Efficient finite element modelling of Z-pin reinforced composites using the binary model

Z-Pins are employed in reinforcing pre-preg composite laminates in the through-thickness direction. Z-pins provide a resistance to crack opening in mode I through a tri-linear process involving elastic stretching, interface debonding and frictional pullout. The effective crack closure force provided by z-pins subsequently improves the delamination resistance of the material. The major challenges associated with the modelling of z-pin reinforced laminates are attributed to the complexity of the material structure, where relatively small diameter pins are inserted into an orthogonal laminate. Meshing of each z-pin and its interaction with the laminate requires an inordinate number of finite elements and detailed, highly localised material properties. This study investigates the feasibility of the computationally efficient binary model for textile composites in modelling z-pin reinforced composite laminates. In the model, each z-pin is represented by a single one-dimensional truss element that is embedded within the composite laminate. Each truss is given the material properties associated with the global traction response of a z-pin inserted in a laminate. This simplification results in a reduction in the number of degrees of freedom by potentially orders of magnitude. Initial results obtained for double cantilever beam test specimens, for a range of volume fraction of z-pins, demonstrate the ability of the model to rapidly generate z-pin reinforced laminates with a variety of pin sizes, volume fractions, locations and orientations.