Accession Number : ADA195224

Title :   Creep of Carbon Yarn and Carbon-Carbon Composites at High Temperatures and High Stresses.

Descriptive Note : Technical rept.,

Corporate Author : CALIFORNIA UNIV LOS ANGELES DEPT OF MATERIALS SCIENCE AND ENGINEERING

Personal Author(s) : Sines, George ; Yang, Zheng ; Vickers, Brian D

PDF Url : ADA195224

Report Date : May 1988

Pagination or Media Count : 60

Abstract : To better understand the creep-behavior of carbon yarn and carbon-carbon composites, creep experiments were developed that permitted testing at high temperatures (up to 2500 C) and at high stresses (up to 850 MPa) on specially prepared, uniaxial specimens that had a known gage length. Using a Dorn-type power law relation to model steady-state creep the apparent activation energy for the carbon yarn and carbon composite specimens was determined to be 1082 kj/mol. This value represents a single thermally activated process, vacancy diffusion, that compares favorably with the various types of graphitizable carbon. The value determined for the stress exponent was 7.5. It too was found to be independent of the carbon matrix's presence and independent of the specimens' loading history. Values of the pre-exponential constant for the carbon yarn and carbon composites were also calculated. The carbon matrix greatly improves the creep resistance of the carbon composite. This improvement was attributed to the matrix's microstructure. It distributes applied loads more evenly and it may also impose a triaxial stress state in the yarns's filaments. It is proposed that such a stress state may inhibit the flux of vacancies thus accounting in part for this increase in creep resistance.

Descriptors :   *CARBON CARBON COMPOSITES, *CARBON YARN, *TRIAXIAL STRESSES, ACTIVATION, ACTIVATION ENERGY, COMPOSITE MATERIALS, CREEP, CREEP STRENGTH, FILAMENTS, MATRIX MATERIALS, MICROSTRUCTURE, STRESSES

Subject Categories : Ceramics, Refractories and Glass
      Refractory Fibers

Distribution Statement : APPROVED FOR PUBLIC RELEASE