Article Detection and Characterization of Debonding Defects in Aeron...
Dear Bisle,
Please specify the question or what do you want as information to be able to reply
Regards
Georges
O.K. I misused this space a little because I thought this discussion would directly connected with a comment I did.
Please refer to this paper: Article Detection and Characterization of Debonding Defects in Aeron...
The comment is:
Triggered by the fact that this paper was recommended by Mathias Kersemans attracted me to read it. With the background of industrial development of NDT for Honeycomb since more that 35 years as well as having also a history of working with ACUT on CFRP and a lot of Honeycomb and Foam Sandwich structures I am a little sceptical about the modelling. We did already basic modelling work on Ultrasound propagation in honeycomb in the early 1990ties with Prof. Langenberg and the EFIT and AFIT code, and had a lot of discussions about what type of waves contribute to the "real world" effects we saw on different sandwich types. From 2005 on I was involved in a total revision of inspection concepts for honeycomb sandwiches as the experience of an Incident in aeronautics (http://www.tsb.gc.ca/eng/rapports-reports/aviation/2005/a05f0047/a05f0047.pdf) told us, that the previous used inspection methods (TapTest, Bondmaster, UT, other resonance tests etc) did not fulfil the needs - they clearly missed a lot of defect types. (ref. to https://static4.olympus-ims.com/modules/imageresizer/adc/b7d/06b18e60be/400x177.jpg) We found out that the best method to get most defects with high POD even in case of thick (stiff) skin but also with nearly every type of core (cell size, wall size, core thickness) was Pulse/Echo-Ultrasound tuned in frequency depending on core height, just to half wavelength equal to thickness. Especially the effect of humidity in core (Damping effects) told us, that we have guided waves. As well core rupture in different depth showed effects on tuned ultrasound frequency. So the cell wall works like a string fixed between to points or like a stick fixed on one side swinging on the other side with max amplitude. (see https://static1.olympus-ims.com/data/Image/appnotes/Fig5_ResonanceTechnique.jpg?rev=F10B )
So I would advice you to do first an experiment with a vibrometer setup or a LaserUT device, where you let the laserbeam scan - from the side - the honeycomb wall up and down the become aware hos the honeycomb wall acts as a membrane.
You have to cut through some cell walls a slit wide enough to get the laserbeam through and put a Transducer on top the skin to excite the honeycomb cell, where the laserbeam will be reflected - this is a really interesting experiment!
This is not only good for conventional UT but als for ACUT!
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