Fracture of anisotropic materials with plastic strain-gradient effects

A unit cell is adopted to numerically analyze the effect of plastic anisotropy on frac-ture evolution in a micro-reinforced fiber-composite. The matrix material exhibit size-effects and an anisotropic strain-gradient plasticity model accounting for such size-effects through a mate-rial length scale parameter is adopted. The fracture process along the fiber-matrix interface is modeled using a recently proposed cohesive law extension having an additional material length parameter. Due to the fiber-matrix fracture a sudden stress-drop is seen in the macroscopic stress-strain response which defines the failure strain of the composite. The effect of the two material length parameters on the failure strain of the composite is studied. For small values of the material length scale parameter conventional predictions are obtained. Larger values of the material length scale parameter result in corresponding larger failure strains, but only up to a material length scale parameter approximately equal to 15% of the reinforcement size. At this point, the failure strain becomes smaller again for further increasing values of the material length scale. It is shown that the cohesive length parameter monotonically affects the failure strain as a decreasing failure strain is predicted for smaller value of the material parameter.