. A micromechanics analysis was used to predict the unidirectional composite response under the various test conditions, using the neat resin experimental results as the required input data. Mechanical and physical test results, the scanning electron microscope observations, and the analytical predictions were then correlated.

Zimmerman, R. S.↗
NASA NTRS1971

Design of optical mirror structures

The structural requirements for large optical telescope mirrors was studied with a particular emphasis placed on the three-meter Large Space Telescope primary mirror. Analysis approaches through finite element methods were evaluated with the testing and verification of a number of element types suitable for particular mirror loadings and configurations. The environmental conditions that a mirror will experience were defined and a candidate list of suitable mirror materials with their properties compiled. The relation of the mirror mechanical behavior to the optical performance is discussed and a number of suitable design criteria are proposed and implemented. A general outline of a systematic method to obtain the best structure for the three-meter diffraction-limited system is outlined. Finite element programs, using the STRUDL 2 analysis system, were written for specific mirror structures encompassing all types of active and passive mirror designs. Parametric studies on support locations, effects of shear deformation, diameter to thickness ratios, lightweight and sandwich mirror configurations, and thin shell active mirror needs were performed.

Soosaar, K.↗
NASA NTRS1976

Observations on the relationship of structure to the mechanical properties of thin TD-NiCr sheet

A study of the relationship between structure and mechanical properties of thin TD-NiCr sheet indicated that the elevated temperature tensile, stress-rupture, and creep strength properties are dependent on grain aspect ratio and sheet thickness. In general, the strength properties increase with increasing grain aspect ratio and sheet thickness. Tensile testing revealed an absence of ductility at elevated temperatures (not less than 1144 K). Significant creep damage as determined by subsequent tensile testing at room temperature occurs after very small amounts (less than 0.1%) of prior creep deformation over the temperature range 1144-1477 K. A threshold stress for creep appears to exist. Creep exposure below the threshold stress at T not less than 1366 K results in almost full retention of room temperature tensile properties.

Whittenberger, J. D.↗
NASA NTRS1981

Single pass rub phenomena - Analysis and experiment

An experimental and analytical investigation is presented of contact phenomena for the case of a fully-dense copper gas path seal segment which is rubbed by a single steel blade tip at room temperature. The experiments were executed on a pendulum-type test device, with forces, rub energy, surface temperature and residual deformation being determined for each single-path rub test. The thermal and mechanical factors influencing single-pass rub surface temperatures were modeled analytically. It is found that large plastic strains occurred on or near the contact surface of the copper rub specimens. A study of the influence of various material properties on surface temperature showed that increased thermal conductivity of the stationary component played a role in lowering contact temperatures. Increased thermal conductivity of the moving blade tip component and increased thermal diffusivity of the stationary material also had a beneficial effect.

Kennedy, F. E.↗
NASA NTRS1986

Degradation studies of SMRM teflon

Teflon samples returned from the Solar Max Satellite (SMS) suffered noticeable damage such as cracking and yellowing. This is in contrast to teflon exposed aboard STS-5 and STS-8 which showed no detectable changes. Selected teflon tape samples from SMS were studied to evaluate the extent and mechanism of degradation. ESCA studies revealed that these teflon samples contain hydrocarbon segments which were susceptible to oxygen atom degradation. Mechanical measurements also showed bulk property changes as a result of LEO exposure. A molecular model of material and energetic oxygen atom interaction was proposed. SMS data and the importance of developing correlation between accelerated exposure data from STS and ground-based testing and real time data will be presented.

Liang, Ranty H.↗
NASA NTRS1992

Effect of braze processing on the microstructure and mechanical properties of SCS-6/beta21S titanium matrix composites

An investigation is conducted of the effects of braze processing on the microstructure and tensile properties of SiC fiber-reinforced Ti-15Mo-2.7Nb-3Al-0.25Si-matrix composite (TMC) laminates; the brazing alloy was the commercial Ti-15Cu-15Ni, in both its conventional and metglass forms. Tensile tests conducted at room temperature, 1200 F, and 1500 F showed that the braze processes (1) had little effect on tensile properties, and (2) appeared to degrade neither the reinforcing fibers not the fiber/matrix interfacial bondline.

Hoffman, Eric K.↗
NASA NTRS1998

Elevated Temperature Crack Growth Behavior in HSCT Structural Materials

Structures in super-sonic aircraft are subjected to conditions of high temperature and cyclic and sustained loading for extended periods of time. The durability of structures fabricated from aluminum and certain titanium alloys in such demanding conditions is of primary concern to the designers and manufacturers of futuristic transport aircraft. Accordingly, the major goal of this project was to evaluate the performance and durability of high temperature aluminum and titanium alloys for use in high speed civil transport (HSCT) structures. Additional goals were to develop time-dependent fracture mechanics methodology and test methods for characterizing and predicting elevated temperature crack growth behavior in creep-brittle materials such as ones being considered for use in HSCT structures and to explore accelerated methods of simulating microstructural degradation during service and measuring degraded properties in these materials.

