Search

A nonlinear multivariable feedback controller was defined for the idle to military operating regime (9 to 100 percent thrust) of the Pratt and Whitney Aircraft F401 variable cycle turbofan engine. The analytical design involved linearizing the F401 engine dynamics about five steady-state operating points between idle and military thrust, applying linear optimal control synthesis methods at each point, and combining the five optimal linear controllers into a single nonlinear controller which has feedback gains that are scheduled with high compressor speed. Variable fan, compressor and exhaust geometries as well as main burner fuel flow are coordinated by the controller to achieve rapid engine dynamic response., See also AD767425.

Various experimental techniques for the production of unidirectionally solidified oxide eutectics were examined. These included a modified Bridgman-Starkbarger technique and bottom cooling of melts held in platinum crucibles. It was concluded that the best approach, at least for experimental purposes, was the floating molten zone technique and the successful use of a number of variations of this technique was demonstrated. Many different eutectic systems were directionally solidified and the mechanical properties of the Al2O3-ZrO2 (Y2O3), Y2O3-ZrO2, CaZrO3-ZrO2 and MgO-CaO systems are described in considerable detail. The strength results indicate that oxide materials prepared in this manner can exhibit exceptional strengths and significant increases in toughness at elevated temperatures. The various reasons and requirements for obtaining exceptional mechanical properties in this class of materials are considered., See also report dated Jun 72, AD-745 328.

The long-range objective of this program is to develop an efficient and reliable ultra-wideband waveguide modulator for CO2 lasers that will be useful for high resolution, imaging optical radars and high-data-rate optical communication systems. During this reporting period three significant advances have been made in the modulator development. The first development involves improvements in the quality of the GaAs waveguide structure and the reliability of producing thinfilm waveguides with acceptable quality; the second development, involves improvements in optical coupling efficiency; and the last development involves improvements in the reproducibility of the microwave characteristics of the waveguide modulator. With the exception of the growth of the bulk GaAs crystals, which are currently purchased from two different vendors, the complete material processing and waveguide synthesis are being carried out at our laboratory under controlled procedures. Waveguide structures with lengths in excess of 2 cm, which include two 3 mm x 3 mm grating couplers at the ends can now be reliably made with any desirable average thickness., See also report dated 25 Sep 1974, AD787471.

The reactive rf sputtering technique was applied to the preparation of a wide variety of materials. Single crystal films of ZnO, TiO2, WO3 AlN and GaN were grown on one or more of the insulating crystalline substrates of Al2O3, MgAl2O3, SiC and LiNbO3. Data on the deposition parameters, structure and optical waveguiding characteristics of the heteroepitaxial structures are presented. Reactive sputtering using sublimed arsenic as the sputtering gas inside a heated vacuum chamber was used to grow epitaxial films of GaAs. The controlled growth of single crystal alloys of Ga(1-x)Al(x)As at low temperatures was also demonstrated. Structural, optical and electrical characteristics of these films are presented. Conditions were determined for the deposition of amorphous neodymium ultraphosphate films. Low loss optical wave guide structures were fabricated. Charge storage characteristics of MIS structures were investigated. These employed a composite insulator formed by sputtering 1000A of strontium titanate over a 20A thick thermally grown silicon dioxide layer on silicon., Sponsored in part by DARPA. See also AD0780277.

The objective of the program is to design, fabricate, and test unidirectional and angleply multi-fiber laminates for improved impact strength and other mechanical properties. The effects of several variables on the mechanical properties of epoxy matrix materials are described. These include fiber type (HMS and AS graphites, glass, and Kevlar 49), ratio of primary to hybridizing fiber and hybrid configuration. It is demonstrated that AS graphite/S-glass in an intraply configuration results in the best combination of static and Charpy impact properties as well as superior ballistic impact resistance. Pendulum impact tests which were conducted on thin specimens are shown to produce different ranking of materials than tests conducted on standard thickness Charpy specimens, and it is shown that the thin specimen results are in better agreement with the ballistic impact data. Additional static test data are reported as a function of temperature for the seven best hybrid configurations having epoxy, polyimide (PMR-15) and polyphenylquinoxaline resins as the matrix.

