Yarn Elongation and Work-to-Break Testing

Elongation-at-break and work-to-break (specific energy of rupture) from the yarn force-extension curve provide complementary mechanical information to tenacity — elongation determines yarn extension capacity under loom shed formation tension and knitting loop formation stress, while work-to-break quantifies total energy absorption capacity relevant to impact and abrasion resistance. Elongation measurement (ISO 2062, calculated as % extension at maximum force relative to pretensioned gauge length 500 mm): ring cotton Ne 30 50th percentile 6.8%, 5th percentile 8.5%; polyester DTY 167 dtex 50th percentile 22.5%, 5th percentile 18.0%; Lycra covered yarn 200% minimum elongation for adequate stretch recovery in legwear and activewear. Work-to-break (specific work W = area under force-extension curve / linear density, cN·cm/tex = mJ/tex): W = tenacity × elongation / 2 (triangular approximation for linearly elastic yarn) — ring cotton Ne 30 W ≈ 18.2 × 6.8 / 2 = 6.2 cN·cm/tex; impact-absorbing yarns (nylon, UHMWPE) require W > 15 cN·cm/tex for cut resistance applications. Elasticity ratio (elastic recovery after 5% extension, ISO 2062 adapted: extend to 5% → hold 1 min → return to zero force → measure permanent set — elastic recovery% = (extension − permanent set) / extension × 100): ring cotton 50–65% elastic recovery, textured PET 85–95%, elastane-covered 95–100% — recovery below 80% indicates inadequate texturing crimp or insufficient elastane draft in covered yarn. Dynamic tensile testing (Uster Tensorrapid 4 at 5,000 mm/min versus 500 mm/min standard): dynamic breaking tenacity 5–15% higher than quasi-static at high extension rates relevant to rapier loom weft insertion (4 m/s insertion = effective extension rate 200–400%/sec on 500 mm gauge) — dynamic testing better predicts weft breakage resistance than quasi-static ISO 2062.