Accession Number : ADA333876

Title :   Micromechanical Prediction of Tensile Damage for Ceramic Matrix Composites under High Temperature

Descriptive Note : Final rept. 15 Aug 90-14 Dec 94

Corporate Author : CITY COLL NEW YORK DEPT OF MECHANICAL ENGINEERING

Personal Author(s) : Delale, F. ; Liaw, B. M.

PDF Url : ADA333876

Report Date : 15 FEB 1994

Pagination or Media Count : 140

Abstract : This report documents the experimental and theoretical results obtained in studying the tensile damage behavior of ceramic matrix Composites (namely Nicalon/CAS II Composites) at room and elevated temperatures. First the composite Specimens were machined into dog-bone shape and polished to increase efficacy of observation in the SEM. Then the specimens were placed inside the chamber of a Scanning electron microscope (SEM) and subject to tensile loading at room and higher temperatures up to 700 deg c. At each temperature, the load was increased until failure of the specimen and the progression of damage was observed and recorded from first crack to total failure. Damage usually started with matrix cracking, followed by debonding along fiber-matrix interface, fiber pullout and finally fiber breakage. At each load level, the displacement was measured, resulting in a stress-strain curve with linear and non-linear portion. Similar behavior was observed at higher temperatures. Theoretical models to predict and simulate the observed behavior were also developed. A singular integral with periodic matrix cracking and interface debonding explains well the fact that embedded matrix cracks almost always propagate to the interface and are arrested by the fibers. The results obtained from finite element model with multiple rows of matrix cracks and debonding at the fiber-matrix interface, compare extremely well with the experimental data.

Descriptors :   *CERAMIC MATRIX COMPOSITES, *CRACKING(FRACTURING), *FIBER REINFORCED COMPOSITES, STRESS STRAIN RELATIONS, TENSILE STRENGTH, SCANNING ELECTRON MICROSCOPES, INTERFACES, HIGH TEMPERATURE, FINITE ELEMENT ANALYSIS, CRACK PROPAGATION.

Subject Categories : Laminates and Composite Materials
      Mechanics

Distribution Statement : APPROVED FOR PUBLIC RELEASE