Mode mixity and crack tip yield zones in TSD sandwich specimens with PVC foam core

In an effort to examine the relation between core fracture toughness and face/core debond toughness, fracture mechanics analysis was conducted on core and debond fracture specimens. H30, H80, H100, H200 and R400 PVC foam cores were examined. Stress intensity factors and size of the plastic zone around the crack tip in foam core Single-Edge Notch Bend (SENB), and Tilted Sandwich Debond (TSD) specimens with foam core were estimated from the elastic displacement and stress fields near the crack tip. Analysis of the influence of core thickness and crack depth on the plastic zone size was performed on TSD specimens with H 100 and R400 cores. It was found that the crack loading in the TSD specimen is essentially mode 1, and that shear loading is not a factor explaining the higher debond than core toughness. At onset of fracture, the plastic zone height in the TSD specimen is much larger than that in a corresponding foam SENB specimen. It is believed that the plastic zone enlargement is a major factor explaining the elevation of debond toughness over the core toughness.