[lgalla]

:violin: I feel badly for quartz being outlawed as a good aggregate.Good or high quality granite is 60 or 70 % quartz.Does this also outlaw granite as a filler.Copy from a paper"
Synthetic Fused Quartz 0.7
Spinel 1.3
Chalcedony 1.3
Chert 1.4
Flint 1.4
Agate, Banded 1.8
Sapphire 2.1
Aluminum Oxide 3.9
Silicon Carbide 4.0
Silicon Nitride 4.0"
Synthetic fused quartz is basically melted quartz,or glass.Most items on the chart are gemstone minerals.You cannot walk in to a supplier and get a bag of spinel.Surfing for fracture toughness on granite produces little info.
Cast iron is full of micro cracks and the reason for damping properties.
Some machine builders use quartz as a high end aggregate.Nearly all sands and small aggregates will have high quartz content.In our case,is fracture toughness the ability to resist hammer blows or forklift bumbs.
Fracture toughness of aluinium is 36Mpa,steel50Mpa.From the Mpa's they appear to be better choices,but we know their damping sucks.Steel or alu will bend of flex to reduce fracture cracking as they are ductile.Ducile= vibration.We are attempting to reduce vibrations with extremely stiff materials.Hope someone understands my jist,I don't
Larry

[ckelloug]

Larry,

I wouldn't outlaw quartz or granite just yet. They are just more likely to crack under stress. Very similar to engineers My comments on strategy above are based on making an epoxy aggregate combination with the absolute maximal strength. Maximal strength is likely not be necessary for most E/G machine parts but I find it interesting to explore that part of the problem space because making the minimum strength material appears to have already been accomplished.

The precise characteristics for transmitting vibration are relatively complicated. From my understanding, it is a combination of the density, the damping properties of the material, and the modulus that are the main factors. As metals go, Aluminum is one of the worst. I am not sold on ductility being the prime cause of vibration transmission.

Because epoxy has a low modulus and a much higher viscous damping than metals or aggregates, even epoxy diamond would probably have good damping. Epoxy diamond would probably not do as well from a fracture toughness standpoint as say Epoxy Boron Nitride however But before I digress and get more silly. . .

I cited the mineral data for fracture toughness because it was available and depending on the exact location of the quartz quarry you are using, it may behave similar to the other materials or be sold as quartz. The paper from the minerologists called them forms of quartz.

Many of the others like garnet (for which I do not have data) as well as silicon carbide and silicon nitride are available as abrasives and thus probably cost effective on the order of quartz.

I've blithered enough on this thread lately and it's once again time to quit for the day.

--Cameron

[greybeard]

Time for a party - we've just passed the 1500 post mark, so to entertain you briefly, a link to something very silly but somehow wonderful.

http://www.youtube.com/watch?v=D2f1KEEtRyk

John