Accession Number : ADB026143

Title :   Characterization of Reaction Sintered Silicon Nitride Radomes.

Descriptive Note : Final rept. 1 Jan-1 Sep 1977,

Corporate Author : AIR FORCE MATERIALS LAB WRIGHT-PATTERSON AFB OHIO

Personal Author(s) : Land,Peter L. ; Ruh,Robert

Report Date : OCT 1977

Pagination or Media Count : 49

Abstract : This report describes the observations and characterization of reaction-sintered silicon nitride radomes produced by Raytheon Corporation for the Air Force. The radomes were tested at NASA-Ames with a CO2 laser and failed under less stringent conditions than expected. Portions of the radomes removed for flexure specimens had extensive flawed areas consisting of many voids of approximately 100 micron diameter. The strength and bulk density of the flexure specimens ranged from 12,000 to 18,000 psi and from 2.1 to 2.2 gm/sq. cm which is substantially lower than the values anticipated by Raytheon, approximately 25,000 psi and 2.35 - 2.6 gm/cm. Most of the flaws identified as fracture origins in the AFML flexure specimens consisted of one or two voids about 100 microns in diameter. The fractures under laser irradiation may have initiated at one of the large defects = or > 500 microns in diameter - which are present on the fracture surface near the periphery of the irradiated region. Since tensile strength decreases with the inverse square root of the linear dimension of the flaws in a homogeneous material, it is estimated that the radomes may have fractured at stress levels below 8,000 psi. Several thermal stress models for laser irradiation of ceramic radome materials were reviewed; none specifically addressed the failure mode which may have occurred in the radomes.

Descriptors :   *SILICON NITRIDES, *RADOMES, *FRACTURE(MECHANICS), LASER DAMAGE, SINTERING, CARBON DIOXIDE LASERS, FLEXURAL STRENGTH, MICROSTRUCTURE, X RAY DIFFRACTION, IMPURITIES, CERAMIC MATERIALS

Subject Categories : Lasers and Masers
      Ceramics, Refractories and Glass
      Active & Passive Radar Detection & Equipment

Distribution Statement : APPROVED FOR PUBLIC RELEASE