Interpreting high temperature deformation behavior of a ceramic matrix composite via high energy x-rays and numerical simulation

Abstract

All-oxide Ceramic Matrix Composites (CMC), due to their damage tolerance and thermal stability, are promising candidates for high temperature applications, including combustion liners and thermal protection systems in aerospace. In these applications, mechanical loads are introduced at high temperatures up to 1200°C or even higher, which results in complex deformation behavior. For understanding the complex behavior of an all oxide CMC under such extreme environments, laboratory tests and numerical simulations have been performed. The material investigated in this study comprises Nextel R 610 alumina fiber bundles and a porous α alumina matrix, and the composite has been produced by a computer controlled winding process. Analytical and numerical work has been performed for developing a constitutive law describing the observed creep behavior of specimens with unidirectional fiber orientation under compressive load. While for fiber orientations parallel to the compressive load a model with isochoric matrix behavior captured the experimental results well, discrepancies occurred for other fiber orientations. Parameter studies indicated that depending on fiber orientation and matrix properties the composite deformation is due to a combination of matrix compaction and fiber rotation. In-situ synchrotron studies at Argonne National Laboratory's Advanced Photon Source have been conducted on unidirectional fibre reinforced CMC specimens at 1200°C while stepwise increasing compressive mechanical load. For investigating the local strain in the composite, diffraction measurements were conducted under representative loading, and transmission radiography was utilized to study the evolution of matrix deformation and fiber rotation. First results indicate that the strain in the fiber and matrix grains of the all alumina composites may be isolated during analysis, providing information on load transfer between fiber and matrix and on elastic and creep behavior of the composite. These results will be used to inform computational simulation to produce more accurate lifetime prediction in application.