Identification of the Process of Dynamic Stretching of Threads in Warp Knitting Technology Part II: Experimental Identification of the Process of Stretching Threads, with Verification of Rheological Models

Abstract

Abstract 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.