Date of Award

3-23-2018

Document Type

Thesis

Degree Name

Master of Science in Aeronautical Engineering

Department

Department of Aeronautics and Astronautics

First Advisor

Marina B. Ruggles-Wrenn, PhD.

Abstract

Creep behavior of an oxide-oxide ceramic matrix composite (CMC) containing an array of effusion holes was investigated at 1200⁰C in air and in steam. The composite (N720/A) consisted of a porous alumina matrix reinforced with alumina-mullite NextelTM 720 fibers. Test specimens had an array of 17 effusion holes with 0.5-mm diameter. The effusion holes were drilled through the specimen thickness normal to the specimen surface using a CO2 laser. Effect of the effusion holes on tensile properties was evaluated tension tests to failure at 1200°C in air. Creep of specimens with effusion holes at 1200°C was studied for creep stresses ranging from 40 to 100 MPa in air and from 30 to 90 MPa in steam. Creep run-out was defined as 100 h creep stress. Effect of the laser-drilled effusion holes on creep was assessed by comparing the results of the present study with the results from prior work on unnotched N720/A specimens. The presence of laser-drilled holes significantly reduced creep lifetimes in both air and steam. Post-test microstructure of the composite was examined; damage and failure mechanisms were assessed. Dramatic loss of creep resistance in specimens with holes is due to extensive composite degradation caused by laser drilling.

AFIT Designator

AFIT-ENY-MS-18-M-279

DTIC Accession Number

AD1056611

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