A Double Cantilever Beam Specimen for Foam Core Fracture Characterization

This article presents the analysis and test results for a new sandwich double cantilever beam specimen for foam fracture characterization. The foam is sandwiched between two stiff and strong aluminum adherends. The specimen is analyzed using a modified version of the classical Kanninen elastic foundation model. Finite element analysis is conducted to determine the stress state near the crack tip and compliance of the double cantilever beam sandwich specimen. Model predictions are compared to experimental compliance data and crack growth paths for double cantilever beam specimens with polyvinyl chloride and polyethersulfone foams. The elastic foundation model and finite element analysis compliance results were in close agreement with experimental data over a range of crack lengths. The experiments revealed crack kinking for double cantilever beam specimens with 25.4mm thick cores, whereas the crack path was stable in specimens with thinner (12.7 mm) cores. The distributions of T-stress ahead of the crack tip indicate crack instability for thicker cores while thinner cores promote stable growth, in agreement with experimentally observed crack paths. Hence thinner foam cores should be considered when conducting fracture testing of foam cores. An expression for the minimum admissible length of the uncracked specimen region was determined from the foundation model.