Packings of 3D stars: stability and structure
We describe a series of experiments involving the creation of cylindrical packings of star-shaped particles, and an exploration of the stability of these packings. The stars cover a broad range of arm sizes and frictional properties. We carried out three different kinds of experiments, all of which involve columns that are prepared by raining star particles one-by-one into hollow cylinders. As an additional part of the protocol, we sometimes vibrated the column before removing the confining cylinder. We rate stability in terms of r, the ratio of the mass of particles that fall off a pile when it collapsed, to the total particle mass. The first experiment involved the intrinsic stability of the column when the confining cylinder was removed. The second kind of experiment involved adding a uniform load to the top of the column, and then determining the collapse properties. A third experiment involved testing stability to tipping of the piles. We find a stability diagram relating the pile height, h, versus pile diameter, \(\delta \), where the stable and unstable regimes are separated by a boundary that is roughly a power-law in h versus \(\delta \) with an exponent that is less than unity. Increasing vibration and friction, particularly the latter, both tend to stabilize piles, while increasing particle size can destabilize the system under certain conditions.
KeywordsGranular Cylindrical packing Star-shaped particle Stability Friction Vibration Aggregate
We thank Dong Wang and Hu Zheng for fruitful discussions and Stephen Teitel and Scott Franklin for a critical review of this manuscript. Y.Z., J.B. and R.P.B. are funded by National Science Foundation (NSF grant DMR-1206351) and W. M. Keck Foundation. K.D. has benefitted from support of ITASCA Educational Partnership Program.
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