Viscoplastic finite element analysis of matrix crack propagation in model continuous-carbon fibre/epoxy composites

Non-linear finite element (FE) analysis was used to investigate the effect of matrix viscoplasticity in a continuous carbon fibre/epoxy composite subject to tensile loading. During fibre fracture, the sudden increase in the strain rate near the fracture location reduces matrix ductility which results in catastrophic failure involving rapid matrix crack-growth. By applying the minimum strain energy density criterion to the FE results, the semi-cone angle of a matrix crack was predicted to be in the range 32°–36°, twice the value for the corresponding short fibre system. The FE results were compared with experimental results obtained from laser Raman spectroscopy (LRS), and it was found that the fibre stress profiles are characteristic of conical matrix crack geometries. Good correlation was observed with the experimental results confirming matrix cracking as the primary mode of failure for this composite system. The energy balance model was used to determine the available strain energy to propagate the crack.