Detection of porosity in glass ceramic matrix composites using an ultrasonic multiple-gate C-scan technique
- Univ. of Dayton Research Inst., OH (United States)
- WL/MLLN, Wright-Patterson AFB, OH (United States)
Ceramic matrix composite (CMC) plates consisting of silicon carbide fibers in a barium magnesium aluminosilicate matrix (SiC/BMAS) were obtained for mechanical and thermal properties characterization. Each plate had dimensions of 150 x 150 x 3 mm (6 x 6 x 0.12 in.) from which mechanical test specimens, each 150 mm (6 in.) long, were to be cut. To ensure that the material was properly consolidated and free of porosity, the plates were inspected using an ultrasonic multiple-gate C-scan technique previously developed for graphite epoxy composites. This technique allowed the placement of multiple peak-detection gates between the front and back surface echoes on the A-scan signal. Because each gate recorded the amplitude variation for a very narrow time-of-flight range, the frequent fluctuations in signal amplitude due to the inhomogeneity of the material affected one or two gates at times, while the other gates remained sensitive to small amplitude signals from defects. The increased sensitivity allowed the detection of very small material defects such as porosity. Using this technique for each plate revealed an isolated area of manufacturing abnormalities, presumed to be porosity, near the center of one plate. Based on the C-scan information, the pattern for cutting out the mechanical test specimens was altered and the region containing the abnormalities was sectioned, polished, and optically inspected. Optical microscopy clearly showed extensive porosity and a region of poor consolidation in the matrix material at the depth indicated by the C-scans. Details of the multiple-gate ultrasonic C-scan technique, results of the ultrasonic evaluation, and destructive analysis are discussed.
- OSTI ID:
- 276578
- Journal Information:
- Materials Evaluation, Vol. 54, Issue 7; Other Information: PBD: Jul 1996
- Country of Publication:
- United States
- Language:
- English
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