An improved viscoelastic model for tufted carpet yarn

To overcome the problem that the existing mathematical model cannot characterize the viscoelastic properties of tufted carpet yarn completely and accurately, an improved viscoelastic model is built using the semi-empirical method. Using the test data of creep and stress relaxation, the parameters of the improved model are determined. Through the evaluation of fitting effect, the optimal mechanical model to characterize the viscoelastic properties of tufted carpet yarn is obtained. The results show that compared with the standard linear model, the improved model is more suitable to characterize viscoelastic mechanical properties of tufted carpet yarns, such as the creep and stress relaxation properties, which provides a solid theoretical foundation for analysis of vibration characteristics and dynamic tension control of tufted carpet yarn.     

The role of geometry on the viscoelastic materials properties: tensile and stress relaxation of the yarn

The time-dependent mechanical behavior of textiles has particular importance. One of such behaviors is stress relaxation. When strain is applied constantly, there is a decreased stress with time in viscoelastic materials, which is called stress relaxation. The aim of this study is to investigate the effect of knot’s geometry (surgeon, square and eight) and the number of knots on the tensile and stress relaxation properties of the polyester yarn. Significant differences were observed for the tensile characteristics of the yarn in the presence of the knot. Generally, the knotted yarns demonstrated lower tensile stress and strain at failure. Moreover, the results revealed that the stress relaxation behavior of the yarn is affected by the number of knots and their geometry. The yarn without knot exhibited the highest stress relaxation percent while the yarn with the surgeon’s knot displayed the least stress relaxation percent. On the other hand, increasing the number of knots led to a decrease in the percentage of yarn stress relaxation.     

纱线束横向动态振动特性仿真与实验

纱线束振动噪声是簇绒地毯织机噪声源之一,为了识别纱线束振动噪声信号,实现地毯生产空间的噪声控制,研究了簇绒地毯织机纱线束横向动态振动特性。应用Burger四元件本构模型建立粘弹性纱线束轴向运动的横向振动方程。采用Galerkin方法离散横向振动偏微分方程,然后使用Runge-Kutta法对该方程数值求解。设置不同的提花轮转速,分别求解振动方程得到不同的纱线束横向振动频率。设置与仿真求解相同的条件下,采用激光测振仪测试纱线束横向振动特性。测试结果显示仿真结果和实验结果存在倍频关系且频率较低。结果表明：该振动方程适用于研究纱线束横向动态振动特性,且仿真信号为纱线束振动的基频信号;同时,纱线束横向动态振动特性属于低频振动。     

地毯簇绒系统纱线张力建模与分析

为提高簇绒地毯分辨率,提升地毯的品质,建立正确的纱线张力模型是精确控制地毯绒高的关键。首先介绍了簇绒装备系统的组成及纱线的导向路径,然后将米纳科夫的拓展欧拉公式引入纱线张力系统,考虑纱线束为黏弹性负载,分阶段对张力系统进行建模。其中,纱线张力系统模型包括提花罗拉、恒张力导纱罗拉和多层导纱器。通过对比仿真与实验所得的纱线张力变化曲线,验证了模型的准确性,为下一步张力控制器的设计提供了参考。     

酱牛肉应力松弛特性实验

以5个品牌酱牛肉为试样,从压缩试验及应力松弛试验研究中获得力学-流变学性质参数,利用SPSS软件进行非线性回归拟合,建立了广义Maxwell流变模型。结果表明:酱牛肉具有良好的压缩黏弹性力学性质,属黏弹性材料,五元件广义Maxwell模型适用于模拟酱牛肉的应力松弛现象。对应力松弛参数做主成分分析,应力松弛试验的7个参数可以分为两个主成分,归纳为2类,即黏弹特性和松弛时间。     

