daestrom wrote:

"Paul Hovnanian P.E." wrote in message
...
Esther & Fester Bestertester wrote:

See no n.g. for adhesives & epoxies, so if there's a better forum for
this,
just point me to it.

I need an epoxy that is strong to the point of brittle. I want no flex;
it
has to transmit vibration as close to 100% as possible.

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

I believe that (Shore) is a measure of resistance to indentation. In
other words, pressure. You might need something else, depending on which
direction the vibration is acting with respect to the surface. A
pressure wave will result in both pressure and tensile stresses on the
adhesive. A shear wave will result in (duh) shear stresses.

In addition, you need to define what you mean by 'transmit vibration'.
I'm not a mechanical guy, but I'd be willing to bet that the problem of
maximizing mechanical energy transmission is analogous to that of
maximizing electromagnetic energy transmission. That is: It is optimal
when the impedance (modulus of elasticity?) is closely matched and
energy reflection is minimized.

The strength of the adhesive only becomes important if the amplitude of
the vibration approaches the strength limit of the bond.

This appears to be the sort of problems that people designing sonar
transducers have to deal with.


Well, we used an epoxy (simple two part) to 'glue' mounts for vibration
monitoring equipment. The accelerator was in a magnetic housing and we
epoxied steel rings (not much more than washers really) to rotating
equipment at key points of bearings etc...). The mounts/washers provided a
nice flat, properly oriented surface for the vibration pickup so we could do
'sound cuts'.

Two fold, 1) we wanted to know how much noise our equipment was making
(submarines live / die by sound levels transmitted into the water) and 2) we
could predict some equipment maintenance like simple balance, pump-motor
alignment, bearing problems.

Maybe that's what the OP is after. But as I said, we used a simple, two
part epoxy with quite good results.

The selection of a suitable adhesive depends on how much energy one can
afford to lose in a sub-optimally coupled system. In your case, the
signal level of vibrating mechanical equipment is probably high enough
that some attenuation is tolerable.

The other thing to consider is the mass of the sensor, the flexibility
of the adhesive and the resulting natural frequency of the sensor
assembly. A massive sensor and/or flexible coupling will result in a
lower frequency and result in attenuation of signals above that point.

daestrom

--
Paul Hovnanian
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You can discover what your enemy fears most by observing the
means he uses to frighten you. -- Eric Hoffer