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Fluid properties of refrigerant-21 were investigated at temperatures from the freezing point to 423 Kelvin and at pressures to 1.38 x 10 to the 8th power N/sq m (20,000 psia). The fluid properties included were: density, vapor pressure, viscosity, specific heat, thermal conductivity, thermal expansion coefficient, freezing point and bulk modulus. Tables of smooth values are reported.
Efforts to improve the impact resistance of B/Al are reviewed and analyzed. Tensile and dynamic modulus tests, thin sheet Charpy and Izod impact tests, and standard full size Charpy impact tests were conducted on 0.20 mm (8 mil) diameter-B/1100 Al matrix composites. Angleplies ranged from unidirectional to + or - 30 deg. The best compromise between reduced longitudinal properties and increased transverse properties was obtained with + or - 15 deg angleply. The pendulum impact strengths of improved B/Al were higher than that of notched titanium and appear to be enough to warrant consideration of B/Cl for application to fan blades in aircraft gas turbine engines.
Tests were performed on an airfoil in a low-turbulence subsonic wind tunnel at fixed incidence for different speeds of the wind, the airfoil being in translatory motion normal or parallel to the wind. The resulting aerodynamic forces and moment on the airfoil were measured along with local pressure and skin friction. When the incidence is small and the boundary layer attached, no unsteady effects were observed. However, for a large incidence (16 deg), in the case of boundary layer separation, strong unsteady effects are revealed when the boundary layer is reattached in periodic flow. Reattachment can be explained assuming that for the same value of free stream velocity, the gradient of the modulus of the periodic component of the relative airspeed at the upper surface of the airfoil in a direction normal to this surface is greater than the gradient of the relative air speed at the upper surface when the airfoil is not oscillating.
Some effects of post-cure time and temperature on the physicomechanical properties of a phenolic-asbestos and a phenolic-glass composite are studied. The molding and post-curing procedures are discussed along with physical and mechanical test results. It is found that the specific gravity of the panels tested decreased slightly but the hardness always increased with post cure, and that the mechanical properties had different patterns of response to increasing post-cure time and temperature. For tensile properties, strength decreased, modulus increased, and elongation at break exhibited little change. In general, the phenolic-asbestos showed more positive response to post cure than did the phenolic-glass. Mold venting is found to impart better properties to the composites concerned.
A study was carried out to select a state-of-the-art epoxy for wet filament winding. Ten epoxy systems were used to filament wind pressure vessels with a high-modulus, high-strength organic fiber. Data are reported on vessel performance, fiber strand strengths, and shear strengths for the different systems. Using our criteria (processibility, neat resin properties, and vessel performance), we find that an epoxy system based on the rubber-modified bis-phenol-F resin, diluted with vinyl cyclohexane dioxide and cured with mixed aromatic amines, can easily replace bis-phenol-A epoxies diluted with bis-(2, 3-epoxycyclopentyl) ether (such as ERL 2256 epoxy of Union Carbide) with comparable overall performance.
Investigations concerned with a development of large-diameter carbon fibers are considered, taking into account the employment of vapor deposition techniques. In the experiments a carbon monofilament substrate is used together with reacting gases which consist of combinations of hydrogen, methane, and boron trichloride. It is found that the described approach can be used to obtain a large-diameter carbon filament containing boron. The filament has reasonable strength and modulus properties.
Results of an experimental and analytical investigation of the compressive strength of unidirectional boron-epoxy composite material are presented. Observation of fiber coordinates in a boron-epoxy composite indicates that the fibers contain initial curvature. Combined axial compression and torsion tests were conducted on boron-epoxy tubes and it was shown that the shear modulus is a function of axial compressive stress. An analytical model which includes initial curvature in the fibers and permits an estimate of the effect of curvature on compressive strength is proposed. Two modes of failure which may result from the application of axial compressive stress are analyzed - delamination and shear instability. Based on tests and analysis, failure of boron-epoxy under axial compressive load is due to shear instability.
The time-dependent deformation of boron fibers over the temperature range from -190 to 800 C is studied by flexural stress relaxation and flexural internal friction techniques on 203-micron diam specimen fibers commercially produced by chemical vapor deposition (CVD) on a 13-micron tungsten substrate. It is shown that up to at least 800 C all nonelastic behavior observed during axial deformation of CVD boron fibers can be explained solely by anelastic mechanisms and that although creep strains are small, boron fiber anelasticity can produce significant mechanical effects which would otherwise be neglected under the elastic approximation. Relations are obtained to demonstrate the considerable effects of anelasticity on such fiber/composite properties as modulus, creep, creep recovery, stress relaxation, and damping capacity. For an elastic-core/anelastic-sheath model, boron fibers on tungsten substrates are shown to have predictable fracture stresses for time-temperature conditions ranging from impact to long-time stress rupture. Possible techniques for altering these stresses are discussed.
An experimental investigation was conducted to determine the strain rate effects in fiber composites. Unidirectional composite specimens of boron/epoxy, graphite/epoxy, S-glass/epoxy and Kevlar/epoxy were tested to determine longitudinal, transverse and intralaminar (in-plane) shear properties. In the Longitudinal direction the Kevlar/epoxy shows a definite increase in both modulus and strength with strain rate. In the transverse direction, a general trend toward higher strength with strain rate is noticed. The intralaminar shear moduli and strengths of boron/epoxy and graphite/epoxy show a definite rise with strain rate.
