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At least 235 records · Page 13

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NASA NTRS1987

Optimal cure cycle design of a resin-fiber composite laminate

Fibers reinforced composites are used in many applications. The composite parts and structures are often manufactured by curing the prepreg or unmolded material. The magnitudes and durations of the cure temperature and the cure pressure applied during the cure process have significant consequences on the performance of the finished product. The goal of this study is to exploit the potential of applying the optimization technique to the cure cycle design. The press molding process of a polyester is used as an example. Various optimization formulations for the cure cycle design are investigated. Recommendations are given for further research in computerizing the cure cycle design.

Hou, Jean W.↗

NASA NTRS1988

Heavy-Duty Rescue Straps For Coveralls

New type of strap on coveralls helps rescuers lift victims of industrial accidents. Made of heavy twill. New material, 1 in. wide and has breaking strength of 600 lb, sewn to coveralls with polyester thread in box "X" stitching. Reinforcing nylon webbing, 1 3/4 in. wide sewn with strap at attachment points.

Waddell, Henry M.↗

NASA NTRS1988

Heat-Shrinkable, Seamless Fabric Tube

Weaving produces generally tapered shape; heat-shrinking gives final shape. Tube woven in tapered shape from polyester yarn. Placed on heated mandrel. Heat shrinks fibers so sheath assumes shape of mandrel. Sheath coated with impermeable material. Useful on Earth for protective garments.

Lapointe, Donat J. E.↗

NASA NTRS1987

Use of a liquid-crystal and heater-element composite for quantitative, high-resolution heat-transfer coefficients on a turbine airfoil including turbulence and surface-roughness effects

Local heat transfer coefficients were measured along the midchord of a three-times-size turbine vane airfoil in a static cascade operated at room temperature over a range of Reynolds numbers. The test surface consisted of a composite of commercially available materials: a Mylar sheet with a layer of cholestric liquid crystals, which change color with temperature, and a heater made of a polyester sheet coated with vapor-deposited gold, which produces uniform heat flux. After the initial selection and calibration of the composite sheet, accurate, quantitative, and continuous heat transfer coefficients were mapped over the airfoil surface. Tests were conducted at two free-stream turbulence intensities: 0.6 percent, which is typical of wind tunnels; and 10 percent, which is typical of real engine conditions. In addition to a smooth airfoil, the effects of local leading-edge sand roughness were also examined for a value greater than the critical roughness. The local heat transfer coefficients are presented for both free-stream turbulence intensities for inlet Reynolds numbers from 1.20 to 5.55 x 10 to the 5th power. Comparisons are also made with analytical values of heat transfer coefficients obtained from the STAN5 boundary layer code.

Hippensteele, S. A.↗

NASA NTRS1987

Crack diffusion coefficient - A candidate fracture toughness parameter for short fiber composites

In brittle matrix composites, crack propagation occurs along random trajectories reflecting the heterogeneous nature of the strength field. Considering the crack trajectory as a diffusive process, the 'crack diffusion coefficient' is introduced. From fatigue crack propagation experiments on a set of identical SEN polyester composite specimens, the variance of the crack tip position along the loading axis is found to be a linear function of the effective 'time'. The latter is taken as the effective crack length. The coefficient of proportionality between variance of the crack trajectory and the effective crack length defines the crack diffusion coefficient D which is found in the present study to be 0.165 mm. This parameter reflects the ability of the composite to deviate the crack from the energetically most efficient path and thus links fracture toughness to the microstructure.

Mull, M. A.↗

NASA NTRS1988

Graft copolymers from poly(2,6-dimethylphenylene oxide) and pivalolactone

The copolyether-polyester system resulting from the anionic graft polymerization of pivalolactone onto poly(2,6-dimethylphenylene oxide) has been formulated with differing graft densities and graft segment lengths. Wide angle X-ray scattering studies on these materials indicated an increased crystalline order with increased PVL segments/graft for similarly annealed specimens and a decrease in such order with increasing carboxylation.

