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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 19 records
All sourcesNASA NTRSDOE OSTI
NASA NTRS2001

Uncertainties in the Thermal and Mechanical Properties of Particulate Composites Quantified

Particle-reinforced composites are candidate materials for a wide variety of aerospace and nonaerospace applications. The high costs and technical difficulties involved with the use of many fiber-reinforced composites often limit their use in many applications. Consequently, particulate composites have emerged as viable alternatives to conventional fiber-reinforced composites. Particulate composites can be processed to near net shapepotentially reducing the manufacturing costs. They are candidate materials where shock or impact properties are important. For example, particle-reinforced metal matrix composites have shown great potential for many automotive applications. Typically, these materials are aluminum matrix reinforced with SiC or TiC particles. Reinforced concrete can also be thought of as a particle-reinforced composite. In situ ceramics can be modeled as particulate composites and are candidate materials for many high-temperature applications. The characterization of these materials is fundamental to their reliable use. It has been observed that the overall properties of these composites exhibit scatter because of the uncertainty in the constituent material properties, and fabrication-related parameters.

Murthy, Pappu L. N.↗
NASA NTRS1988

Elevated temperature slow plastic deformation of NiAl/TiB2 particulate composites

The 'XD' process for production of discontinuously-reinforced metal-matrix composites has been used to enhance the high-temperature strength of NiAl-TiB2 composites with particulate densities of up to 30 vol pct. SEM, TEM, and optical characterizations of the resulting microstructures showed the average TiB2 particle size to be about 1 micron, while the average grain of the NiAl matrix was of the order of 10 microns. Elevated temperature compression tests conducted at 1200 and 1300 K indicated flow strengths to increase with TiB2 content, so that the 20 vol pct TiB2-reinforced composite was three times stronger than the unreinforced NiAl; this is ascribed to the very high density of microstructural tangled dislocations, loops, and subgrain boundaries connecting the particles.

Whittenberger, J. Daniel↗
NASA NTRS1991

Mechanical properties of monolithic and particulate composites of L12 forms of Al3Ti

Preliminary studies of simple compressive properties of particulate composites with L1(2)-modified Al3Ti's as the matrices were performed as functions of matrix composition, amount of TiB2, processing technique, temperature, and strain rate. At and below about 900 K the introduction of TiB2 particles overwhelms minor chemical effects, and extremely high-yield strengths (about 2000 MPa at the 20 vol pct TiB2 level) were obtained. As L1(2)-modified Al3Ti has about half the density of the Ni-base superalloys, such values translate to strength/density ratios approximately four times those for superalloys. This advantage is not maintained by the Al3Ti-based composites above about 1000 K, particularly under slow strain rate plastic flow conditions, and it is proposed that this behavior could be due to the dissolution of intermetallic second phases as well as grain boundary creep mechanisms.

Whittenberger, J. D.↗
NASA NTRS1996

ICAN/PART: Particulate composite analyzer, user's manual and verification studies

A methodology for predicting the equivalent properties and constituent microstresses for particulate matrix composites, based on the micromechanics approach, is developed. These equations are integrated into a computer code developed to predict the equivalent properties and microstresses of fiber reinforced polymer matrix composites to form a new computer code, ICAN/PART. Details of the flowchart, input and output for ICAN/PART are described, along with examples of the input and output. Only the differences between ICAN/PART and the original ICAN code are described in detail, and the user is assumed to be familiar with the structure and usage of the original ICAN code. Detailed verification studies, utilizing dim dimensional finite element and boundary element analyses, are conducted in order to verify that the micromechanics methodology accurately models the mechanics of particulate matrix composites. ne equivalent properties computed by ICAN/PART fall within bounds established by the finite element and boundary element results. Furthermore, constituent microstresses computed by ICAN/PART agree in average sense with results computed using the finite element method. The verification studies indicate that the micromechanics programmed into ICAN/PART do indeed accurately model the mechanics of particulate matrix composites.

Goldberg, Robert K.↗
NASA NTRS1990

Elevated temperature slow plastic deformation of NiAl-TiB2 particulate composites at 1200 and 1300 K

Elevated temperature compression testing has been conducted in air at 1200 and 1300 K with strain rates varying from about 10 to the -4th to about 10 to the -7th/sec on NiAl-TiB2 particulate composites. These materials, which consisted of a B2 crystal structure intermetallic Ni-50 at. pct Al matrix and from 0 to 30 vol pct of approximately 1- micron diameter TiB2 particles, were fabricated by XD synthesis and hot pressed to full density. Flow strength of the composites increased with volume fraction of the strengthening phase with NiAl-30TiB2 being approximately three times stronger than NiAl. Comparison of the light optical and TEM microstructures of as-received and tested samples revealed that reactions did not occur between the two phases, and NiAl-TiB2 interfaces were not cracked during deformation. Additional TEM indicated that the particles stabilize a vastly different microstructure in the NiAl matrix of the composites than that formed in unreinforced NiAl.

