Characterisation of the inter-ply sliding of biaxial non-crimp fabrics during the double diaphragm forming process

An experimental method for quantifying inter-fabric sliding for a ± 45° biaxial NCF in the double diaphragm forming (DDF) process is introduced. The approach employs grease markers with a standardised application and tracking procedure, ensuring consistency. An overlap experiment confirmed that the addition of markers had minimal influence on inter-fabric friction, enabling calibration between the marker elongation length and the actual sliding distance. The method reliably captured sliding when displacements exceeded 3.5 mm in the DDF experiments with different tool geometries. Comparisons with macroscale FE-based simulation results showed agreement in sliding directions, although the magnitudes were numerically underestimated. The discrepancies highlight both experimental and modelling limitations. The proposed method offers a robust tool for investigating the direction of inter-fabric motion, advancing the study of inter-ply friction and guiding the optimisation of forming simulations.