Dynamic fracture of idealized fiber-reinforced materials

Dynamic plane stress of sheets composed of two orthogonal families of inextensible fibers, with infinitesimal elastic shearing stress response, is considered. The fibers through the tip of a propagating tear or crack carry finite forces. Fracture criteria that can be expressed in terms of these tip forces are discussed. In a particular example it is shown that the maximum energy release rate criterion leads to a circular crack trajectory, while the so-called critical force and critical stress criteria imply that the crack is L-shaped, like cracks or tears in real fibrous materials.