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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 253 records · Page 14

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NASA NTRS1983

Spherical micro-glass particle impingement studies of thermoplastic materials at normal incidence

Light optical and scanning electron microscope studies were conducted to characterize the erosion resistance of polymethyl methacrylate (PMMA), polycarbonate (PC), polytetrafluoroethylene (PTFE) and ultra-high-molecular-weight-polyethylene (UHMWPE). Erosion was caused by a jet of spherical micro-glass beads at normal impact. During the initial stages of damage, the surfaces of these materials were studied using a profilometer. Material buildup above the original surface was observed on PC and PMMA. As erosion progressed, this buildup disappeared as the pit became deeper. Little or no buildup was observed on PTFE and on UHMWPE. UHMWPE and PTFE are the most resistant materials and PMMA the least. Favorable properties for high erosion resistance seem to be high values of ultimate elongation, and strain energy and a low value of the modulus of elasticity. Erosion-rate-versus-time curves of PC and PTFE exhibit incubation, acceleration and steady state periods. A continuously increasing erosion rate period was observed however for PMMA instead of a steady state period. At early stages of damage and at low impact pressure material removal mechanisms appear to be similar to those for metallic materials.

Rao, P. V.↗

NASA NTRS1984

Development of an impact- and solvent-resistant thermoplastic composite matrix

Synthesis, moldability and chloroform, acetone and tricresyl phosphate resistance of 16 polymer compositions are described. These aliphatic heterocyclic polymers include polyimides, polybenzimidazoles, and N-arylenepolybenzimidazoles. A solution condensation (cresol) method to prepare imidized aliphaic polyimides is described. Two polyimides and one polybenzimidazole demonstrate no crazing or cracking during 500 hr exposure to the cited solvents under stress. Modification of one aliphatic polyimide with several aromatic amines suggests that m-phenylenediamine is singular in its behavior to improve the chloroform resistance of that class of polyimides.

Delano, C. B.↗

NASA NTRS1984

Preparation and characterization of siloxane-containing thermoplastic polyimides

Copolyimides and homopolyimides of bis(gamma-aminopropyl)tetramethyldisiloxane and 3,3'-diaminobenzophenone have been prepared with benzophenonetetracarboxylic dianhydride. The properties of the copolyimides were compared with those of the homopolyimides to assess the effect of incorporation of siloxane groups in the backbone. Applications of the polymers as adhesives and mouldings are discussed.

Maudgal, S.↗

NASA NTRS1984

Free Volume Considerations in Thermoplastic and Thermosetting Resins

The direct measurement of physical aging and of the volume changes which go on during the course of this aging is discussed. Data on PMMA showing its physical aging as measured by its stress relaxation response and the accompanying volume changes are presented. An indication of how one can measure the free volume both directly from the volume change itself and relatively directly via a new technique is given. The application of this new technique (electron spin resonance spectroscopy) to other polymer systems is demonstrated.

Landel, R. F.↗

NASA NTRS1983

Thermoset-thermoplastic aromatic polyamide containing N-propargyl groups

A composition and method are disclosed for increasing the use temperature of polyamides based on the incorporation of a latent crosslinking agent into the polymer backbone, wherein high temperature performance is achieved without sacrificing solubility or processability.

St.clair, T. L.↗

NASA NTRS1985

Determination of the viscosity number of thermoplastics in dilute solution; polyamides (PA)

This West German Standard presents a test used to determine the viscosity number of polyamides and copolyamides which are easily diluted in sulfuric acid, and for other polyamides which are less easily diluted in sulfuric acid, and which are diluted in m-cresol. As formic acid is often used in industry instead of sulfuric acid, this solvent is also presented as an alternative, however, sulfuric acid is preferred because of the thermodynamic solubility characteristics of the polyamides and the handling safety. In addition, it is shown which solvent should be used for each polyamide. Finally, determinations concerning the preparation of the samples are presented. Using the viscosity number, a determination of the molar mass of the polyamides is possible.

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NASA NTRS1984

Spherical microglass particle impingement studies of thermoplastic materials at normal incidence

Veerabhadra Rao, P.↗

NASA NTRS1985

Graphite fiber reinforced thermoplastic glass matrix composites for use at 1000 F

The fabrication and properties of the graphite fiber reinforced glass matrix composite system are described. By reinforcing borosilicate glass with graphite fibers it has been possible to develop a composite whose properties can be compared favorably with resin matrix counterparts. Both high elastic modulus and strength can be obtained and maintained to temperatures of approximately 600 C. In addition, composite dimensional stability is superior to resin or metal matrix systems due to the low thermal expansion behavior of the glass matrix.

Prewo, K. M.↗

NASA NTRS1985

Angular particle impingement studies of thermoplastic materials at normal incidence

Scanning electron microscope studies were conducted to characterize the erosion resistance of polymethyl methacrylate (PMMA), polycarbonate (PC), polytetrafluorethylene (PTFE), and ultra-high-molecular-weight polyethylene (UHMWPE). Erosion was caused by a jet of angular microparticles of crushed glass at normal incidence. Material built up above the original surface on all of the materials. As erosion progressed, this buildup disappeared. UHMWPE was the most resistant material and PMMA the least. The most favorable properties for high erosion resistance were high values of ultimate elongation, maximum service temperature, and strain energy and a low value of the modulus of elasticity. Erosion-rate-versus-time curves of PC and PTFE exhibited incubation, acceleration, and steady-state periods. PMMA also exhibited a deceleration period, and an incubation period with deposition was observed for UHMWPE.

