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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.

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At least 811 records · Page 45
All sourcesNASA NTRSDOE OSTI
DOE OSTI2015

Use of polypropylene fibers coated with nano-silica particles into a cementitious mortar

Fiber reinforced cementitious composite (FRCC) materials have been widely used during last decades in order to overcome some of traditional cementitious materials issues: brittle behaviour, fire resistance, cover spalling, impact strength. For composite materials, fiber/matrix bond plays an important role because by increasing fiber/matrix interactions is possible to increase the behaviour of the entire material. In this study, in order to improve fiber to matrix adhesion, two chemical treatments of polypropylene fibers were investigated: alkaline hydrolysis and nano-silica sol-gel particles deposition. Treatmtents effect on fibers morphology and mechanical properties was investigated by scanning electron microscopy (SEM) and tensile tests. SEM investigations report the presence of spherical nano-silica particles on fiber surface, in the case of sol-gel process, while alkaline hydrolysis leads to an increase of fibers roughness. Both treatments have negligible influence on fibers mechanical properties confirming the possibility of their use in a cementitious mortar. Pullout tests were carried out considering three embedded length of fibers in mortar samples (10, 20 and 30 mm, respectively) showing an increase of pullout energy for treated fibers. The influence on fiber reinforced mortar mechanical properties was investigated by three-point flexural tests on prismatic specimens considering two fibers length (15 and 30 mm) and two fibers volume fractions (0.50 and 1.00 %). A general increase of flexural strength over the reference mix was achieved and an overall better behaviour is recognizable for mortars containing treated fibers.

36 MATERIALS SCIENCE↗
NASA NTRS1982

Ultrasonic Instrument for Evaluation of Composites

Ultimate strength of composite material is related to normalized stress-wave factor, a measure of attenuation of stress wave. New portable ultrasonic inspection instrument measures strength of composite materials. New commercial instrument has similar specifications to prototype developed at Lewis Research Center. Device may ultimately help to reduce energy consumption and improve efficiencies of vehicles by allowing use of composite materials to their full potential in critical application areas.

Vary, A.↗
NASA NTRS2013

Unit-Sphere Multiaxial Stochastic-Strength Model Applied to Anisotropic and Composite Materials

Models that predict the failure probability of brittle materials under multiaxial loading have been developed by authors such as Batdorf, Evans, and Matsuo. These "unit-sphere" models assume that the strength-controlling flaws are randomly oriented, noninteracting planar microcracks of specified geometry but of variable size. This methodology has been extended to predict the multiaxial strength response of transversely isotropic brittle materials, including polymer matrix composites (PMCs), by considering (1) flaw-orientation anisotropy, whereby a preexisting microcrack has a higher likelihood of being oriented in one direction over another direction, and (2) critical strength, or K (sub Ic) orientation anisotropy, whereby the level of critical strength or fracture toughness for mode I crack propagation, K (sub Ic), changes with regard to the orientation of the microstructure. In this report, results from finite element analysis of a fiber-reinforced-matrix unit cell were used with the unit-sphere model to predict the biaxial strength response of a unidirectional PMC previously reported from the World-Wide Failure Exercise. Results for nuclear-grade graphite materials under biaxial loading are also shown for comparison. This effort was successful in predicting the multiaxial strength response for the chosen problems. Findings regarding stress-state interactions and failure modes also are provided.

Nemeth, Noel, N.↗
NASA NTRS1983

Characteristics of Si3N4-SiO2-Ce2O3 compositions sintered in high-pressure nitrogen

Full-density Si3N4-SiO2-Ce2O3 compositions were prepared by sintering with 2.5 MPa nitrogen pressure at temperatures of 1900 and 2090 C. Room-temperature flexural strengths near 700 MPa for sintered material compared favorably with the strength of hot-pressed material. At 1370 C, where flexural strengths as high as 363 MPa were obtained, it was observed that the coarsest structure was the strongest and the finest structure was the weakest. One of the compositions tested, Si3N4-8.7 wt pct SiO2-8.3 wt pct-Ce2O3, was found to have excellent 200-h oxidation resistance at 700, 1000, and 1370 C, without incidence of 700 to 1000 C phase instability and cracking.