Ultrahigh speed fan blades, designed in accordance with the requirements of an ultrahigh tip speed blade axial flow compressor, were fabricated from a high strength graphite fiber tow and a PMR polyimide resin. The PMR matrix was prepared by combining three monomeric reactants in methyl alcohol, and the solution was applied directly to the reinforcing fiber for subsequent in situ polymerization. Some of the molded blades were completely finished by secondary bonding of root pressure pads and an electroformed nickel leading edge sheath prior to final machining. The results of the spin testing of nine PMR fan blades are given. Prior to blade fabrication, heat resin tensile properties of the PMR resin were examined at four formulated molecular weight levels. Additionally, three formulated molecular weight levels were investigated in composite form with both a high modulus and a high strength fiber, both as-molded and postcured, in room temperature and 232 C transverse tensile, flexure and short beam shear. Mixed fiber orientation panels simulating potential blade constructions were also evaluated. Flexure tests, short beam shear tests, and tensile tests were conducted on these angle-plied laminates.
The layups of the studied laminates are (0, + or - 60) sub s, (0, + or - 45, 90) sub s, (0, + or - 30, + or - 60, 90) sub s (0, + or - 22 1/2, + or - 45, + or - 67 1/2, 90) sub s. The properties determined were tensile modulus, Poisson's ratio, bending stiffness, fracture strength and fracture strain. Measured properties and properties predicted using laminate theory were found to be in reasonable agreement. Reasons for data scatter were determined.
Investigations to aid in the interpretation of seismic data obtained below the lunar surface are reported. Fine grained basalt with about 1.0% open core porosity was encapsulated under hard vacuum and measured. A Q value just under 2,000 at 0.5 kbar was achieved for a terrestrial analog of lunar basalt. In contrast to the modulus which increases by as much as 10%, the quality factor Q shows little or no change with pressure (a well outgassed sample maintains a high Q, whereas one exposed to laboratory atmosphere maintains a low Q). This result suggests that the absence of volatiles plays an important role in determining the q factor even at a depth of 10 km below the lunar surface.
Experimental results of the mechanical behavior of two metal matrix composite systems at room temperature are presented. Ultimate stress, ultimate strain, Poisson's ratio, and initial Young's Modulus are documented for BORSIC/Aluminum in uniaxial tension and Boron/Aluminum in uniaxial tension and compression. Poisson's ratio is used for nonlinear stress-strain behavior. A comparison of compression results for B/Al as obtained from sandwich beam compression specimens and IITRI coupon compression specimens is presented.
Wind vector change with respect to time at Cape Kennedy, Florida, is examined according to the theory of multivariate normality. The joint distribution of the four variables represented by the components of the wind vector at an initial time and after a specified elapsed time is hypothesized to be quadravariate normal; the fourteen statistics of this distribution, calculated from fifteen years of twice daily Rawinsonde data are presented by monthly reference periods for each month from 0 to 27 km. The hypotheses that the wind component changes with respect to time is univariate normal, the joint distribution of wind component changes is bivariate normal, and the modulus of vector wind change is Rayleigh, has been tested by comparison with observed distributions. Statistics of the conditional bivariate normal distributions of vector wind at a future time given the vector wind at an initial time are derived. Wind changes over time periods from one to five hours, calculated from Jimsphere data, are presented.
Sixteen test materials were supplied by NASA-Lewis Research Center as wrought bar or cast remelt stock. The cast remelt stock was cast into test blanks with two such materials being also evaluated after Jocoat coating was applied. Mechanical properties evaluated included tensile, modulus of elasticity, Poisson's Ratio, creep properties and creep rupture strength. Tests were conducted at temperatures applicable to the service temperature of the various alloys. This range extended from room temperature to 1000 C.
The results of a preliminary analysis of a single shaft regenerative design with a single stage radial turbine are presented to show the fuel economy that can be achieved at high turbine inlet temperatures, with this particular advanced design, if the turbine tip speed and regenerator inlet temperature are not limited. The engine size was 100 hp for application to a 3500 lb auto. The fuel economy was analyzed by coupling the engine to the auto through a continuously variable speed-ratio transmission and operating the system at constant turbine inlet temperature over the Composite Driving Cycle. The fuel was gasoline and the analysis was for a 85 F day. With a turbine inlet temperature of 2500 F the fuel economy was 26.2 mpg, an improvement of 18 percent over that of 22.3 mpg with a turbine inlet temperature of 1900 F. The turbine tip speed needed for best economy with the 2500 F engine was 2530 ft/sec. The regenerator temperature was approximately 2200 F at idle. Disk stresses were estimated for one single stage radial turbine and two two-stage radial-axial turbines and compared with maximum allowable stress curves estimated for a current ceramic material. Results show a need for higher Weibull Modulus, higher strength ceramics.
A new high pressure turbine shroud material has been developed from the consolidation of prealloyed powders of Ni, Cr, Al and Y. The new material, a filler for cast turbine shroud body segments, is called Genaseal. The development followed the identification of oxidation resistance as the primary cause of prior shroud deterioration, since conversion to oxides reduces erosion resistance and increases spalling under thermal cycled engine conditions. The NICrAlY composition was selected in preference to NIAL and FeCRALY alloys, and was formulated to a prescribed density range that offers suitable erosion resistance, thermal conductivity and elastic modulus for improved behavior as a shroud.
Five Kevlar based laminates and three Kevlar based coated materials were designed, hand made, and tested against comparative conventional Dacron based materials for strength, peel, tear, puncture, creases, and handle. Emphasis was placed on evaluating geometric orientation of constituents, use of elastomeric film in place of high modulus films, and the use of flying thread loom bias reinforcement of Kevlar yarns. Whereas, the performance of the Kevlar laminates was severely degraded by crease effects, significant gains in overall performance factors were shown for the coated Kevlar materials.