The publication presents a theoretical study of the susceptibility of rheological models of threads to dynamic stretching in the context of modern, highly efficient textile technologies. Input parameters of the four analyzed models, the Kelvin-Voigt model, the Maxwell model, Standard model 2, and the Zener model, corresponded to the actual values of the coefficients of viscosity, elasticity, kinematic and dynamic loading, and stretching speed for the analyzed polyester silk threads produced in a knitting process, with knitting speeds from 700 to 1,600 courses/min. The research proves that the tested thread models behave differently in the stretching process-the Kelvin-Voigt model is sensitive to both the increases in kinematic loading and viscosity coefficient, Standard model 2 is only susceptible to dynamic stiffness, and the Zener model is significantly sensitive to kinematic loading. All responses of the models increase with the increase in stretching speeds. The obtained results indicate substantial “accuracy tolerance” in setting input parameters while identifying dynamics of the knitting process on warp-knitting machines.
The study is a continuation of the first part of the publication, concerning the theoretical analysis of sensitivity of rheological models of dynamically stretched thread. This part presents the experimental research on the characteristics of stretching forces as a function of time, in the context of comparing the obtained results with theoretical data.
The selected research material was three types of polyester silk threads with linear densities 84, 110 and 334 dtex. During the tests, threads of 400 to 1300 mm were stretched at speeds in the range of V ∈ [0.65, 1.47] m/s, which corresponds to the knitting speed n ∈ [700, 1600] courses/min. An original measuring device for empirical identification of dynamic processes of threads stretching was used during the tests. In total, 36 tests variants were performed. The procedures of mathematical equivalence were also worked out for the rheological models of Kelvin-Voigt, Zener and the three-parameter Standard model 2, which enabled the description of threads stretching phenomena in technological processes with the help of generalized rheological model, taking into account the visco-elastic qualities of threads.
Experimental results showed that for the assumed deformation speeds ε(t) ∈ [0.53, 4.00] 1/s, the open three-parameter models – Standard model 2 and Zener model most reliably describe the stretching process.