A viable process for multilevel interconnects was developed. Silicon dioxide sputtered at a substrate temperature of 200 C controlled by gallium heat sinking to a heater block, at argon pressure of 5 millitorr, and at a power density of 14 watts/sq. in. was demonstrated to have appropriate etching characteristics and to be virtually free of pinholes. Pure aluminum and 4% copper in aluminum were shown to be compatible with the silicon dioxide process and to give good level-to-level electrical contact at feedthroughs sputter cleaned just prior to the metal deposition. Beryllium oxide was deposited by rf sputtering from a beryllium oxide target and by reactive rf sputtering from a beryllium target using oxygen-argon mixtures. In both cases stress levels in the films deposited were very high, producing pronounced bowing of substrates. Layers on the order of 2 micrometers thick shattered silicon substrates 5 centimeters in diameter and 325 micrometers thick. Reactively sputtered films deposited at about 3000A/hr. while films rf sputtered from a beryllium oxide target deposited at a rate of about 6500A/hr for 500 watts into a 3.5 inch diameter target.

An important consideration in the design of military aircraft engine exhaust diffusers is the need to reduce infrared radiation emanating from the engine, coupled with the need to maximize shaft horsepower. To aid the engineer in the solution of this problem, advanced mathematical techniques developed in this report have been applied to the solution of turbulent compressible swirling flow through curved-wall annular diffusers. This analysis has developed a generalized method for calculating an orthogonal coordinate system for arbitrary curved-wall annular ducts with cooling slots which is based on the Schwartz- Christoffel transformation. In addition, this analysis has developed a stable implicit numerical integration scheme for solving a nonlinear parabolic partial differential equation which does not require an iterative procedure to maintain second-order accuracy. Finally, it is noted that the procedure does not require an iterative procedure coupling the inviscid and viscous portion of the flow field but treats the entire flow field as a whole. A computer program has been developed using this analysis and applied to sample cases to demonstrate the capability of the analysis. Cases with and without slot-cooled walls have been calculated and compared with experimental data taken from the ST9 demonstrator IR suppression diffuser operating at different slot cooling flow rates for one engine operating condition.

The chemical vapor process for preparing a large diameter carbon-base monofilament from a BCl3, CH4 and H2 gas mixture with carbon substrate fiber was further studied. The effects of reactor geometry, total gas flows and deposition temperature on the tensile strength of the monofilament were investigated. (it was noted that consistent results could only be obtained when the carbon substrate fiber was cleaned. The strength of the monofilament was found to depend on the highest temperature and the temperature profile of the monofilament in the reactor. The strength of monofilament produced in the DC and RF reactors were found to be similar and similar alloy compositions in the monofilament were attained when the same gas ratios were used. The tensile strength of the monofilament at 500 deg C was found to be 60 to 70% of the room temperature tensile strength. No degradation was noted after exposure to molten aluminum. jg p2

The concepts and operational characteristics of cw laser injection locking to achieve compact, efficient, frequency stable CO2 transmitters are discussed. The basic physical phenomena involved and the role of gain saturation in laser injection locking are explored analytically by means of appropriate lower frequency and microwave circuits. Experimental results with a variety of regenerative and injection-locked CO2 amplifiers are presented and compared with the analytical predictions. To demonstrate the potential of the injection-locking technique, a 60 W sealed-off CO2 laser was locked in frequency to a 0.5 W stable oscillator. The experimental data are in close agreement with theory. A master-oscillator injection-locked transmitter for frequency stable operation was designed and tested. This experimental prototype design which was built to evaluate various concepts to be employed in a ruggedized frequency stable transmitter is described. A CO2 design suitable for frequency stable operation at 50 W, life tests with various metal-ceramic master-oscillator and amplifier discharge tubes and air-cooled operation are also discussed.

A summary is presented of the results achieved in an exploratory research and development program on III-V semiconductor crystals. High quality single crystals of undoped and doped GaAs and GaSb were grown in a horizontal Bridgman furnace. Selected lots of 400 grams of GaSb and 600 grams of GaAs were cut into < 100 > oriented wafers and delivered to Night Vision Laboratories. Two techniques were investigated for the preparation of homogeneous single crystals of Ga1-xInxAs with 0.3 < x < 0.7. Melt growth in a horizontal Bridgman furnace produced homogeneous ingots but no single crystals. Vapor phase transport of presynthesized Ga1-xInxAs in a closed tube, using iodine as the transport agent, produced single crystals platelets as large as 0.8 cm x 0.4cm and appears to be a promising technique for preparing single crystals of large dimensions. (Author)

The objective of this program was to investigate intracavity electrooptical phase modulation of a CO2 waveguide laser with the aim of constructing a frequency-chirped master oscillator for application in a 10 micrometer imaging radar. During this six-month program a special phase sampling technique for frequency locking of the modulated master oscillator to an unmodulated reference laser was investigated. An important experimental result was the measurement of the relative phase between the two lasers by this sampling technique. The development of the UARL waveguide lasers was continued resulting in a sealed-off, reliable laboratory device of 0.3 W output power and a lifetime of about 1,000 hrs yielding repetitive linear chirps of 75 MHz width and 2 microsec duration.