Sanders, W. A.↗
NASA NTRS2009

Research for Lunar Exploration: ADVANCE Program

This viewgraph presentation reviews the work that the author has been involved with in her undergraduate and graduate education and the ADVANCE Program. One project was the Lunar Entry and Approach Platform For Research On Ground (LEAPFROG). This vehicle was to be a completely autonomous vehicle, and was developed in successive academic years with increases in the perofmamnce and capability of the simulated lander. Another research project for the PhD was on long-term lunar radiation degradation of materials to be used for construction of lunar habitats. This research has concentrated on developing and testing light-weight composite materials with high strength characteristics, and the ability of these composite materials to withstand the lunar radiation environment.

Rojdev, Kristina↗
NASA NTRSDate not supplied

Design and Fabrication of the Langley Aerodrome No. 8 - Distributed Electric Propulsion VTOL Testbed

The Langley Aerodrome No. 8 (LA-8) is a distributed electric propulsion, vertical takeoff and landing (VTOL) aircraft that is being used for wind tunnel testing and free flight testing at the NASA Langley Research Center. The intent of the LA-8 project is to provide a low-cost, modular test bed for technologies in the area of Advanced Air Mobility which includes electric urban and short regional flight. The methods used on the LA-8 provide a rapid means to verify aerodynamic, acoustic, and flight dynamics analysis of new electric VTOL and short takeoff and landing (STOL) designs. In addition, the flight vehicle will be used to help develop test processes for FAA flight vehicle airworthiness certification and for the development of robust flight control algorithms that are tolerant of failures. A new approach is being used on test vehicle design that makes extensive use of 3-D printing. Although materials used in 3-D printing have less strength than traditional materials used for NASA’s wind tunnel and flight models, strategic placement of load-carrying structures allows the aircraft to meet structural criteria while also enabling easy changes to be made in the vehicle design, such as the outer mold line. Modularity of the vehicle’s main components allows rapid changes to the vehicle configuration for comparative evaluation of alternate designs. Finally, a description is given of detailed inertia measurements of the flight vehicle using compound pendulum swing methods.

Urban air mobility↗
NASA NTRS1979

The influence of microstructure on the strength of reaction bonded silicon nitride /RBSN/

The effect of the microstructure of reaction bonded silicon nitride on strength is examined. The morphologies of the various microconstituents (alpha-matte, beta-spikes, residual silicon and porosity) each play a role in determining the strength of the material. While density and hence percent porosity greatly affect strength, it is shown that the pore size and pore size distribution affect strength with equal importance. By minimizing the pore size and distribution and maximizing the alpha-beta ratio, a reaction bonded material (2.4 kg/cu m) has been produced with a room temperature modulus of rupture (three-point bending) of 297 MPa from a low green density starting material (1.5 kg/cu m).

Danforth, S. C.↗
DOE OSTI2017

Data-driven reduced order models for effective yield strength and partitioning of strain in multiphase materials

There is a critical need for the development and verification of practically useful multiscale modeling strategies for simulating the mechanical response of multiphase metallic materials with heterogeneous microstructures. In this contribution, we present data-driven reduced order models for effective yield strength and strain partitioning in such microstructures. These models are built employing the recently developed framework of Materials Knowledge Systems that employ 2-point spatial correlations (or 2-point statistics) for the quantification of the heterostructures and principal component analyses for their low-dimensional representation. The models are calibrated to a large collection of finite element (FE) results obtained for a diverse range of microstructures with various sizes, shapes, and volume fractions of the phases. The performance of the models is evaluated by comparing the predictions of yield strength and strain partitioning in two-phase materials with the corresponding predictions from a classical self-consistent model as well as results of full-field FE simulations. The reduced-order models developed in this work show an excellent combination of accuracy and computational efficiency, and therefore present an important advance towards computationally efficient microstructure-sensitive multiscale modeling frameworks. - Graphical abstract:.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2021

