Study On The Influence Of Yarn Shape Retention Capacity On The Fabric Appearance Based On Elliptical Cross-section Discrete Packing Yarn Model

The quality of yarn appearance is closely related to that of the of the fabric.The former is the dominant factor in determining the fabric appearance quality.As a hot topic in the textile field,understanding and evaluation the appearance quality of the yarn from the perspective of the fabric appearance quality has not been elaborated clearly according to the current research.In this paper,it is considered that the yarn undergoes deformation during the weaving process.The ability to resist this deformation during change is an essential aspect of evaluating the appearance quality of the yarn,and it is also a crucial factor that influences the appearance of the fabric.Based on this,the concept of yarn shape retention was proposed,and some relative evaluating indicators for yarn shape preservation capacity were established.This paper carries out model research and experimental analysis on these shape retention capacity indicators.The results show that the cross-section perimeter of the yarn（L）has the best shape retention capacity and L is a bridge connecting the appearance of the yarns before and after weaving.Then,a novel device based on biaxial CCD was developed for measuring the cross-section perimeter of the yarn and utilized for fabric simulation.Finally,analyzing the influence of the yarn appearance on the fabric appearance combining the relevant experiments with simulations.The research content and relevant conclusions of this thesis are as follows:（1）Some shape retention capacity indicators were put forward.Through the literature study,it is necessary that proposing the yarn shape quality theory and establishing the relevant evaluation indicators referring to the effect of yarn appearance quality on the fabric appearance quality.By analyzing the yarn cross-section profile and optimizing parameters,the yarn shape retention capacity indicators were determined,including a change in the rate of yarn cross-section major length_{（6）,the rate of yarn cross-section perimeter,the rate of yarn cross-sectional area,the rate of yarn cross-section aspect ratio1},and the rate of cross-section fill rate.（2）The elliptical discrete packing model of yarn cross-section was proposed,and the model was analyzed and verified by experiments.It was considered that the shape retention capacity evaluation was closely related to the changes of fiber packing and distribution in the yarn before and after weaving.This change is particularly noticeable among relatively bulky low density spun yarns with large inter-fibre gaps.As the existing yarn packing model cannot meet the research requirements of fiber arrangement and distribution of low-density spun yarns,this thesis proposes a geometric model of yarn cross-sections based on elliptical packing.The model analysis and experimental verification were carried out.The model analysis shows that the packing density of the i-th layer₄)is negatively correlated with the total number of fiber layers I,which in turn has nea gative correlation with the coefficient of the m-plane of the inter-fiber gaps,and the ratio of the short-radius and long-radius of the yarn cross-section.Afterwards,five kinds of pure cotton yarns with different linear densities were tested and cross-section images of the yarns were obtained by curing and polishing the cross-section.The cross-sectional parameters of the yarns were obtained by image processing technology.The results were compared with the theoretical analysis and the model was verified by the tested yarns.The results show that the theoretical values of five kinds of yarns are lower than the experimental values,and the deviation percentages are 20.27%,20.66%,12.23%,13.36%,and 3.77%,respectively.As the fiber density increases,the deviation tends to become smaller.The theoretical value of₄)of each layer is smaller than the experimental value,and with the outward shift of the fiber layers,the deviation tends to become larger.Correlation analysis showed that the determination coefficients of₄)for each layer were 0.8082,0.9851,0.9878,0.9725 and 0.9345 respectively,and the experimental values of the model were in good agreement with the theoretical values.（3）The finite element model of the weaving process was established,and the changes of shape retention capacity indicators of the five yarns before and after the weaving process were analyzed.The model analysis showed that in the simulated fabric S1,the change rate of the cross-section perimeterduring the weaving process is the smallest at 7.42%among all the changes of the five yarn retention capacity indicators.The changes of₁)were most dramatic in the five yarn retention capacity indicators.Further study of the influence of linear density on the five yarn retention capacity indicators,results show that the rate of the indicators exceptandwere generally changed nearly to zero,which indicates that,as the yarn linear density increases,the ability of the yarn interweaving into the fabric to resist deformation becomes stronger,leading to a better retention.Finally,through the study the distribution of the five indicators along the yarn in the simulated fabric S1,results showed that>_（6）>>>1（considering the positive and negative）.In order to verify the model,the yarn cross-section sequence pictures in the simulated fabric S1and the yarn cross-section sequence pictures in the real fabric F1 were compared and analyzed.Results shown that in the real fabric F1,the distribution of each yarn retention capacity indicators obtained is completely consistent with the trend in the simulated fabric S1.The above indicators satisfy the following conditions:>_（6）>>>1（considering the positive and negative）.The deviation analysis showed that all deviations are within the ideal range,and the percentage deviation of_{（6） is 3.66%,7.29%for1},14.95%for,13.03%for,and 45.21%for,respectively.（4）A yarn cross-section perimeter testing device based on two biaxial CCD was developed.As the single yarn cross-section perimeter undergoes minimal changes during the weaving process,the cross-sectional circumference of the yarn is regarded to be a bridge connecting yarns both in the natural state and in the fabric.In order to measure the yarn cross-section perimeter quickly and further study the effect of yarn appearance on the appearance of the fabric,the report designed a biaxial CCD yarn cross-section perimeter test device and verified it with experiments.Ten kinds of yarn samples with different linear densities,blending ratios and various types were tested.Comparing the results with those measured by the yarn appearance uniformity testing instruments,including USTER TESTER 5 and LAWSON-HEMPHILL EIB-S,as well as the single circumference measurement method.It indicated that the value of CV_d1tested by our uniaxial CCD device is generally corresponding to the result of LAWSON-HEMPHILL EIB-S yarn appearance uniformity testing equipment.They have strong correlation with a correlation association of 0.945（R²）.The result of CVP in our device had the same variation tendency with the CV_m of USTER TESTER 5capacitance yarn evenness tester.However,they have weak correlation since the correlation association of R² is 0.658.The value of CVP is smaller than CV_m.In addition,the CVP tested in our device is in accordance with CV_d tested by the equipment of EIB-S.The uniaxial linear correlation coefficient of R² between them is 0.836.The fluctuation of CVP which has a standard deviation of 0.610 is obviously slighter than that of CV_d.Considering that the cross-sectional shape of the yarn is not a standard circle,the biaxial measuring method is more stable than the uniaxial method,and it is more accurate to describe the unevenness feature of the yarn.（5）A simulation model of fabric deformation based on elliptical yarn cross section was proposed.The fabric simulation experiments were conducted.The subjective and objective aspects of the simulation fabric and the real fabric were compared and analyzed.In this research,the fabric simulation deformation model based on the elliptical yarn cross section is set up and the fabric simulation test is performed according to the yarn image data collected by the self-made device and the better maintainability of the yarn cross-sectional perimeter L.A fabric sample is woven on the machine and scanned to obtain the three-dimensional data of the fabric sample.The three-dimensional data of real fabrics and simulated fabrics are compared with each other from subjective and objective perspectives.The results of comparative analysis show that the simulated fabrics have good consistency with real fabrics.During the objective analysis process,three objective evaluation indicators for evaluating the uneven appearance of fabrics were proposed:FDCV、FHCV and FSCV.FSCV has an advantage over the other two indicators of FDCV and FHCV,which appears higher correlation with the uneven feature of actual fabrics whose determination coefficient of R² is 0.9592.Hence,FSCV is more appropriate to objectively evaluate the uneven appearance of the fabric.The conclusion of this report can provide a theoretical basis for analyzing the relationship between yarn appearance quality and fabric appearance quality and supply better technology for the simulation of woven fabrics based on real yarns.It is expected to be applied in the future.