The report describes experimental and theoretical studies of a new technique for pumping high-pressure electric-discharge lasers. Diffuse discharges in mixtures of He/N2 and He/N2/Ar at electron densities in excess of 10 to the 15th power/cc and pressures of 15 atm were obtained. Calculations for a He/Xe mixture operating on the 1730A transition in molecular Xe show efficiencies for conversion from the 10.6 micrometer field into the uv radiation field in excess of 60%. Kinetic studies of the excimer energy transfer in He/Ar/ N2 mixtures are described along with new pumping configurations which will allow operation with a uv optical cavity., Sponsored in part by DARPA.

During this reporting period four significant advances have been made. The first two concern the structural quality of GaAs waveguides. The grating couplers which are an integral part of the waveguide structure are now being made by ion-beam milling technique instead of rf sputter-etching. This change of etching technique has provided remarkable improvement in the fabrication procedure. The second improvement involves the ruggedization of GaAs waveguide structure. The strength of a chemo-mechanically polished GaAs slab is very weak and has caused some difficulties during handling and processing cycles. The authors have developed a relatively strain-free metalization process by which thin layers of nickel-copper are deposited on the surfaces of GaAs slab. The metallic layer has provided a considerable strength to the GaAs waveguide structure. The next two significant accomplishments relate to the microwave aspects of the modulator development. One of the most significant result during this interm period is the experiment employing very high power to test the modulator. The result indicates that no failure is expected under a cw mode operation of this modulator at an input microwave power level in excess of 100 watts., Sponsored in part by DATPA. See also report dated 29 Mar 1974, AD0776663.

The report describes modifications made to the previously reported high power dye laser to allow for increased power handling capability, repetition rate and operating times. Present problems are primarily involved with dye circulation and heat dissipation and the solution to these should lead to powers output from the dye laser that are well in excess of the presently available level of 41 watts. Sections cover the following: Design and testing of new flashlamps; Theory of power distribution in flashlamp; Rotary spark gap; Ray tracing program; and Dye flow system and laser power measurements., See also AD775577.

The feasibility of producing stimulated emission in the 3 to 5 micrometer wavelength band by direct electron impact excitation OF HYDROGEN CHLORIDE VIBRATIONAL LEVELS IS BEING INVESTIGATED THEORETICALLY AND EXPERIMENTALLY. Theoretical analysis predicts an optical gain coefficient in excess of 0.4%/cm. The importance of high electron density and low initial gas temperature is predicted. The results of electric discharge/laser experiments are described. Experiments have been conducted in 5% HCl/95% Argon mixtures at p=10 Torr in the e-beam sustained discharge. These conditions were insufficient to demonstrate stimulated emission., See also report dated 1 Jun 1974, AD0779311. Sponsored in part by DARPA.

The investigation is directed towards the evaluation of the feasibility of a magnetohydrodynamic laser concept (MHDL) employing nonequilibrium electron kinetics to provide efficient energy transfer in a molecular laser system. To achieve this goal comprehensive modeling of the MHD plasma which has been based upon a detailed knowledge of electron and heavy particle kinetics has been developed. Experimental investigations conducted on small scale laminated and solid wall generator configurations have confirmed theoretical modeling predictions and indicate the potential attractiveness of the MHDL concept for high power laser applications. Major emphasis in the report has been placed on the additional experimental information obtained from small scale generator tests as well as experimental results obtained in a generator configuration suitable for optical power extraction investigations.

Amorphous films of neodymium ultraphosphate and neodymium lanthanum ultrophosphate have been deposited by r.f. sputtering. Optical waveguide structures were fabricated and scattering losses were measured to be less than one dB/cm. Fluorescence lifetime measurements of Nd sup (3 tau) are presented. Data on growth of single crystal films of gallium nitride and tungsten trioxide by reactive sputtering is given. Reduced scattering losses in optical waveguide structures of zinc oxide grown on sapphire have been effected by reduction of secondary electron bombardment of the substrate during film growth. Data is presented on the effect of magnetic field configuration on suppressing secondary electron bombardment and its effect on film uniformity., Sponsored in part by DARPA. See also report dated Oct 1973, AD0769972.

