DEBONDING AND CRACK KINKING IN FOAM CORE SANDWICH BEAMS .2. EXPERIMENTAL INVESTIGATION

Debonding and crack kinking in sandwich beams was experimentally exami ned, and also analyzed using the finite element method. Double cantile ver beam (DCB) and shear fracture specimens employing aluminum facings bonded to a wide range of PVC and PMI foam cores using two types of a dhesives were considered. It was found that the Young modulus of the c ore has a profound effect on the tendency of the facing/core interfaci al crack to deflect (kink) into the core in DCB testing. In shear test ing, crack kinking occurred for all core materials considered. The typ e of adhesive strongly influences the debond fracture resistance, but not the kink resistance and kink angle. The critical load for onset of kinking increased with increased core density. Finite element analysi s of the fracture specimens enabled determination of mixed mode interf acial fracture toughness for the specimens that failed by debonding. F or specimens that failed by kinking, interfacial stress intensity fact ors at the onset of kinking were determined. Measured kink angles comp ared favorably with kink angles calculated based on the interfacial st ress intensity factors prior to kinking.