A lot of research has been done on structural adhesives, as we've covered here http://www.designnews.com/document.asp?doc_id=237011 and here http://www.designnews.com/document.asp?doc_id=236816 Fabrico, which doesn't make adhesives, but uses them assembling all kinds of structural components, has articles and a Q&A on many of these subjects here http://fabricoforum.com/2012/06/structural-adhesives/
It certainly is a valid question, adhesive lifetime, and how does one speed the aging process so as to find a correct answer? And the very important question is how reliableare the bond lifetime results? Many adhesives primarily fail through long term creep type of fault, while in others t6he ridgid bond becomes brittle and does not stand up to shocks. Two different failure mechanisms, it seems. And he experience of how things stick to a composit is not the level that we are looking for. So the solution is to understand the failure mechanism, and use that information.
Ttemple, it sounds like there is an good long track record on the adhesives, at least a couple decades. So, while these adhesives may be new to the auto industry, they seem to be well tested in aerospace.
ttemple, thanks for telling us about your direct experience. Anything going into the construction of commercial aircraft has very strict specifications and requirements, including extensive testing on the ground and in the air, and everything is 100% traceable. Whether structural adhesives or fasteners are used in a particular part of the plane depends on several factors, but stresses in aircraft are much more extreme than in cars.
I would say around 1996 or so. They were manufacturing the (Kingair?)"1900D" heavily at that time. It says on wikipedia that the 1900D was introduced in 1991, and produced through 2002. I'm sure that many 1900D's are still in use as regional commuters.
I don't know when they started using adhesives though. The part I remember specifically was the window attachment to the fuselage skin. There was sort of an aluminum porthole looking piece that was glued to the fuselage. The joint had the appearance of a weld, and it held together like it.
I think they use adhesives in the wing compartments too, at least in the areas where there is going to be fuel stored. The adhesives seal the compartments, I think. They also use special fuel resistant coatings on the skin inside those areas.
That's very encouraging, Ttemple. Was that a number of years ago? I would guess if adhesives had any durability problems we would know by now. In manufacturing, I would think using adhesives is more efficient than welding.
I did some work at Raytheon (Beech) quite a number of years back. They routinely used adhesives to bond aluminum aircraft parts together. The parts were also riveted (sparingly), but the engineers referred to the rivets as "chicken rivets", because they insisted the glue was more than strong enough. Supposedly the FAA wouldn't let them get rid of all of the rivets. I don't know how it ages, however. We had to disassemble some of the parts that were glued, and the aluminum would tear before the glue would let go. As I remember it, the stuff was basically inseparable.
These are structural adhesives, and many of them are being adapted from aerospace applications, where they've been used with composites for some time. We covered structural adhesives here http://www.designnews.com/document.asp?doc_id=237011
Fascinating story, Ann, on how to join materials that can't be welded. One thing that gives me pause is that as they develop appropriate adhesives, it will still only be a guess on how the joining materials will hold up after 20 years. Only time will tell whether the adhesives will hold the car together over decades.
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