The long-range objective of this program is to develop an efficient and reliable ultra-wideband thin-film modulator for CO2 lasers that will be useful for high-resolution, imaging optical radars and high-data-rate optical communication systems. During the present reporting period (September 26, 1973 to Mar 25, 1974), the goal of this program is the demonstration of efficient sideband generation at microwave frequencies (X-band or Ku-band) from the 10.6 micrometer CO2 molecular resonance. For the remaining contractual period (March 26, 1974 to June 25, 1974), the goal is to experimentally demonstrate the generation of frequency-chirped 10.6 micrometer CO2 laser waveforms using the microwave-driven thin-film modulator developed under the present contract. Characteristics of the frequency chirped optical signals, sideband power limitations and total optical insertion loss of the microwave-driven thin-film modulator will be investigated. In particular, techniques for improving coupling efficiency of both optical and microwave power will be determined.

The report describes the operation of a high power, repetitively pulsed, flashlamp pumped dye laser. To date an average power of 39 watts at a repetition rate of 100 Hz has been obtained. The techniques employed should be scalable to higher power and higher repetition rate. Experiments to produce frequency sweeping of the laser during the pulse are described. Altimate flashlamp geometries are discussed as are experiments to achieve better spectral matching of the lamp output to the dye., See also report dated 30 Jul 1973, AD764098.

The report discusses the application of picosecond optical pulses to high resolution imaging optical radar. A novel type of signal processing is described. An extensive bibliography of previous work on this contract is included., See also AD689548.

The report describes experimental investigations of stimulated rotational and vibrational Raman scattering in gases, analytical investigations of nonlinear propagation effects in Kerr active liquids and a discussion of the generation of Cerenkov radiation by light pulses.

The report discusses work under the contract for the period 1 August 1970 to 31 January 1971. Topics discussed include theoretical and experimental work on dynamic spectroscopy of ultrashort light pulses, stimulated scattering effects, nonlinear propagation, organic dye lasers, and flashlamps for organic dye lasers., See also AD698557.

The report covers work under contract N00014-66-C-0344 for the period 1 August 1970 to 31 July 1971. Topics discussed include theoretical and experimental work on dynamic spectroscopy of ultrashort light pulses, stimulated scattering effects, nonlinear propagation, organic dye lasers, and flashlamps for organic dye lasers., See also report dated 25 Feb 1971, AD0719415. Sponsored in part by the Defense Advanced Research Projects Agency.

The purpose of this project was to determine, for 10 rock types, the viscosity and electrical conductivity as a function of temperature in the molten state, and the heat of vaporization. The rock types are (1) St. Cloud gray granodiorite (charcoal granite), (2) Westerly granite, (3) Barre granite, (4) Dresser basalt, (5) Sioux quartzite, (6) Bera sandstone, (7) Tholeiitic basalt, (8) Duluth gabbro, (9) Newberry ryholite, and (10) granodiorite. Viscosity and electrical resistivity measurements were made at temperatures as high as 2200C, for all rocks except the quartizite. Using the resistivity data, an approximation of the thermal conductivity of the molten rocks was made using the Wiedemann-Franz-Lorenz law, which gives a relationship between the electrical and thermal conductivity. Heat of vaporization of the rocks was measured by vaporizing samples with a CO2 laser beam. Samples were vaporized in a calorimeter, which measures the partition of input energy among rock heating, rock vaporization, and other losses.

A research investigation was performed to investigate a high-power, closed-cycle CO2 cross-beam electric-discharge convection laser (EDCL). In the cross-beam EDCL, the electric discharge is aligned with the flow and laser output power is extracted transverse to the flow. Based upon results of cross-beam EDCLscaling studies, a laser amplifier channel capable of amplifying an optical input of 100 watts to 25 kw was designed and fabricated. Techniques of continuously processing the laser gases were also investigated. The pulse amplification characteristics of the amplifier with a continuously operating discharge were also investigated analytically and experimentally. (Author)

The report discusses the technical background, design features, hardware and performance of a line selectable CO laser system. This laser was designed to operate with a high degree of amplitude stability and provides for line selection from 5.04 to 5.6 microns. The laser utilizes a three - element (two mirrors and one grating) optical resonator to achieve wavelength selectivity in a very high Q (low loss) optical configuration. This optimized configuration along with other design features has resulted in long term sealed tube operation with power outputs on single line from 0.1 to 1.00 W in the TEM sub (oo) mode.

A brief research and analytical investigation was conducted to determine the impact of powerplant radar, noise, and vibration characteristics on propulsion system selection and design for the airborne tactical control mission. Turboprop and turbofan noise, vibration, and radar cross section characteristics were compared on the basis of data available in the literature and data obtained by simplified analytic methods. Aircraft noise and vibration levels attributable to the powerplant were compared with criteria established for crew comfort for mission durations of the length required for the airborne tactical control mission. Radar cross sections for turboprop and turbofan powerplants were compared as to their influence on the relative detection range of the aircraft. The effects of propeller modulation of the reflected radar signal and the detection of this signal using moving-target-indication (MTI) radar were considered. It was found that the reduction of powerplant noise levels and radar cross sections warrant significant attention in the selection and design of the powerplant. The conventional turboprop installation presents a significant vibration problem because of blade passing in close proximity to the cabin. Propeller modulation of radar signals greatly increases the range at which the aircraft can be detected. It was concluded that unconventional turboprop designs warrant serious consideration; in particular, a shrouded turboprop may present an attractive alternative.

