DID YOU KNOW? DTIC has over 3.5 million final reports on DoD funded research, development, test, and evaluation activities available to our registered users. Click
HERE to register or log in.
Accession Number:
ADA334604
Title:
Transformation Weakening of Ceramic Composite Interfaces
Descriptive Note:
Final rept. 15 Sep 96-31 May 97
Corporate Author:
ILLINOIS UNIV AT URBANA DEPT OF MATERIALS SCIENCE AND ENGINEERING
Report Date:
1997-10-31
Pagination or Media Count:
121.0
Abstract:
A new concept for achieving graceful failure in oxide composites is studied. It is based on debonding of a weak interphase between a matrix and an interphase in a laminated composite. The interphase can be thermally or shear stress induced by transformation weakening, which results from an accompanying significant volume contraction andor unit cell shape change, on cooling from a high temperature to low temperature crystal structure. Mullitecordierite laminates with a beta -- alpha-cristobalite transformation weakened interphase were investigated in order to demonstrate interphase debonding behavior. The laminate showed fracture behavior dependent on a critical size effect. The grain size of polycrystalline beta-cristobalite was controlled by annealing. With increasing annealing time, the strength decreased due to the formation of internal microcracks in the cristobalite layer which occurred spontaneously during thermally-induced transformation. A hot-pressed laminate, annealed for 10 h at 1300 deg C, had an average grain size of 4.2 micrometers and a strength of 131 MPa. Its work of fracture was 2.38 kJsq m with a non-catastrophic fracture behavior. The indentation response indicated crack deflection along the cristobalite debonding interphase.
Distribution Statement:
APPROVED FOR PUBLIC RELEASE