Rao, P. V.↗

NASA NTRS1986

Evaluation of a novel thermoplastic polyimide for bonding titanium

A novel hot-melt processable polyimide has been synthesized and characterized as an adhesive for a titanium alloy. This system shows potential for applications with service temperatures near 200 C. A bonding cycle was developed from preliminary processing studies. The bonded specimens were tested at room temperature, 177 C and 204 C both before and after aging in air at 204 C for times up to 1000 hours. There was no appreciable change in strength after aging. Bonded specimens were exposed to boiling water continuously for a 72 hour period. These specimens exhibited some loss in strength due to this rather severe exposure.

Progar, D. J.↗

NASA NTRS1987

Thermoplasticity of coupled bodies in the case of stress-dependent heat transfer

The problem of the thermal stresses in coupled deformable bodies is formulated for the case where the heat-transfer coefficient at the common boundary depends on the stress-strain state of the bodies (e.g., is a function of the normal pressure at the common boundary). Several one-dimensional problems are solved in this formulation. Among these problems is the determination of the thermal stresses in an n-layer plate and in a two-layer cylinder.

Kilikovskaya, O. A.↗

NASA NTRS1986

Estimation of crystallinity in a model thermoplastic composite

Crystallinities as low as 16 percent have been estimated by determination of the interplanar spacing on PET/carbonaceous filament composites with resin content of aobut 25 percent w/w using wide-angle X-ray scattering (WAXS) in the angular range 2 theta = 16-18 deg. The diffraction pattern of the carbonaceous reinforcements masks the major reflections of the resin, and the resin content and the crystallinity are kept low to make the simulation reasonable.

Wakelyn, N. T.↗

NASA NTRS1986

Resolution of wide-angle X-ray scattering from a thermoplastic composite

Wide-angle X-ray scattering from a polyetheretherketone/carbonaceous-fiber composite has been resolved using a curve-fit procedure. This resolution yielded under-curve areas for crystalline, amorphous, and fiber scatter which could be used as the basis for an estimation of crystallinity.

Wakelyn, N. T.↗

NASA NTRS1987

Thermoplastic matrix composites - LARC-TPI, polyimidesulfone and their blends

Composites were fabricated from unidirectional unsized AS-4 carbon fiber and two baseline polyimides: benzophenone dianhydride-3,3'-diaminodiphenylsulfone (PISO2) and benzophenone dianhydride-3,3'-diaminobenzophenone (LARC-TPI). In addition, each polymer solution prior to prepregging was doped with various amounts of crystalline LARC-TPI powder to enhance melt flow during press molding. The 2:1, 1:1, and 1:2 ratios of crystalline to amorphous resin, respectively, were studied in the LARC-TPI system and the 1:2 ratio in the PISO2 system. Matrix characterization, prepreg fabrication/characterization and composite fabrication and physical/mechanical properties are described. The latter include three point short beam shear and flexure, dry and wet, as well as fracture toughness properties in selected compositions.

Johnston, Norman J.↗

NASA NTRS1986

Fatigue delamination behavior of PEEK thermoplastic composite laminates

The delamination resistance of graphite-reinforced PEEK composites was quantified by conducting static and cyclic edge delamination tests on (35n/-35n/0n/90n)s AS4/PEEK laminates, where n = 1, 2. The experimentally determined mechanical delamination onset strains were used to calculate the critical strain-energy release rate for delamination onset as a function of fatigue cycle. The delamination onset strains decreased dramatically with fatigue cycles and then began to level off to an endurance limit at 1 million cycles. Although the static interlaminar fracture toughness of the AS4/PEEK composite is much greater than the toughness of graphite epoxy composites, the delamination fatigue threshold, calculated from the cyclic strain endurance limit at 1 million cycles, was only slightly greater than the threshold for graphite epoxy composites. The contribution of residual thermal stresses to delamination in the AS4/PEEK is substantial due to the large temperature range between the manufacture and the room temperatures.

O'Brien, T. K.↗

NASA NTRS1986

Resolution of wide angle X-ray scattering from a thermoplastic composite

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Wakelyn, N. T.↗

NASA NTRS1988

Field Repair Of Thermoplastic Windows And Canopies

Toroid bonding techniques further developed to meet typical field-repair requirements. Induction-heating power supply engineered into "ruggedized" solid-state unit, in a 1-ft to the third power package weighing 20 lb. Hand-held bonding gun weighing 3 lb plugs into this power supply on long cord. Maximum power required is 300 W. Lightly loaded repair bonds made in several minutes at average power input of 150 W on metallic, polymeric, or polymermatrix materials.

Fox, Robert L.↗

NASA NTRS1987

Development of an impact- and solvent-resistant thermoplastic composite matrix, phase 4

Polyimides from BTDA with m-phenylenediamine and three aliphatic diamines were prepared in cresol and characterized. Characterization tests included compression strength and modulus, stressed solvent resistance, and melt-flow tests. Efforts to reduce the molecular weights of these polymers by either stoichiometric imbalance or phthalic anhydride end capping produced opacity in the polymer moldings when the stoichiometry was less than 99 percent. Use of 2,4-diaminotoluene in place of the m-phenylenediamine allowed clear polymer moldings to be obtained at all stoichiometries by end capping or stoichiometric imbalance. After melt-flow/molecular-weight studies, carbon fabric composites were prepared from three polyimide compositions containing BTDA, 2,4-diaminotoluene and two aliphatic diamines. Flexural strengths of two of the resins were in excess of 689 MPa (100 ksi) at both room temperature and 93 C. The polyimide from BTDA was selected for scale-up and neat resin characterization tests. The Tg of this polymer was 233 C.

Delano, C. B.↗