Progress on the process development as it relates to the optical quality of sputtered single crystal films of ZnO, AlN, and TiO2 is discussed. Optical attenuation data for optical waveguide structures comprised of zinc oxide, aluminum nitride, titanium dioxide films grown on sapphire substrates and titanium dioxide on YZ cut lithium niobate is presented. The effect of depositon parameters on the carrier mobility of single crystal gallium arsenide films grown by reactive sputtering is presented., Sponsored in part by DARPA. See also report dated 27 May 1973, AD0760715.

A study of the amounts of specific contaminants present in propellant grade (Mil Spec) hydrazine obtained from a number of users has been carried out. A total of twenty-four samples from twelve user groups was analyzed. The contaminants examined included particulate materials, organic impurities, water, carbon dioxide, metals and chloride. The level of particulate contamination, the particle size distribution and approximate identification of chemical types were established by appropriate techniques. Major metal contaminants were determined by atomic absorption and trace metal contaminants were determined by emission spectroscopy. Other contaminants were assayed by gas chromatographic, ultraviolet spectroscopic or colorimetric techniques.

An analytical investigation was conducted to evaluate quantitative applications of available model rotor tip vortex patterns from a water tunnel. This evaluation consisted of reducing selected photographic wake data to coordinate form, and comparing the resulting wake geometries with both theoretical results and available experimental data taken in air. Additionally, the study included an examination of the sensitivity of water tunnel wake geometry to the water tunnel test parameters which did not duplicate full-scale rotor values and the applicability of a water tunnel wake geometry to determine the airloads of a full-scale rotor. Finally, the possibility of developing simplified wake documentation and generalization procedures and improved water tunnel test techniques was assessed.

The research had as its objective the development of an electrolytic ignition system for monopropellant-fueled millipound thrusters. The report describes the electrochemical decomposition of hydrazine-based monopropellants which was studied as a function of propellant composition and electrode materials. It was found that a 77% hydrazine-23% hydrazine azide composition yielded the highest heat output with the lowest power input provided platinum was used as an anode. Performance data was obtained on prototype engines incorporating the electrolytic ignition concept.

The objective was the selection of an electrolyte and electrode materials for an electrolytic ignition system for millipound thrusters. This report describes the evaluation of electrode polarization effects, ohmic effects due to both electrolytes and electrodes, and possible catalytic effects on electrode surfaces. Electrical conductivity measurements indicate that hydrazine-based salts must be added to hydrazine in order to minimize ohmic effects and that the mixture of 77% hydrazine-23% hydrazine azide is the most promising electrolyte candidate. Polarization studies have shown that platinum or pyrolytic graphite should be the best anode material for the electrolytic cell and that AM350 or 304SS should be the best cathode material in terms of minimizing the power needs for the cell. These electrodes were also found to catalyze the propellant decomposition reaction in addition to providing simple electrolytic decomposition. This result indicates that the reaction will be self-propagating at power inputs considerably below theoretical.

The report summarizes the work performed during the second year of an experimental and theoretical research program concerning the self-induced thermal distortion effects on cw CO2 laser radiation propagating in absorbing media. The research program is directed toward improving the understanding of the possible limitations imposed by the atmosphere on the propagation of high power laser radiation. The work presented is concerned with essentially the following three different areas: (1) wind simulation experiments using a high pressure gas cell; (2) studies of the kinetic cooling of a gas by absorbing of CO2 laser radiation; and (3) studies of turbulence effects on the self-induced thermal distortion of laser beams.

The influence of aerosols, or particulates, on thermal blooming and gas breakdown of 10.6 micrometer wavelength radiation was measured. When particles are irradiated with high intensity pulsed CO2 laser beams, gas breakdown is initiated and the plasma formed limits the propagation of the beam. Experimental measurements of the threshold for ionization of single particles electrodynamically suspended at the focus of a beam was measured. Streak photographs of the plasma expansion and schlieren studies are also reported. A theoretical analysis of solid particles laser radiation interaction indicates that the mechanism leading to breakdown is superheating of the particle material with subsequent ionization of the solid or of the material directly adjacent to the solid., See also report dated Jan 1973, AD775222.

