Microscopic investigation of tow geometry of a dry satin weave fabric during deformation

In this paper the changes in tow geometry during deformation of dry woven carbon-fibre satin-weave fabric are measured and correlated with the in-plane forces applied. The evolution of geometric tow parameters such as tow spacing, crimp angle, tow amplitude and wavelength is investigated. To observe the change in the fabric architecture, specimens from bias extension, biaxial and picture frame tests are sectioned and observed under the microscope. It is found that the different loading conditions cause differences in the evolution of tow architecture during deformation, in particular affecting the onset of ‘lock-up’. (At lock-up interactions between tows prevent further significant shear deformation.) In one picture frame test the fabric is deliberately misaligned with respect to the sides of the frame so that, during subsequent deformation, one set of tows is under tension, while the other is compressed. There is a significant difference in behaviour between the two sets of tows. The variation in deformed tow geometry with shear angle is fitted using a simple parametric model.