An investigation of matrix damage in composite laminates using continuum damage mechanics

Transverse and shear damage in the polymer matrix of fiber reinforced composites are often treated independently, while the associated cracks are similar in appearance and effect. Matrix damage is often quantified by its crack density. However, damage also can be presented as a state variable. The definition of damage state variables and their evolution laws are the foundation of continuum damage mechanics, yet experimental data for shear damage evolution is limited. The effect of crack closure on the transverse stiffness of laminates was already incorporated in the damage models. However, the shear modulus sensitivity to crack closure has received little attention due to the complicated constitutive equations. This paper focused on the in-plane shear modulus reduction due to matrix transverse cracks and the evolution of transverse and shear damage. The comparison of existing models with experimental data showed that shear damage is currently not suitably described. Accordingly, a shear damage evolution model was proposed that included the effect of internal traction and crack closure on the in-plane shear modulus. The numerical predictions of the modified shear model resulted in good agreement with experimental data by predicting the same saturation crack density, axial and shear responses. (C) 2015 Elsevier Ltd. All rights reserved.