An investigation of various problems to be encountered in technically difficult physical environments as a result of ambient lightning, vibration and suspended aerosols is reported. Successful pulsed holographic experiments on composite rotor blades are also reported. An evaluation of the effects that various surface finishes have on the holographic construction process which indicated that surface roughnesses from 4 microinches (very smooth) to 1000 microinches are amenable to the method. The development of the theory required to relate holographic records to the strain patterns and areas of maximum strain present on the large structures, together with experimental studies exhibiting good correlation between the holographically calculated strain and that measured with gages.

The goals of the program include a critical property evaluation of the best aluminum and titanium alloy matrix boron composite systems available today and improvement of the understanding of fracture in metal matrix composites. This program is intended to develop criteria for material selection and metallurgical processing and to generate data to guide the structural engineer in designing with metal matrix composites. Areas of concentrated studies include: environmental effects, including exposure to sea water, high temperatures, and thermal cycling; transverse properties; off-axis properties; failure mechanisms of fatigue; notch bending fracture; and notched tensile fracture.

An experimental investigation was conducted of laser welding of Navy ship construction materials. Bead-on-plate penetrations were formed in 1/4-in.- thick HY-130 steel, 1/16-in.-thick HY-180 steel, 1/8- and 1/4-in.-thick Ti-6Al- 4V titanium alloy and in 1/8-in.-thick 5456 aluminum alloy. Continuous carbon- dioxide laser power levels to 8 kW were used; welding speed was varied from 20 to 180 ipm in order to establish appropriate welding parameters. The bead-on- plate penetrations were initially screened by visual, metallographic, NDT and mechanical tests and then forwarded to NSSC for more detailed evaluation. The finished samples, which were 5 x 7 in. in size, exhibited excellent top and bottom surface bead characteristics and defect-free fusion zones.

Emphasis on the consideration of glass formation as a kinetic process made it possible to think of glass compositions different from those normally employed in the manufacture of glass fibers. Approximately 450 new glass compositions were prepared and three dozen of these compositions have values for Young's modulus measured on bulk specimens greater than nineteen million pounds per square inch. Of the new glasses about a hundred could be drawn into fibers by mechanical methods at high speeds. The fiber with which we have the most experience has a Young's modulus measured on the fiber of 18.6 million pounds per square inch and has been prepared in ouantity as a nonfilament (to date more than 150 million lineal feet of 0.2 to 0.4 mil fiber have been produced). This fiber has also been successfully incorporated both in epoxy and polyimide matrices. The epoxy resin composite has shown a modulus forty percent better than that achievable using the most common grade of competitive glass fiber, and twenty percent better than that obtainable with the best available grade of competitive glass fiber. Other glass fibers of even higher modulus have been developed but we have very little experience with these as yet. The method of producing modulus from glass composition due to C.J. Phillips has been extended.

Fluid mechanics experiments were performed to obtain information applicable to an open-cycle, coaxial-flow, gaseous nuclear rocket engine. In this engine concept, gaseous nuclear fuel and a surrounding stream of seeded hydrogen propellant pass coaxially through a reactor chamber. The flow was simulated in the present experiments by multi-component, constant-temperature, coaxial-flow jets in short chambers. The flow was studied using flow visualization techniques and concentration measurements.

The purpose of this work was to develop a process for preparing large-diameter carbon monofilament. The process selected involved chemical vapor deposition using boron trichloride, methane and hydrogen gases and a conventional boron type reaction in which the substrate is resistively heated. Amorphous carbon-boron alloys were formed when gas mixtures containing greater than 20 percent methane (80 percent BCl3) were used. The strongest carbon-boron monofilament was achieved using a CH4/BCl3 gas ratio of 0.44. This gas ratio produced a monofilament in which the average composition of the deposit was 75 w/o boron and 25 w/o carbon. When this high an amount of boron is attained, it is suspected that the deposit reacts more readily with the impurities present on the surface of the carbon substrate. The carbon-substrate fiber was precleaned in chlorine and used as a substrate. With the precleaned substrate, the strength of the carbon-boron alloy monofilament was considerably improved. The experimentation showed that high strength, high modulus carbon-boron alloy monofilament can be produced from a BCl3, CH4, and H2 gas system. The modulus of the monofilament appears to be linearly dependent upon the percent of boron in the monofilament. jg p6

