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Results for “structure-property relationships”

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 NTRS1974

Investigation of Structure-Property Relationships in Systematic Series of Novel Polymers

The results are discussed of the on-line interface of the Torsional Braid Analysis experiment to an Hierarchical Computer System for data acquisition, data reduction and control of experimental variables. Some experimental results are demonstrated and the data reduction procedures are outlined. Several modes of presentation of the final computer-reduced data are discussed in an attempt to elucidate possible interrelations between the thermal variation of the rigidity and loss parameters.

Gillham, J. K.↗
NASA NTRS1975

Structure-property relationships in thermomechanically treated beryllia dispersed nickel alloys

BeO dispersed nickel alloys, produced by powder metallurgy techniques, were studied extensively in stress rupture at 815, 982, and 1093 C (1088, 1255, and 1366 K) and by transmission electron microscopy. The alloys were subjected to a variety of thermomechanical treatments (TMT) to determine the benefits of TMT on properties. It is shown that the use of intermediate annealing treatments after 10 pct reduction steps is highly beneficial on both low and high temperature properties. It is indicated that the high temperature strength is not primarily dependent on the grain aspect ratio or texture but depends strongly on the dislocation density and distribution of dislocations in a stable substructure which is pinned by the fine oxide dispersion.

Grewal, M. S.↗
NASA NTRS1976

Investigation of structure-property relationships in systematic series of novel polymers

Solid state transitions in polymeric materials was associated with the onset of sub-molecular motions of the polymer chains. Although these were considered to be intramolecular in general, the local environment of the polymer molecule exerts a strong influence through, for example, the effects of crystallinity, polarity and diluents. The manner of specimen preparation and previous history also affect transitions. The transitions are considered to arise when sufficient free volume is available to permit the occurrence of these side chain and backbone reorientations. The glass transition is the principal transition of amorphous polymeric materials and is associated with the onset of long range segmental motion of the polymer backbone. The various types of shorter range motion occurring below the glass transition have been catalogued.

Gillham, J. K.↗
NASA NTRS1976

Structure-property relationships in block copolymers

Block copolymers are a class of relatively new materials which contain long sequences of two (or more) chemically different repeat units. Unlike random copolymers, each segment may retain some properties which are characteristic of its homopolymer. It is well known that most physical blends of two different homopolymers are incompatible on a macro-scale. By contrast most block copolymers display only a microphase (eg. 100-200 A domains) separation. Complete separation is restricted because of a loss in configurational entropy. The latter is due to presence of chemical bond(s) between the segments. Novel physical properties can be obtained because it is possible to prepare any desired combination of rubber-like, glassy, or crystalline blocks. The architecture and sequential arrangement of the segments can strongly influence mechanical behavior.

Mcgrath, J. E.↗
NASA NTRS1977

Structure-property relationships in low-temperature adhesives

Adhesive materials of aliphatic polyester, linear hydroxyl end-capped polybutadienes, or SBS block copolymers are studied with the objective to replace conventional partially aromatic end-reactive polyester-isocyanate adhesives that have shown embrittlement

Schoff, C. K.↗
NASA NTRS1976

Structure-property relationships in eutectic composites

The preparation of a composite material of eutectic composition directly from the molten state is investigated. The manufacture of eutectic composites by unidirectional solidification is reviewed, and it is shown how two-phase composite structures of given relative volume fraction can be produced with a range of particle sizes. Crystallographic relationships and the thermal stability of interfaces in controlled eutectic structures are examined, the mechanical behavior of aligned eutectic microstructures is discussed, and characteristics of eutectic composites having mechanical properties of engineering significance are evaluated. Specific properties of the Ni-Nb eutectic alloy are reviewed to demonstrate the effect of structure control (through directional solidification) on the mechanical response of a eutectic composite. It is noted that unidirectionally solidified eutectic composites possess highly aligned and thermally stable microstructures and also exhibit excellent combinations of strength and ductility to very high temperature levels.

