Engineering Papers⌕ Search

SEARCH · Engineering Papers

Results for “polyimide”

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.

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 1,621 records · Page 90
All sourcesNASA NTRSDOE OSTI
NASA NTRS1997

Titanium Layer Influence on the Strength of a Hybrid Titanium Composite Laminate

An experimental study was undertaken to investigate the mechanical response of four hybrid titanium composite laminate (HTCL) systems, each prepared using a graphite fiber reinforced thermoplastic polyimide as the adhesive in a unidirectional prepreg. Two of the four HTCL systems were fabricated with the titanium Ti-15-3 alloy, while the other two systems were fabricated with the titanium Timetal Beta-21S alloy. Each HTCL system consisted of either three plies or four plies of the titanium alloy. Systems with only three plies of titanium had plies measuring 10 mils thick, whereas systems consisting of four plies of titanium had plies measuring 5 mils thick. The improvement in mechanical properties achieved by comparing the uniaxial tensile results of static strength at room temperature. Results included stress-strain curves, ultimate strength, strain-to-failure, initial modulus of the HTCL's, and the description of the observed modes of failure.

Veazie, David R.↗
NASA NTRSDate not supplied

AXAF Hypervelocity Impact Test Results

Composite and honeycomb panels are commonly used for spacecraft structural components. The impact test results and analysis of six different composite and honeycomb combinations for use on the advanced X-ray astrophysics facility (AXAF) are reported. The AXAF consists of an X-ray telescope and the associated detecting devices attached to an octagonal spacecraft with an internal propulsion system. The spacecraft's structural panels and optical bench are made of two different graphite fiber reinforced polyimides or composite panels bonded to either side of an aluminum honeycomb. The instrument is required to have at least a 0.92 probability of no failure of any of the critical elements due to meteoroids and debris. In relation to the no-failure probability determination in its low earth orbit environment, hypervelocity impact testing was performed to determine the ballistic limit range and the extent of damage due to impact. The test results for a power and signal cable bundle located behind a panel are presented. Tests planned for a multilayer insulation (MLI) blanket and four types of cable bundles are discussed.

Cynthia L Frost↗
NASA NTRS1997

Organometallic Polymeric Conductors

For aerospace applications, the use of polymers can result in tremendous weight savings over metals. Suitable polymeric materials for some applications like EMI shielding, spacecraft grounding, and charge dissipation must combine high electrical conductivity with long-term environmental stability, good processability, and good mechanical properties. Recently, other investigators have reported hybrid films made from an electrically conductive polymer combined with insulating polymers. In all of these instances, the films were prepared by infiltrating an insulating polymer with a precursor for a conductive polymer (either polypyrrole or polythiophene), and oxidatively polymerizing the precursor in situ. The resulting composite films have good electrical conductivity, while overcoming the brittleness inherent in most conductive polymers. The highest conductivities reported (approximately 4/Scm) were achieved with polythiophene in a polystyrene host polymer. The best films using a polyamide as base polymer were four orders of magnitude less conductive than the polystyrene films. The authors suggested that this was because polyimides were unable to swell sufficiently for infiltration of monomer as in the polystyrene. It was not clear, however, if the different conductivities obtained were merely the result of differing oxidation conditions. Oxidation time, temperature and oxidant concentration varied widely among the studies.

Source record↗
NASA NTRS1997

Low Cost Manufacturing Approach of High Temperature PMC Components

The overall objective is to develop a satisfactory sheet molding compound (SMC) of a high temperature polyimide, such as PMR-11-50, VCAP-75, or NB2-76, and to develop compression molding processing parameters for a random, chopped fiber, high temperature, sheet molding compound that will be more affordable than the traditional hand lay-up fabrication methods. Compression molding will reduce manufacturing costs of composites by: (1) minimizing the conventional machining required after fabrication due to the use of full 360 deg matched tooling, (2) reducing fabrication time by minimizing the intensive hand lay-up operations associated with individual ply fabrication techniques, such as ply orientation and ply count and (3) possibly reducing component mold time by advanced B-staging prior to molding. This program is an integral part of Allison's T406/AE engine family's growth plan, which will utilize technologies developed under NASA's Sub-sonic Transport (AST) programs, UHPTET initiatives, and internally through Allison's IR&D projects. Allison is aggressively pursuing this next generation of engines, with both commercial and military applications, by reducing the overall weight of the engine through the incorporation of advanced, lightweight, high temperature materials, such as polymer matrix composites. This infusion of new materials into the engine is also a major factor in reducing engine cost because it permits the use of physically smaller structural components to achieve the same thrust levels as the generation that it replaced. A lighter, more efficient propulsion system translates to a substantial cost and weight savings to an airframe's structure.

