Seam Strength and Seam Slippage Testing

Seam strength and seam slippage testing evaluates the mechanical integrity of sewn seams and the tendency of yarns to pull out from fabric at seam lines under stress — failure modes that cause garment splitting and seam gaping in use. ISO 13935-1 (seam tensile strength grab method, 100 mm × 300 mm sewn specimen, 25 mm jaw width, gauge 200 mm, 100 mm/min) and ISO 13935-2 (strip method, 50 mm × 300 mm, full width specimen) measure force to break the seam system (fabric or seam thread failure — whichever occurs first). Seam efficiency = seam strength / parent fabric strength × 100: minimum 70% for apparel seams, 80% for workwear, 90% for safety-critical harness and lift sling seams. Seam slippage (ISO 13936-1 fabric-on-fabric method and ISO 13936-2 fixed seam method, 150 mm × 250 mm specimens with sewn seam 12 mm from specimen edge, tensile extension until 6 mm seam gap measured under 50 N load for lightweight, 200 N for medium, 500 N for heavy fabrics) measures tendency of seam yarns to slide apart — slippage failure visible as open seam gap in trousers seat, jacket armhole, and dress shoulder seams. Seam slippage specification: woven apparel maximum 6 mm gap at 200 N force (ISO 13936-2); tight construction woven lining minimum 160 N before 6 mm slippage. Slippage influenced by: yarn count (finer yarns slip more easily — lightweight plain weave Ne 80 cotton slippage 6 mm at 80 N versus Ne 30 slippage 6 mm at 180 N), weave structure (plain weave more slippage than twill), fabric sett (loosely sett fabrics more prone), and seam allowance (12 mm seam allowance reduces slippage 30–40% versus 6 mm allowance).