VISCOELASTICITY OF A SIMULATED POLYMER AND COMPARISON WITH CHICKPEA FLOUR DOUGHS

An integrated approach consisting of compression and stress relaxation is performed with a simulated model system of poly dimethyl siloxane (PDMS), a viscoelastic polymer material when the compressive strain, height of sample and crosshead speed were varied. The parameters derived are the forces at the end of compression and relaxation, energy for compression and the extent of elasticity of the sample based on the ratios of forces as well as the proposed energy values. The results were verified with food doughs undergoing large deformations that show a nonlinear behavior. The proposed extent of elasticity based on the ratios of energy stored and compression can be used as an index for the characterization of viscoelasticity. A nonlinear three‐parameter model had also been proposed to predict the stress decay characteristics as a function of time, which was found suitable for the PDMS system, and was better than the two‐parameter Peleg model as judged by lower variance values (0.0006–0.018 and 0.002–0.048, respectively). Further, an actual system of food doughs in the form of chickpea (Cicer arietinum L.) flour dough was used to verify the proposed model and viscoelastic index at different moisture contents (27–39%) subjected to compressive strains of 25–75%. The nonlinear relaxation characteristics of the food dough are sensitive to moisture content as well as to strain level.     

彩棉喷气涡流纺纱线应力松弛机制分析

以四元件模型为基础,利用玻尔兹曼叠加原理建立了纱线应力松弛变化过程的理论方程,并分别对彩棉喷气涡流纺及环锭纺纱线进行松弛实验。基于应力松弛理论模型,利用Origin 7.5软件求得纱线应力松弛的回归方程,分析了喷气涡流纺纱线应力松弛机制。结果表明:理论值与实测值具有良好的相关性,可以利用该模型预测纱线的松弛性能;喷气涡流纺纱线的松弛时间较短,弹性比例较小;通过预测纱线的松弛性能,可有效改善彩棉产品手感较软的问题。     

Modeling of Coupled Water Transport and Large Deformation During Dehydration of Apple Tissue

Water loss of fruit during storage has a large impact on fruit quality and shelf life and is essential to fruit drying. Dehydration of fruit tissues is often accompanied by large deformations. One-dimensional water transport and large deformation of cylindrical samples of apple tissue during dehydration were modeled by coupled mass transfer and mechanics and validated by calibrated X-ray CT measurements. Uni-axial compression–relaxation tests were carried out to determine the nonlinear viscoelastic properties of apple tissue. The Mooney–Rivlin and Yeoh hyperelastic potentials with three parameters were effective to reproduce the nonlinear behavior during the loading region. Maxwell model was successful to quantify the viscoelastic behavior of the tissue during stress relaxation. The nonlinear models were superior to linear elastic and viscoelastic models to predict deformation and water loss. The sensitivity of different model parameters using the nonlinear viscoelastic model using Yeoh hyperelastic potentials was studied. The model predictions proved to be more sensitive to water transport parameters than to the mechanical parameters. The large effect of relative humidity and temperature on the deformation of apple tissue was confirmed by this study. The validated model can be employed to better understand postharvest storage and drying processes of apple fruit and thus improve product quality in the cold chain.     

簇绒地毯织机提花装置的绕纱动态张力分析

簇绒地毯织机纱线张力是影响提花质量的关键因素,为对其进行有效控制,本文研究了步进电机输入对簇绒提花装置区间绕过纱线张力的动态变化情况。首先建立提花装置的步进电机的负载模型,并分析其角频率输入对输出电磁转矩的对应关系;然后,根据米纳科夫定理的原理,建立纱线段绕过提花罗拉前后纱线动态张力模型。同时,进一步分析步进电机的输入与提花装置绕纱的输出动态张力之间的数学模型,在选定提花罗拉半径r、中心距 、纱线包角 等初始条件下,利用迭代-欧拉法分析其数值变化情况,得出角频率输入与纱线张力输出之间的定量关系,并探究不同包角对纱线动态张力的影响机制,为不同绒高的簇绒地毯甚至满幅簇绒提花地毯的制造和研究提供参考。     

轴向运动纱线束的非线性横向振动特性

为控制纱线张力波动,提高毯面质量,研究了建立地毯织造过程中粘弹性纱线束振动模型及其影响因素。为此,应用三参数本构关系表征纱线束粘弹性,结合轴向几何非线性变形和材料非线性因素,应用牛顿第二定律建立纱线束横向振动方程。经无量纲化和一阶Galerkin截断,应用四阶Runge-Kutta法求解常微分方程,可得纱线束喂入速度、张力波动幅度以及阻尼系数对振动特性的影响。结果显示,在纱线束材料确定下,降低纱线束振动振幅从而减少张力波动的方法主要是增加阻尼系数,如增加提花罗拉表面摩擦系数。     