Whittenberger, J. Daniel↗
NASA NTRS1991

Compression studies on particulate composites of ternary Al-Ti-Fe, and quaternary Al-Ti-Fe-Nb and Al-Ti-Fe-Mn L1(2) compounds

Compression studies were conducted on monolithic and TiB2 particulate-reinforced composites of Al22Fe3Ti8, both with and without minor quaternary alloying additions (2 at. pct Nb and 2 at. pct Mn) as a function of temperature and as a function of strain rate at high temperature. The volume fraction of reinforcement was varied between 0 and 20 percent. The particulate reinforcements were found to be effective in increasing ambient- and warm-temperature strength; at high temperatures, the monolithic material is stronger than the composites, although the composites are superior at slow strain rates. The microstructures of the monolithic and composite specimens were examined before and after deformation to explain these observations.

Kumar, K. S.↗
NASA NTRS1980

Mechanical properties of Al-mica particulate composite material

Cast aluminum alloy mica particle composites of varying mica content were tested in tension, compression, and impact. With 2.2 percent mica (size range 40-120 microns) the tensile and compression strengths of aluminum alloy decreased by 56 and 22 percent, respectively. The corresponding decreases in percent elongation and percent reduction are 49 and 39 percent. Previous work shows that despite this decrease in strength the composite with 2.5 percent mica and having an UTS of 15 kg/sq mm and compression strength of 28 kg/sq mm performs well as a bearing material under severe running conditions. The differences in strength characteristics of cast aluminum-mica particle composites between tension and compression suggests that, as in cast iron, expansion of voids at the matrix particle interface may be the guiding mechanism of the deformation. SEM studies show that on the tensile fractured specimen surface, there are large voids at the particle matrix interface.

Nath, D.↗
NASA NTRS1989

Mechanical properties of particulate composites based on a body-centered-cubic Mg-Li alloy containing boron

The effect of substituting the Mg metal in Mg-B composites by a Mg-14 wt pct Li solid solution on the ductility of the resulting composite was investigated using elastic modulus measurements on the P/M composite material prepared with a dispersion of B particles (in a vol pct range of 0-30) in a matrix of Mg-14 wt pct Li-1.5 wt pct Al. It was found that the elastic modulus of the composites increased rapidly with increasing boron, with specific stiffness values reaching about two times that of most structural materials. The values of the compression and tensile strengths increased significantly with boron additions. Good tensile ductility was achieved at the level of 10 vol pct B. However, at 20 vol pct B, the Mg-Li composite exhibited only limited tensile ductility (about 2 percent total elongation).

Whalen, R. T.↗
NASA NTRS1990

Slow plastic deformation of extruded NiAl-10TiB2 particulate composites at 1200 and 1300 K

A dispersion of 1-micron TiB2 particles in the B2 crystal structure NiAl intermetallic can effectively increase its elevated temperature strength, in association with increasing deformation resistance with TiB2 volume fraction. Attention is presently given to alternative densification methods, which may increase the initial as-fabricated dislocation density and lead to enhanced elevated-temperature strength. The 'XD' extrusion method was used to produce NiAl with 10 vol pct TiB2. Although apparent extrusion defects were occasionally found, neither grain-boundary cracking nor particle-matrix separation occurred.

Whittenberger, J. D.↗
NASA NTRS1994

Elevated-Temperature Deformation Properties of a HfC Modified Ti-48Al-2Mn-2Nb Matrix Particulate Composite

Rapid solidification techniques in combination with HIPing have been used to produce Ti-48Al-2Mn-2Nb and a Ti-48Al-2Mn-2Nb+15 wt% HfC composite. While the composite does contain several second phases within the gamma + alpha(sub 2) matrix, none was identified to be HfC. The elevated-temperature properties were determined by constant velocity compression and constant load tensile testing in air between 1000 and 1173 K. Such testing indicated that the elevated temperature strengths of the HfC-modified aluminide was superior to those of the unreinforced matrix with the best 1100 K temperature slow strain rate properties for both materials being achieved after high-temperature annealing prior to testing. Examination of the microstructures after deformation in combination with the measured stress exponents and activation energies suggest that creep resistance of the HfC-modified form is due to solid-solution strengthening from carbon and hafnium rather than the presence of second phases.

Whittenberger, J. D.↗
NASA NTRS2014

Novel Epoxy Particulate Composites for Mitigation of Insect Residue Adhesion on Future Aircraft Surfaces

Drag is reduced significantly for airflow over surfaces when laminar flow can be maintained over greater chord lengths, the distance from the leading edge of an airfoil.1 However, surface imperfections, such as chipped paint, scratches, and events that change topography on a microscopic scale can introduce airflow instabilities resulting in premature transition to turbulent flow.1 Although many of these surface imperfections can be avoided with proper maintenance, advanced materials, and advanced manufacturing practices, topographical surface anomalies arising during flight from insect impacts cannot be controlled and can influence laminar flow stability. Practical solutions to this operational challenge need to be developed for future aircraft to have full advantage of laminar flow designs that improve fuel efficiency.2 Researchers have investigated various methods to mitigate insect residue adhesion for decades.3 Although several techniques have demonstrated efficacy including mechanical scrapers, active liquid discharge systems, and sacrificial paper coatings, they have not been commercially implemented due to increased manufacturing and operational complexity, environmental impact, and weight penalties. Coatings offer a simple route for passive insect residue adhesion prevention without many of the challenges associated with maintenance of laminar flow.4 In our previous work, we determined that most commercially available materials were not effective at insect residue adhesion.5 We also identified improvements when both surface energy could be controlled by surface modifying agents and the topography could be altered through the use of micron-sized and nanometer-sized filler materials.6 In this work, these general principles were applied to an epoxy system to evaluate the behavior of the surface modifying agent, a fluorinated alkyl ether oligomer, on surface energy and insect residue adhesion properties.

