| Staple yarn is an important part of textile materials,and it occupies an important position in the fields of clothing,decoration,and industry.As an assembly of staple fibers,the staple yarn is prepared by twisting the former fiber assembly,and the entanglement and arrangement of fibers inside the staple yarn are extremely random.There is obvious diversity in the configuration of fibers,and the research on the spinning process and structure of the staple yarn have always been an uninterrupted direction in textile research.It can be confirmed that understanding the yarn-forming process of the staple yarn is a necessary condition for improving spinning equipment and developing new staple yarns or related products.Especially,the analysis of the yarn-forming process at fiber scale can explore the yarn-forming mechanism from a more microscopic perspective.However,limited by the microscale and high-speed behavior of the densely packed fiber assembly during the yarn-forming process,it is still impossible to obtain the complete real fiber motion.The theoretical analysis based on the mechanics and statistics methods is mostly carried out with some indicators as a substitute for the staple yarn structure,and the analyzed physical quantities and motion equations have problems of low versatility and one-sidedness.Instead,the experiment-oriented research shows the overall morphology and fiber configuration of the assemblies at macroscopic,local,static or specific stages,and the specific changes in fiber configuration and the interaction between fibers cannot be covered.Overall,it remains challenging to systematically elucidate the entire yarn-forming process and fully characterize the structure of the staple yarn.Focusing on the above problems,this paper expounds the necessity of constructing fiber-scale textile structures,and on the premise of fully analyzing the spinning process of the staple yarn,the simulation of the fiber-scale staple yarn formation process is carried out based on the dynamic theory of the fiber assembly,meanwhile,the actual spinning process is used as the key reference.In addition,a fiber-scale woven fabric model is constructed using the simulated staple yarn model unit.The research contents are as follows:Firstly,the concept of fiber-scale textile structure is expounded,and the advantages and disadvantages of using fiber-scale in the analysis of textile structure formation and structural representation are analyzed,and the formation mechanism analysis and structural model construction strategy of the fiber-scale staple yarn and woven fabric are also proposed.Subsequently,the twisting mechanism in the forming process of the staple yarn is discussed emphatically,and the structure and twisting analysis were assumed as three models of isotropy,no-slip contact,and slip contact respectively.On the basis of assuming that the sliver is isotropic,and taking the torsional stiffness coefficient of the sliver as the key index of its physical properties,a calculation formula for quickly solving the twisting behavior of the sliver is proposed;On the basis of the isotropy assumption,the physical properties of a twisted sliver are calculated with the number of fiber contacts as the main index,and the stress-strain constitutive equation of the weak-twist sliver is analyzed;Considering the unavoidable slippage phenomenon,a calculation method for the fiber-scale sliver twisting process based on finite element theory is proposed,and the theoretical basis is also discussed.Specifically,the assembly of several regular units is used as the fiber unit,the node gap function is used as the trigger condition of the fiber contact,and the actual twisting behavior is used as the boundary condition.Next,based on the assumption that each fiber is in a slender cylindrical configuration,isotropic,and randomly distributed in the sliver domain,a sliver model containing 250 fibers is constructed.The physical parameters of the sliver refer to the real sliver from the nip of the ring-spinning front roller.On the basis that the fibers in the twisting process are considered to only undergo linear elastic changes,a pair of twisting fixtures is used as the twisting boundary condition of the sliver model,while a pair of fixed fixtures are used as the holding boundary condition.In the ABAQUS software,the simulation calculation of the non-free-end twisting of the sliver is carried out.The calculation obtains the configuration change of all the fibers in the sliver during the twisting process,and the structural model of the staple yarn is also obtained.For the first time,we subdivide the various links of twist propagation through the overall morphology change of the sliver at different stages.The mechanism of twist propagation and the reasons for the variety of fiber configurations are explained,and the morphology of the sliver during the specific twisting stage is verified by real twisting experiments.For the verification of the structure of the calculated staple yarn model,a quality comparison experiment of 1.5cm length yarn is carried out subsequently.Small deviations(<12%)between real and simulated structures of 32 Ne,40Ne,and 48 Ne ring-spun yarns confirm the accuracy of the calculated fiber-scale staple yarn model.Furthermore,aiming at the problem of weak integrity in the process of the sliver twisting simulation,a method of constructing the sliver model with buckled fibers is proposed.We extract the two-dimensional configurations of 2500 fibers,and a two-dimensional fiber configuration generation model based on the Generative Adversarial Networks(GAN)algorithm is established.The algorithm can generate 15 sets of data points as the configuration of one fiber.Then,a three-dimensional fiber model is constructed with a rounded polyline as the axis and a circle as the cross-section.Fiber contact-separation experiments are carried out subsequently,and it find that mutual attraction between fibers is another key reason for the integrity of the sliver,and using the buckled fiber model as the smallest unit,a two-step simulation method of "arrangement-compression" is proposed to create the modified sliver model.Then,a sliver model containing 250 fibers is generated,and the twisting simulation is also carried out.The simulation process confirms the integrity characteristics of the modified sliver model,and also constructs a staple yarn model with a length of 10 cm.In the structural analysis of the staple yarn model,the fiber configuration characteristics in the 8mm yarn segment are counted,and the fibers are distinguished into four types: the through fiber,the left-end-through fibers,the right-end-through fibers,and the hairiness fiber.Statistically,the through fiber accounts for the main proportion,the proportion is 64.8%.At the same time,the hairiness fiber is distinguished into three types: the head hairiness fiber,the tail hairiness fiber,and the loop hairiness.Statistically,the tail hairiness accounts for the highest proportion,about 49.4%.Finally,different from the woven fabric model construction method based on the subjective experience,this paper carries out a woven fabric structure simulation dominated by real weaving motion.During the simulation process,it fully refers to the heald motion,the weft motion,and the beating-up motion.The previously fiber-scale staple yarn model is used as the warp and weft yarns,and the warp and weft yarn stress distribution,the morphology change,the interweaving friction behavior,and the plain-woven fabric model in the three major movements are calculated.Meanwhile,the weaving process simulation explains the mechanisms of the yarn damage and hairiness increasing.Next,the modulus of the fiber is set to 50 MPa,500MPa,and 900 MPa respectively,and the simulations are carried out under the same boundary conditions.The displacement changes of the nodes at the same warp and weft positions in different simulations are calculated,and some nodes exhibit obvious evidence of differentiated motion,up to 60% displacement difference,and more than80% abnormal fluctuations reflect the unique advantage of the woven fabric model obtained by this simulation method.Subsequently,we simulate two colored yarn models using two fibers with different colors,and this simulation refers to the package blending process and the sliver blending process in the real spinning process.The small-scale yarn-dyed fabric models are generated with the simulated colored yarns,meanwhile,the large-scale yarn-dyed fabric models are also constructed by a convenient stitching algorithm.To sum up,the fiber-scale simulation of the twisting process of the staple yarn in this paper realizes the sliver morphology characteristic at any twisting moment,and the stress distribution and dynamic configuration changes are also obtained simultaneously.This is the first time to achieve a systematic simulation of the twisting process,and it is also the first time to construct a fiber-scale staple yarn model according to the objective process.On the basis of fully considering the arrangement of the fibers in the sliver,the simulated twisting process,the initial configuration of fibers,the mutual attraction between fibers,the calculated sliver model,the twisting process,and the staple yarn structure show high actual structural characteristics and effective reference value.The weaving process and woven fabric structure simulated based on this staple yarn model not only proves the value of the staple yarn model in subsequent applications but also provides an effective mean and model basis for the field of fabric texture generation. |
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