Observations of wrinkling in Non-Crimp Fabrics during multi-ply stack forming using in situ XCT scanning

Abstract

This paper shows the internal evolution of wrinkles occurring in a single diaphragm forming process using time-resolved in situ XCT scanning. Forming trials were carried out over a curved C-spar geometry using Non-Crimp Fabric (NCF) plies of 45°/135°, 0°/90° and 0°/45° orientations arranged in single-orientation and mixed-orientation stacks. Results show most of the diaphragm movement and change in wrinkle size, shape, and location occurs in the early application (<0.1 bar) of vacuum. The further application of vacuum shows consolidation, with wrinkle size decreasing but shape and location remaining largely unchanged. Single-orientation stacks of 45°/135° plies showed the closest resemblance between initial and final wrinkling, while mixed-orientation stacks showed complex wrinkling due to the 0° plies creating internal ply separation due to excess length. Overall, the study shines a light on the internal interaction between layers that occurs during wrinkling, showing mechanisms only observable with XCT.