The manufacturing process of this material is very expensive. Therefore, defects such as delaminations, inclusions and extreme porosity should be detected as soon as possible. As already found from testing of the CFRP material, the above-mentioned defects can be detected by means of ultrasonic testing. Contrary to CFRP as a laminate, CMC shows a higher acoustic attenuation by absorption and scattering. Ultrasonic testing within the individual intermediary stages of the manufacturing process is very difficult. In the condition after pyrolysis, the plastic matrix is removed from the laminate and an open-pore material is provided. In the subsequent processes (re-infiltration), the material shall not absorb humidity, which prevents ultrasonic C-scan testing with water coupling.
In order to be able to carry out this testing method, the principle of dry coupling with roller dry-coupling probes has been used by vacuum-packaging the material into a silicone bag. Coupling was produced by the contact pressure on the silicone skin of the test part. Thus, normal ultrasonic scan testing in Squirter technology could be performed from the outside. Only the through-transmission method can be carried out at this stage of the infiltration phase. In the final condition, i.e. when the porous structure is filled with ceramic, wet testing of the material in the pulse-echo method is possible at a test frequency of 2.25 MHz.
Abstract Source:
Book of Abstracts, 7th European Conference on Non-Destructive Testing, 26-29 May 1998, ISBN: 87-986898-0-00
Full-Text Source:
Proceedings of the 7th European Conference on Non-Destructive Testing, 26-29 May 1998, ISBN:
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