Damage Behaviour of Ncf Carbon / Epoxy Laminates Under Tension

Composites reinforced by non-crimp fabrics (NCF) reach stiffness level close to the ideal cross-ply laminates with unidirectional plies, but damage behaviour of NCF-composites exhibit significant differences from the behaviour of the laminates with unidirectional plies(non-stitched laminates). The paper presents results of experimental studies of the initiation and development of damage in NCF-composites. Some of the observed phenomena can be explained and predicted using FE modelling of the composite deformation. Others are difficult to explain; they present a challenge for understanding the behaviour of NCF-composites. The materials are carbon/epoxy composites, reinforced by biaxial NCF 0°/90° and ±45°. Two different sets of fabrics (different producers) were used for the reinforcement, and the fibre volume fraction of the plates had two different levels: about 45% and about 55%. The samples were loaded in different directions in tension. Damage initiation and development was studied using acoustic emission and X-ray investigation.