Developing an experimental-computational framework to investigate the deformation mechanisms and mechanical properties of Al-8Ce-10Mg alloys at micro and macroscales

There is a promising future for the use of aluminum-cerium-magnesium alloys in a broad range of applications, including devices that operate at high temperatures. With cerium currently considered a waste product of rare earth mining validation studies of possible applications are essential to reduce the environmental waste. Here, a computational-experimental framework is developed to investigate the role both the intermetallic and matrix have on the mechanical properties of these alloys. A set of experiments, including SEM/EBSD imaging, nanoindentation, in-situ SEM tensile testing, and in-situ SEM-DIC tests are performed to characterize the microstructure and mechanical properties of these alloys. Furthermore, the elastic, plastic, and failure deformation mechanisms of the microstructure, and their correlation with the bulk scale mechanical properties are investigated. Experimental results are also used to calibrate parameters for a crystal plasticity finite element model, by performing a computational framework that minimizes the error between the computational and experimental results. This model is then utilized to investigate how the area percentage of intermetallics and the crystallographic texture control the mechanical properties of the alloy. Simulation results show that an increase in the percentage of intermetallics increase the strength but decrease the ductility of the alloy. Also, a change in material texture improves strength and reduces damage that leads to material failure. The development of the crystal plasticity model, as discussed in this work, opens opportunities for future investigations of similar aluminum-cerium-magnesium alloys.

36 MATERIALS SCIENCE↗
DOE OSTI2014

Biopolymer foams - Relationship between material characteristics and foaming behavior of cellulose based foams

Biopolymers are becoming increasingly important to both industry and consumers. With regard to waste management, CO{sub 2} balance and the conservation of petrochemical resources, increasing efforts are being made to replace standard plastics with bio-based polymers. Nowadays biopolymers can be built for example of cellulose, lactic acid, starch, lignin or bio mass. The paper will present material properties of selected cellulose based polymers (cellulose propionate [CP], cellulose acetate butyrate [CAB]) and corresponding processing conditions for particle foams as well as characterization of produced parts. Special focus is given to the raw material properties by analyzing thermal behavior (differential scanning calorimetry), melt strength (Rheotens test) and molecular weight distribution (gel-permeation chromatography). These results will be correlated with the foaming behavior in a continuous extrusion process with physical blowing agents and underwater pelletizer. Process set-up regarding particle foam technology, including extrusion foaming and pre-foaming, will be shown. The characteristics of the resulting foam beads will be analyzed regarding part density, cell morphology and geometry. The molded parts will be tested on thermal conductivity as well as compression behavior (E-modulus, compression strength)

36 MATERIALS SCIENCE↗
NASA NTRS1993

Characteristics of an Elevated Temperature ALN Particulate Reinforced NiAl

High energy milling of NiAl in liquid nitrogen (cryomilling) leads to the formation of a discontinuously AlN particle reinforced aluminide which has shown good potential as a high strength oxidation resistant material. Experiments have demonstrated that cryomilling is repeatable, and materials with reproducible chemistries and mechanical properties result. Furthermore, it is possible to vary the AlN content through control of the milling parameters. Tensile creep as well as compressive creep testing has been undertaken on a lot of NiAl-AlN. While this material is weaker in tension than compression, the tensile strength is respectable: for example, the creep rupture life exceeds 2700 h at 1300 K, 50 MPa. Heat treatment of the particulate reinforced aluminide at 1600 K promotes AlN growth which weakens the material but does not change the deformation mechanism. Cyclic oxidation testing of lots of NiAl-AlN which were cryomilled with and without yttria reveal that Y2O3 promotes better oxidation resistance. However, the presence or absence of yttria had no affect on the mechanical properties.