The optical properties of hand-woven carpet

Abstract

The reflectance spectra and color properties of yarn when used in carpet are different from its cross-sectional direction as the pile of hand-woven carpet. This paper presents a comprehensive study of reflectance spectra and color properties of the pile in longitudinal direction and hand-woven carpet. For this purpose, the wool yarns were dyed with madder as a natural dye in various concentrations from 10% to 100% on the weight of sample. In order to study of the optical properties of the pile of hand-woven carpet, the dyed yarns were used to weave the hand-woven carpet. The obtained results showed that the yarn in longitudinal direction is lighter than the pile of hand-woven carpet, and so, the color strength of hand-woven carpet is more than the color strength of yarn. The spectrophotometric properties of samples were also studied by Principal Component Analysis (PCA). The difference between reflectance spectra of yarn in longitudinal direction and reflectance spectra of the pile of hand-woven carpet was also shown by PCA results.     

Analysis of the effect of traffic exposure on the recovery properties of cut pile carpet using analytical and viscoelastic modeling

Viscoelastic models composing of different combination of spring and dashpot are usually used to explain the mechanical behavior of textile materials. In this work, a viscoelastic model was presented to analyze the effect of traffic exposure on the compression and recovery performance of the pile carpet. Wear test, performed by a Hexapod tumbling machine, was conducted to simulate the traffic exposure. Using a tensile tester, adjusted in compression mode, one cycle of compression–decompression was applied to the samples. The standard nonlinear model was presented to fit the experimental data. Best curve fitting based on the least square method was then used to fit the model to the experimental curve. Different attributions of compression were then analyzed and discussed. The results showed that the standard nonlinear model was fitted to the experimental curves with an acceptable coefficient of regression (R²). The district model parameters, i.e. the spring and dashpot constants, were both decreased as the wear cycles increased. At the higher level of wear cycles, the model parameters showed some increment. The initial compression modulus showed the same trend. This may be explained by the more compactness of the carpet at higher wear cycles. The decompression modulus, compression and the decompression work also decreased with the increase of wear cycles. However, no significant increase of the formers was observed at the higher wear cycles.     

Modelling of acrylic cut-pile carpet compression properties by means of expert systems based on carpet structural parameters

Abstract

Compression properties of carpet are a detrimental factor influencing carpet wear performance. In fact, carpet compression behavior determines carpet serviceability which in turn affects carpet appearance. Therefore, it is important to predict the carpet compression behavior in order to reduce the product cost. In this paper, a fuzzy logic model for prediction of compressional properties of acrylic cut-pile carpets is implemented in terms of the carpet structural parameters including carpet pile density, linear density of pile yarns and carpet pile height. In order to provide experimental data, six different acrylic cut-pile carpet samples fabricated by using six different acrylic spun pile yarns with yarn count of 18/3, 21/3, 27/3, 30/3, 33/3 and 36/3?Nm. Half of each provided carpet subjected to re-shearing process. All 12 carpet samples in two different cases (normal and reduced pile height) have been tested by standard carpet static and dynamic loading tests to measure thickness-loss as one of compression properties. Fuzzy logic model has been implemented and improved using genetic algorithm. Results show that correlation coefficients of model predictions with experimental values are 0.97, 0.98, 0.98 and 0.98 for carpet thickness-loss after low dynamic, high dynamic and static loading with short and long relaxation times, respectively. Also, linear regression trend between predicted and experimental values represented with a slope near to 1 and almost small bias (intercept). The result indicates that the developed fuzzy logic model is a reliable model predicting the acrylic cut-pile compression behavior.     

