Assessment of damage in ceramics and ceramic matrix composites using ultrasonic techniques

Technical Report · Sat May 01 00:00:00 EDT 1993

OSTI ID:5785188

Chu, Y C; Baaklini, G Y; Rokhlin, S I

This paper addresses the application of ultrasonic sensing to damage assessment in ceramics and ceramic matrix composites. It focuses on damage caused by thermal shock or oxidation at elevated temperatures, which often results in elastic anisotropy. This damaged-induced anisotropy is determined by measuring the velocities of ultrasonic waves in different propagation directions. Thermal shock damage is assessed in ceramic samples of reaction bonded silicon nitride (RBSN). Thermal shock treatment from different temperatures up to 1000 C is applied to produce the microcracks. Results indicate that most microcracks produced by thermal shock are located near sample surfaces. Ultrasonic measurements using the surface wave method are found to correlate well with measurements of degradation of mechanical properties obtained independently by other authors using destructive methods. Oxidation damage is assessed in silicon carbide fiber/reaction bonded silicon nitride matrix (SCS-6/RBSN) composites. The oxidation is done by exposing the samples in a flowing oxygen environment at elevated temperatures, up to 1400 C, for 100 hr. The Youngs' modulus in the fiber direction as obtained from ultrasonic measurements decreases significantly at 600 C but retains its original value at temperatures above 1200 C. This agrees well with the results of destructive tests by other authors. On the other hand, the transverse moduli obtained from ultrasonic measurements decrease continually until 1200 C. Measurements on the shear stiffnesses show behavior similar to the transverse moduli. The results of this work show that the damage-induced anisotropy in both ceramics and ceramic matrix composites can be determined successfully by ultrasonic methods. This suggests the possibility of assessing damage severity using ultrasonic techniques.

• Research Organization: National Aeronautics and Space Administration, Cleveland, OH (United States). Lewis Research Center
• OSTI ID: 5785188
• Report Number(s): N-94-11237; NASA-TM-106121; E-7785; NAS-1.15:106121; CNN: RTOP 510-01-50
• Country of Publication: United States
• Language: English

Related Subjects

36 MATERIALS SCIENCE
CERAMICS
CRACKS
ULTRASONIC TESTING
COMPOSITE MATERIALS
MATRIX MATERIALS
DAMAGE
MECHANICAL PROPERTIES
NONDESTRUCTIVE TESTING
SILICON CARBIDES
SILICON NITRIDES
ULTRASONIC WAVES
ACOUSTIC TESTING
CARBIDES
CARBON COMPOUNDS
MATERIALS
MATERIALS TESTING
NITRIDES
NITROGEN COMPOUNDS
PNICTIDES
SILICON COMPOUNDS
SOUND WAVES
TESTING
360203* - Ceramics
Cermets
& Refractories- Mechanical Properties
360603 - Materials- Properties