Preform variability propagation in non-crimp fabric (NCF) forming

Eliminating wrinkles generated during the manufacturing of structures made from composite materials is challenging due to large material and process variabilities. In this work, an effort is made to quantify the wrinkling variability when forming dry non-crimp fabric (NCF) and to correlate this with measured material (and process) variabilities. A forming cell instrumented with a multi-camera 3D digital image correlation (DIC) system was built to enable precise reconstruction of the morphology of the formed 3D preforms and any wrinkles that occur. Quantification of wrinkles and their variability was conducted and their (lack of) correlation with the NCF material's macro-scale shear and bending behaviour was analysed. Meso-scale material and process variabilities were also measured and quantified. This was followed by a sensitivity analysis on their effect on wrinkling variability and highlighted the prime importance of tow-orientation and fabric pre-shear. This work deepens the understanding of NCF wrinkling behaviour and open the door to the development of more accurate modelling tools and digital twin systems that can help robustly eliminate wrinkles. • A multi-camera 3D DIC system is developed to study wrinkling in NCF forming. • Material variability of NCF is classified and measured. • Wrinkling in bias-extension and forming tests are quantified and statistically analysed. • Correlation between material variability and wrinkle variability is established.