epoxy joint

[rick wallace]

I'm not an engineer by any stretch, but it seems there are two issues
here - bond strength and fillets. 

 

Bond strength - I think a sounds epoxy joint will be stronger than the
materials bonded in just about any case - the joint seldom fails usually
it's the material pas the joint. (ergo slow setting epoxy, poly-u or
whatever to penetrate the material and spread the stress on the joint?)
A well known pilot uses Elmers or similar to set wood spars in foam
wings - the joint's stronger than the surrounding foam so no prob. 

 

Fillets - I think the purpose of a fillet is to spread the load across a
larger area than just the mating surfaces, and thus dissipate stress
risers or focused points of stress? They're often an easy/ cheap/ light
way of getting more durable joints. 

 

Can't wait to hear someone w/ more than seat of the pants experience on
this - 

 

-Rick 

-----Original Message-----
From: discussion-request at nsrca.org [mailto:discussion-request at nsrca.org]
On Behalf Of John Crozier
Sent: Saturday, January 15, 2005 10:35 AM
To: discussion nsrca
Subject: epoxy joint

 

Sometime in my crafting life, I have acquired the notion that adding
milled glass, micro-balloons, etc.,  to epoxy when making a good fitting
joint, only weakens the joint. (diminishes, or dilutes the bonding
strength of the epoxy).

In this case it would be composite horns to balsa.  No fillet is needed.

Anybody wanna jump in?

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