Prediction of Damage Zone Growth in Composites Using Continuum Damage Mechanics

The continuum damage mechanics (CDM) approach is widely used to model damage in polymer matrix composite materials which are represented using the homogenized properties of the fiber and matrix constituents. CDM simplifies the problem of accounting for a large number of defects in a material by considering the homogenized effect of the defects as a change in constitutive properties of the material. However, recent investigations of textile composites have shown that CDM inaccurately predicts the direction of damage zone growth for some composite architectures which fail under shear load, tending to predict failure transverse to the fibers. This behavior is fundamentally attributable to the fact that shear failure in textiles results in large (tow-scale) matrix cracks, while CDM is intended to model distributed micro-cracks. It is shown that when CDM is used to model shear failure in anisotropic continua, material anisotropy tends to cause CDM to predict failure contrary to what is expected for these structures. An approach is presented that may allow CDM to better predict damage growth for shear failure in composites by encouraging the creation of an intial damage zone with sufficient directional bias to overcome the effect of material anisotropy.