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Static and fatigue loading tests of bonded lap joints were conducted. The specimens were designed to fail in the bondline and all fatigue tests included monitoring the crack growth to failure. Detailed crack length readings for 106 fatigue specimens are provided.
Trade-off studies and screening evaluations were made of commercial polymers and silicone foam sheet stock. A low modulus, low density 0.26 gm/cc modification was developed of the GE-RESD PD-200 system based upon GE RTV-560 silicone polymer. The bond system modification was initially characterized for mechanical and thermal properties, evaluated for application methods, and its capability demonstrated as a strain arrestor bond system.
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Gas adsorption measurements on an Apollo 12 ultrahigh vacuum-stored sample and Apollo 14 and 15 N2-stored samples, show that the cosmic ray track and solar wind damaged surface of lunar soil is very reactive. Room temperature monolayer adsorption of N2 by the Apollo 12 sample at 0.0001 atm was observed. Gas evolution of Apollo 14 lunar soil at liquid nitrogen temperature during adsorption/desorption cycling is probably due to cosmic ray track stored energy release accompanied by solar gas release from depths of 100-200 nm.
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Degradation of high performance polyimide precursor resins was investigated by measuring the molecular weight of the polymers in solution, using a membrane osmometer. It was found that polyimide precursor resins composed of BTDA and ODPA combined with DABP and MDA were unstable in DMAC. The degradation rate was found to depend upon the chemical nature of the isomeric diamine and the geometric structure about the amide linkage. The polymers of DABP were less susceptible to degradation than those of MDA and p,p'-compounds were more stable than m,m'-compounds. These results suggest that degradation is correlated with the basicity of the diamine. That is, the rate of the degradation reaction increases with the basicity of the diamine group in the polyimide precursor resin. The presence of water and a higher temperature increased the degradation rate of the polymers.
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Nonflammable tape adheres well, can be written on, and has other properties making it extra-safe general-purpose tape.
Resolution of neutron radiographic images of thermally conductive film is increased by replacing approximately 5 percent of aluminum powder, which provides thermal conductivity, with gadolinium oxide. Oxide is also chemically stable.
Removable overlay keeps thickness variations small, saving material and application time. In comparative tests against roller, brush, and spray application, thickness variations in the conventional techniques were at least three times greater.
Carbonate pretreatment produces highly bondable surface without harming film. Treatment is useful in developing low-cost mirrors and solar concentrators fabricated from metal-coated plastic films. Treatment should cost no more than standard degreasing and rinsing procedures.
The Hohenberg-Kohn and Kohn-Sham formalisms are used to examine binding (binding energy as a function of separation) for combinations of the simple metals Al(111), Zn(0001), Mg(0001), and Na(110) in contact. Similar metal contacts between Al, Zn, Mg, and Na are examined self-consistently in an ab initio calculation using the Kohn-Sham formalism. Crystallinity is included using the Aschroft pseudopotential via first order perturbation theory for the electron-ion interaction; and the ion-ion interaction is included exactly via a lattice sum. Binding energy was determined both in the local-density approximation and including gradient corrections to the exchange and correlation energy. Binding was found in all cases. In dissimilar metal contacts, interfacial bonding was greater than that in the weaker material predicting the possibility of metallic transfer. The nonzero position of the energy minimum in like metal contacts is explained in terms of consistency between the Ashcroft pseudopotential and the bulk charge density. Good agreement with experimental surface energies is obtained in the self-consistent calculation when nonlocal terms are included.
Studies of dust impingement on a duplicate Viking Lander camera window indicated the possibility of window obscuration after several days of exposure even at low dust concentration levels. As a result the following corrective measures were recommended: (1) The clearance between the housing surface and the camera post should be eliminated by using an appropriately designed plastic skirt: (2) The three horizontal ledges below the window inside the cavity act as bases for pile-up of dust that slides down the window surface; they should be replaced by a single inclined plane down which the dust will slide and fall out on the ground: (3) Adhered dust on the window surface can be removed by high pressure CO2 jets directed down against the window; the amount of CO2 gas needed for the entire mission can be carried in a 3 1/2-inch diameter sphere equipped with a remotely programable valve. These measures were incorporated in the design of the lander camera system. The continued high quality of photographs transmitted from the Viking spacecraft several months after landing attests to their effectiveness.
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An electron bombardment argon ion source was used to ion etch various metals and fluoropolymers. The metal and fluoropolymers were exposed to (0.5 to 1.0) keV Ar ions at ion current densities of (0.2 to 1.5) mA/sq cm for various exposure times. The resulting surface texture is in the form of needles or spires whose vertical dimensions may range from tenths to hundreds of micrometers, depending on the selection of beam energy, ion current density, and etch time. The bonding of textured surfaces is accomplished by ion beam texturing mating pieces of either metals or fluoropolymers and applying a bonding agent which wets in and around the microscopic cone-like structures. After bonding, both tensile and shear strength measurements were made on the samples. Also tested, for comparison's sake, were untextured and chemically etched fluoropolymers. The results of these measurements are presented.
A system was developed for bonding RSI tiles to a graphite/polymide composite substrate which would withstand the full range of environmental conditions. The bonding system, designated RA59, consists of a mixture of glass (sesquisiloxane) resin in RTV 560 silicone. A significant number of data points for the RA59 are in the 65-psi failure range both when tested, and after exposure to 700 F. This is over two times the best shear and tensile values obtained with RV60 at this temperature. It is concluded that with a thorough understanding of the critical parameters involved, the higher values should be obtained consistently with the RA59. This is of particular significance if higher strength tiles were to be used in a hard-bonded configuration.