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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 307 records · Page 17

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NASA NTRS1989

Mechanical properties of several neat polymer matrix materials and unidirectional carbon fiber-reinforced composites

The mechanical and physical properties of three neat matrix materials, i.e., PEEK (polyetheretherketone) thermoplastic, Hexcel F155 rubber-toughened epoxy and Hercules 8551-7 rubber-toughened epoxy, were experimentally determined. Twelve unidirectional carbon fiber composites, incorporating matrix materials characterized in this or earlier studies (with one exception; the PISO(sub 2)-TPI matrix itself was not characterized), were also tested. These composite systems included AS4/2220-1, AS4/2220-3, T500/R914, IM6/HX1504, T300/4901A (MDA), T700/4901A (MDA), T300/4901B (MPDA), T700/4901B (MPDA), APC2 (AS4/PEEK, ICI), APC2 (AS4/PEEK, Langley Research Center), AS4/8551-7, and AS4/PISO(sub 2)-TPI. For the neat matrix materials, the tensile, shear, fracture toughness, coefficient of thermal expansion, and coefficient of moisture expansion properties were measured as a function of both temperature and moisture content. For the unidirectional composites, axial and transverse tensile, longitudinal shear, coefficient of thermal expansion, and coefficient of moisture expansion properties were determined, at room temperature and 100 C.

Coguill, Scott L.↗

NASA NTRS1989

Effects of tacky mat contamination on bond degradation for Chemlok/liner and NBR/liner bonds

Tacky mats are placed by the rubber lay-up areas for the solid rocket motor segments. These mats dust off the shoes prior to entering the platform where the lay-up work is performed. The possibility exists that a tacky mat could be touched with gloved hands prior to handling the uncured nitride butadiene rubber (NBR). Tests were run to determine if NBR were accidentally touched would there be any degradation of the liner/NBR bond. The tacky mats were judged solely on the basis of bond degradation caused by either direct or indirect contamination. Test results all indicate that there was no notable NBR/Chemlok or liner/NBR bond degradation on samples that came into contact with the tacky mat material. Testing procedures are described. The tacky mat adhesive composition does not contain fluorocarbons or release agents that would affect bonding.

Padilla, A. M.↗

NASA NTRS1989

Pressure rig for repetitive casting

The invention is a pressure rig for repetitive casting of metal. The pressure rig performs like a piston for feeding molten metal into a mold. Pressure is applied to an expandable rubber diaphragm which expands like a balloon to force the metal into the mold. A ceramic cavity which holds molten metal is lined with blanket-type insulating material, necessitating only a relining for subsequent use and eliminating the lengthy cavity preparation inherent in previous rigs. In addition, the expandable rubber diaphragm is protected by the insulating material thereby decreasing its vulnerability to heat damage. As a result of the improved design the life expectancy of the pressure rig contemplated by the present invention is more than doubled. Moreover, the improved heat protection has allowed the casting of brass and other alloys with higher melting temperatures than possible in the conventional pressure rigs.

Vasquez, Peter↗

NASA NTRS1990

Rubberlike elasticity experiment

Four rubber erasers from the campus bookstore, two green and two white, have been cut to have identical dimensions. These are loaded in compression with a mechanical test machine capable of applying cyclic loads and providing output to an X-Y plotter. The anelastic behavior of rubber as well as the relative stiffnesses of composite materials loaded transversely and longitudinally may be demonstrated to beginning students or used as input for computer analysis by students.

Greet, Richard↗

NASA NTRS1991

The full-scale process and design changes for elimination of insulation edge separations and voids in tang flap area

Qualification of the full-scale process and design changes for elimination of redesigned solid rocket motor tang nitrile butadiene rubber insulation edge separations and voids was performed from 24 March to 3 December 1990. The objectives of this test were: to qualify design and process changes on flight hardware using a tie ply between the redesigned solid rocket motor steel case and the nitrile butadiene rubber insulation over the tang capture features; to qualify the use of methyl ethyl ketone in the tang flap region to reduce voids; and to determine if holes in the separator film reduce voids in the tang flap region. The tie ply is intended to aid insulation flow during the insulation cure process, and thus reduce or eliminate edge unbonds. Methyl ethyl ketone is intended to reduce voids in the tang flap area by providing better tacking characteristics. The perforated film was intended to provide possible vertical breathe paths to reduce voids in the tang area. Tang tie ply testing consisted of 270 deg of the tang circumference using a new layup method and 90 deg of the tang circumference using the current layup methods. Tie ply process success was defined as a reduction of insulation unbonds. Lack of any insulation edge unbonds on the tang area where the new process was used, and the presence of 17 unbonds with the current process, proves the test to be a success. Successful completion of this test has qualified the new processes.

