Cohesive zone modelling of mesoscale thin ply bridging in CFRP composites

Fibre bridging is a phenomenon which resists crack propagation during Mode I fracture toughness (G_IC) tests of Fibre Reinforced Polymer (FRP) composite materials, causing an increased demand for energy with increasing crack extension. Ply bridging, where the entire ply locally bridges the propagating crack, has not been studied for its toughening effects. A thin Spread Tow (ST) Uni-directional (UD) tape (32 g/m²) is applied to the mid-plane of a Carbon Fibre Reinforced Polymer (CFRP) composite laminate to induce ply bridging. This stochastic generation of ply bridging increased the Mode I fracture toughness at initiation and propagation by 118.8 % and 126 % respectively, compared to the control, which is a non-ST UD interface, with an areal weight of 150 g/m². Both interfaces were modelled using a bi-linear softening law embedded in the cohesive elements during cohesive zone modelling. Excellent agreement in terms of force–displacement behaviour, peak force, crack front shapes taken from micro-CT (micro-Computed Tomography) evaluation and also crack extensions were observed. This study highlights the possibility of this phenomenon to greatly increase the fracture toughness of CFRP composites by splitting the matrix-rich interlaminar region into two smaller planes surrounding the thin ply interleaf.<br/><br/>