Textile Structure
how cloth is put together
Series

Buckling — the series

3 essays on one idea, from the one that introduces it to the one that assumes the rest.
  1. Wrinkles 127 mm apart. A 300 mm width of a 120 g/m² cloth whose bending length is 20 mm, held under 5 newtons per metre across it and compressed. It cannot carry the compression in the plane, so it leaves the plane, at a wavelength the bending rigidity and the tension settle between them: 127 mm, which is 2.4 wrinkles across the width. The amplitude is drawn and is not computed — this arithmetic sets the spacing and says nothing about the depth.

    A cloth cannot carry a push

    The net model that runs this site's mechanics has no bending stiffness at all, so it buckles under any compression whatever, into wrinkles of any wavelength whatever. What picks the wavelength is the competition the net leaves out — and the answer is a quarter power, which is why a wrinkle is so hard to change.

    part 1 · mechanics
  2. The number the drape test does not record. A 150 mm specimen over a 90 mm pedestal, for fabrics from limp to stiff. The curve is the fold count the buckling argument predicts — three quarters of a power of the specimen's radius over its own bending length — and it runs from 2 folds to 11. The number beside each mark is the drape coefficient the same specimen would report, which moves by a few points across the whole range.

    The nodes a drape test throws away

    A drape test lays a circular specimen over a pedestal, photographs the shadow and reports one number. The specimen also falls into a definite number of folds, which is a buckling mode set by the fabric's own bending length — and the standard method observes it, does not record it, and reports the number it is least sensitive to.

    part 2 · mechanics
  3. One surplus, three depths, one slope. A 300 mm width of three cloths under 5 newtons per metre, each shortened by 1.0%, drawn at one scale in both directions. a chiffon has wrinkles 43 mm apart and 1.4 mm deep; a shirting has wrinkles 127 mm apart and 4.1 mm deep; a coating has wrinkles 249 mm apart and 8.0 mm deep. All three leave the plane at the same steepest slope, 11.5°, because that slope is set by the surplus alone.

    A stiff cloth's wrinkle is deeper and no steeper

    Stiffness sets how far apart a wrinkle's crests lie, and the surplus length it has to hide sets the rest. Scale a wrinkle up and its slopes do not change, so one per cent of surplus leaves a chiffon, a shirting and a coating all at 11.5 degrees, 1.4 to 8 millimetres deep. The steepness has no cloth in it — and steepness is what a light reads.

    part 3 · mechanics

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