Kannmacher, Kevin↗
NASA NTRS1998

Evaluation of Composite Honeycomb Sandwich Panels Under Compressive Loads at Elevated Temperatures

Fourteen composite honeycomb sandwich panels were tested to failure under compressive loading. The test specimens included panels with both 8 and 24-ply graphite-bismaleimide composite facesheets and both titanium and graphite-polyimide core materials. The panels were designed to have the load introduced through fasteners attached to pairs of steel angles on the ends of the panels to simulate double shear splice joints. The unloaded edges were unconstrained. Test temperatures included room temperature, 250F, and 300F. For the room and 250F temperature tests, the 24-ply specimen failure strains were close to the unnotched allowable strain values and failure loads were well above the design loads. However, failure strains much lower than the unnotched allowable strain values, and failure loads below the design loads were observed with several of the 8-ply specimens. For each individual test temperature, large variations in the failure strains and loads were observed for the 8-ply specimens. Dramatic decreases in the failure strains and loads were observed for the 24-ply specimens as the test temperature was increased from 250F to 300F. All 8-ply specimens appeared to have failed in a facesheet strength failure mode for all test temperatures. The 24-ply specimens displayed appreciably greater amounts of bending prior to failure than the 8-ply specimens, and panel buckling occurred prior to facesheet strength failure for the 24-ply room and 250F temperature tests.

Walker, Sandra P.↗
NASA NTRS1998

Monte Carlo Simulation of Endlinking Oligomers

This report describes initial efforts to model the endlinking reaction of phenylethynyl-terminated oligomers. Several different molecular weights were simulated using the Bond Fluctuation Monte Carlo technique on a 20 x 20 x 20 unit lattice with periodic boundary conditions. After a monodisperse "melt" was equilibrated, chain ends were linked whenever they came within the allowed bond distance. Ends remained reactive throughout, so that multiple links were permitted. Even under these very liberal crosslinking assumptions, geometrical factors limited the degree of crosslinking. Average crosslink functionalities were 2.3 to 2.6; surprisingly, they did not depend strongly on the chain length. These results agreed well with the degrees of crosslinking inferred from experiment in a cured phenylethynyl-terminated polyimide oligomer.

Hinkley, Jeffrey A.↗
NASA NTRS1995

Effects of Endcaps on the Properties of Polyimide/Carbon Fiber Composites

Carbon fiber (T650-35) composites were fabricated from polyimide resins, using 4,4'-(hexafluoroisopropylidene) diphthalic acid, dimethyl esters (HFDE) and p-phenylenediamine (p-PDA) with three different endcaps; namely, nadic ester (NE), p-aminostyrene (p-AS) and 4-phenylethynylphthalic acid, methyl ester. The curing chemistry of these endcaps will be reviewed. The thermo-oxidative stability as well as the physical and mechanical properties of these polyimide/carbon fiber composites will be discussed.

Chuang, Kathy C.↗
NASA NTRS1998

Monte Carlo Computational Modeling of the Energy Dependence of Atomic Oxygen Undercutting of Protected Polymers

A Monte Carlo computational model has been developed which simulates atomic oxygen attack of protected polymers at defect sites in the protective coatings. The parameters defining how atomic oxygen interacts with polymers and protective coatings as well as the scattering processes which occur have been optimized to replicate experimental results observed from protected polyimide Kapton on the Long Duration Exposure Facility (LDEF) mission. Computational prediction of atomic oxygen undercutting at defect sites in protective coatings for various arrival energies was investigated. The atomic oxygen undercutting energy dependence predictions enable one to predict mass loss that would occur in low Earth orbit, based on lower energy ground laboratory atomic oxygen beam systems. Results of computational model prediction of undercut cavity size as a function of energy and defect size will be presented to provide insight into expected in-space mass loss of protected polymers with protective coating defects based on lower energy ground laboratory testing.

Banks, Bruce A.↗
NASA NTRS1998

The Optical Design of a System using a Fresnel Lens that Gathers Light for a Solar Concentrator and that Feeds into Solar Alignment Optics

The Marshall Space Flight Center (MSFC) has been developing a space deployable, lightweight membrane concentrator to focus solar energy into a solar furnace while remaining aligned to the sun. For an inner surface, this furnace has a cylindrical heat exchanger cavity coaligned to the optical axis; the furnace warms gas to propel the spacecraft. The membrane concentrator is a 1727 mm (68.00 in.) diameter, F/1.7 Fresnel lens. This large membrane is made from polyimide and is 0.076 mm (0.0030 in.) thick; it has the Fresnel grooves cast into it. The solar concentrator system has a super fast paraboloid reflector near the lens focus and immediately adjacent to the cylindrical exchanger cavity. The paraboloid collects the wide bandwidth and some of the solar energy scattered by the Fresnel lens. Finally, the paraboloid feeds the light into the cylinder. The Fresnel lens also possesses a narrow annular zone that focuses a reference beam toward four detectors that keep the optical system aligned to the sun; thus, occurs a refracting lens that focuses two places! The result can be summarized as a composite Fresnel lens for solar concentration and alignment.

