Abstract:

Objective The main aim of this study is to quantitatively study the influence of the meso-structure of staple yarns under low stress on its macroscopic mechanical properties, so as to solve the problems of low efficiency, high time consumption in the current simulation research on the tensile properties of staple yarns. A detailed discussion of meso-structural parameters, such as twist, fiber orientation, scale effect between fibers, and the related physical properties was conducted to reveal the meso-mechanical mechanism and macro-mechanical behavior of staple yarns.

Method An equivalent staple yarn stretching model was established. By leveraging finite element analysis, the yarn stretching process with embedded meso-mechanical factors was simulated and analyzed. Briefly, the yarn sample was observed by VHX-5000 ultra-depth digital microscope to obtain geometric parameters, and the yarn finite element modeling was performed with the help of SoliWorks software. Combined with actual measurement, the effectiveness of the finite element simulation stretching yarn model was demonstrated. Finite element analysis software ABAQUS was utilized to simulate and analyze the three influencing factors i.e. the staple yarn twist, overlap fiber length and the fiber curve angle. The influences of friction coefficient and elastic modulus on the tensile properties of yarn were discussed, and the mechanisms affecting the macroscopic mechanical properties of yarn were investigated.

Results According to the simulation results, the stress changes of the yarn were observed. It was found that yarn twist was the main factor affecting the mechanical properties of spun yarns, and the twist of 4 twists/(10 cm) was determined as the critical value for converting the fiber slip failure to the fiber broken failure in the yarn. The overlap fiber length was also identified as the main factor affecting the mechanical properties of spun yarns, and the maximum yarn strength and the overlap fiber length showed a typical nonlinear relationship and the critical conversion value of the overlap length was 200 mm. The simulation also revealed that the larger was the fiber orientation angle in the yarn, the smaller were the tensile modulus and strength of the yarn. When the fiber orientation angle was smaller than 5°, the yarn strength became very low, leading to early failure, indicating that the fiber orientation angle was governed by the yarn twist and was a key factor affecting the tensile properties of the spun yarn. The inter-fiber friction coefficient and elastic modulus of the fiber demonstrated a great influence on the tensile behavior of the yarn. With the increase of the friction coefficient and elastic modulus of the yarn, the tensile force shows an increasing trend. For every 0.1 increase in the friction coefficient, the maximum tensile force increases by 3.63 N; the elastic modulus increases by 50 MPa, and the maximum tensile force increases by 6.98 N. Comparing the simulation results with the test results, it is found that the morphology and deformation of the yarn are highly similar during the stretching process, and the relative errors of each mechanical parameter are within 4%. The correlation coefficient between the test displacement and the simulated tensile force is 0.962, and the correlation coefficient between the simulated displacement and the test tensile force is 0.967. Both are significantly correlated at the 0.01 level.

Conclusion In order to quantitatively study the influence of the microstructure of spun yarn under low stress conditions, specifically, the mechanical behavior prior to yarn failure dominated by mechanisms such as fiber slippage and structural reorganization rather than breaking of the fibers within the yarn, on its macroscopic mechanical properties and better evaluate the mechanical properties of spun yarn, this paper simulates and verifies the tensile process of spun yarn using the finite element method. With the help of professional modeling software SolidWorks, an equivalent yarn geometric model is established using an array of interlaced continuous yarns, namely a novel and simplified approach that effectively captures key meso-structural features of staple yarn while maintaining computational efficiency in simulation. The finite element analysis software ABAQUS is utilized to simulate and verify the micro-mechanism of yarn tensile mechanical behavior from three perspectives, including fiber overlap length (scale effect), fiber orientation (deflection angle) and yarn twist. The finite element simulation results were compared with the experimental results. The simulation results show high consistency with experimental data, with a correlation coefficient of 0.962 (p<0.01), confirming the validity of the finite element model for analyzing the tensile properties of spun yarn. In subsequent studies, yarns with different raw materials and different structural parameters can be selected for simulation tests to further study the tensile properties of spun yarn.

Key words: staple yarn, numerical simulation, yarn mechanical property, mesostructure, macro-meso correlation law, finite element analysis