Debonding and crack kinking in foam core sandwich beams—II. Experimental investigation

Abstract Debonding and crack kinking in sandwich beams was experimentally examined, and also analyzed using the finite element method. Double cantilever beam (DCB) and shear fracture specimens employing aluminum facings bonded to a wide range of PVC and PMI foam cores using two types of adhesives were considered. It was found that the Young modulus of the core has a profound effect on the tendency of the facing/core interfacial crack to deflect (kink) into the core in DCB testing. In shear testing, crack kinking occurred for all core materials considered. The type 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 analysis of the fracture specimens enabled determination of mixed mode interfacial fracture toughness for the specimens that failed by debonding. For specimens that failed by kinking, interfacial stress intensity factors at the onset of kinking were determined. Measured kink angles compared favorably with kink angles calculated based on the interfacial stress intensity factors prior to kinking.