The Ni3Al (gamma') - Ni3Cb (delta) eutectic alloy was directionally solidified in a plane front manner at rates varying from 0.3 to 10.6 cph. The lamellar spacing which decreased with increasing rate affected the strength of the eutectic according to a Hall-Petch correlation. By decreasing the spacing by a factor of 4.7, the tensile strength was increased by 35 percent at room temperature and by 100 percent at 2000F. The eutectic grown at 10.6 cph possessed the phenomenal strength of 140,000 psi at 2000F. The resistance of the eutectic to a tension-tension fatigue cycle proved excellent. This resistance was provided by the strength of the phases, as well as the presence of debondable interfaces which affect crack propagation. Thermal fatigue tests conducted on the directionally solidified eutectic showed no adverse effect due to the differences in thermal expansion of the phases. Quenching the eutectic produced a res dual tensile stress in the gamma' which lowered the proportional limit of the composite. Studies of the strength anisotropy showed that the strength is decreased in directions nonparallel to the growth axis with brittle behavior at room temperature and ductile behavior at 2000F. (Author)

The research and development on microwave power combinatorial techniques for active semiconductor devices covered in this report is significant to the Air Force because it delineates the problems and limitations of quasi-optical approaches for high power, microwave power sources. The general approach investigated under this program was primarily directed toward broadband operation and utilizing arrays of simple reflection amplifier elements and non-resonant power combiner structures. The combiners investigated under this program contained no networks of transmission lines or other additional circuit elements, hence; the approach was essentially quasi-optical. The work concentrated on a broadband reflection power amplifier comprised of a 5 by 5 array of elements and included some work, for further experimental support, on circular arrays of both 8 and 24 elements. The individual amplifier elements and combiners designed, fabricated, and tested under the program met the bandwidth objectives of the program; (i.e., 10% bandwidth of center frequency). However, the complete active power combiner could not be made to function as a useful amplifier because of spurious signals. These spurious signals were concluded to be caused by mutual interaction between the wide band amplifier elements. This interaction, resulted in undesirable input impedance variations with frequency. These input impedance variations with frequency together with the strong nonlinearities in the diodes results in the generation of many spurious signals by parametric interactions.

The primary emphasis of the report pertains to the metal matrix composite system aluminum plus boron fiber with a protective coating. Alloys and fibers have been considered which are deemed most useful for aerospace applications. Further research and development will concentrate on composite systems for higher temperature application. It was found that, although environmental attack by salt water could be characterized by the matrix properties, degradation of properties at high temperatures in air (700C) were better related to the fibers. The transverse strength of boron-aluminum was related for the most part to the problem of fiber splitting and such effects as matrix, heat treatment, volume fraction fiber, test temperature, test specimen configuration, fiber properties, and secondary reinforcement were studied. Axial, transverse, and cross-ply composites were studied in low-cycle fatigue tests. Charpy 'V' notch bend tests and center-notched tensile tests were investigated to determine the effect of stress concentration factors and general fracture behavior. (Author)

The objective of the work reported herein is to achieve stable mode-locked, second harmonic power output from a Nd:YAG laser. Particular emphasis is placed on amplitude stability and on conversion efficiency. The experimental results of this program are 200 mW of 0.53 micron mode-locked power output at a PRF of 500 MHz. The amplitude fluctuations are + or - 4%. The intracavity barium sodium niobate crystal, used as both the second harmonic generator and mode-lock modulator, was driven at 250 MHz. Stability control techniques successfully demonstrated include: (1) cladding of the laser rod; (2) amplitude equalization of the output pulse train; (3) maintaining the relative frequency difference between the modulator drive and the cavity c/2L frequency within narrow limits by use of a phase-lock loop; (4) series regulation of the lamp current and the use of ballast resistors; and (5) maintaining the nonlinear crystal at the phase-match temperature by closed-loop control of the oven temperature. Thermal effects in the banana crystal arising from absorption of the fundamental wavelength radiation were found to limit the amplitude stability of the laser output. The same effects distort the 0.53 micron far-field beam profile and reduce the conversion efficiency., See also Rept. no. AFAL-TR-72-411, AD-907 116L.

The objective of the work reported herein is to achieve stable, single-frequency second harmonic power output from a Nd:YAG laser. Particular emphasis is placed on frequency and amplitude stability and on conversion efficiency. The experimental results of this program indicate that frequency and amplitude stable frequency-doubled operation of the single-frequency Nd:YAG laser can be achieved. Single-frequency operation is obtained by the use of a ring cavity containing a differential loss and frequency-doubled operation by the use of an intracavity 5 cu mm barium sodium niobate crystal. The 1.06 microns laser output is 3/4 to 1 W and the maximum 0.53 microns output is 140 mW. Degradation of the crystal reduced this level to a repeatable 50 to 100 mW frequency stable to + or - 12 MHz and amplitude stable to + or - 4 percent over a number of minutes operating period. Thermal effects in the nonlinear crystal arising from absorption of the fundamental wavelength radiation were found to limit the amplitude and frequency stability of the laser output. The same effects distort the 0.53 microns farfield beam profile and reduce the conversion efficiency. Techniques necessary to achieve stable frequency-doubled operation of the single-frequency Nd;YAG laser were established during this program. Further improvement in the stability and conversion efficiency depends on the availability of barium sodium niobate crystals with low absorption at 1.06 microns. (Author), See also Rept. no. AFAL-TR-72-410, AD-907 115L.