Bell, Vernon L.↗

NASA NTRS1989

Electrostatic Spraying With Conductive Liquids

Thin, uniform polymer coatings applied in water base normally impossible to charge. Electrostatic sprayer modified so applies coatings suspended or dissolved in electrically conductive liquids. Nozzle and gun constructed of nonconductive molded plastic. Liquid passageway made long enough electrical leakage through it low. Coaxial hose for liquid built of polytetrafluoroethylene tube, insulating sleeve, and polyurethane jacket. Sprayer provided with insulated seal at gun-to-hose connection, nonconductive airhose, pressure tank electrically isolated from ground, and special nozzle electrode. Supply of atomizing air reduced so particle momentum controlled by electrostatic field more effectively. Developed to apply water-base polyurethane coating to woven, shaped polyester fabric. Coating provides pressure seal for fabric, which is part of spacesuit. Also useful for applying waterproof, decorative, or protective coatings to fabrics for use on Earth.

Kosmo, Joseph J.↗

NASA NTRS1988

High-resolution liquid-crystal heat-transfer measurements on the end wall of a turbine passage with variations in Reynolds number

Local heat-transfer coefficients were experimentally mapped on the end-wall surface of a three-times turbine vane passage in a static, single-row cascade operated with room-temperature inlet air over a range of Reynolds numbers. The test surface was a composite of commercially available materials: a Mylar sheet with a layer of cholesteric liquid crystals, which change color with temperature, and a heater made of a polyester sheet coated with vapor-deposited gold, which produces uniform heat flux. After the initial selection and calibration of the composite sheet, accurate, quantitative, and continuous heat-transfer coefficients were mapped over the end-wall surface. The local heat-transfer coefficients (expressed as nondimensional Stanton number) are presented for inlet Reynolds numbers (based on vane axial chord) from 0.83 x 10(5) to 3.97 x 10(5).

Hippensteele, Steven A.↗

NASA NTRS1989

On processing development for fabrication of fiber reinforced composite, part 2

Fiber-reinforced composite laminates are used in many aerospace and automobile applications. The magnitudes and durations of the cure temperature and the cure pressure applied during the curing process have significant consequences for the performance of the finished product. The objective of this study is to exploit the potential of applying the optimization technique to the cure cycle design. Using the compression molding of a filled polyester sheet molding compound (SMC) as an example, a unified Computer Aided Design (CAD) methodology, consisting of three uncoupled modules, (i.e., optimization, analysis and sensitivity calculations), is developed to systematically generate optimal cure cycle designs. Various optimization formulations for the cure cycle design are investigated. The uniformities in the distributions of the temperature and the degree with those resulting from conventional isothermal processing conditions with pre-warmed platens. Recommendations with regards to further research in the computerization of the cure cycle design are also addressed.

Hou, Tan-Hung↗

NASA NTRS1988

A comparison of pure mode I and mixed mode I-III cracking of an adhesive containing an open knit cloth carrier

Static and fatigue tests were carried out on two commercial modified epoxy film adhesives with a wide open knit polyester carrier in order to compare crack resistance in mode I and mixed mode I-III loading. The carrier cloth is found to have a significant influence on the cracking behavior of the adhesives. The open air net carrier used in this study separates from the adhesive in mode I cracking but shreds during mixed-mode crack extension. This decreases the opening mode toughness but increases the mixed-mode toughness as compared with results obtained earlier using a heavier knit carrier. The results suggest that the type of carrier may have a far larger influence on crack resistance than is generally recognized.

Ripling, E. J.↗

NASA NTRS1988

High-resolution liquid-crystal heat-transfer measurements on the endwall of a turbine passage with variations in Reynolds number

Hippensteele, S. A.↗

NASA NTRS1990

The assessment of metal fiber reinforced polymeric composites

Because of their low cost, excellent electrical conductivity, high specific strength (strength/density), and high specific modulus (modulus/density) short metal fiber reinforced composites have enjoyed a widespread use in many critical applications such as automotive industry, aircraft manufacturing, national defense, and space technology. However, little data has been found in the study of short metal fibrous composites. Optimum fiber concentration in a resin matrix and fiber aspect ratio (length-to-diameter ratio) are often not available to a user. Stress concentration at short fiber ends is the other concern when the composite is applied to a load-bearing application. Fracture in such composites where the damage will be initiated or accumulated is usually difficult to be determined. An experimental investigation is therefore carefully designed and undertaken to systematically evaluate the mechanical properties as well as electrical properties. Inconel 601 (nickel based) metal fiber with a diameter of eight microns is used to reinforce commercially available thermoset polyester resin. Mechanical testing such as tensile, impact, and flexure tests along with electrical conductivity measurements is conducted to study the feasibility of using such composites. The advantages and limitations of applying chopped metal fiber reinforced polymeric composites are also discussed.

