Effect of Hold Times on Fatigue Behavior of Nextel 720/Alumina Ceramic Matrix Composite at 1200°C in Air And in Steam Environment
Mehrman, John M.
Synopsis "Effect of Hold Times on Fatigue Behavior of Nextel 720/Alumina Ceramic Matrix Composite at 1200°C in Air And in Steam Environment"
The aerospace field requires structural materials that can maintain superior mechanical properties while subjected to high temperatures and oxidizing environments. This research investigated the effect of hold times at maximum load on fatigue performance of a Nextel"720/Alumina ceramic matrix composite at 1200-C, explored the influence of environment on material response to cyclic loading with hold times at maximum load, and assessed the effects of loading history on material behavior and environmental durability. The N720/A composite relies on an oxide/oxide composition for inherent oxidation resistance and a porous matrix with no interphase between the fiber and matrix for damage tolerance. Mechanical testing results showed a significant decrease in material life and performance in a steam environment when compared to tests conducted in a laboratory air environment. Prior fatigue of specimens tested in an air environment resulted in an order of magnitude increase in creep life. Fracture surface observations with a Scanning Electron Microscope showed a correlation between an increase in fiber pull-out and increased time to failure. A qualitative spectral analysis indicated evidence of silicon species migration from the mullite phase of the fiber to the matrix, especially in the steam environment. This may be the cause of the decreased creep performance of the material in the steam environment.This work has been selected by scholars as being culturally important, and is part of the knowledge base of civilization as we know it. This work was reproduced from the original artifact, and remains as true to the original work as possible. Therefore, you will see the original copyright references, library stamps (as most of these works have been housed in our most important libraries around the world), and other notations in the work.This work is in the public domain in the United States of America, and possibly other nations. Within the United States, you may freely copy and distribute this work, as no entity (individual or corporate) has a copyright on the body of the work.As a reproduction of a historical artifact, this work may contain missing or blurred pages, poor pictures, errant marks, etc. Scholars believe, and we concur, that this work is important enough to be preserved, reproduced, and made generally available to the public. We appreciate your support of the preservation process, and thank you for being an important part of keeping this knowledge alive and relevant.