The purpose of this study was to provide information to guide the development of improved fiber reinforced composites. Various instrumental and analytical procedures were used to characterize graphite fiber surfaces, determine fiber and fiber surface composition and to study the interaction between fiber surfaces and epoxy resin, resin components, coupling agents and model compounds. Surface tension and adhesion tension results showed that high temperature (1200C) hydrogen treatment or evacuation markedly improved the adhesion between the treated graphite surfaces and certain coupling agents and organic compounds and also that the adsorbed films were retained even after consecutive treatment with toluene, ethyl acetate and boiling water. Electron micrographs of graphite fibers, treated in a manner similar to the coupons, supported the adhesion tension results on graphite coupons. The surface reactivity of graphite yarn, employing gas phase chromatographic techniques using graphite yarn as the column substrate was studied. Retention time as a function of temperature indicates only a relatively weak physical adsorption of organic materials on as received (water sized) graphite yarn. In general, air oxidation and high temperature treatments (1200C) in hydrogen, argon, and in vacuo activate the surface of as received graphite yarns as is shown by the increased affinity of the treated graphite surfaces for certain organic compounds and for water. (Author)

When unidirectionally solidified at rates below 3 cm/hr, the Ni3Al (gamma')-Ni3Cb (delta) alloy grew with the eutectic phases as alternating lamellae aligned parallel to the direction of solidification. The lamellar phase morphology was examined by transmission electron microscopy, and the planes were found to exhibit preferred growth directions, (110) gamma' and (100) delta parallel to the direction of solidification. The interfacial planes most commonly observed were (-111) gamma' parallel to (010) delta. The tensile properties of the eutectic were evaluated in the temperature range of 75 to 2200F and the creep and rupture properties in the temperature range of 1600 to 2200F. Its high temperature tensile and creep properties, measured in the direction of alignment, were found to be superior to all nickel base superalloys. The dynamic elastic modulus of the eutectic and its thermal expansion were measured from 75 to 1800F. The modulus was higher and the expansion lower than that which is typical for nickel base superalloys. Other properties of the eutectic which are reported include its notched tensile strength, the effect of interlamellar spacing on the strength, the temperature dependence of its impact properties, microhardnesses of the eutectic phases, compressive properties at room temperature, and oxidation behavior. (Author)

High strength, high modulus boron reinforced metal matrix composites were fabricated by plasma spraying. A new fabrication technique which includes the plasma spraying of monolayer fiber reinforced tapes and the subsequent diffusion bonding of these tapes was found to be an excellent method to insure reproducible properties in the composites. Boron fibers coated with silicon carbide were found to have superior resistance to degradation at elevated temperatures compared to that of boron. The elastic and strength properties of the composites were characterized for unidirectional composites. Strengths of up to 189,000 psi in tension and 297,000 psi in compression were measured for composites with 50% volume fraction BORSIC fiber in aluminum. Other properties measured include fatigue strength, creep, stress rupture, impact resistance, and high temperature strength. Analytical mechanics, fractography, metallographic examination and nondestructive testing were used to better understand the properties of the composite structures. (Author)

Research was conducted to study the chemical and physical nature of silicon carbide fiber and graphite yarn surfaces and surface interactions of these fibers with various materials. Various instrumental and analytical procedures were used to characterize fiber surfaces, determine fiber and fiber surface composition and to study the reaction between fiber surfaces and epoxy resin, resin components, coupling agents and model compounds. The purpose of this study is to provide information to guide the development of improved fiber reinforced composites. Silicon carbide fibers analyzed by electron microprobe and X-ray diffraction qualitatively showed the presence of a moderate concentration of oxygen. Silicon carbide fiber surfaces with a specific surface area of 0.016 m2/g appear granular by optical microscopic examination but smooth by electron microscopic examination. Surface tension and adhesion tension results showed that oxidation and oxidation-hydration of silicon carbide fibers markedly improved the adhesion between the silicon carbide surfaces and certain coupling agents, and also that the adsorbed film was retained after consecutive treatment with water, toluene, ethyl acetate and boiling water.