Danforth, Richard A.↗

NASA NTRS1992

Piezoelectric Measurement Of Bulk Modulus

In method of measuring bulk modulus of elasticity of elastomeric material, piezoelectric crystals of various sizes and energized by alternating voltage embedded in material. Concept demonstrated in test cell in which piezoelectric crystal mounted either unconstrained or between two rubber pads and connected as actuator in loud-speaker. The 1-in. diameter crystal excited with 24 Vac at 60 Hz. When crystal was unconstrained, it drew current of 0.8 mA. When crystal was constrained between rubber pads, current fell to 0.65 mA. Low current, minimal heating, and absence of arcing makes technique suitable for measurement of bulk moduli of elasticity of flammable or explosive rubbery materials.

Butler, Barry L.↗

NASA NTRS1992

Graphite intercalation compound with iodine as the major intercalant

Halogenated CBr(sub x)I(sub y) (1 less than y/x less than 10) was made by exposing graphite materials with interplanar spacing in the 3.35 to 3.41 A range to either pure Br2 or an I2-Br2 mixture, and then to iodine vapor containing a small amount of Br2. The electrical resistivity of this product is from 3 to 6.5 times the pristine value. The presence of a small amount of isoprene rubber in the reaction significantly increased the iodine to bromine ratio in the product. In this reaction, rubber is known to generate HBr and to slowly remove bromine from the vapor. The halogenation generally caused a 22 to 25 percent weight increase. The halogens were found uniformly distributed in the product interior. However, although the surface contains very little iodine, it has high concentrations of bromine and oxygen. It is believed that the high concentrations of bromine and oxygen in this surface cause the halogenated fiber to be more resistant to fluorine attack during subsequent fluorination to fabricate graphite fluoride fibers.

Hung, Ching-Cheh↗

NASA NTRS1987

NDE of Space Shuttle Solid Rocket Motor field joint

One of the most critical areas for inspection in the Space Shuttle Solid Rocket Motors is the bond between the steel case and rubber insulation in the region of the field joints. The tang-and-clevis geometry of the field joints is sufficiently complex to prohibit the use of resonance-based techniques. One approach we are investigating is to interrogate the steel-insulation bondline in the tang and clevis regions using surface-travelling waves. A low-frequency contact surface wave transmitting array transducer is under development at our laboratory for this purpose. The array is placed in acoustic contact with the steel and surface waves are launched on the inside surface or the clevis leg which propagate along the steel-insulation interface. As these surface waves propagate along the bonded surface, the magnitude of the ultrasonic energy leaking into the steel is monitored on the outer surface of the case. Our working hypothesis is that the magnitude of energy received at the outer surface of the case is dependent upon the integrity of the case-insulation bond, with less attenuation for propagation along a disbond due to imperfect acoustic coupling between the steel and rubber. Measurements on test specimens indicate a linear relationship between received signal amplitude and the length of good bend between the transmitter and receiver, suggesting the validity of this working hypothesis.

Patrick H. Johnston↗

NASA NTRS1930

The Prevention of the Ice Hazard on Airplanes

A review of various methods to prevent ice formation and adhesion to aircraft surfaces is given. It was concluded that the adhesion of ice to a surface may be reduced somewhat by the application of certain waxes and varnishes. In the experiments described, the varnishes containing calcium stearate and calcium oleate gave the best results. In wind tunnel tests, the adhesion was further reduced by the application of these waxes and varnishes to a thin, heat insulating layer of rubber. The adhesion of ice is greatly reduced when the surface consists of a vehicle which carries an oil in sufficient quantity so that the surface of the vehicle is self lubricating. Ice may be removed from wings, struts, wires and other parts of an airplane during flight by the inflation of properly constructed pneumatic rubber members, providing that these members have been previously treated with a suitable low adhesion oil.

