Bagging Behavior Research Articles

Viscoelastic Behavior of Fibers During Woven Fabric Bagging

The aim of this paper is to study the viscoelastic behavior of fibers during the woven fabric bagging process through a series of experiments and a mathematical model to simulate bagging under the testing conditions. Through a large number of computational experiments, the elastic modulus E1 , viscoelastic modulus E2, fiber relaxation time T, and three weighting coefficients ( k3, k4, k5) are determined for six woven fabrics made from different fibers. A comparison of the experimental measurements with the predicted bagging behavior of the fabrics reveals that the mathematical model is able to predict bagging behavior with reasonable accuracy. The results show that the viscoelastic behav ior of fibers in the six fabrics is significantly different during bagging. Nylon and polyester have a high elasticity ratio ( E, ), a low viscoelasticity ratio ( E2), and a large relaxation time T. Silk, viscose, and cotton fibers have a low elasticity ratio ( E, ), a high viscoelas ticity ratio ( E2), and a small relaxation time T. For cotton and wool, with the same level of viscoelasticity ( E2), the stress relaxation process is determined by relaxation time T. These results suggest that fiber viscoelastic behavior plays a key role in determining fabric rheological behavior during bagging.

Mathematical Simulation of Fabric Bagging

A mathematical model is developed to simulate the rheological behavior of fabric bagging. The model is based on the assumption that stress-strain relationships in fabric consist of three essential components: elastic deformation and viscoelastic deformation of fibers and the friction between fibers and yarns within the fabric structure. The nonlinear strain of the fabric, the elastic and viscoelastic deformation of fibers, and interfiber friction during the bagging process have been taken into account in the model. By specifying the fundamental parameters of fiber mechanical properties and yarn-fabric structural features, the model is able to predict fabric bagging behavior under test conditions, such as loading and unloading processes in each cycle, change of bagging force with cycles, relative contributions of the three components (elasticity, viscoelasticity, and frictional forces) in each cycle, and residual bagging height in each cycle. A comparison of theoretical predictions with experimental measurements for two wool fabrics with different structures reveals good agreement between them. The results indicate that the mathematical model is able to quantitatively simulate fabric bagging rheological behavior and predict fabric bagging performance by specifying basic fiber mechanical properties and yarn-fabric structural parameters.

Fabric-bagging: Stress Distribution in Isotropic and Anisotropic Fabrics

The internal stress distribution of bagged fabric is studied theoretically and experimentally to investigate the influence of the stress distributions on fabric-residual-bagging deformation. A model is derived by using membrane theory to analyse the stress distributions for isotropic fabrics under different boundary conditions, including consideration of different bagging heights and the friction between the fabric sample and the steel ball deforming the fabric. The results indicate that a non-uniform distribution of meridian stress and a non-continuous distribution of hoop stress, along with bagging height, are important factors that may influence residual-bagging deformation and may cause localised damage of the fabric. To investigate the influence of fabric anisotropy on the bagging behaviour of a fabric, the stress distribution of an anisotropic fabric is studied on the basis of the measurements of tensile moduli in seven directions by using fabric strips and of the fabric strain calculated from the relation between the geometrical deformation and bagging height of a fabric. The analysis shows that a non-uniform stress distribution along the meridian direction and variation of the tensile angle θ may cause the difference in the yarn stresses between the warp and weft directions, resulting in different bagging shapes. Comparing predicted bagging forces with measured forces, it is found that the method is able to predict the trend of bagging force with some deviations.

Relative Contributions of Elasticity and Viscoelasticity of Fibres and Inter-fibre Friction in Bagging of Woven Wool Fabrics

This paper reports an investigation of the relative contributions of elasticity and viscoelasticity of fibres and inter-fibre friction to fabric-bagging behaviour of woven wool fabrics, by carrying out a series of experiments and applying a mathematical model to simulate fabric-bagging behaviour under the testing conditions. Through a large number of computation experiments, the relaxation time of the fibres, τ and three weighting coefficients (κ3, κ4, κ5) were determined for eight woven wool fabrics made from different fibres. It was found that the frictional weighting coefficient, κ5, and the relaxation time, τ are constant across all the fabrics, with κ5 = 0.1 and τ = 100 seconds. The relative contributions of the elasticity and viscoelasticity of the fibres have a narrow distribution, with average values of κ3 = 0.6 and κ4 = 0.3. These results indicate that the three weighting coefficients and the fibre-relaxation time are relatively stable and insensitive to fabric structural differences. The consistent agreement between experimental results and the mathematical simulation over a range of fabrics shows that the model is quite reliable in simulating fabric-bagging behaviour. Using the identified values of the parameters, we simulated the bagging behaviour of a new set of wool fabrics. Reasonably good agreement between simulation and experimental measurement further confirmed that the three weighting coefficients and fibre-relaxation time are relatively stable and that the identified values can be used to simulate woven-wool-fabric-bagging behaviour with reasonable accuracy.

Fabric Bagging

Part I of this series reports on the psychophysical relationship between the subjective perception of bagging and the residual bagging height. Subjective perception is mainly influenced by residual bagging height, accounting for 94% of all variations. In Part II, we investigate the physical mechanism of fabric bagging by developing an equation to describe the fatigue process as decreasing fabric internal energy. On the basis of the equation, we identify three fundamental mechanical parameters (elastic energy U, vis coelastic-frictional energy Qo, and its decay rate δ) and develop a procedure for objec tively evaluating fabric bagging using the Instron tension machine. For practical use, we select two criteria (bagging fatigue F fatig and bagging resistance Fresist) to characterize bagging behavior. As the physical stimulus to subjective perception of bagging, fabric bagging residual height depends on these mechanical parameters. Further, subjective ratings on bagging are predictable from the two criteria selected (bagging fatigue and resistance) and from the three parameters (elastic energy U, viscoelastic-frictional energy Qo, and its decay rate 8) describing the bagging fatigue process.