Fracture Mechanics Analysis of Tilted Sandwich Debond (TSD) Specimen

Abstract

The Tilted Sandwich Debond (TSD) specimen has recently been introduced for characterization of debond fracture of foam core sandwich panels. A precracked sandwich specimen is attached to an incline, and debonding is achieved by loading the partially debonded top face until further crack propagation occurs. In this paper we present finite element analysis of several configurations of the TSD specimen, viz. a homogeneous and isotropic specimen, interface crack specimen, and sub-interface crack specimen. Stress intensity factors are determined using various mesh refinements over a range of tilt angles, and the mode mixity is related to the potential for crack deflection (kinking) into the core. Irrespective of the tilt angle, it was found that cracks located at the face/core interface displayed amode mixity favorable for kinking into the core. Experiments on a sandwich with a H100 PVC foam core revealed kinking at an angle in reasonable agreement with the prediction. After kinking, analysis of sub-interface crack configurations showed that the crack loading becomes highly mode I dominated, which indicates crack propagation parallel to the face/core interface, again in agreement with experimental observations. Fracture mechanics analysis of foam materials, based on assumption of homogeneous material, however, becomes questionable when the singular domain becomes comparable to the cell size of the foam.