Intra-ply shear locking in finite element analyses of woven fabric forming processes

This study was motivated by the observation of physically unrealistic wrinkles, named spurious wrinkles, seen in finite element simulations of diaphragm forming of woven fabrics. Essential intra-ply shear modes for 4-node and 3-node shell elements were investigated. When these essential modes, which show dependency on mesh orientations, are not fully implemented, the stiffness of an element may be overestimated. The phenomenon is termed intra-ply shear locking. It explains the spurious wrinkles in the forming simulations. A simple remedy, based on aligned meshes, is suggested to eliminate the locking problem. The effectiveness of the remedy is demonstrated by simulations of small patches, a bias extension test and diaphragm forming of a 3-ply simple cup.