Analysis of multiple off-axis ply cracks in composite laminates

This paper presents a synergistic methodology to analyze damage behavior in composite laminates with transverse matrix cracks in plies of multiple orientations. The approach combines the strengths of micro-damage mechanics (MDM) and continuum damage mechanics (CDM) in predicting the stiffness degradation due to presence of transverse cracks. The micromechanics is performed on a representative unit cell using a three-dimensional finite element analysis to calculate the crack opening displacement (COD) accounting for the influence of the surrounding plies, the so-called constraint effect. This information is then incorporated in the CDM formulation dealing with laminates containing cracks in different ply orientations through a ‘constraint parameter’. In CDM, a separate damage mode is defined for each type of crack and the expressions for engineering moduli of the damaged laminate are derived in terms of crack density and the constraint parameter. The COD and stiffness degradation predictions agree well with published experimental data for [0/±θ4/01/2]s[0/±θ4/01/2]s laminate configuration. To enable damage analysis of other configurations of [0m/±θn/0m/2]s[0m/±θn/0m/2]s laminate, a parametric study of the CODs is performed and using the computations a master equation is developed.