Whittenberger, J. D.↗
DOE OSTI2020

Mechanical behavior and texture evolution of WE43 magnesium-rare earth alloy in Split-Hopkinson Pressure Bar and Taylor Impact Cylinder Testing

Mechanical behavior and texture evolution of Mg rare-earth alloy WE43 is investigated for strain-rates 10 -3 /s to upwards of 10 5 /s for the two material conditions - as-cast (AC) and T6 age hardened, rolled plate (RT6). The high strain-rate behavior is tested using both Taylor cylinder impact tests (TC) and split Hopkinson pressure bar tests (SHB) and bulk textures are obtained using neutron diffraction. Unlike the quasi-static strained material, AC and RT6 SHB retained high hardening rates throughout the test, even up to 30% true strain. Moreover, the high strain-rate data revealed that the RT6 material has a much higher strength than the AC material, but similar hardening rates despite significantly different initial texture. The flow stress near yield increased up to I 0% for RT6 and up to 30% for AC as the strain-rate increased six orders of magnitude from quasi-static rates 10 -3 /s to 10 3 /s. Neither material exhibited significant plastic anisotropy over the broad range of strain rates, despite the fact that the RT6 material had a moderately strong initial texture. In the TC tests, the geometric cross-sectional changes and texture along the cylinder from the cylindrical sample foot to head are measured and from the neutron diffraction texture analysis, upper-bound estimates of twin volume fraction are obtained as well as dislocation density from analyzing diffraction peak broadening. Recorded geometrical changes along several loading directions show that the material has deformed remarkably homogeneously under impact. Analysis of deformed textures indicates that {101¯2} extension deformation twinning occurred in the RT6 condition over the range of strain rates, with an upper bound estimate of 40% twin volume fraction for approximately 0.10-0.25 true strain. The peak texture components after the impact have their c-axes closely aligned with the impact direction. As a result, these observations are presented and rationalized in the paper.

42 ENGINEERING↗
DOE OSTI2021

Irradiation stability and thermomechanical properties of 3D-printed SiC

Neutron irradiation tests were carried out on 3D-printed SiC derived from binderjet additive manufacturing and chemical vapor infiltration. Irradiation was carried to 2.3 dpa over a temperature range of 400–850 °C. Anisotropy that had been observed in the thermal conductivity of 3D-printed SiC prior to irradiation vanished after irradiation as the irradiation defect thermal resistivity accumulated in the material. No degradation in strength was observed in the material before or after irradiation, at various temperatures, or in different orientations. Electron microscopy of the microstructure after neutron irradiation showed distinct defect morphologies in the heterogenous material, but no evidence for irradiation-induced cracking or degradation in the microstructure was observed.

36 MATERIALS SCIENCE↗
NASA NTRS1980

A NASTRAN investigation of simulated projectile damage effects on a UH-1B tail boom model

A NASTRAN model of a UH-1B tail boom that had been designed for another project was used to investigate the effect on structural integrity of simulated projectile damage. Elements representing skin, and sections of stringers, longerons and bulkheads were systematically deleted to represent projectile damage. The structure was loaded in a manner to represent the flight loads that would be imposed on the tail boom at a 130 knot cruise. The deflection of four points on the rear of the tail boom relative to the position of these points for the unloaded, undamaged condition of the tail boom was used as a measure of the loss of structural rigidity. The same procedure was then used with the material properties of the aluminum alloys replaced with the material properties of T300/5208 high strength graphite/epoxy fibrous composite material, (0, + or - 45, 90)s for the skin and (0, + or - 45)s for the longerons, stringers, and bulk heads.

Futterer, A. T.↗
NASA NTRS1969

Lunar Surface Material - Spacecraft Measurements of Density and Strength

The relation of the density of the lunar surface layer to depth is probably best determined from spacecraft measurements of the bearing capacity as a function of depth. A comparison of these values with laboratory measurements of the bearing capacity of low-cohesion particulate materials as a function of the percentage of solid indicates that the bulk density at the lunar surface is about 1.1 grams per cubic centimeter and that it increases nearly linearly to about 1.6 grams per cubic centimeter at a depth of 5 centimeters.

Jaffe, L. D.↗