Abstract:

Objective In order to achieve robotized automatic thread jointing technology and the automated production of the whole process of spinning, the breaking strength of yarn was analyzed in this research. Aiming at the problem that yarns are easy to break under the influence of environmental factors, this study is proposed to analyze the influence of yarn clamping length and stretching speed on the breaking strength distribution, and simulate the characteristics of breaking strength distribution of ring-spun yarn under dynamic environment.

Method Tensile experiments were firstly carried out on a YG020A electronic single-yarn strength machine to analyze the performance of ring-spun spinning yarns, and a constitutive model for ring-spun staple fiber yarns was constructed to characterize their tensile properties. A finite element analysis simulation model was constructed based on the idealized parametric modeling of yarn geometry. The model was used to simulate the fracture process of staple fiber yarns at a constant tensile rate in order to understand the inter-fiber load propagation at the four stages of yarn tensile loading. The distribution parameter model was established based on the maximum likelihood estimation method to analyze the statistical characteristics of the yarn strength data, and further verified by using the Kmogorov-Smirnov test.

Results The results of yarn tensile experiments, showed that when the yarn stretching speed was low, the measured breaking strength of single yarns deviated from the constant-rate-of-extension (CRE) method within 6 cN, with an overall fluctuating. When the stretching speed was close to twice that of the CRE method, the measured breaking strength of single yarns showed a significant decrease. The effect of clamping length on yarn strength was not obvious. The load-displacement curves of the yarns in the tensile experiments was divided into three stages of the tensile deformation process of the yarns. In the first stage, the static friction between fibers accumulated rapidly, and the tension increases while the displacement was small. The second stage saw the relative displacement between fibers and deformation under stress, and the yarn elongates at a higher constant rate. In the third stage, fiber failure gradually appearred in the weak ring segments of the yarn until the yarn broke completely. During the yarn tensile fracture stage, the inner fiber stress was generally greater than that of the outer fiber. The fitting accuracy of distribution parameters, based on the maximum likelihood estimation method, indicates that the lognormal distribution model exhibits the smallest fitting error. And the residual sum of squares amounts to 0.000 6. The Kmogorov-Smirnov test p-value of the strength data sample was 0.068, which is greater than the significance parameter threshold of 0.05, confirming reliability for analyzing the statistical patterns of the strength at break data of single yarns using the lognormal distribution. According to the inverse cumulative distribution function corresponding to the quantile, when the confidence level was 0.98, the strength data fluctuation interval was [123.4,182.0].

Conclusion Due to the random distribution of fibers, the average yarn strength tends to decrease with the increase of stretching speed, while the yarn clamping distance has no significant effect on the average strength. The overall distribution of single yarn strength is more in line with the lognormal distribution compared to the Weibull distribution, showing a right skewness. When the confidence level is 0.98, controlling the weak ring tension below 123.4 cN will greatly reduce the probability of breakage.

Key words: ring-spun, yarn breaking strength, finite element simulation, distributed parameter model, log normal distribution