Mechanical performance of GFRP laminates manufactured from deformed stitched and three-dimensional woven preforms

The aim of the work is an assessment of the effect of the deformation (curvature) of reinforcing fibre preform caused by insertion into a mould on the laminate properties. The basis for the assessment is a comparison with an analogous laminate without deformation, i.e., made in a flat mould. The work includes the production of laminate panels by way of resin transfer moulding, on the basis of three types of preforms: plain woven fabric (classic), stitched plain woven fabric and three-dimensional woven fabric, as well as an evaluation of their mechanical properties in static bending tests (in the radial direction of the curved panels) and tensile tests (in the axial direction of the curved panels). The state of the laminate reinforcement structure was assessed by the means of computer tomography. The strength of the curved laminates, both in the radial and in the axial directions, is lower than in case of the equivalent flat laminates. The strength decrease proceeds together with the deformation degree. The stitched and three-dimensional laminates are much less prone to strength loss resulting from deformation than the classic laminate; they also exhibit lesser strength drops in the direction transverse to the stitch lines or the interweave strands than in the parallel direction. The curved classic laminate shows the biggest deviations of the fibre strands from rectilinearity as well as local structure anomalies, in comparison to the two other laminate types. In the curved three-dimensional laminate, the fibre strands are much more uniformly oriented than in the other two.