Geer, William C↗

NASA NTRS1954

Flight Tests of a Man Standing on a Platform Supported by a Teetering Rotor

Because previous flight tests of a man standing on a jet-supported platform were very successful, a series of flight tests were made to determine the flying qualities of a man standing on a platform supported by a teetering rotor. The rotor was 7 feet in diameter and was driven by air jets at the rotor tips fed by hollow blades and air hoses connected to an external air supply. The machine was tested with a free-teetering rotor and with a spring-restrained rotor, and, as an alternate arrangement, with the rotor and foot platform isolated from the framework by rubber connections to reduce the inertia of the moving parts. The machine was tested indoors in hovering and in limited translational flight and outdoors in light and in strong gusty winds. The stability and controllability with the spring-restrained rotor were uniformly good. The stability with the free-teetering rotor was marginal, but, when an experienced flyer placed his hands on a hand rail, the stability and controllability were good. The stability and controllability with the rubber-isolated frame and spring-restrained teetering rotor were very good and quite like the jet-supported platform.

Paul R Hill↗

NASA NTRS1921

Moisture Resistant Finishes for Airplane Woods

This report describes briefly a series of experiments made at the Forest Products Laboratory, Madison, Wisconsin, to determine the comparative moisture resistance of linseed oil, impregnation treatments, condensation varnishes, oil varnishes, enamels, cellulose varnishes, rubber, electroplated and sprayed metal coatings, and metal-leaf coatings when applied to wood. All coatings except rubber and electroplated metal coatings, which were not developed sufficiently to make them practical, admitted moisture in varying degrees. The most effective and most practical coating was found to be that of aluminum leaf.

Dunlap, M E↗

NASA NTRS1931

Airplane landing gear

This report presents an investigation of the design and construction of various types of landing gears. Some of the items discussed include: chassises, wheels, shock absorbers (rubber disk and rubber cord), as well as oleopneumatic shock absorbers. Various types of landing gears are also discussed such as the Messier, Bendix, Vickers, and Bleriot.

Maiorca, Salvatore↗

NASA NTRS1995

Requirements for energy based constitutive modeling in tire mechanics

The history, requirements, and theoretical basis of a new energy based constitutive model for (rubber) material elasticity, hysteresis, and failure are presented. Energy based elasticity is handled by many constitutive models, both in one dimension and in three dimensions. Conversion of mechanical energy to heat can be modeled with viscoelasticity or as structural hysteresis. We are seeking unification of elasticity, hysteresis, and failure mechanisms such as fatigue and wear. An energy state characterization for failure criteria of (rubber) materials may provide this unification and also help explain the interaction of temperature effects with failure mechanisms which are described as creation of growth of internal crack surface. Improved structural modeling of tires with FEM should result from such a unified constitutive theory. The theory will also guide experimental work and should enable better interpretation of the results of computational stress analyses.

Luchini, John R.↗

NASA NTRS1995

ANSYS tools in modeling tires

This presentation summarizes the capabilities in the ANSYS program that relate to the computational modeling of tires. The power and the difficulties associated with modeling nearly incompressible rubber-like materials using hyperelastic constitutive relationships are highlighted from a developer's point of view. The topics covered include a hyperelastic material constitutive model for rubber-like materials, a general overview of contact-friction capabilities, and the acoustic fluid-structure interaction problem for noise prediction. Brief theoretical development and example problems are presented for each topic.

Ali, Ashraf↗

NASA NTRS1994

Graphite intercalation compound with iodine as the major intercalate

Halogenated graphite CBr(x)I(y) (I less than y/x less than 10) was made by exposing graphite materials to either pure Br2 or an I2/Br2/HBr mixture to initiate the reaction, and then to iodine vapor containing a small amount of Br2/HBr/IBr to complete the intercalation reaction. Wetting of the graphite materials by the I2/Br2/HBr mixture is needed to start the reaction, and a small amount of Br2/HBr/IBr is needed to complete the charge transfer between iodine and carbon. The interplanar spacings for the graphite materials need to be in the 3.35 to 3.41 A range. The X-ray diffraction data obtained from the halogenated HOPG indicate that the distance between the two carbon layers containing intercalate is 7.25 A. Electrical resistivity of the fiber product is from 3 to 6.5 times the pristine value, The presence of a small amount of isoprene rubber in the reaction significantly increased the iodine-to-bromine ratio in the product. In this reaction, rubber is known to generate HBr and to slowly remove bromine from the vapor. The halogenation generally caused a 22 percent to 25 percent weight increase. The halogens were found uniformly distributed in the product interior. However, although the surface contains very little iodine, it has high concentrations of bromine and oxygen. It is believed that the high concentrations of bromine and oxygen in this surface cause the halogenated fiber to be more resistant to structural damage during subsequent fluorination to fabricate graphite fluoride fibers.

