Oscillating Crack Migration in Mode I Fracture Specimens

Abstract

Damage propagation in [90°/0°10/90°]s double cantilever beam (DCB) specimens, previously studied experimentally, was shown to exhibit an oscillating, trapezoidal fracture pattern throughout the central two 90° plies. Interface delamination between 0° and 90° plies tended to periodically migrate through the 90° plies, producing the oscillating damage pattern. Additionally, the experimental study showed significant toughening of the [90°/0°10/90°]s DCB specimens when compared with a standard 0° DCB of the same material. Both standard 0° and [90°/0°10/90°]s DCB specimens were modeled in the present work. Damage was modeled using a regularized formulation of the eXtended-Finite Element Method (Rx-FEM) to represent transverse matrix cracking and a standard interface cohesive zone method to represent interface delamination. A series of plane-strain models were produced to examine the effects of interfacial ply strength and fracture toughness properties. Qualitatively, the oscillating migrating crack pattern was reproduced. However, in all cases the spacing of the crack migrations was larger than observed. Additionally, the large toughening region observed experimentally was not reproduced. Of the various cases examined, it was found that increasing interfacial Mode I fracture toughness and reducing load step size decreased migration spacing the most effectively. Slight increases in toughness were observed, however, it is concluded that the primary mechanism for increased toughness is a 3D, fiber bridging phenomenon as described in the experimental effort.