Thread: Alloy stringers-anyone got any failure pictures?

Howdy Antony,

I don't think the harmony argument is a strong one.

However it will be up to the builder to show that he can attach then securely and is sure that their stiffness is close to the structure they replace.

We know wood works in this type of structure - so the problem really becomes .. we don't know how alloy works.

The biggest weakness of the method is how do you attach the alloy. We know that they glue alloy in aircraft structures, but they use around 8 processes to get it to stick - treating the surfaces with different chemicals and different abrasives.

Getting alloy to stick reliably is very difficult. Teh biggest problem is peel strength - that to get something to move initially is hard, but once you have one end up a bit the rest just peels off the surface.

If you fasten it ... what can you use for fastenings? The only alloy building method that really makes sense is to weld it so all materials are similar. Alloy stringers with fastenings sound like batteries in the bilges to me! Electrolysis is such a tricky beast.

So if you cannot fasten it and you cannot glue it ...

You could glass it in. In this case the low peel strength may mean that voids will appear between the resin matrix and the alloy, setting up a rather interesting mix of chemicals and metals - yep traces of metal in polyester resin - or one metal filing at the right part of the electrolytic table will eat through the lot if water gets in there - like a 2c coin in a tinnie bilge!

MIK

Just tell him he's a dill because it won't be a wooden boat any more and the purists will all laugh at him

Richard
suffering 'assignmentitis'

I can't help Antony, but it's an interesting thread anyway, so here goes:

Mik, 3M make a tape that is a one-way fixing. It's used in aircraft and heavy vehicle body building and it seems to work! Sika with the appropriate primers would also work but may be subject to the peeling of which you speak.

I don't think the problems of differential movement will be huge, as they are being used as stiffeners only, to cut down the spans, and there's probably no more movement between aluminim and ply than there would be between say oregon and ply.

Metal timber composites have been around a while, after all. The Herreshoffs among others used bronze floors and some even cast iron.

It doesn't matter though, none of it makes too much sense to me.

In another life, (a suggestion for Antony) we moulded a deep top-hat section which was laid up in a single layer of (S-Glass I think) glass to do the same thing. The flanges were then epoxied on to the surface. These ranged between two and six inches deep. On curved areas, we simply glassed over foam shaped similarly.

Cheers,

P

Howdy Midgy!

(a tad informal that)

Herreshoffs would use fasteners. The aircraft people jump hoops to make the stuff stick. I know the 3m stuff is generally state-of-the art - but only when used where they expect. And they would give no guarantees.

Also - what sort of extrusion. can't be L or T or U as the bit standing up will fold down flat as soon as there is any load. So it has to be a box section.