Testing and modeling of yarn pull-out in plain woven Kevlar fabrics

Yarn pull-out behavior of five styles of plain woven Kevlar fabrics, K310, K706, K720, K745 and K779 from Hexcel, was studied. These fabrics were different in fabric count, yarn size, fiber type, thickness and weight. Single yarn pull-out tests showed that the pull-out forces of the five styles of fabrics differ substantially. The yarn pull-out force was found to have positive correlation to the impact performance: fabrics with higher pull-out force performed better in impact tests. A 2D finite element model was proposed to simulate the single yarn pull-out procedure and predict the maximum pull-out force. Several factors were considered in this model: fabric count, yarn size, yarn waviness, fiber modulus, fiber diameter, cross-yarn friction, parallel-fiber friction. The predicted peak pull-out forces showed good agreement with the experimental results. Finally a simple formula was proposed to estimate the yarn pull-out force as a function of fabric count, fiber diameter, fiber modulus, yarn waviness and friction.