Wohl, Christopher J.↗
NASA NTRS1996

Micromechanics for particulate reinforced composites

A set of micromechanics equations for the analysis of particulate reinforced composites is developed using the mechanics of materials approach. Simplified equations are used to compute homogenized or equivalent thermal and mechanical properties of particulate reinforced composites in terms of the properties of the constituent materials. The microstress equations are also presented here to decompose the applied stresses on the overall composite to the microstresses in the constituent materials. The properties of a 'generic' particulate composite as well as those of a particle reinforced metal matrix composite are predicted and compared with other theories as well as some experimental data. The micromechanics predictions are in excellent agreement with the measured values.

Murthy, Pappu L. N.↗
NASA NTRS1999

Quantifying Uncertainties in the Thermo-Mechanical Properties of Particulate Reinforced Composites

The present paper reports results from a computational simulation of probabilistic particulate reinforced composite behavior. The approach consists use of simplified micromechanics of particulate reinforced composites together with a Fast Probability Integration (FPI) technique. Sample results are presented for a Al/SiC(sub p)(silicon carbide particles in aluminum matrix) composite. The probability density functions for composite moduli, thermal expansion coefficient and thermal conductivities along with their sensitivity factors are computed. The effect of different assumed distributions and the effect of reducing scatter in constituent properties on the thermal expansion coefficient are also evaluated. The variations in the constituent properties that directly effect these composite properties are accounted for by assumed probabilistic distributions. The results show that the present technique provides valuable information about the scatter in composite properties and sensitivity factors, which are useful to test or design engineers.

Mital, Subodh K.↗
NASA NTRS1981

In situ sensors for measurements in the global trosposphere

Current techniques available for the in situ measurement of ambient trace gas species, particulate composition, and particulate size distribution are reviewed. The operational specifications of the various techniques are described. Most of the techniques described are those that have been used in airborne applications or show promise of being adaptable to airborne applications. Some of the instruments described are specialty items that are not commercially-available. In situ measurement techniques for several meteorological parameters important in the study of the distribution and transport of ambient air pollutants are discussed. Some remote measurement techniques for meteorological parameters are also discussed. State-of-the-art measurement capabilities are compared with a list of capabilities and specifications desired by NASA for ambient measurements in the global troposphere.

Saeger, M. L.↗
NASA NTRS1993

Advanced particulate fibrous composite for thermal control of re-entry vehicles

Combining the selectively reflective properties of particulate reflective coatings with the low density and high temperature capability of ceramic fibrous materials results in a novel composite material with useful optical properties. Numerical predictions of the radiative properties of zirconia and silica composites for a range of mixture fractions and wavelengths show the improvements attainable by dispersing spheres throughout a fiber matrix. The radiation conductance is controlled by the percentage of spheres in the composite. Results show that specific wavelength domains are controlled by either the spheres or the fibers, so the optical properties can be tailored for reentry applications.

White, Susan↗
NASA NTRS1985

Fracto-emission from fiber-reinforced and particulate filled composites

Fracto-emission (FE) in the emission of particles and photons during and following crack propagation. The types of particles observed include electrons (EE), positive ions (PIE), photons (phE), and excited and ground state neutral emission (NE). In this paper work is presented on the characterization of the various FE components and measurements relating FE to the fracture events and material properties involved. FE characteristics measured include total emission, time dependence relative to crack propagation, species of neutral and ionic components, energy of charged species, and time correlations between pairs of FE components. Experiments on fracture of epoxy, single fibers, fiber/epoxy strands, particulate filled epoxy, and multi-ply fiber/epoxy systems will be presented.

Dickinson, J. T.↗
NASA NTRS1991

Compression behavior of TiB2-particulate-reinforced composites of Al22Fe3Ti8

The compression behavior of both the monolithic L1(2) compound Al22Fe3Ti8 and discontinuous composites obtained by incorporating about 1 micron TiB2 particles was studied for various volume percent reinforcements as a function of temperature and at high temepratures as a function of strain rate. In this study, by varying the Fe and Ti contents, the nature and volume fraction of the minor phases coexisting with the dominant L1(2) phase were changed and were examined with and without TiB2 reinforcement. At high strain rates, the TiB2 reinforcements significantly enhance ambiant and warm-temperature strength, although a crossover is observed at about 1000 K, above which the monolithic material is stronger than the composite. At slow strain rates representative of creep conditions, however, the TiB2-containing composites retain their superiority at least up to 1200 K.

Dipietro, M. S.↗