NEW DELHI, Nov 20: There’s more to the snap, crackle and pop of puffed rice cereal than meets the ear, says civil engineering professor Julio Valdes of San Diego State University. Highly porous, brittle materials can deform in different ways depending on compaction velocity. Valdes used the breakfast cereal to discover this new phenomenon in materials science. The findings could have applications in manufacturing, -in the pharmaceutical industry, for example, as well as in assessing the stability of snowpack after an avalanche. In 2011, Valdes and former SDSU graduate student Johan Gallay were experimenting with compaction using puffed rice cereal in an acrylic tube. As a piston crushed the cereal, the experimenter could see the material being compacted. The researchers came up with the idea of using microphones at both the bottom and top of the tube to record the crushing sounds and identify which parts of the cereal pack would crush when. Based on classic friction experiments, Valdes theorised that as the piston compressed the cereal, the top of the pack would compact and the bottom would not, given that the cereal would transfer force to the cylinder’s sidewalls via friction; the microphones would provide evidence of this. Gallay performed the experiments and came back to Valdes with something unusual. Instead of the crackling pattern they expected, the microphones recorded an alternating wave of popping. “I said, ‘Johan, you’ve clearly made some kind of mistake. Go run it again,'” Valdes recalled. So Gallay did, and the results were the same: a rising wave of snap-crackle-pop as the piston compressed the cereal. And this time, Gallay wanted Valdes to watch the experiment, not just listen. The visual results were just as striking. As the cereal compacted, the researchers could see a rising band in the tube, indicating where the material was being crushed, or deformed, in the materials science lingo. “It was the first time anyone had seen a propagating compaction band in granular matter,” Valdes said. “We could see it clearly. It was beautiful.” These results further explain the complex mechanics underlying porous, brittle material–a fairly new area of study which has been dubbed “crunchy matter.” (UNI)
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