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M&M's Pack Tighter Than Gumballs
icantblvitsnotbutter writes "In a rather humorous article, the New York Times reports that M&M's pack more tightly than gumballs (registration, blah blah... alternate source here). The upshot of this is what it means for manufacturing denser glass (here, the generic term for solids made of random arrangements of molecules). Some basic solid geometry and tongue-in-cheek quotes fill out the story, but the immediate applications are mind-boggling for the next time you grab munchies on a road trip."
For those too lazy/rushed to RTFA, the key point of this research is this:
Given a load of spheres, shaking them about won't get them packed as tight as if you stacked them all up neatly by hand. But take a load of squashed spheres (e.g. M&Ms) and shake them about randomly, and they take up much less room, because they naturally find a good formation. Even better if they're asymetrical in another dimension too (e.g. nutty M&Ms).
Yeah, great. But I suppose it's important to someone to know what shape will find its way into tight formations best.
Denser packing of powders in sintered materials should improve their strength. But I bet the ultimate properties of materials made with ellipsoidal powders will be more complex than predicted from the packing density.
Granular materials tend to be weakest at the grain interfaces. Such materials tend to fail by breaking the grain-to-grain contacts, rather than shearing through the grains themselves. Thus, the geometry of the contact points will play a big role in the material's strength. I'd bet that ellipsoidal particle aggregates have more contact points because the elongated grains reach across the aggregate to touch more other grains. This should increase strength (materialsmade from ellipsoidal powers will be eve stronger than expected).
But the story might be even more complicated if large collections of grains have correlated orientations. If all of the grains in a region are oriented in the same way, that region will have highly anisotropic properties (extra weak in some directions and extra strong in other). Parts made with ellisoidal powders may have nonuniform strength in two senses. First, the parts may be weak in some directions, stronger in others(very good or very bad depending on how the design handles strength vis a vis the particle orientations). Second, if the packing orientations vary from part to part (or within macroscopic domains in parts), then the parts may vary in strength across different parts or across batches of parts (bad because inconsistent quality is bad).
Interesting story, but more research is needed.
Two wrongs don't make a right, but three lefts do.
I won't be impressed unless I see transparent aluminum M&M's.
--Guns don't kill people, abortion clinics kill people.