Ansysis And Fabrication Of Knitted Fabric With Low Mechanical Hysteresis Under Large Deformation

With the rapid development of healthcare products,smart wearable devices and information technology,more and more traditional fabrics are applied to different kinds of usage,where large deformation and stable tensile property are needed.Mechanical hysteresis is one of the most important characteristics to describe the stability of mechanical property since larger hysteresis often induces less stability of the fabric.Due to looped configurations,knitted fabric has much larger deformation than others,which bring great prospects in applications.However,large deformation of the fabric usually causes transfer of yarns as well as sliding of interpoints,which make the knitted fabric difficult to return to its initial statue,resulting in poor mechanical hysteresis and unstable mechanical property.It will be of great significance to decrease mechanical hysteresis of the knitted fabric under large extension.Few studies were carried out to systematically investigate the effect on mechanical hysteresis of the knitted fabric from the aspects of the fiber material and structure of the yarn and fabric.To fill up the gaps,the current research is carried out from the following parts.(1)Through analyzing the mechanism and influential factors of mechanical hysteresis,we employed polyamide and spandex filaments as the fiber materials to discover the relationship between liner density and hysteresis.In addition to this,the influence of the structural parameters on the mechanical hysteresis of the covered yarn is studied as well.(2)Experiments were taken to select the types of knitted fabrics whose mechanical hysteresis are low from 26 knitted fabrics,and the change of loops under deformation was observed by microscope to give the reasons to this advantage.Future correlation analysis was taken of this type of knitted fabric to find the effect of structural parameters on mechanical hysteresis.(3)Fabrication of the knitted fabric with low mechanical hysteresis was taken under the control of knitting parameters.Then structural parameters and hysteresis tests were taken to evaluate the validity of former conclusions.The result shows that the mechanical hysteresis of two-thread fleecy fabric and weft insertion chain stitch fabric are about 10%,which depend on the high-elastic structure,limited yarn slippage and stable fabric structure.Compactness coefficient TF is a key factor to affect the hysteresis of two-thread fleecy fabric,and the linear relationship between them is H=7.985×TF-0.073.The following two factors that have an impact on hysteresis are stitch length and pre-stretching ratio of elastic fleecy yarns.There is a close relationship between the length of stitch and the pre-stretching ratio of elastic fleecy yarns,which indicates that the existence of elastic fleecy yarns makes great difference on the geometric statues of loops.With the increase of pre-stretching ratio of elastic fleecy yarns,the mechanical hysteresis of two-thread fleecy fabric grows as well.Mechanical hysteresis tends to accumulate and deteriorate when the fabricating process becomes more complex.The mechanical hysteresis of spandex filament is the inherent property of material,and has nothing to do with its liner density.Besides,spandex is a kind of material that are prone to aging under the condition of ultraviolet,which may cause increment of hysteresis ratio,so consideration of the storage and production should be taken to reduce the degree of aging.The cover of polyamide filament yarn leads to the deterioration of the covered yarn.In the range of 10-40 twist/cm,larger degree of coverage is good to reduce the adverse effect of cover yarn.Besides,double covered yarn is more effective to reduce the hysteresis than the single one.There is a liner correlation relationship between the liner density ratio of cover yarn and core yarn R and the mechanical hysteresis ratio H,which could be fitted as H=4.47R+3.68.It means that covered yarn with larger linear density of the core yarn and smaller linear density of the wrapping yarn could reduce mechanical hysteresis of the covered yarn.Decreasing the hysteresis of fleecy yarn and simplifying the fabricating process have a positive effect to reduce the one of two-thread fleecy fabric.In the progress of fabrication,the pre-stretching ratio of elastic fleecy yarns tends to be decreased with the feeding tension and sinking depth getting smaller.Same tendencies take place as well for fabric density and TF,while thickness and stitch length increase instead,which show an agreement with the conclusions achieved above.The mechanical hysteresis of two-thread fleecy fabric reduces with the decrease of the pre-stretching ratio of elastic fleecy yarns,but this is not unlimited,for the exceed amount of fleecy yarns will cause the instability of fabric and damage the looking of fabric surface.Fact shows that when the pre-stretching ratio of elastic fleecy yarn is more than-20%,the influence on the apparent morphology of fabric can be tolerated.The lowest mechanical hysteresis of homemade two-thread fleecy fabric is 7.49%,which achieves our target 8%,and we make a knitted fabric with low mechanical hysteresis under large deformation successfully.