For spacecraft vibration testing we use Dental cement. It's extremely non-compliant so it is good for transmitting vibration from a structure to an accelerometer. It is brittle so we remove them by just taping them with a hammer and breaking them off the surface. We first put a layer of thin tape on the surface to protect the surface. the tape does not affect the vibration response. bob
Sounds to me as if you're actually looking for stiffness, not necessarily strength?
I think you'd want to look for (or make) a filled epoxy. A high-strength epoxy which is loaded up with (e.g.) chopped or milled fiberglass would be very stiff.
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Filled epoxies (loaded with various mineral and glass bits) are much more rigid than plain epoxy. But if you start with a slow cure epoxy (30 minute versus 5 minute) the epoxy, itself will also be a lot harder. Glass micro spheres are a good filler if you want to lower the density, and glass micro beads or aluminum oxide if you want to raise it. Even adding talcum powder adds to the rigidity, but the gas bubbles it entrains lowers it (foams are less rigid than solids of the same material), so vacuum degassing increases the rigidity.
A very rigid mineral filled epoxy is Hysol 1C:
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A slighter harder aluminum filled formula is Hysol 9434:
I cannot suggest a harder epoxy but you pressed a sensitive button on me so here I go.
Many years ago (1991, to be precise) I opted to epoxy-fill my first
5kV coils I did for my then employer in Cologne, Germany. I used no multiplier, straight flyback @ 5kV; about 1000 windings on an RM8 core, winding and insulation layers being an art of their own. I located some very liquid epoxy meant for that purpose, then the whole module went filled, using vacuum to make sure there were no cavities. Everything worked fine, the filling was perfect - I got asked how come the space between the *windinds* was not filled (0.05 wire, mylar foil between each layer) by my then employer... Some years later I had founded TGI in Bulgaria and did the first HV source making the coil more or less the same. However, I used off-the-shelf epoxy; it did not get as hard (although it was by far not as liquid before hardening), and after some warmup it began to conduct just enough to make the thing noisy... I wasted more than one coil (wound with a lot of work) until I got what was going on, I spent days if not weeks on that nightmare... Eventually I learned I needed no filling at all, just a few drops of melted silicon at the right spots did the job (still does) quite well.
And on another occasion I had a guy from a detector repairshop in Sofia use the same effect trying to cheat on me... The HPGe gamma detectors are very sensitive things, the front FET is cooled to -90C or so for lowest noise. The bias is a few kV (3.5 in that case), and the HV input is filtered through a 1Gohm/0.47uF group. Well, he had had the detector in his hands to "check it" for me and had put a stripe of such epoxid along the resistor between its pins... (The resistor is a rectangle, say 20x5mm, 1mm thick). After some warmup - the preamp consumes not so little, they have not changed its design for >20 years - the detector begins to behave like when it needs repair. Well he did not get it for repair because I looked and discovered what he had done and cleaned the mess up -and the detector worked fine. A few years later he got the same detector in his hands directly from customers and did the same, this time he had added a stripe across the capacitor, though, and had scratched the paint of the resistor between the pins. Mind you, I had told him I knew what he had done the first time and he had done it again. I guess the epoxy must have had braindamaging effect as well.... (and I had refused to believe other people telling me he was sabotaging detectors before I got burned, the epoxy must have worked on my brain as well - perhaps while dealing with my coils... :-).
With the way you worded this, it would seem that a technical response would go right over your head.
Epoxy mix ratios are NEVER meant to be altered. You need to find an epoxy that matches your needs. The only time I ever saw mix ratio ranges to alter behavior, it was with an epoxy branded as "stycast". Which, would oddly meat your needs.
: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. : :Is this something that I can achieve by changing the mix of the 2 parts? If :so, what do I lose if I use more hardener? : :Any personal experiences with epoxies that you found to be harder than :others? : :Thanks. :FBt
Devcon specialise in making epoxy materials for repairs to machinery. For example their Titanium Putty
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is specified for repairs to machinery where the repair requires a machined finish. This must be extremely hard material when cured.
There are single component epoxies used in IC fabrication which have 94D hardness ie. ME-430
sci.polymers or sci.materials might be a better bet. There are two general ways you can make a given epoxy harder: bake it (an hour at 100C does wonders) or put filler in it.
If you're bonding hard materials, you might want to use a glass bead filler. When you squeeze the bondline down, the spheres contact the surface, and as the epoxy shrinks (1% or so), it applies a preload to the glass/substrate interfaces. That's a pretty stiff joint.
If you're trying to do something in shear, e.g. attach a strain gauge, glue is not your friend at all. You might be better off using solder or indium bonding or something like that.
I have been waiting a few minutes until the epoxy is no longer runny. I turn the oven on to 200, but turn it off before it reaches temperature. Have also used a heat gun on something that was part of a large stationary object (toilet). I haven't bothered, but this information should be available from the manufacturer.
Rubinno cement made by Singer Kearfott in the 70's was used on guidance systems for the Sram missile, PC3, and A7 navey fighter jets. It is the best there is.
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