Do concrete bridges emit electrical signals before they fail? Lab tests on the powders used to make bleached flour, pharmaceutical fillers, and plastics suggest they might. Researchers spun cylinders or tipped boxes filled with these so-called granular materials to cause mini-avalanches in the powder. In both tests the team detected a voltage spike about 5 seconds before the avalanche started. In tests where the researchers dragged one box across another and created cracklike voids in the powder (image), the opening and closing of the defects triggered substantial changes in voltage, as well. The scientists, who report their findings online today in the Proceedings of the National Academy of Sciences, say the reasons for the voltage blips aren't clear. However, they speculate that similar voltage changes could be warning signs of internal defects or of impending catastrophic failures in objects made of consolidated powders, such as concrete bridges or ceramic turbine blades used in some advanced aerospace and automobile engines.
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