Hertzberg, R. W.↗
NASA NTRS1977

Structure-property relationships in oxide-dispersed iron-beryllia alloys

Two BeO dispersed iron alloys containing about 2.5 and 5.5 v/o dispersoid were produced by attritting, internally oxidizing, and extruding dilute, prealloyed Fe-Be powders. As-extruded alloys were given various thermomechanical treatments involving room temperature swaging and annealing above and below the allotropic transformation temperature. The elevated temperature rupture strengths were measured and correlated with changes in structure; strengthening trends were examined in the light of proposed models for such strengthening. The results obtained showed that the elevated temperature strength was determined by the oxide interparticle spacing (IPS) in recrystallized material and IPS as well as prior deformation in swaged specimens. In fact, a parametric correlation was found between rupture strength values in the longitudinal direction with prestrain during swaging. The overall pattern in strength and microstructural observations were more consistent with a strength-stored energy (substructure) dependence than a strength-grain shape (grain aspect ratio) relation.

Wolf, S.↗
NASA NTRS1987

Structure-property relationships in semiconductor alloys

It is presently noted that the atomic distribution of constituents in semiconductor alloys is never truly random, since there are always interactions giving rise to correlations whose degree and character depend on which interactions are dominant, as well as on the growth conditions. Although most of the interactions that can be expected to generate correlations have been identified, the fact that not all have been thus far treated exhaustively leaves several details unclear. A characterization of the primary effects in general terms is accordingly achieved.

Sher, A.↗
NASA NTRS1987

Structure-property relationships in directionally solidified single crystal NiAl

The ordered intermetallic alloy NiAl is being considered as a potential high temperature structural material, but lack of ductility at ambient temperatures, especially in polycrystalline form, is presently a major obstacle in achieving this goal. Even general agreement of the intrinsic ductility that can be achieved in monocrystals is in dispute. In order to understand this problem, two directionally solidified ingots of NiAl which displayed known differences in ductility were characterized in sufficient detail to identify the corresponding microstructural differences. It was found that the type and size of casting defects, i.e., porosity, present in the material were the major factors in controlling ductility of NiAl single crystals and could explain the order of magnitude variance in fracture strains reported in the literature.

Noebe, R. D.↗
NASA NTRS1981

Recent developments in polyimide adhesives at NASA-Langley Research Center

Adhesive development is directed towards elevated temperature applications (200-300 C). Because of thermal stability considerations, the most attractive adhesives for this temperature range are linear and addition polyimides. The linear polymide adhesive research encompassed basic structure-property relationships, solvent studies and formulations to meet various requirements. The most recent research in linear polyimide systems was in the development of thermoplastic systems in an effort to eliminate the undesirable evolution of water classically associated with the cure going through an amide-acid intermediate step in the cure process. Addition polyimide adhesive research was undertaken in order to avoid water evolution during cure. Basic structure-property relationships for these materials led to an adhesive which was used extensively for high temperature adhesive needs. Since addition systems are of a highly crosslinked nature, they are not as resistant to impact as their linear counterparts. In order to overcome this problem, research was done in the area of elastomer-toughening these polymers.

St.clair, T. L.↗
NASA NTRS1972

Thermally stable macromolecules.

Man-made polymers are compared with certain naturally occurring polymers which have long been used at elevated temperatures. The pyrolysis of model compounds is discussed together with aspects of thermogravimetric analysis, torsional braid analysis, and questions of chemical and radiation stability. Some structure-property relationships are examined, giving attention to asbestos, mica, graphite, and diamond. Questions of bond strengths are investigated along with the stability of ladder polymers and some fundamental concepts in the synthesis of aromatic and heteroaromatic polymers. The substances considered include aromatic single-strand polymers, heteroaromatic polymers, polymers obtained by addition polymerizations, and nonhydrogen-containing polymers. Future trends are also explored.

