Procedure for generating entangled fiber networks for numerical finite element simulation: Application to the case of needle-punching

Pseudo-unidirectional fiber networks are used in a variety of applications, such as woven fabrics and needling. A method for generating pseudo-unidirectional fiber networks by extruding linear portions of fibers is described here, and consists of two steps: $\left(i\right)$ Initially, a deliberately disorganized pseudo-unidirectional fiber network was generated geometrically from a stochastic algorithm according to the fiber volume ratio and the distribution law of the angles formed between the portions. $\left(ii\right)$ Then, the fibers were flattened and mechanically deformed using a finite element calculation until restoring the pseudo-unidirectional fiber network geometry, having stored elastic energy. Mechanical inter-fiber contact interactions were finally activated in a relaxation step to obtain a disorganized network in mechanical equilibrium. Angular deviation and migration criteria were defined to geometrically characterize the network disorder before and after mechanical rearrangement, and were shown to correlate with the algorithm’s input parameters. Finally, the generated networks were mechanically characterized using a needle-punch, quantifying the transfer fraction. The mechanisms by which the needle carried and broke the fibers are discussed, and simulations demonstrate the influence of initial network disorder on fiber transfer. The particular case of needling involves transferring fibers present in a 2D web in its transverse direction in order to increase the out-of-plane stiffness of the final product. In this case, entanglement seemed to play a decisive role, as it favored fiber transfer.