Hung, Ching-Cheh↗

NASA NTRS1996

Analysis of Thick Sandwich Shells with Embedded Ceramic Tiles

The Composite Armored Vehicle (CAV) is an advanced technology demonstrator of an all-composite ground combat vehicle. The CAV upper hull is made of a tough light-weight S2-glass/epoxy laminate with embedded ceramic tiles that serve as armor. The tiles are bonded to a rubber mat with a carefully selected, highly viscoelastic adhesive. The integration of armor and structure offers an efficient combination of ballistic protection and structural performance. The analysis of this anisotropic construction, with its inherent discontinuous and periodic nature, however, poses several challenges. The present paper describes a shell-based 'element-layering' technique that properly accounts for these effects and for the concentrated transverse shear flexibility in the rubber mat. One of the most important advantages of the element-layering technique over advanced higher-order elements is that it is based on conventional elements. This advantage allows the models to be portable to other structural analysis codes, a prerequisite in a program that involves the computational facilities of several manufacturers and government laboratories. The element-layering technique was implemented into an auto-layering program that automatically transforms a conventional shell model into a multi-layered model. The effects of tile layer homogenization, tile placement patterns, and tile gap size on the analysis results are described.

Davila, Carlos G.↗

NASA NTRS2000

Development and Application of Tools to Characterize the Oxidative Degradation of AP/HTPB/Al Propellants in a Propellant Reliability Study

The oxidative thermal aging of a crosslinked hydroxyl-terminated polybutadiene (HTPB)/isophorone diisocyanate (IPDI) polyurethane rubber was studied at temperatures between 25 C and 125 C. Changes in tensile elongation, mechanical hardening, polymer network properties, density, O2 permeation, and molecular chain dynamics were investigated as a function of age. The techniques used include solvent swelling, detailed modulus profiling, and NMR relaxation measurements. The Arrhenius methodology, which normally assumes a linear extrapolation of high temperature aging data, is critically evaluated by using extensive data superposition and highly sensitive oxygen consumption measurements. Significant curvature in the Arrhenius diagram of these oxidation rates is observed to be similar to previous results found for other rubber materials that have been evaluated by this technique. Preliminary gel/network properties suggest that crosslinking is the dominant process at higher temperatures. The effect on the oxidation rate of the binder when other constituents found in propellants are present, such as ammonium perchlorate, plasticizer and aluminum powder, is presented.

Celina, Mathew↗

NASA NTRS2002

A Thermodynamic Theory Of Solid Viscoelasticity. Part 1: Linear Viscoelasticity.

The present series of three consecutive papers develops a general theory for linear and finite solid viscoelasticity. Because the most important object for nonlinear studies are rubber-like materials, the general approach is specified in a form convenient for solving problems important for many industries that involve rubber-like materials. General linear and nonlinear theories for non-isothermal deformations of viscoelastic solids are developed based on the quasi-linear approach of non-equilibrium thermodynamics. In this, the first paper of the series, we analyze non-isothermal linear viscoelasticity, which is applicable in a range of small strains not only to all synthetic polymers and bio-polymers but also to some non-polymeric materials. Although the linear case seems to be well developed, there still are some reasons to implement a thermodynamic derivation of constitutive equations for solid-like, non-isothermal, linear viscoelasticity. The most important is the thermodynamic modeling of thermo-rheological complexity , i.e. different temperature dependences of relaxation parameters in various parts of relaxation spectrum. A special structure of interaction matrices is established for different physical mechanisms contributed to the normal relaxation modes. This structure seems to be in accord with observations, and creates a simple mathematical framework for both continuum and molecular theories of the thermo-rheological complex relaxation phenomena. Finally, a unified approach is briefly discussed that, in principle, allows combining both the long time (discrete) and short time (continuous) descriptions of relaxation behaviors for polymers in the rubbery and glassy regions.

Freed, Alan D.↗