Chung, Wenchiang R.↗

NASA NTRS1991

Superfiber For Strong, Light Fabrics

New ultrahigh-molecular-weight fiber offers major advantages as fabric for space suits, diving suits, sporting goods, sails, and ultralight aircraft. Polyolefin fiber has extremely high modulus of elasticity, low elongation, high specific strength, low specific gravity, resistance to chemicals, low moisture absorption, and high resistance to damage by flexure and abrasion. Consists of elongated, highly aligned, highly crystalline polyethylene molecules. Structure not only results in high strength-to-weight ratio but also gives high resistance to tearing and ripping. Fibers woven in many patterns. Offers combination of desirable properties not found in nylon, polyester, or aramid fabrics.

Dawn, Frederic S.↗

NASA NTRS1989

Evaluation of Composite Materials for Use on Launch Complexes

Commercially available composite structural shapes were evaluated for use. These composites, fiberglass-reinforced polyester and vinylester resin materials are being used extensively in the fabrication and construction of low maintenance, corrosion resistant structures. The evaluation found that in many applications these composite materials can be successfully used at the space center. These composite materials should not be used where they will be exposed to the hot exhaust plume/cloud of the launch vehicle during the liftoff, and caution should be taken in their use in areas where electrostatic discharge and hypergolic propellant compatibility are primary concerns.

Finchum, A.↗

NASA NTRS1991

Preliminary investigation of thin film polymers exposed to low Earth orbit

Preliminary results of thin film polymers exposed to low-Earth orbit aboard the Long Duration Exposure Facility (LDEF) are discussed. Dynamic testing of a 0.92/0.92 mil. polyester laminate film indicated that the modulus loss of the exposed specimens may be very small. When the storage modulus of the exposed specimen was compared to the storage modulus of a control specimen over a temperature range of minus 150 degrees to 100 degrees, there was very little change. Fourier Transform Spectroscopy performed on the same exposed material indicated crosslinking of the polyethylene, which was verified by an increase in the storage modulus above the glass transition temperature. Optical microscopy of the sample showed micrometeoroid strikes and contamination in spots by what is thought to be silicon outgassed from a nearby experiment.

Strganac, Thomas↗

NASA NTRS1991

Study of balloon and thermal control material degradation aboard LDEF

The initial results of analysis performed on a number of polymeric materials which were exposed aboard the Long Duration Exposure Facility (LDEF) are discussed. These materials include two typical high altitude balloon films (a polyester and a polyethylene) and silver-backed Teflon from thermal control blanket samples. The techniques used for characterizing changes in mechanical properties, chemical structure and surface morphology include Fourier Transform Infrared (FTIR) spectroscopy, scanning electron microscopy, and dynamic mechanical analysis.

Letton, Alan↗

NASA NTRS1991

The influence of flowing afterglow exposure on the degradation of various polymeric materials

Changes in polymer properties which result after exposure to an atomic oxygen-rich environment of a flowing afterglow are presented. Dynamic mechanical and Fourier Transform Infrared (FTIR) spectra as well as scanning electron microscopy micrographs were employed to monitor variations in mechanical properties and chemical and physical structure. Polymers analyzed include polystyrene, PEKK, and a polyester.

Letton, Alan↗

NASA NTRS1990

High temperature polymers - A review of novel thermally stable hexafluoroisopropylidene-containing polymers

The synthesis and properties to date of several novel HFIP-containing polymers and copolymers are presented. Thermal analyses of polyether ketones (PEK), aromatic polyesters, and polymers from a novel 18F-diacid were performed on a thermal analyzer. All three polymer types exhibited enhanced solubility, thermal stability, and low dielectric constants that are predicted for polymers containing the HFIP moiety. The moderate thermal stability observed in the polymers derived from the 18F-diacid is attributed to the oxidatively weak methylene linkage between the HFIP groups and the phenyl rings. PEKs and polyarylates show potential as high emissivity coatings under conditions where atomic oxygen is present.

Kane, K. M.↗