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Analysis of deformation characteristics of twisted woolen yarns
Abstract
Defining thresholds for yarn strain in manufacturing process is crucial for appropriately adjusting these processes and keeping high yarn quality. That is the main reason why the issue has drawn so much intention. The knowledge of elasticity limits and yield points is very important for the optimization of the production process and further twisted woolen yarns processing. Therefore, this paper defines the limits for elasticity and yield points and breaking forces of woolen yarns with the linear density of 21x2 tex, 23x2 tex and 25x2 tex, obtained by two-for-one twisting method. The interrelationship between the forces and the elongations at elasticity limits, yield points and breaking force of these yarns are also analyzed. Besides, on the basis of experimental results and equations, real mathematical dependences are set, which can be used to predict forces and elongations of woolen yarns at elasticity limits, yield points and breaking limits.
This paper analyzes the impact of knitwear’s fiber composition, linear density and finishing of yarn used in the dimensional stability of the 1x1 RIB knitwear made on the same circular knitting machine. Dimensional stability of these samples was analysed by FAST 4 method. Different samples were compared across multiple indicators. The results show that the most stable dyed knitted fabric are made of cotton 96% and 4% of Lycra and of yarn with linear density 19.14 tex. Tightness factor’s values in the dry relaxation stood at 17.90, in the wet 18.45, in total 18.73 and 18.59 in air conditioned terms. Knitwear with the highest values of dimensional instability are raw knitted fabric made of 100% CO, and yarn with linear density of 13.39 tex. Tightness factor’s values in the dry relaxation stood at 12.16, in the wet 12.36, in total 13.26 and 13.35 in air conditioned terms
In twisting, three different tension force intensities were used for each type of wound and doubled yarns. On the basis of the F-ε curve, elasticity limits were defined, as well as the yield point of the analysed twisted yarns assessed. Breaking forces and elongation at break for all registered tension forces, as well as the work to the elasticity limit and the work to the yield and breaking point were also determined.
This paper presents the second part of our study describing the modelling of the yarn stretching phenomena recently published in F&T in EE [1]. The continuation of this approach involves the identification of unknown parameters in the model as well as proper stress-strain curve division, in order to avoid problems of identification. In order to avoid the effects of parametric compensation, which has been very often observed, when the number of model parameters becomes significant we use a new strategy of identification. The division of the model into submodels contributes to the correct operation of the identification, because we use a method which partially identifies with submodels which have a small number of parameters. The parameters of the proposed model were identified using MATLAB software. Various types of yarns were tested according to whether their origin was natural and man-made. Finally, the superposition of the practical and simulated curves was carried out, with the aim of verifying the correctness of the proposed model. The results show that the model was adapted perfectly in almost all types of the yarns used.
The first part of this paper presents a modelling of the stretching phenomena of linear textile products, specifically yarns. The stretching phenomena are described by a model of the yarn stress-strain curve which was developed by a team from the GEMTEX laboratory. This analysis of the yarn stress-strain curve is an attempt to interpret this curve in the form of a set of various models. This differentiation is due to the change of the yarn's state at the time of its stretching. The model differs very clearly from the other models presented in literature. In order to compare our research with that described in literature, the sensitivity of the parameters of various models was studied. Dividing the model into sub-models is crucial, because this enables the identification of vector parameter as a whole, by assembling parameters of sub-models. The secondpart of this approach to modelling the stress-strain curve is concerned with modelling the stress-strain curves of real natural and synthetic yarns.
In the twisting process yarn was exposed to various influences that caused various tensions in various sectors. All that influenced the resulting tension with which yarn was twisted onto the bobbin. Yarn tensions were defined under various twisting conditions. Afterwards, poly-cyclic mechanicalproperties of these yarns were examined. Fastness of twisted yarns to poly-cyclic extensions was examined by the method of repeated extensions to the constant elongation, on INSTRON-tester. Elongation of 4 %, corresponding to the warp elongation on the loom, was taken. As experimental material, worsted wool yarn spun from T-63 wool fibres was chosen.
In this work the study of yield point of thread and stress in flow point is shown. The determination of this point is done with the well-known Meredith’s and Coplan’s construction, which has the basis in tangent method and numerical method, which is developed from sufficient smooth approximation of the curve. The approximation polynomial expression of the ninth order was chosen for the construction of the mean curve s (e) which, as the sufficiently smooth curve, fits the measured values.
Presents the influence of rheological properties of a sewing thread on its dynamical loads in a stitch formation process, or on change of thread strength as a consequence of dynamical loads in the sewing process, respectively. Research work shows the change in thread strength, as a result of the stitch formation process forming dynamic loads of a thread, as a function of rheological properties of a thread.