Loom Setting
A third of one per cent of strain, applied 2,200 times a metre. That is what sizing is for.
— %
Extra path length over the straight warp line
This is the static geometric strain at full shed and it understates the true loading in two ways. The shed opens and closes once per pick, so the strain is dynamic and the yarn sees a strain rate rather than a held extension; at 550 rpm the full cycle occupies about 0.1 s. And beat-up superimposes a further tension peak, typically 20 to 40% above the static value, at the moment the reed drives the pick home. The calculation treats one heald frame with one pair of distances; on a loom with graduated shed the frames differ and each should be computed separately. Back rest height and its vertical offset from the warp line change the top-bottom split substantially and are not modelled here - only the deflections at the heald are taken as given. The abrasion index is a relative ranking quantity for comparing constructions on one machine, not an absolute break rate.
Shed Geometry, Warp Strain & Abrasion Exposure — free, with the formula and a worked example, at Textile School.