Pezdirtz, G. F.↗
NASA NTRS1982

Polymer research at NASA Langley Research Center

Polymer synthesis programs involve the development of Novel thermoplastics, pseudothermoplastics, and thermosets. These systems are prepared to elucidate structure-property relationships involving thermal capabilities, toughness, processability and environmental stability. Easily processable polyimides, solvent-resistant polysulfones and polyphenylquinoxalines, and tougher high and intermediate temperature polymers were developed. Characterization efforts included high pressure liquid chromatography methodology, the development of toughness tests for fiber reinforced composites, a study of electrical properties of metal ion filled polyimides, and a study of the mutagenicity of aromatic diamines. Also the mechanism of cure/degradation of experimental polymers was studied by rheology, mechanical behavior, separation techniques and spectroscopy. The degradative crosslinking of alkyl-containing polyimides, the separation and identification of crosslinked phenylquinoxalines, the rheological behavior of hot-melt polyimides, and the elucidation of the cure of norbornene endcapped imides were also studied.

Terry L. St. Clair↗
NASA NTRS1985

Electrical conduction in polymer dielectrics

The use of polymer dielectrics with moderate resistivities could reduce or eliminate problems associated with spacecraft charging. The processes responsible for conduction and the properties of electroactive polymers are reviewed, and correlations drawn between molecular structure and electrical conductivity. These structure-property relationships led to the development of several new electroactive polymer compositions and the identification of several systems that have the requisite thermal, mechanical, environmental and electrical properties for use in spacecraft.

Cotts, D. B.↗
NASA NTRS1985

Optically transparent/colorless polyimides

Several series of linear aromatic polyimide films have been synthesized and characterized with the objective of obtaining maximum optical transparency. Two approaches have been used as part of this structure-property relationship study. The first approach is to vary the molecular structure so as to separate chromophoric centers and reduce electronic interactions between polymer chains to lower the intensity of color in the resulting polymer films. A second and concurrent approach is to perform polymerizations with highly purified monomers. Glass transition temperatures of thermally cured polyimide films are obtained by thermomechanical analysis and thermal decomposition temperatures are determined by thermogravimetric analysis. Transmittance UV-visible spectra of the polyimide films are compared to that of a commercial polyimide film. Fully imidized films are tested for solubility in common organic solvents. The more transparent films prepared in this study are evaluated for use on second-surface mirror thermal control coating systems. Lightly colored to colorless films are characterized by UV-visible spectroscopy before and after exposure to 300 equivalent solar hours UV irradiation and varying doses of 1 MeV electron irradiation. The effects of monomer purity, casting solvent and cure atmosphere on polyimide film transparency are also investigated.

Stclair, A. K.↗
NASA NTRS1986

Activities of the Center for the Space Processing of Engineering Materials

Topics addressed include: containerless processing and purification; directional and rapid solidification; high temperature alloys; oxidation resistant niobium alloys; metallic bonding; effects of solidification mode on structure-property relationships; and dispersion strengthened metal alloys. Each of the projects is reported by company association and follow according to alphabetical order of the company names.

Source record↗
NASA NTRS1987

Adhesive evaluation of new polyimides

During the past 10 to 15 years, the Materials Division at NASA Langley Research Center (LaRC) has developed several novel high temperature polyimide adhesives for anticipated needs of the aerospace industry. These developments have resulted from fundamental studies of structure-property relationships in polyimides. Recent research at LaRC has involved the synthesis and evaluation of copolyimides which incorporate both flexibilizing bridging groups and meta-linked benzene rings. The purpose was to develop systems based on low cost, readily available monomers. Two of these copolyimides evaluated as adhesives for bonding titanium alloy, Ti(6Al-4V), are identified as LARC-STPI and STPI-LARC-2. Lap shear strength (LSS) measurements were used to determine the strength and durability of the adhesive materials. LSS results are presented for LARC-TPI and LARC-STPI lap shear specimens thermally exposed in air at 232 C for up to 5000 hrs. LARC-TPI was shown to perform better than the copolymer LARC-STPI which exhibited poor thermooxidative performance possibly due to the amines used which would tend to oxidize easier than the benzophenone system in LARC-TPI.

Stclair, Terry L.↗