Many people have likely found themselves watching oddly satisfying videos of random objects being squashed by a powerful hydraulic press, but rarely people consider why things squash the way they do.
One object that caught the eye of researchers at The University of Manchester was a simple drinks can. When crushed while filled with liquid, it behaves completely differently from an empty one. Instead of collapsing suddenly, it produces an ordered sequence of circular rings that appear one by one.
But it turns out there's more going on than just a satisfying visual. Published in the journal Communications Physics, the Manchester team has discovered that the formation of corrugations follows a rare mathematical process - and the discovery could have implications for safety across multiple industries.
Lead researcher, Shresht Jain, PhD researcher at The University of Manchester, said: "Most of us have stamped on an empty can and watched it collapse instantly. But a full can behaves completely differently. It forms one buckle after another in an orderly fashion, until the whole can is wrapped in evenly spaced corrugations. We were fascinated and wanted to understand what was driving that behaviour - particularly as liquid-filled containers are found everywhere in our day-to-day lives."
To find out, the researchers combined laboratory experiments with a type of mathematical modelling typically used to study natural pattern formation, such as water ripples or wave formations.
They discovered that the sequence of buckles is anything but random. Because the liquid inside the can is almost incompressible, it changes the way the aluminium can carries force.
"A standard can usually starts to buckle near the middle," explained Dr Draga Pihler-Puzovic, Reader in Nonlinear Dynamics at The University of Manchester. "But tiny variations in shape or size of the can, can shift where the first ring appears. After that, however, the physics takes over, and the sequence becomes extremely predictable. As the can compresses, the metal softens and then stiffens again - this cycle naturally forms the rings. Even changes in the can's internal pressure don't alter the overall pattern much. That tells us that the buckling sequence is a fundamental property of any liquid-filled cylinder made from metal, not just a quirky effect of a drinks can."
The team discovered that this step-by-step pattern matches a mathematical process known as homoclinic snaking - a phenomenon where bumps or ripples appear one by one in a precise, controlled order. Although mathematicians have suggested that this 'snaking' could underpin the buckling of cylinders, uncovering its trace in a real physical system is exceptionally rare.
The findings could also have far broader implications. Liquid-filled metal cylindrical shells are used throughout modern engineering - in industrial storage, transportation, construction, energy systems, and even in parts of rockets.
Yet, despite their ubiquity, engineers have lacked a clear understanding of how these structures might buckle when compressed.
Dr Finn Box, Royal Society University Research Fellow at The University of Manchester. said: "Understanding the exact sequence of buckles could help engineers spot the early warning signs of failure long before a system collapses. That could lead to safer designs, better monitoring techniques, and more reliable structures in a whole range of industries. It might even open up possibilities for manufacturing. For example, it could be possible to create corrugated cans after filling without needing a mould."