Saxena, Ashok↗
NASA NTRS2008

Mechanical Properties and Durability of "Waterless Concrete"

Waterless concrete consists of molten elementary sulfur and aggregate. The aggregates in lunar environment will be lunar rocks and soil. Sulfur is present on the Moon in Troilite soil (FeS) and by oxidation soil iron and sulfur can be produced. Iron can be used to reinforce the sulfur concrete. Sulfur concrete specimens were cycled between liquid nitrogen (approximately 191 C) and room temperature (approximately 21 C) to simulate exposure to a lunar environment. Cycled and control specimens were subsequently tested in compression at room temperatures (approximately 21 C) and approximately 101 C. Test results showed that due to temperature cycling, compressive strength of cycled specimens was 20% of those non-cycled. Microscopic examination of the fracture surfaces from the cycled samples showed clear de-bonding of the sulfur from the aggregate material whereas it was seen well bonded in those non-cycled. This reduction in strength can be attributed to the large differences in thermal coefficients of expansion of the materials constituting the concrete which promoted cracking. Similar sulfur concrete mixtures were strengthened with short and long glass fibers. The glass fibers from lunar regolith simulant was melted in a 25 cc Pt-Rh crucible in a Sybron Thermoline high temperature MoSi2 furnace at melting temperatures of 1450 to 1600 C for times of 30 min to 1 hour. Glass fibers were cast from the melt into graphite crucibles and were annealed for a couple of hours at 600 C. Glass fibers and small rods were pulled from the melt. The glass melt wets the ceramic rod and long continuous glass fibers were easily hand drawn. The glass fibers were immediately coated with a protective polymer to maintain the mechanical strength. The glass fibers were used to reinforce sulfur concrete plated to improve the flexural strength of the sulfur concrete. Prisms beams strengthened with glass fibers were tested in 4-point bending test. Beams strengthened with glass fiber showed to exhibit an increase in the flexura strength by as much as 45%.

Toutanji, Houssam↗
NASA NTRS1981

Design, analysis, and test verification of advanced encapsulation systems

Thermal, optical, structural, and electrical isolation analyses are decribed. Major factors in the design of terrestrial photovoltaic modules are discussed. Mechanical defects in the different layers of an encapsulation system, it was found, would strongly influence the minimum pottant thickness required for electrical isolation. Structural, optical, and electrical properties, a literature survey indicated, are hevily influenced by the presence of moisture. These items, identified as technology voids, are discussed. Analyses were based upon a 1.2 meter square module using 10.2 cm (4-inch) square cells placed 1.3 mm apart as shown in Figure 2-2. Sizing of the structural support member of a module was determined for a uniform, normal pressure load of 50 psf, corresponding to the pressure difference generated between the front and back surface of a module by a 100 mph wind. Thermal and optical calculations were performed for a wind velocity of 1 meter/sec parallel to the ground and for module tilt (relative to the local horizontal) of 37 deg. Placement of a module in a typical array field is illustrated.

Garcia, A.↗
NASA NTRS2005

Ultrasonic Guided-Wave-Scan System Used to Characterize C-Enhanced Silicon Carbide Composite During Creep- Rupture Tests

Ceramic matrix composites (CMCs) are being developed for advanced aerospace propulsion applications in order to save weight, improve reuse capability, and increase performance. However, mechanical and environmental loads applied to CMCs can cause degradation in the form of discrete flaws and distributed microdamage that can play a significant role in reducing desirable physical properties. Categories of microdamage include fiber/matrix debonding (interface failure), matrix microcracking, fiber fracture and buckling, oxidation, and second-phase formation. Distributed microdamage in CMCs has proven difficult to characterize nondestructively because of the complex microstructure and macrostructure of these materials, and a recent study regarding the durability of a ceramic matrix composite discussed the requirement for improved nondestructive evaluation (NDE) methods for monitoring degradation in these materials.

Roth, Don J.↗
NASA NTRS1974

Effects of sigma-phase formation on some mechanical properties of a wrought nickel-base superalloy (IN-100)

The effect of sigma phase formation on an extruded and forged nickel base superalloy with the composition of the casting alloy IN-100 was studied. By adding only aluminum and titanium to remelt stock, three compositions were produced which had varying propensities for sigma formation. These compositions were given a four step heat treatment and were stress-ruptured or tensile tested. The very sigma prone composition had a shorter rupture life than the sigma-free or moderately sigma prone compositions when tested at 843 and 885 C. Elongation in room temperature tensile tests was considerably lower for the very sigma prone composition than for the other two wrought compositions after prolonged exposure at 732 or 843 C.

Dreshfield, R. L.↗
NASA NTRS1999

Quantitative Interpretation of Optical Emission Sensors for Microgravity Experiments

Microgravity flight experiments uniquely test our knowledge and understanding of the coupling between chemistry and fluid mechanics. However, compared to ground based laboratory experiments the number of useful diagnostic tools suitable for microgravity environments is severely limited by the space, weight, power consumption, and operator complexity requirements. One of the available tools is the observation of optical emission, and total emission has already proven useful for observations of stable "flame balls" on the space shuttle. Wavelength resolved tomographic measurements of flame emission offer the promise of diagnostics to test our understanding of flame chemistry and structure. Individual emissions from electronically excited radicals, e.g., CH*, OH*, and C2*, can be identified in a methane/air flame. Spatially resolved measurements of the intensity of this resolved optical emission from a specific excited molecule enable chemically resolved flame structure studies. Wavelength resolved emission measurements to determine such structure in diffusion flames are being readied for flight experiments by a group at Yale headed by Profs. Smooke and Long. A quantitative relationship between emission intensity and flame properties, as expressed by a flame model, is needed for species specific optical emission measurements to fulfill its promise. The Yale group compared models and measurements of optical emission in laboratory tests at 1-g. Unfortunately, these experiments show disagreement between measurement and state-of-the-art flame models by over a factor of 50. Therefore, an improved chemical mechanism for optical emission from flames is needed to enable quantitative tests of microgravity flame models. The connection between excited state emission and flame chemistry is not yet adequate.

Jeffries, Jay B.↗