Epoxy stiffness?

I need an epoxy that is stiff to the point of brittle. I want no flex; it has to transmit vibration as close to 100% as possible. It's not carrying any weight, so strength isn't important. I'm just tired of finding only epoxies that seem to keep their resin-y qualities after curing.

What property am I looking for in data sheets? Am I looking for a high Shore Hardness value? That's what Devcon uses in its data sheets to specify hardness.

Is this something that I can achieve by adding a hardener? If so, do I lose something if I add this?

Any personal experiences with epoxies that you found to be stiffer than others?

Thanks. FBt

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Esther & Fester Bestertester
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Off the top, and untested, but I imagine that regular epoxy well-loaded with either metal powder, or fine sand might well be stiff and hence brittle.

Brian W

Reply to
Brian Whatcott

In my experience, stiffness (and vibration transmission) are optimized by making the epoxy layer thinner. Thickness is often more important than the epoxy's modulus. Epoxies using a filler often make a thicker layer than those without, so I try to avoid fillers for jobs like mounting accelerometers.

I've used Shell's EPON 828 resin mixed with 3140 hardener at ratios

100:33 to make a thin, stiff joint. Based on Shell's extreme unwillingness to provide tech support, I wouldn't recommend their product unless you already have experience with it. Since that experience with their tech support, I've tried Loctite Hysol M-121HP, and early indications are that it has pretty similar properties. But I have far less experience with that epoxy and no recent experience with their tech support.

How about a non-epoxy? Cyanoacrylates (superglues) can make a pretty thin joint.

Of course, your application may constrain the thickness of the epoxy layer. If that's the case, then ignore everything I've said.

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I think of CA as a not-serious adhesive (the TV ad of the guy hanging from his hard hat comes to mind). China mending, etc.

I suspect that I'm not giving it its due. How does it stack up to epoxy for adhesion and strength?

I stopped by the local hobby store which has a quite sizable range of different CAs, mostly differing by their set speed. There is also a spray-on accelerator.

Reply to
Esther & Fester Bestertester

I have only done a very small amount of testing (shear lap strength) that compared a few epoxies to one CA. So my experience is based on a very small sample size. In those experiments, the CA had similar shear lap strength to epoxies.

You want maximal vibration transmission, and that suggests that you may be mounting accelerometers or a similar application. I think it's quite telling that a set of accelerometers that I bought a few years back each included a tube of Loctite CA (I can't remember which one... 411, maybe?). And CA is often recommended by accelerometer manufacturers.

So if you can live with the limitations of CA (short work life, inability to fill large gaps, susceptibility to solvents, etc), you might like to try it. If you can't live with those limitations, I'd recommend an epoxy without fillers to produce the thinnest joint possible.

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