Wilkerson, Gary W.↗
NASA NTRS1998

Experimental Performance of a Micromachined Heat Flux Sensor

Steady-state and frequency response calibration of a microfabricated heat-flux sensor have been completed. This sensor is batch fabricated using standard, micromachining techniques, allowing both miniaturization and the ability to create arrays of sensors and their corresponding interconnects. Both high-frequency and spatial response is desired, so the sensors are both thin and of small cross-sectional area. Thin-film, temperature-sensitive resistors are used as the active gauge elements. Two sensor configurations are investigated: (1) a Wheatstone-bridge using four resistors; and (2) a simple, two-resistor design. In each design, one resistor (or pair) is covered by a thin layer (5000 A) thermal barrier; the other resistor (or pair) is covered by a thick (5 microns) thermal barrier. The active area of a single resistor is 360 microns by 360 microns; the total gauge area is 1.5 mm square. The resistors are made of 2000 A-thick metal; and the entire gauge is fabricated on a 25 microns-thick flexible, polyimide substrate. Heat flux through the surface changes the temperature of the resistors and produces a corresponding change in resistance. Sensors were calibrated using two radiation heat sources: (1) a furnace for steady-state, and (2) a light and chopper for frequency response.

TEMPERATURE SENSITIVE ELEMENTS↗
NASA NTRS1998

A Comparison of Space and Ground Based Facility Environmental Effects for FEP Teflon

Fluorinated Ethylene Propylene (FEP) Teflon is widely used as a thermal control material for spacecraft, however, it is susceptible to erosion, cracking, and subsequent mechanical failure in low Earth orbit. One of the difficulties in determining whether FEP Teflon will survive during a mission is the wide disparity of erosion rates observed for this material in space and in ground based facilities. Each environment contains different levels of atomic oxygen, ions, and vacuum ultraviolet (VUV) radiation in addition to parameters such as the energy of the arriving species and temperature. These variations make it difficult to determine what is causing the observed differences in erosion rates. This paper attempts to narrow down which factors affect the erosion rate of FEP Teflon through attempting to change only one environmental constituent at a time. This was attempted through the use of a single simulation facility (plasma asher) environment with a variety of Faraday cages and VUV transparent windows. Isolating one factor inside of a radio frequency (RF) plasma proved to be very difficult. Two observations could be made. First, it appears that the erosion yield of FEP Teflon with respect to that of polyimide Kapton is not greatly affected by the presence or lack of VUV radiation present in the RF plasma and the relative erosion yield for the FEP Teflon may decrease with increasing fluence. Second, shielding from charged particles appears to lower the relative erosion yield of the FEP to approximately that observed in space, however it is difficult to determine for sure whether ions, electrons, or some other components are causing the enhanced erosion.

Rutledge, Sharon K.↗
NASA NTRS1998

Passively Adaptive Inflatable Structure for the Shooting Star Experiment

An inflatable structural system is described for the Shooting Star Experiment that is a technology demonstrator flight for solar thermal propulsion. The inflatable structure is a pressurized assembly used in orbit to support a fresnel lens for focusing sunlight into a thermal storage engine. When the engine temperature reaches a preset level, the propellant is injected into the storage engine, absorbs heat from a heat exchanger, and is expanded through the nozzle to produce thrust. The inflatable structure is an adaptive system in that a regulator and relief valve are utilized to maintain pressure within design limits during the full range of orbital conditions. Further, the polyimide film material used for construction of the inflatable is highly nonlinear, with modulus varying as a function of frequency, temperature, and level of excitation. A series of tests is described for characterizing the structure in response to various operating conditions.

Tinker, Michael L..↗
NASA NTRS1998

Fire Resistant, Moisture Barrier Membrane

A waterproof and breathable, fire-resistant laminate is provided for use in tents, garments, shoes, and covers, especially in industrial, military and emergency situations. The laminate permits water vapor evaporation while simultaneously preventing liquid water penetration. Further, the laminate is fire-resistant and significantly reduces the danger of toxic compound production when exposed to flame or other high heat source. The laminate may be applied to a variety of substrates and is comprised of a silicone rubber and plurality of fire-resistant, inherently thermally-stable polyimide particles.

