Characterization And Modeling For Bending Behaviour Of Yarns And Fabrics In-Situ

The bending behaviour of yarns and fabrics plays an important role on processing, formability and wearability, which not only affect the smooth, softness and drapability of underwear, but also determine stiffness and shape characteristics of outwear, as well as comfortability of apparel. Thus, it is necessary to choose the proper and optimum mechanical properties, which include bending, weight, friction, tensile and thickness properties for end-use textile products in the application of yarns and fabrics.The basic principle for designing textile products is to measure the properties of yarns and fabric, especially to be quantitatively characterized. So far, the bending meters in principle for yarns and fabrics are mainly divided into three categories. One is single property through single test (briefly called SPST), which just gets single property and is behind the times and bad practicability. Another is multiple properties through single test (MPST), which is up-to-date, however, limited to laboratory investigation and have no standard application. The last is multiple properties through multiple tests (MPMT), whose apparatus is expensive and low automatization.The extending technology of SPST is MPST, which represents the leading and trend of measurement and laboratory. The nature of MPST is assembledly measuring technology in-situ. The MPST to measure the properties and handle of yarns and fabrics is adopted in this dissertation to realize multiple functions and fast measurements as well as the "one sample" comprehensive testing.The purpose was to develop an apparatus, method and standard with self-intelligent property for measuring bending behaviour of yarns and fabrics based on MPST principle. The method can also measure weight, friction, tensile and thickness properties, and characterize the relationship of bending behaviour between yarns and fabric through one pulling-out deformation, in order to build a solid foundation for comprehensively characterizing fabrichandle. The developed apparatus is not only basically low cost and price, also can measure mechanical properties and handle of yarns and fabrics smartly. The apparatus based on MPST principle is greatly helpful and highly efficient in analyzing mechanical property, determining fabric handle, realizing quick textile products checking and quality control, and providing effective and accurative up-to-date technology.In this present thesis, the bending behaviour of yarns and fabrics with the same bending in principle based on quasi three-point bending theory has been measured, and the weight, friction, tensile and thickness properties have also been tested in the same time. The corresponding comprehensive handle evaluation system for yarns and fabrics (abbreviated as CHES-FY) was developed to measure and characterize weight, bending, friction, tensile and thickness properties. Based on the pulling-out force and distance curve of CHES-FY system, the correspondingly index and characteristics of the five steps, i.e., weight, bending, friction, tensile and thickness were separated and obtained. In weight step, it could obtain yarn linear density and fabric weight square meter;in bending step, it could obtain bending slope, bending work and maximum bending force as well as bending rigidity;in friction step, it could obtain friction coefficient;in tensile step, it could obtain tensile slope, tensile work, tensile extension and tensile curve linear degree as well as tensile elastic constant;and in thickness step, it could obtain yarn diameter and fabric thickness.The conclusions have been drawn out through the experimental and theoretical studies asfollows:(1) The linear regression slope coefficient and correlation coefficient of weight betweentheoretical and experimental results were 1.36 and 0.95, which shows there are difference and the theoretical results are larger than experimental results, but also the CHES-FY system can effectively measure and characterize weight of yarn and fabric.(2) Based on elastic theorem and mechanical analysis of bending behaviour of yarn and fabric, shifting-point and fixed-point bending models were developed. The pulling-out force and distance curve was obtained based on the two bending models. It indicates that the relationship between bending rigidity and curvature is nonlinear, and the bending rigidities in curvature ranging from 1.5 to 2.5 cm"1 are averaged as the bending rigidity of yarn and fabric. The shifting-point bending model is chosen as the optimum-bending model. Based on Abbott et al.'s rectangular model, Abbott et al.'s point model, Leaf et al's model and Wei et al's model,the discussion of the relationship between yams and fabrics bending rigidity indicates that the Abbott et al.'s model is closest to the actual prediction results, and the relative error between theoretical and experimental results was 0.16. The Abbott et al.'s point model is selected as the optimum model for the prediction of fabric to yam bending rigidity.The bending model was modified through friction coefficient and tensile modulus obtained from friction and tensile steps of the CHES-FY system, and the relative error, linear regression slope coefficient and correlation coefficient of bending rigidity between pre-modified and modified results were not larger than 10%, 1.095 and 0.997, respectively. It exhibits that the bending rigidity between pre-modified and modified results can both be used to measure andcharacterize bending rigidity of yam and fabric, and calculated from each other.(3) CHES-FY was based on Capstan equation to calculate the friction coefficient, and the linear regression slope coefficient and correlation coefficient between theoretical and experimental results were 1.154 and 0.848, respectively, which indicates that there exists high correlation and can both be used to measure and characterize friction coefficient.(4) CHES-FY system can obtain tensile elastic constant {E\ and E2) before and after friction force involved and their correlation coefficient was as high as 0.994. Moreover, E\ and E2 had also high correlation coefficients with experimental tensile elastic constant (ï¿¡3) measured by KES-FB1 were 0.857 and 0.870, which shows that E\ and ï¿¡2 can both be used to measure tensile elastic constant of yams and fabrics.(5) CHES-FY system can measure the diameter of yams and thickness of fabrics (T\). The relative error of thickness results between T\ and T2 measured by FAST-1 is not more than 16%, which shows good accordance. Moreover, one order coefficient of linear equation and correleation coefficient are 1.066 and 0.97, respectively;in addition, the confidence (0.95) prediction value is not more than 0.022, which exhibits there are high correlation of thickness between the theoretical and experimental results and can be utilized to accurately and effectively measure the thickness and to characterize the thickness properties.In general, the CHES-FY system is effective and accurate in measuring and characterizing weight, bending, friction, tensile and thickness properties of yams and fabrics based on MPST principle.