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COMPOSITE MATERIALS

JPRS-UMS-92-003 16 March 1992

Calculation of the Adhesion Characteristics of a System of Two Different Metals Separated by a Dielectric Layer

927D0067D Moscow POYERKHNOST: FIZIKA, KHIMIYA, MEKHANIKA in Russian No 12, Dec 91 (manuscript received 3 Aug 90; after remion 24 Jan 91) pp 72-75

[Article by A.N. Vakilov and V.V. Prudnikov, Omsk State University]

UDC 539.612.001

[Abstract] Working within the framework of the density functional method, the authors of the study analyzed the adhesion characteristics of a system of two different metals separated by a dielectric layer. In essence, the functional density method entails solving a variational problem to find the minimum energy of the electron system examined against the background of a specified positive charge distribution. In the present study, the authors considered two semibounded metals occupying the regions z < -D and z > D with an intermediate dielectric layer with a thickness of 2D and a dielectric constant of e. By solving a linearized Thomas-Fermi equation using boundary conditions reflecting the conti-nuity of the electrostatic potential (p(z) and electric induction ed<p/dz with z - +/-D and the finiteness of the potential in infmity, they derive an expression for the density of the electron distribution n(z) in the said system (assuming that <p(z) - -4rcn(z)/p²). They also find the interface interaction energy and the adhesion energy and force of the adhesion interaction with consideration for the discreteness of the crystal lattice of the contacting metals as a function of the distance between the metal surfaces and the dielectric constant of the intermediate layer. The authors acknowledge that using the concept of the dielectric constant for a layer with a thickness on the order of interatomic quantities is not strictly correct but is instead a model abstraction. They further notę that for pD/e^,/2 >> 1, the adhesion properties of a metal-dielectric-metal system will be determined by the characteristics of the metal-dielectric contact and that giving consideration to the vacuum gap between them will result in a replacement of repulsive forces by attractive forces. They conclude by stating that for distances of pDe^l/2 >> 1, disperse attractive forces begin to come into play along with electrostatic forces and that these disperse attractive forces become decisive at values of D of about 100 angstroms or morę. Figures 2; references 6: 5 Russian, 1 Western.

Radiarion Strength of Carbon-Carbon Composite Materials Under High-Temperature Neutron Irradiation

927D0068Q Moscow IZVESTIYA AKADEMII NAUK SSSR: SERIYA NEORGANICHESK1YE MATERIAŁY in Russian Vol 27 No 12, Dec 91 pp 2664-2666

[Article by R.G. Khanbekov, Kh.M. Rasulkulov, Yu.S. Virgilyev, I.P. Kalyagina, T.N. Shurshakova, Nuclear Physics Institute at the Uzbek Academy of Sciences]

UDC 546.26

[Abstract] Fabric-based carbon-carbon composite mate-rials (UUKM) which are distinguished from others by their structure and composition are studied in order to determine the following characteristics: density, bending strength and compressive strength, dynamie modulus of elasticity, thermal conductivity, electric resistivity, thermal coefticient of linear expansion, and the crystal lattice constant c. To this end, 4x4, 5x5, and 8x8 mm samples were irradiated in a helium atmosphere in the high-temperature chamber of a WR-SM reactor at the Nuclear Physics Institute at the Uzbek Academy of Sciences at a temperaturę of 1,800-1,900 and 2,100-2,300K; the temperaturę was measured by W-Re ther-mocouples. The properties of fabric-based carbon-carbon composites are summarized and tabulated and the relationship between the relative changes in resis-tivity and the fabric-based carbon-carbon composite materiał sample size is established and plotted. A slight anisotropy in properties of some materials is established. It is noted that in all fabric-based carbon-carbon composite materials and in the reactor-grade graphite, an improvement in rcsistivity may be attributed primarily to the compaction of the materiał. Irradiation of various fabric-based carbon-carbon composite materiał samples at 1,800-2,300K temperatures by a 1 x 10²° neutron/cm² fluence leads to their shrinkage and decreases their resistivity due to a matrix compaction; the change in strength does not exceed 50%. Figures l; tables l; references 1.

An Investigation of Destruction of Composite Materials by Laser Radiation and a Supersonic Nitrogen Flow

927D0089G Moscow FIZIKA I KHIMIYA OBRABOTKIMATERIALOY in Russian No 6,

Nov-Dec 91 (manuscript received 13 Jul 90) pp 58-65

[Article by A.A. Betev, V.T. Karpukhin, M.M. Malikov, and N.I. Shalnova, Moscow]

UDC 539.4:678.067

[Abstract] The authors of the study examined the com-bined effect of laser radiation and a supersonic nitrogen flow on specimens of composite materials (i.e., laycred carbon-filled plastic and porous chlorosulfonated filled polyethylene) that included a phenol-formaldehyde resin binder. Composite specimens with an initial layered and porous structure were studied at oncoming flow Mach numbers of about 4.1, an impact temperaturę of 1,100 to 1,300 K, and an impact pressure of about 2.5 MPa. The laser radiation had a wavclength of 10.6 pm and a radiating power of 10² to 10⁴ W/cm². The irradiation spot measured 30 x 40 mm in most of the experiments and had a diameter of 10 mm in some of the experi-ments. The duration of the irradiation was varied from 3 to 20 seconds and that of the supersonic flow was varied from 10 to 30 seconds. The effects of the nitrogen flow and the laser radiation were studied in combination and