Avalanches don’t just happen on mountains! Scientists use the concept of an “avalanche” to describe other phenomena that evolve in similar ways, such as forest fires, a stock market crash, or solar flares. In a recent paper released on arXiv, French physicists made the argument that knit fabrics also behave in this “avalanche” fashion. This makes them very useful for studying the properties of avalanche behavior, since a knit is much easier than a mountain to fit into a lab!
An important part of describing avalanches is the phrase “stick-slip.” Imagine you are trying to push a heavy box of antiques across the floor of your grandmother’s basement. You push it, but it is heavier than you expected, and it doesn’t move. As you push harder and harder, eventually the box slips, and you can now push it across the floor with less force than what was needed to make it move in the first place. The moment when the box stopped sticking and started slipping is called a stick-slip event. You could also describe the very beginning of an avalanche–the instant when the soil/snow/sand at the top of the mountain begins to slip–as a stick-slip event.
Knit fabrics are made of a network of threads; these physicists showed experimentally that stick-slip events happen at the intersections of these threads when the fabric is stretched. The threads can hold on to each other for a time, but eventually they slip; the first intersection to stretch causes the next intersection to stretch, and the knit network expands in an avalanche-like fashion. This is slightly unusual because avalanche behavior is not typically expected in things that are as neat and ordered as textile fabrics (think of how chaotic a landslide is!).
Hopefully this discovery helps improve our knowledge of avalanches, and systems that act like them!
Knits: an archetype of soft amorphous materials. Samuel Poincloux, Mokhtar Adda-Bedia, Frédéric Lechenault