Secondary damage modes in laminates initiated by intralaminar cracks

Damage developing within laminated composites is a result of complex combinations of thermo-mechanical and environmental loads. Intralaminar (transverse) cracking is the first mode of damage appearing. The cracks act as stress concentration locations resulting in the development of additional damage modes. These modes include fibres breakage, matrix yielding, longitudinal splitting and local delaminations. The mode of damage that will grow depends on the laminate lay-up and local statistical strength of the layers and interfaces. In the present paper the stress state in the proximity of the transverse crack tip is investigated in a Glass Fibre/Epoxy composite system. An analytical model is proposed, in which the intact layers are divided into appropriate sub-layers for the stress components calculation. Knowing the SCF value at the tip of the crack, the possibility of fibres breakage in the adjacent layer is calculated using a statistical model, while the matrix failure is examined through a matrix failure criterion. SCF is recalculated taking into account the possible local stiffness reduction due to new modes of damage and the theoretical results are correlated with experimental findings.Godkänd; 2008; 20081208 (ysko