Updated

Updated · Quanta Magazine · Jul 10

Drexel Researchers Show Simple Fluids Fracture at 500-1,500 m/s, Challenging 2 MPa Liquid Theory

Updated

Updated · Quanta Magazine · Jul 10

Drexel Researchers Show Simple Fluids Fracture at 500-1,500 m/s, Challenging 2 MPa Liquid Theory

Q: If oil can shatter like glass, what does it take to make everyday liquids like water crack?

To make a liquid like water “crack,” it would likely have to be pulled apart extremely fast so that the tearing stress reaches a critical threshold before the liquid can simply flow away. That is the implication of Drexel University’s finding that even nonelastic “simple” fluids such as crude oil can undergo brittle fracture. In the experiments, the fluid snapped at a critical stress of about 2 megapascals, and the team found that the stress needed to break a liquid scales with viscosity and strain rate — essentially, how thick the liquid is and how quickly it is stretched. Because water is far less viscous than oil, it would need a much higher stretching rate to reach that breaking point. The likely mechanism is not elasticity, as scientists long assumed, but molecular cohesion: the forces holding the liquid together. Under sufficiently intense tensile stress, those cohesive forces can fail. Researchers also point to cavitation — the rapid formation of tiny voids or bubbles — as a possible trigger or companion process when the liquid can no longer sustain the tension. Once a crack starts, it can race through a simple fluid at extraordinary speed, measured in these tests at roughly 500 to 1,500 meters per second. So water probably can crack, but only under extreme, very rapid pulling conditions that ordinary lab setups or everyday experience rarely produce.

1 articles · Updated · Quanta Magazine · Jul 10

A Drexel team found that a nonelastic simple fluid can snap apart under extensional stress, overturning the long-held view that such liquids only flow rather than fracture.
High-speed imaging showed a brittle, glass-like crack that raced through the hydrocarbon blend at about 500 to 1,500 meters per second—far faster than the roughly 0.07 m/s seen earlier in complex polymer fluids.
The researchers said both simple and complex fluids they tested tended to fail near a critical stress of 2 megapascals, while the least viscous sample did not fracture under their machine’s 500 millimeters-per-second limit.
The result revives a 1990s idea that cavitation and molecular cohesion—not elasticity alone—may govern when liquids break, with possible implications for fiber spinning, inkjet printing, soft robotics and protective materials.