Mode I fracture specimens exhibiting oscillatory crack migration

Damage propagation in [90/010/90]s double cantilever beam specimens, previously studied experimentally, was shown to exhibit an oscillating fracture pattern throughout the central two 90° plies. Interface delamination between 0° and 90° plies periodically migrated through the 90° plies in an oscillating manner. The experimental study showed significant toughening of the [90/010/90]s specimens when compared with a standard 0° DCB of the same material. The [90/010/90]s specimens were modeled in the present work. Damage was modeled using a Regularized eXtended-Finite Element Method to represent transverse matrix cracking and a standard interface cohesive zone method to represent interface delamination. A series of plane-strain and 3D models were produced to examine the effects of varying interfacial/ply strength and fracture toughness. 2D models qualitatively reproduced the oscillating migrating crack pattern, generally with a larger period of oscillation and lower fracture toughness. The 3D models illustrated that the oscillating migration is not responsible for the majority of toughening. Rather, it is concluded that the primary mechanism for increased toughness is a 3D, fiber bridging phenomenon as described in the experimental effort.