Abstract:

Objective Staple yarn is the basic element of most textiles, and its tenacity is jointly determined by fiber properties at the microscopic scale and yarn parameters at the macroscopic scale, which profoundly affects the processing efficiency and performance of subsequent products. To reveal the influence mechanism of fiber properties and yarn parameters on staple yarn tenacity and to predict the tenacity, a dual-scale micro-macro prediction model for staple yarn tenacity was constructed.

Method Based on the single-fiber tensile curve, a mesoscopic mechanical model was constructed by integrating fiber properties with staple yarn parameters through inter-fiber stress analysis. The influence of yarn linear density and twist factor on fiber stress and inter-fiber friction was quantified, and a criterion for fiber breakage/slip was established (i.e., at any cross-section of a fiber, if the total friction force on one side is less than the tensile strength the fiber can withstand, the fiber will slip toward that side; otherwise, the fiber will break) leading to the creation of a dual-scale prediction model for predicting staple yarn tenacity. Staple yarns were made with different linear densities and twist factors from the commonly used fibers including cotton, polyester, vinylon, and viscose and tested to validate the accuracy and applicability of the model.

Results The staple yarn tenacity is the ratio of the sum of the effective strength contributed by broken fibers and the effective friction force generated by slipping fibers to the staple yarn linear density. Different macro-parameters of the staple yarn such as the twist factor and linear density were used, and it was found that increasing the twist factor while maintaining the linear density caused the fiber helix angle to increase, leading to a decrease in the effective strength at fiber breakage, and to an increase in the effective friction per unit length thereby inhibiting fiber slip. When the twist factor remained constant, increasing the yarn linear density did not affect the effective strength at fiber breakage but increasing the number of outer-layer fibers would enhance the effective friction per unit length of inner-layer fibers which also inhibits fiber slip. Comparing the predicted and tested tenacity of cotton, polyester, vinylon, and viscose staple yarns at different linear densities and twist factors, it was found that the change patterns of the predicted and the tested tenacity both increased to the peak and then decreased when increasing twist factor, which agrees with the traditional spinning theory. Furthermore, the mean error between predicted and tested tenacity is less than 5%. Three main causes were identified for the prediction error in staple yarn tenacity. First, the overly simplified assumption of staple yarn structure, under which the model neglected migration of fibers in the staple yarn, thereby neglecting the migration-induced entanglement that would otherwise enhance inter-fiber friction, further inhibiting fiber slip. Second, the failure to account for the impact of multiple fiber breaks on yarn tenacity. During the actual tensile process, fibers may break multiple times within the breakage zone. Third, for cotton yarn, the model neglects fiber length distribution, instead using average fiber length to predict yarn tenacity. Nevertheless, the prediction error was sufficiently small.

Conclusion A dual-scale prediction model for staple yarn tenacity based on single-fiber tensile curve was constructed. By investigating the influence of linear density and twist factor on fiber stress and inter-fiber friction, the model reveals the cross-scale interaction mechanism of fiber properties and staple yarn parameters on staple yarn tenacity. The accuracy and applicability of the model were validated using experimental data. The results show that under the same conditions, increasing either yarn linear density or twist factor can inhibit fiber slip; for various staple yarns, the correlation coefficients between the predicted and tested yarn tenacity are all greater than or equal to 0.95; and the mean error is less than 5%, indicating that the model has good accuracy and applicability to predict staple yarn tenacity.

Key words: ring spinning, single-fiber tensile curve, staple yarn tenacity, dual-scale prediction model, twist factor, fiber slip, fiber breakage