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Modeling of Time-Dependent Strength Degradation of SiC/SiC Ceramic Matrix Composites via MAC/GMC Computer CodeSilicon carbide fiber reinforced silicon carbide (SiC/SiC) ceramic matrix composites (CMCs) display time-dependent strength degradation at intermediate temperatures (600 to 900 degrees Centigrade). This is generally believed to be an oxidation induced phenomenon. The understanding of the effect of temperature with environment (oxidation) is key towards development of SiC/SiC CMCs with a reliable load carrying capacity. Various theories have been proposed to explain the strength degradation. One suggests that the boron nitride (BN) coating deposited on the fibers oxidizes causing fusion of fibers. Another theory proposes that the SiC fibers are oxidized forming a silica scale leading to premature fiber failure. A more recent theory suggests that SiC fiber strength is intrinsically time-dependent due to slow crack growth of flaws in the fibers. An empirical model, termed as a "fiber classic model," which is based on a standard slow crack growth type power-law, has been implemented within NASA's micromechanics-based MAC/GMC computer code as a user routine. Model parameters for this "classic model" were calibrated from stress-rupture data of Hi-Nicalon (TM) monofilaments using the maximum likelihood estimation (MLE) technique. This new capability in the MAC/GMC computer code was then used to predict the stress-rupture behavior of Hi-Nicalon (TM) tows as well as 2-D SiC/SiC composites reinforced with Hi-Nicalon (TM) fibers. Results demonstrate that the MAC/GMC with this new capability successfully predicts the time-to-failure vs. applied stress within the intermediate temperature range at various scales as well as laminated composites in an oxidizing environment.
Document ID
20180006436
Acquisition Source
Glenn Research Center
Document Type
Technical Memorandum (TM)
Authors
Mital, Subodh K. (Toledo Univ. Toledo, OH, United States)
Arnold, Steven M. (NASA Glenn Research Center Cleveland, OH, United States)
Murthy, Pappu L. N. (NASA Glenn Research Center Cleveland, OH, United States)
Bednarcyk, Brett A. (NASA Glenn Research Center Cleveland, OH, United States)
Pineda, Evan J. (NASA Glenn Research Center Cleveland, OH, United States)
Date Acquired
October 18, 2018
Publication Date
August 1, 2018
Subject Category
Composite Materials
Report/Patent Number
E-19553
NASA/TM-2018-219939
GRC-E-DAA-TN56873
Funding Number(s)
CONTRACT_GRANT: NNC13BA10B
WBS: WBS 109492.02.03.01.30
Distribution Limits
Public
Copyright
Public Use Permitted.
Keywords
Environmental degradation
static fatigue
Oxidation

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