A research team has mapped how knitted fabrics transition from rigid to flexible under varying force, revealing the mechanics behind jamming. Previously studied mostly in granular systems, this behaviour is now documented in industrial textiles, offering insights for production methods aiming for mechanical precision without depending on synthetic fibre blends, potentially transforming performance control in textile manufacturing.
- Knitted fabrics become unexpectedly rigid under light pulling yet soften once stitches rearrange under higher tension, showing a surprising mechanical transition.
- Directional jamming is linked to yarn stiffness along rows and to yarn contact points across columns, revealing two distinct mechanical causes.
- These findings could enable manufacturers to fine-tune textile performance through production settings instead of altering fibre composition.
- The results have been detailed in the July 2025 Physical Review E study ‘Pulling Apart the Mechanisms That Lead to Jammed Knitted Fabrics’ by Sarah E Gonzalez and colleagues at Georgia Institute of Technology, US.
THE STUDY: Led by Georgia Institute of Technology graduate student Sarah Gonzalez, the investigation combined industrial knitting experiments with computer simulations to examine jamming mechanics. The study found that machine tension and yarn thickness influence stiffness, with effects varying depending on whether fabric is stretched along rows or columns. According to the researchers, these differences demonstrate that yarn properties and machine settings can be used to influence fabric stiffness in industrially knitted materials.
- Stretching along rows showed jamming caused by yarn stiffness, as fabric resistance increased when yarns were more rigid.
- Stretching across columns showed jamming caused by yarn contacts between stitches, affecting the fabric’s ability to stretch.
- Changing machine tension altered stiffness differently depending on the fabric’s stretch direction, as shown in experiments and modelling.
WHAT’S AT STAKE: Understanding how to influence jamming through yarn and machine adjustments could reduce the need for blended fibres. The study indicates that desired elasticity might be achieved through stitch manipulation rather than synthetic materials. This approach could reduce the environmental impact of production and provide manufacturers with a means to design fabrics with specific mechanical properties for varied industrial applications.
- Adjusting stitch topology could create elasticity similar to blends of polyester, cotton, and elastane, but using only natural fibres.
- Reducing petroleum-based fibre use supports sustainability objectives referenced in the study’s discussion of material design.
- Applications suggested include wearable electronics, soft robotics, and textiles with tunable stiffness and flexibility.
WHAT THEY SAID:
I was using model simulations to characterise how different yarn properties affect the behaviour of knitted fabrics and noticed a strange stiff region. In our previous research, we had also seen this behaviour in lab experiments, which suggested that what we were seeing in the simulations was a genuine phenomenon. I wanted to investigate it further.
— Sarah Gonzalez
Graduate Student
Georgia Institute of Technology
In fabrics, when you pull softly, the response is surprisingly stiff, but when you start pulling harder and harder, the stitches rearrange, and the material softens. In granular systems, this is a little like how avalanches work. At low forces, the snow pack is solid, but when the slope is steep, the force of gravity liquidises that snow pack into an avalanche.
— Elisabetta Matsumoto
Associate Professor
Georgia Institute of Technology
