Accession Number:

ADA063745

Title:

Fracture of Brittle Materials at High Temperature.

Descriptive Note:

Final rept. Jan 76-Dec 77,

Corporate Author:

NATIONAL BUREAU OF STANDARDS WASHINGTON DC NATIONAL MEASUREMENT LAB

Personal Author(s):

• Tighe,Nancy J.
• Wiederhorn,Sheldon M.

Report Date:

1978-07-01

Pagination or Media Count:

48.0

Abstract:

Ceramic materials offer the potential for significantly increased operating temperatures, increased efficiency and lower costs for gas turbine engines. However, the brittle nature and resulting catastrophic mode of failure of ceramic materials requires a design approach based on consideration of crack nucleation and growth. If both the initial size of pre-existing cracks and the rate at which they grow under an applied stress are known then the time to reach critical size at which failure occurs can be predicted. In principle, the initial size can be determined by non-destructive test techniques. However, state-of-the-art NDT equipment does not have the required sensitivity to detect the flaws in question, which are generally 100 micro m or less. An upper limit on tolerable flaw size can be obtained by proof testing, but the validity of this approach needs to be demonstrated. There is little information on the strength of turbine ceramics which can be used for component design and the relationship between material behavior and microstructure is not well understood. Author

Descriptors:

• *FRACTURE(MECHANICS)
• *CERAMIC MATERIALS
• *GAS TURBINES
• MICROSTRUCTURE
• NONDESTRUCTIVE TESTING
• HIGH TEMPERATURE
• HOT PRESSING
• NUCLEATION
• CRACK PROPAGATION
• DEFECTS(MATERIALS)
• TOLERANCES(MECHANICS)
• SILICON NITRIDES

Subject Categories:

• Ceramics, Refractories and Glass
• Mechanics
• Jet and Gas Turbine Engines

Distribution Statement:

APPROVED FOR PUBLIC RELEASE