View Full Version : Composite and adhesive bonding issues

16th Dec 2009, 11:52
Fellow PPRuNers

For some time I have been addressing composite and adhesive bonding issues with regard to specific events. This has evoked various responses ranging from total support and appreciation for my advice but also extending to concerns (to some extent justifiable) that my comments are too specific in relation to particular manufacturers, and I am scaring the public away from companies which fly particular types of helicopter.

I would therefore like to start this thread as a forum for open discussion of repair procedures in a more generic manner. As anyone who has read the Rotorheads threads to which I have contributed will know, one of the specific issues I have been addressing lately is the problem of strength reduction caused by micro-voids in adhesive bonds on one particular helicopter type. Let me assure you I have seen exactly the same problem on helicopters produced by other manufacturers and I have seen these deficiencies on fixed wing components as well. I have also seen them occur in adhesive bonded repairs and fibre-composite structures.

These micro-voids are small and difficult to detect using any NDI inspection method, but can produce substantial reductions in bond strength. I have extensive experience in this area, and much of my recent posting traffic (and attempts to contact the OEM by direct and indirect means, even via the regulator) has been aimed at providing advice on how significant these defects can be, the causes, and how to reduce the occurrence of micro-voids.

Naturally, as a consultant, I would hope that I would be appropriately engaged to provide my advice. However, the total lack of response by the specific OEM, together with a recent repair assessment of voids in fibre composite structures on another European helicopter, and several less recent occurrences of micro-voids in a further brand of helicopter from a US manufacturer indicates that the issue of micro-voiding may be more widespread.

My assessment is that the implications to airworthiness are such that it is no longer appropriate for me to seek to contract individual OEMs so that their specific problems can be addressed on a case by case basis. Coincidentally, I am dealing with a family medical condition which would prevent me for the next six months from engaging on-site with any OEM who could be interested. It was never about money anyway, as many people who have PM'd me and a few who know me personally already know. I did actually meet with the US manufacturer (at an exceptionally nominal fee) and did provide advice which I hope they followed.

I have therefore decided to waive my IP and to openly publish a discussion paper on management of micro-voiding in the hope that if it is free, then maybe, just maybe, someone at this and other manufacturers will actually read the document and actually address what is a potentially serious air safety issue.

The web address is http://www.adhesionassociates.com/papers/Managing%20Micro-Voiding%20of%20Adhesive%20Bonds.pdf

I am happy to provide similar material on:

Injection repairs for disbonds
Injection repairs for composites
Surface preparation for production and repairs
Temperature measurement and control equipment, methods and process management for hot-bonded repairsIs there any interest out there, or should I just get my coat and leave?

Merry Christmas


16th Dec 2009, 12:29
Hi Blakmax,

From WWII Liberty Ship weld cracks (due hydrogen gas bubbles from water), through Rolls Royce RB211 Carbon Fan blades complete failure - I'm sure there much to be apprehensive about any process involving composite adhesive bonding.

It was OK if one of my carbon fan blades failed on one of my 3 Engines - but I'm going to be very concerned when it's one of my wing joints.