Mixed mode fracture toughness characterization for interface and interlayer cracks in adhesive bonded joints

An approach based on fracture mechanics was employed to assess adhesive bond failure. Two types of fracture specimens were investigated. The Brazil nut sandwich (BNS) specimen and the compact mixed mode (CMM) specimen were used to determined the fracture toughness of adhesive joints. Fracture toughness measurements for interface crack and interlayer crack specimens were investigated. Mixed mode fracture criteria for interface or interlayer cracks in adhesive bonded joints were developed. The results showed that the mode II fracture toughness generally displayed a larger value than the mode I toughness. In the case of the CMM specimen, fracture toughness for interface crack feature toughness is lower than that for a cohesive interlayer crack failure. Failure analysis diagrams were generated for both interlayer and interface crack configurations.