The science behind Christmas sweaters: How friction shapes the shape of knitted fabrics
(a) Photograph of jersey knit stitches. (b) Experimental setup. (c) Geometric and numerical model. Credit: arXiv (2024). DOI: 10.48550/arxiv.2404.07811
Through experiments, three physicists from the University of Rennes, Aoyama Gakuin University, and the University of Lyon discovered that it is the friction between the fibers that causes knitted fabric to take on a specific shape. Jérôme Crassou, Samuel Pointcru, and Audrey Steinberger set out to understand the fundamental mechanisms involved in the shape of knitted products. Their paper is published in Physical Review Letters.
The research team notes that while many factors related to fabric entanglement have been studied to better understand its properties (for example, why sweaters retain warmth despite having gaps between seams) He pointed out that little is known about clothing made using such fabrics. Technology is required.
To learn more, they conducted an experiment using nylon thread and a well-known jersey knit stitch called stockinette, a technique that uses stockinette needles to form interlocked loops. They knitted a piece of fabric using 70×70 stitches and attached it to a biaxial tension machine.
The team then used a tensioning machine to stretch the fabric in different ways to take a closer look at how this affected the stitching. They discovered that the clothing had no unique shape. By stretching the fabric in different ways, it can come to rest in different shapes, which are called metastable shapes.
The researchers noted that the length-to-width ratio of these metastable shapes changes depending on how much twist is applied, meaning that the fabric can assume many different metastable shapes. This suggests that it is possible.
The researchers then created a simulation of the fibers to show what happens when they are twisted and pulled in a tension machine. The simulations showed the same results, but they were able to change one property of the virtual fibers that cannot be changed in the real fabric: the amount of friction between the strands.
They found that setting friction to zero results in only one metastable shape. Friction therefore turns out to be the driving force behind the shapes that knitted fabrics can take.
Further information: Jérôme Crassous et al, Metastability of a Periodic Network of Threads: Shapes of a Knitted Fabric, Physical Review Letters (2024). DOI: 10.1103/PhysRevLett.133.248201. For arXiv: DOI: 10.48550/arxiv.2404.07811
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Citation: The Science Behind Christmas Sweaters: How Friction Shapes Knitted Fabrics (December 30, 2024), January 5, 2025 https://phys.org/news/2024-12 Retrieved from -science-christmas-sweater-friction- fabric.html
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