山羊绒纤维的拉伸性能

研究了山羊绒纤维的拉伸性能以及单纱的拉伸松弛性能,并与细支羊毛纤维进行对比。研究结果表明:山羊绒纤维的比强度、拉伸模量,松弛时间高于羊毛;在较小定伸长条件下,山羊绒纱线拉伸应力松弛速率慢于羊毛纱线,即山羊绒纱线比羊毛纱线难定形,这些力学性能的差异是由于山羊绒纤维α-结晶度高于羊毛;在80~130℃干热条件下,山羊绒纱线的拉伸应力松弛速率及其定形率均随温度的提高而提高;当温度高于120℃时,提高不显著。     

Rheological modeling of tubular weft knitted textiles

Tubular-knitted fabrics are used in various medical and tissue engineering applications. The mechanical behavior of such structures is important and therefore, it should be considered to design the artificial grafts and prosthesis prior to specific applications. Twenty different structures of tubular silk weft-knitted fabrics (five knitting patterns, two different yarn counts, and two different stitch lengths) were produced, and their mechanical properties were measured in longitudinal and circumferential directions under the constant rate of elongation. Twelve samples were used to study the performance of seven rheological models in order to investigate the mechanical performance of tubular-knitted structures. The results showed that the rheological model of a non-linear spring (that followed the power rule) parallel with a Newtonian dashpot could properly estimate the stress–strain curves of the tubular fabrics under loading. Mathematical equations of this model were derived based on the rheological parameters of the structural elements of the weft-knitted fabrics. The model validation was also investigated using the eight different remaining tubular structures. The results showed that the developed model could be used to describe the mechanical behavior of the knitted structures based on the viscoelastic coefficients of the knitted fabrics.     

LINEAR VISCOELASTIC BEHAVIOR OF FRANKFURTERS

Normal creep and stress relaxation experiments were performed on seven commercial brands of frankfurters. A nonlinear procedure was used to determine the model best fitting the data for each test. Re assumption of linear viscoelasticity was tested by the equivalence of model parameters. Results showed fankfurters to be linear viscoelastic materials at strain levels up to 3.8%.     

Durability of Handmade Wool Carpets: A Review

This paper presents various aspects related to the durability characteristics of handmade carpets. Various kinds of materials and knots used in handmade carpet have been explained at the beginning. Then the mechanism of carpet durability has been explained with respect to mechanical and appearance aspects. The various techniques for measuring the mechanical and appearance related durability characteristics have also been presented in this article. Finally, the influence of wool fibre, yarn, and carpet structural parameters on the durability has been explained. The shortcomings in terms of durability, characterization of carpets, and scope of further research have been presented at the end of the review.     

膨体弹力真丝超分子结构与特性研究

通过测定膨体弹力真丝的结晶度、取向程度、力学松弛和断裂比功等特性，研究膨体弹力真丝与普通生丝在超分子结构、应力松弛和蠕变等方面的特征，探讨其分子结构与力学特性的内在联系以及它们对膨体弹力真丝性能的影响。     

导电纤维包覆防静电地毯纱的研制

化纤地毡吸湿性差，易产生静电，而在地毡纱中混用导电纤维是一种理想的防静电方法。文章介绍了用摩擦纺纺制包覆防静电地毯纱的纺纱工艺，结果表明，其导电纤维的含量只要2％，就具有良好的导电性能，可以有效防止地毯的静电现象。     

On the dynamic model of yarn with time-dependent tension

In order to control yarn vibration and improve carpet quality, it is essential to research the fluctuation of yarn tension and its influences during tufting process. Assuming the polypropylene yarn has linear elasticity with a circular cross-section, we take the dynamic tension as the output and the friction acted on yarn by Jacquard roller as the input. At the moment of clutch operation and release, the tension fluctuation of polypropylene yarn during transmission from pulling roller to Jacquard roller was theoretically analyzed. A mathematical model describing yarn tension fluctuation was derived based on the moment of momentum theorem and mass conservation. The dynamic tension was obtained by applying Laplace’s transformation, providing the input-breaking moment as a step response. The result shows that tension fluctuation has an important influence on the carpet quality; therefore, it is necessary to carefully design the Jacquard roller and the control friction plate of clutch. Moreover, the effects of the yarn length between Jacquard rollers and pulling rollers on natural frequency and damping coefficient of yarn tension fluctuation were analyzed.