COUPON SCALE MODELLING OF THE BRIDGING MECHANICS OF HIGH-RATE LOADED Z-PINS

This work presents an advanced finite element model that can be used to investigate and understand the high-loading-rate bridging mechanisms of z-pins. A group of ply-level meshes are used to consider the microstructures of z-pin array reinforced laminates. Resin matrix is described by an elasto-plastic model that is dependent on both hydrostatic pressure and loading rate. The interface between the z-pin and the laminate is described by a coupled cohesive and friction contact algorithm; a friction term is added on top of Coulomb friction to consider the singularities and roughness of z-pin and hole surfaces, which are difficult to mesh out by finite elements. To improve computational efficiency, each z-pin is described by a homogenised mesh and a nonlinear shear constitutive law to account for the variation of z-pin bending stiffness due to splitting. Rupture of z-pin is described by the maximum tensile stress criterion with the tensile strength described by the Weibull criterion. The model was preliminarily applied to simulate the mode I high rate bridging behaviour of a 4 × 4 T300/BMI composite z-pin array when inserted in a quasi isotropic laminate. The numerical model has successfully captured z-pin/laminte debonding and frictional pullout.