An experimental study and analysis of the geometrical properties of mesoscopic buckle defects

This study investigates the shape and other geometrical features of out-of-plane buckle defects in woven-glass fabrics. A dedicated laboratory device, operated according to a specific protocol, was developed to create calibrated buckle defects under optimal conditions. Several plain-woven fabric samples were prepared by gradually adjusting the device to deform glass fabric specimens, increasing the shear angle in the lateral regions of the buckling defect zone to generate different buckle amplitudes. The geometry of the deformed specimens was extensively characterised at the mesoscopic level using 3D surface scanning and 3D X-ray tomography. To this end, comprehensive data on the geometric properties of the yarns on both sides of the deformed reinforcements were extracted and analysed. The results reveal significant changes in yarn geometry, such as changes in the ellipticity parameters, with decreases up to 30 % in the major axis and increases up to 28 % in the minor axis and decreases up to 10 % in the yarn cross-sectional area. Additionally, the variation in geometric properties emphasises that tooling contact plays a crucial role in shaping the buckled yarn and deciding its out-of-plane rotation, which ultimately influences the performance of the composite.