Cyclic Standard
Standardized tensile testing defines the mechanical elastic recovery of bare or covered elastomeric yarns subjected to cyclic elongation. Compliance with ASTM D2731 establishes how bare polyurethane filaments behave under repeated mechanical extension up to specified elongation limits. The procedure isolates dynamic stretch characteristics from static breaking strength.
Testing applies strictly to continuous elastomeric yarns prior to fabric integration.
Hysteresis Measurement
Laboratory apparatus cycles yarn specimens through specified stretch limits at constant rates of extension. Testing under ASTM D2731 records force curves during loading and unloading sequences across defined extension loops. The difference between extension stress and retraction stress yields numerical hysteresis value.
Higher hysteresis values reflect internal friction losses within the polymer network during extension cycles.
Stress Decay
Holding elastomeric filament at fixed elongation induces relaxation over time. Under ASTM D2731 specifications, tension loss recorded at maximum elongation reveals immediate stress relaxation behaviour within raw continuous filaments. Garment mills evaluate this parameter to prevent structural sagging in activewear side panels and swimwear bands.
Low stress relaxation values ensure finished stretch fabrics maintain constant compression against human skin throughout wear cycles.
Contractual Limit
Sourcing contracts establish acceptable elastic recovery percentages alongside maximum allowable tension decay rates. When laboratory evaluation under ASTM D2731 demonstrates recovery below ninety percent, shipment lots fail technical approval checkpoints before fabric formation. Mill buyers reject out-of-spec filament lots prior to knitting.
