Analytical Study on the Fracture Toughness Characterization Tests of Foam Core Sandwich Specimens

This study shows two fundamental aspects related to fracture characterization of sandwich beams for aerospace application; 1) formulation of energy release rates associated with face sheet debonding or core cracking in sandwich beams with residual thermal stresses, and 2) crack kinking analysis of foam core sandwich beams. Energy release rates are formulated using the bi-layer shear deformable beam model with consideration of residual thermal stresses. This formulation is specifically applied to double cantilever beam (DCB), end notched flexure (ENF) and mixed mode bending (MMB) tests of sandwich structures. The derived analytical results are verified by comparison with finite element analysis. Next, the present formulation is applied to the prediction of crack kinking behaviors in foam core sandwich beams. It is demonstrated that overall crack kinking behaviors in foam core sandwich beams are well predicted using the present method. Some discussions on the fracture toughness measurement considering residual thermal stresses are also provided.