Initiation and evolution of transverse matrix cracks in composite laminates

Damage due to matrix cracks in a laminate with symmetric, but otherwise general laminate stacking sequence (LSS) is predicted by a novel analytical solution for the damage activation function and a return mapping algorithm to restore equilibrium upon damage. In order to use Hahn's energy criterion, the strain energy release rates in mode I and II are calculated analytically from novel expressions for the degrading stiffness of a cracking lamina embedded in a laminate. The degrading stiffness is calculated using shear lag analysis of the cracked lamina. Provision for multiple laminae damaging simultaneously under in-plane state of stress/strain is achieved by a modified return mapping algorithm. A novel definition of composite damage model (CDM)-inspired damage variables allows crack density to be used as state variable. The proposed formulation accurately predicts crack initiation, evolution, degraded stiffness, and stress redistribution.