Stress-dependent matrix cracking in 2D woven SiC-fiber reinforced melt-infiltrated SiC matrix composites

Abstract

The matrix cracking of a variety of SiC/SiC composites has been characterized for a wide range of constituent variation. These composites were fabricated by the 2-dimensional lay-up of 0/90 five-harness satin fabric consisting of Sylramic fiber tows that were then chemical vapor infiltrated (CVI) with BN, CVI with Sic, slurry infiltrated with Sic particles followed by molten infiltration of Si. The composites varied in number of plies, the number of tows per length, thickness, and the size of the tows. This resulted in composites with a fiber volume fraction in the loading direction that ranged from 0.12 to 0.20. Matrix cracking was monitored with modal acoustic emission in order to estimate the stress-dependent distribution of matrix cracks. It was found that the general matrix crack properties of this system could be fairly well characterized by assuming that no matrix cracks originated in the load-bearing fiber, interphase, chemical vapor infiltrated Sic tow-minicomposites, Le., all matrix cracks originate in the 90' tow-minicomposites or the large unreinforced Sic-Si matrix regions.Also, it was determined that the larger tow size composites had a much narrower stress range for matrix cracking compared to the standard tow size composites.

Monitoring damage accumulation in ceramic matrix composites using electrical resistivity

“…As stress on the samples is increased, the number of matrix cracks increases, leading to the increases in resistivity and acoustic energy. The acoustic energy released during loading has been shown to be directly proportional with the number of matrix cracks in SiC/SiC CMC [15]. Since the resistance is closely related to the acoustic energy it is expected that a quantitative correlation between the resistance change and crack density could be established for SiC/SiC composites.…”

“…The acoustic sensors were clamped to the specimen surface and vacuum grease was used as a couplant between the two. The waveforms were recorded by an 8 channel fracture wave detector produced by Digital Wave Corp. Software from the same company was used to filter the acoustic events and analyze those which only occurred within the gage section [14,15].…”

“…The acoustic sensors were clamped to the specimen surface and vacuum grease was used as a couplant between the two. The waveforms were recorded by an 8 channel fracture wave detector produced by Digital Wave Corp. Software from the same company was used to filter the acoustic events and analyze those which only occurred within the gage section [14,15].Figures 2a-c are plots of the applied stress, acoustic energy, and resistance change of the samples as they were tensile tested in hysteresis loops. For each stress loop, the resistance increases at first and then reduces, in response to the stress change in the loop.…”

Stochastic Virtual Tests for High-Temperature Ceramic Matrix Composites

“…Such measurements include those via optical microscopy (108)(109)(110)(111)(112)(113), scanning electron microscopy (114-119), speckle interferometry (120)(121)(122), acoustic waves (123)(124)(125), and electrical resistance (126,127). Most of these measurements were at room temperature; only a few studies tackled in situ measurements at high temperatures (e.g., References 114 and 128).…”

Health monitoring of Ceramic Matrix Composites from waveform-based analysis of Acoustic Emission

“…Using few remote sensors, AE allows real-time monitoring and localization of damage. In CMCs, the cumulative energy of acoustic emission signals has been shown to be directly related to transverse matrix crack density [1,2]. In static fatigue at intermediate temperatures, the energy of AE events has also been used as an indicator for lifetime prediction [3,4].…”