St.Clair, Terry L.↗
NASA NTRS1998

Dimensionally Stable Poyimide Copolymers for Microelectronics Applications

Polyimides are finding increased applications in microelectronics due to their high thermal stability, good chemical resistance, good adhesion, low moisture absorption, good mechanical properties, and low coefficient of thermal expansion (CTE). Four series of random copolyimides were synthesized and characterized for potential application as encapsulants, stress-relief layers, and interlevel dielectrics. Several candidates exhibited good combinations of physical and mechanical properties with inherent viscosities from 1.21 to 1.42 dL/g, T(sub g)'s ranging from 251 to 277 C, 10% weight loss temperatures between 503 and 527 C, and CTEs ranging from 33 to 39 ppm/deg C. Mechanical properties at room temperature for the best candidates included tensile strengths of 17.8-21.3 ksi, moduli between 388 and 506 ksi, and elongations of 11-43%. Moisture absorption for these copolyimides ranged between 0.85 and 1.38 wt %.

Fay, Catherine C.↗
NASA NTRS1999

Copolyimides Prepared from 3,4'-Oxydianiline and 1,3-Bis(3-Aminophenoxy) Benzene with 3,3', 4,4'-Biphenylcarboxylic Dianhydride

Polyimide copolymers were prepared by reacting different ratios of 3,4'-oxydianiline (ODA) and 1,3-bis(3- aminophenoxy)benzene (APB) with 3,3',4,4'- biphenylcarboxylic dianhydride (BPDA) and endcappfng with an effective amount of a non-reactive endcapper. Within a narrow ratio of diamines, from -50% ODA/50% APB to -95% ODA/5% APB, the copolyimides prepared with BPDA have a unique combination of properties that make them very attractive for various applications. This unique combination of properties includes low pressure processing (200 psi and below), long term melt stability (several hours at 390 C.), improved toughness, improved solvent resistance, improved adhesive properties, and improved composite mechanical properties.

Jensen, Brian J.↗
NASA NTRS1998

Optical Waveguide Output Couplers Fabricated in Polymers

Waveguide output couplers fabricated in Norland Optical Adhesive (NOA) #81 and AMOCO Ultradel 9020D polyimide are investigated. The output couplers are implemented using periodic relief gratings on a planar waveguide. Design theory of the couplers is based on the perturbation approach. Coupling of light from waveguide propagation modes to output radiation modes is described by coupled mode theory and the transmission line approximation of the perturbed area (grating structure). Using these concepts, gratings can be accurately designed to output a minimum number of modes at desired output angles. Waveguide couplers were designed using these concepts. These couplers were fabricated and analyzed for structural accuracy, output beam accuracy, and output efficiency. The results for the two different materials are compared.

Watson, Michael D.↗
NASA NTRS1998

Computational Materials Research

High temperature thermoplastic polyimide polymers are incorporated in engineering structures in the form of matrix materials in advanced fiber composites and adhesives in bonded joints. Developing analytical tools to predict long term performance and screen for final materials selection for polymers is the impetus for intensive studies at NASA and major industry based airframe developers. These fiber-reinforced polymeric composites (FRPCs) combine high strength with lightweight. In addition, they offer corrosion and fatigue resistance, a reduction in parts count, and new possibilities for control through aeroelastic tailoring and "smart" structures containing fully-integrated sensors and actuators. However, large-scale acceptance and use of polymer composites has historically been extremely slow. Reasons for this include a lack of familiarity of designers with the materials; the need for new tooling and new inspection and repair infrastructures; and high raw materials and fabrication costs.

Veazie, David R.↗
NASA NTRS1999

An Instrument for Real-Time Measurement of Solid Rocket Motor Insulation Erosion

An instrument (eroding potentionmeter) has been designed to measure real-time case wall and inhibitor insulation char depth within a rocket motor during firing. Thus measurement can be close to the real-time recession of the insulation surface. The eroding potentionmeter consists of two small (3 mils 9in diameter) twisted resistive wires that are polyimide insulated. The wire pair form an electrical circuit and will recede with the erosion of the rocket motor internal insulation. A constant current applied along the wires will detect the resistance change via a voltage drop across the wires as the wire pair recedes with the decomposition fo the insulation. The eroding potentionmeter, as presently designed, can be an effective tool for real time measurement of internal insulation recession of a solid rocket motor. This tool will provide a way to accurately measure inhibitor performance or to measure flight effects of insulation erosion on a flight test. The eroding potentiometer has been verified on a plasma torch test and two static tests of a small solid rocket motor. There are some irregularities in the measured date, but the data remains useful in determining the real-time performance of internal insulation during a motor firing.

McWhorter, B. B.↗