Mechanical properties of knitted fabrics under uniaxial and strip biaxial extension as estimated by a linearizing method

To check the application limit of the linearizing method by Kawabata et al. to fabrics, four knitted fabrics are used to study the deformation mode under strip biaxial extension (corresponding to uniaxial extension with the fixed dimension in the direction perpendicular to stretching). More detailed analysis than their treatment is proposed to check the application limit in terms of Hook's law. The treatment is done in the rectangular coordinate system rotated by an arbitrary angle theta from the coordinate system along the principal structural axis direction. Of the four knits, two are chosen mainly to pursue a detailed analysis of the application limit. One is a typical knit with simple symmetrical deformation of threads, and the other has a more complicated deformation. For the first, the predicted results of load (stress) versus strain associated with Hook's law agree well with the experimental results, while for the latter fabric, the results are poor. The same tendency is also confirmed for the uniaxial deformation mode with the dimension free in the direction perpendicular to stretching. Good agreement for the different extension modes is due to the symmetrical mechanical properties of the former fabric, while the poor agreement is due to the strong nonlinearity and considerable mechanical anisotropy of the latter fabric.