G'day Cattletruck
Sorry but I am not familiar with the bonding processes on the Collins subs. I am aware that the Defence Science and Technology Organisation was involved in the early 1990s with some large bonded composite patches on cracked ship superstructure and that was very successful. I am unaware of any disbonds on these repairs, but that is mainly because I am no longer in the system. The patches were 4m x 1 m and the surface preparation was done using mops! My guess is that they may have taken note of the process used for that project.
My suspicion is that the other sub users suffer from the same problem as the aircraft industry; you use only the recommended procedures provided by the OEM even when there is irrefutable evidence that these processes are manifestly deficient. The AW approved scuff sand and solvent contamination process used to repair AW139 disbonds is a classic example. Everyone who knows anything about adhesive bonding has known for decades that this process may produ ce some short term strength but will without doubt result in later disbonding. The OEM is reluctant to introduce a more effective process because it may require a higher level of skills which may not be available in Blogslovia, and besides to admit the current process is deficient may leave the OEM open to litigation. Unfortunately, if the current repair process does lead to a loss of life, they again may be open to litigation anyway.
We Aussies do have a history of technological innovation. We claim the "black box" as an Aussie invention, and many of the scatter factors for full scale fatigue tests were generated down here. To some extent, we are driven by being a small nation which must maximise the useful life of the assets we have, and do that at minimum cost. (Our F-111s will go out of servide next year after over thirty years service.)
The composite patching technology I was involved in was spawned from the need to gain experience with the composite materials which were gradually entering military service. The problem was that they were expensive, so we focussed on using small amounts of materials on applications which gave high returns for the costs. It has been estimated that we saved over US$100 million by being the only C-130E user in the world not to change the wing planks because we extended their life using composite patches from 1975 to withdrawal. It was only in the 1990's that the USAF finally saw the benefits and saved billions adopting (and extending) this technology for repairs to C-141. The late entry has been attributed by some to the attitude of "Not invented in the USA, can't be good" and there may be an element of truth in it.
In my personal case, I am still trying to convince the FAA (and any other regulator who will listen) that the current regulations for certifying bonded structures are inadequate because it is possible to make a bonded structure which meets current certification requirements yet has a potential to fail in service. (see Davis, M.J. DEFICIENCIES IN REGULATIONS FOR CERTIFICATION AND CONTINUING AIRWORTHINESS OF BONDED STRUCTURES,
International Aerospace Congress, Sydney, 25-27 February 1997
I can send a copy if requested)
There are two basic failure modes for adhesive bonds; cohesion failure where the adhesive fractures and adhesion failure where the adhesive disbonds at the interface between the adhesive and the adherend. Current regulations do not adequately address adhesion failures, or address them in a manner which is open to misinterpretation. Now helicopters have a lot of adhesive bonding in primary structure (blades for example) and I have seen interfacial failures in such structures.
I sometime do feel that there is an element of
yet another case of Australia being considered a technological and cultural backwash
Regards
blakmax