In-situ observation of micro-cracking in a SiC/BN/SiC ceramic matrix composite under tension
Kaitlin N. Detwiler, Reece Hunt, Elizabeth J. Opila
Abstract
Crack spacing and crack opening displacement values are critical for CMC damage and oxidation modeling. A tensile stage used with light and scanning electron microscopy (SEM) was utilized to evaluate micro-cracking under load in SiC/BN/SiC ceramic matrix composites (CMCs). Surface micro-crack spacing and crack composition, a novel measurement introduced in this work, were measured with light microscopy at room temperature. Crack spacing decreased with increasing load, with a majority of cracks being in contact with BN fiber coatings. Crack opening displacement (COD) measurements were taken at room and elevated temperature (600 °C) with scanning electron microscopy. CODS increased nearly linearly with increased load; CODs ranged from 1 to 3 μm at 200–350 MPa at room temperature and at 600 °C ranged from 0.5 to 2 μm at 175–350 MPa. CODs were also related to local microstructure, with CODS being lower near longitudinal fiber tows. Implications on use of the data for CMC oxidation models are discussed.