Original title: We Know Simple Fluids Can Flow. Turns Out, Some Can Fracture.
Article
Researchers at Drexel University report that a nonelastic hydrocarbon blend can crack when stretched, contradicting the long-standing view that simple fluids only flow. In repeated extensional rheology tests, the fluid produced loud pops and split catastrophically, a behavior the team described as brittle fracture. Work on complex fluids had previously tied liquid fracture to elasticity, especially in viscoelastic systems like polymer melts, but this study shows a nonelastic system can fail the same way. The team points to 1990s theory from Daniel D. Joseph and updated measurements suggesting cavitation can nucleate vapor-filled bubbles that then trigger fracture when pulled hard enough. Once a crack starts in simple fluids, propagation is much faster than in complex ones, measured around 500 to 1,500 meters per second versus about 0.07 meters per second in melted polystyrene. Both fluid classes fractured near a similar critical stress of roughly 2 megapascals, with failure appearing proportional to viscosity times strain rate. The experimenters note that their instrument’s speed limit may have prevented observation of even less viscous fluids such as honey or water. They propose transparent fluids, rapid freeze-capture, and nanoscale microscopy to watch crack nucleation and growth more closely. The researchers also see possible relevance for fiber spinning, inkjet printing, protective systems, and soft robotics.
The comments were brief and mixed in tone, with one reader comparing the behavior to silly putty, while another asked for a practical forecast of industries that could benefit and long-term outcomes. No direct applications were provided, but the question highlights uncertainty about immediate industrial impact versus eventual translation into technology over decades.