Accession Number:

ADA238817

Title:

Role of Cracks in the Creep Deformation of Polycrystalline Structural Ceramics

Descriptive Note:

Final rept. 1 May 88-30 Apr 91,

Corporate Author:

VIRGINIA POLYTECHNIC INST AND STATE UNIV BLACKSBURG DEPT OF MATERIALS ENGINEERING

Report Date:

1991-04-30

Pagination or Media Count:

5.0

Abstract:

A study was conducted concerning the role of cracks in the creep deformation and fracture behavior of polycrystalline structural ceramics. Grain boundary cavitation during creep in a course-grained alumina was found to cause a decrease in Youngs modulus by as much as a factor of five, indicative of the contribution from elastic creep by crack growth and crack-enhanced creep to the total creep deformation. Multiple crack formation in a fine-grained alumina was found to increase the strain-rate sensitivity of the failure stress, as the result of strain-rate dependent decreases in Youngs modulus. For alumina with glassy grain boundary phase, the one-to-one correlation between creep rate and time-to-failure presented evidence for crack enhanced creep fracture. Silicon carbides whisker-reinforcement of aluminum oxides was found to suppress cavitation, coupled with an increase in the stress exponent. A micromechanical analysis of this effect indicated that creep deformation of SiC whisker- reinforced alumina appears to be governed by stress-dependent sliding at whisker-matrix interfaces.

Subject Categories:

  • Ceramics, Refractories and Glass

Distribution Statement:

APPROVED FOR PUBLIC RELEASE