The effect of blank holder force on the stamp forming behavior of non-crimp fabric with a chain stitch

摘要

A blank holder force (BHF) is applied to a fabric preform in stamp forming operations to impose a tension onto it, which helps to reduce the occurrence of defects such as wrinkles. The current study aims to quantitatively investigate BHF's effect on formed shapes by carrying out a stamp forming operation on non-crimp fabrics with various BHFs. A non-crimp fabric (NCF) with chain stitches was used as the fabric preform. The NCF exhibits asymmetrical shear behavior due to its stitches, which can be confirmed from a picture frame test. This asymmetrical shear behavior causes NCFs to be formed into asymmetrical shapes when stamped by a symmetrically spherical forming tool. The asymmetrical forming behavior was scrutinized using various BHFs and measuring the local change in fiber angle along the formed parts' arc lines. It was observed that BHF lessens the formed shape's asymmetry and influences the NCF's in-plane buckling and wrinkling behavior. The BHF's effect on wrinkling behavior was quantitatively characterized using an image processing method that can assess a fabric preform's wrinkling level. Finally, using these experiments and simulations, we discuss the feasibility of finding the optimized forming condition that can process the NCF preform into complex shapes with few or no wrinkles.