Fiberglass or plastic over aluminum ? - (insane thought of the day)

I would agree, in a professional boat shop, construction could easily employ all those methods, and be solid and reliable.
To someone who doesn't know what they're doing, and has a good chance of mucking up welding or a glue joint, mechanical fasteners have an advantage, I think.

 

If they *really* don't know what they're doing, it'd be a better idea to make up some sacrificial panels first and test them to destruction while perfecting technique.

PDW

 

That is actually a really interesting thought.
It would be very interesting to test several joints connected weld vs glue vs rivets vs bolts.
It would also be interesting to test steel vs aluminum vs fiberglass.
I realise numbers are easily available, but that isn't the whole story.

I might actually attempt to do something like this in the near future, make the same joint out of several materials and fasters and measure how many pounds it takes to destroy each assembly.

 

I think that the hardest part is testing the long term performance of glue on metal in a marine environment.

 

I don't know much if anything about advanced glues, but I assume that how it's used is obviously going to dictate how well it works. Like many other products.
However, I think the glue operates on a "clean surface area" performance rating, so if I have a 2x2 joint, but only 1 square inch of properly prepped surface, I should recieve the performance of the glue as per MFG designs and performance data.
I could be wrong, but if a glued aluminum joint supports the load it is suppposed to, it shouldn't lose ahdesive strength should it?

As great as glue/ adhesive might be, I have trouble telling myself it is really as strong as it may be. I mean, fiberglass is basically glued together fibers, and it works great, but I just have a mental block trusting it to replace a weld or riveted joint.

 

> but if a glued aluminum joint supports the load it is suppposed to, it shouldn't lose ahdesive strength should it?

Yes, it definitely will.

 

I just don't feel like adhesives are for me.
I wouldn't build an aluminum boat with adhesives even if it was supposed to be stronger.

I also wouldn't fly in an airplane made from transparent lexan, even if it was stronger than aluminum.

 

Epoxy jointed aluminium is used by some auto makers, the snag for amateur use is oxidation film compromising the integrity of the join.

 

If it was something like Sikaflex 291, probably pretty good.

We used to joke that our ship was held together with Sikaflex, Velcro and cable ties. Certainly a lot of the equipment was....

PDW

 

But you have probably flown in an airplane that has bonded aluminum primary structure. It can be done with rigorous phosphoric acid etch surface preparation using specialty epoxy products. Methylacrylates have also been used successfully in automotive aluminum bonding.

Dino

 

Are there examples of glued aluminum in cases with continuous salt spray exposure?

 

Or larger forces applied to the material?

I've seen old steel boats where the hull skin is dented in everywhere, airplanes just don't see that kind of bumping and smashing.

 

Not that I know of. It would be the worst case application for aluminum bonding.

Dino

 

glassover Alum

fiberglass polyester resin ( with glass cloth)expands and contracts at same rate as aluminium, so it would work if metal is clean and sanded to etch for adhesion. epoxy would be better.

 

The bonds are strong and tough. Examples of trashed aluminum bonded helicopter rotor blades normally don't separate at the bond line. The salt spray is the issue as long term exposure would have to be considered. There have been dramatic failures in salt spray exposed bonded aluminum helicopter fuselages in Australia but these have eventually been resolved.

Dino