The Mechanics of Twist in Fine Cotton Yarn

This paper investigates the mechanistic influence of a 0.5 TPI (turns per inch) twist differential on the tensile performance of Ne 61/1 compact combed cotton yarn. Using 20,000 individual break tests conducted on the USTER Tensojet 4 platform at 400 m/min test speed, two yarn samples — designated Sample A (Regular, 33.5 TPI, Twist Factor 4.29) and Sample B (Trial, 33.0 TPI, Twist Factor 4.22) — were evaluated across five primary parameters: breaking force (B-Force), elongation at break, tenacity, breaking work (B-Work), and weak place frequency. Contrary to the intuition that such a marginal twist change would produce negligible differences, the analysis reveals statistically significant and practically meaningful divergence in elongation (4.26% vs. 4.07%), breaking work (248.0 vs. 240.0 cN·cm), and crucially in weak place count (F+E = 1 vs. F+E = 2). The paper presents a first-principles mechanical model grounded in Gegauff's classical formulation, helix geometry analysis, twist distribution probability theory, and USTER scatter plot morphology interpretation. A predictive framework for twist-property sensitivity is established, with direct implications for weaving efficiency and process specification tightness in fine yarn production.