Mechanical Property
Energy required to propagate a crack along the boundary between two dissimilar materials quantifies the bond strength of a composite or a coated system. Interfacial fracture toughness represents the critical value of the energy release rate at which delamination occurs, provided the crack remains at the junction.
Measurement Method
Testing involves loading a specimen in a double cantilever beam or a four point bend configuration to induce separation at the junction. The interfacial fracture toughness is calculated by monitoring the applied load and the resulting crack length. Friction between the two surfaces and plastic deformation near the crack tip can inflate the measured value.
Environmental Sensitivity
Exposure to moisture or elevated temperatures often degrades the chemical bonds at the interface. Bond integrity in epoxy to copper systems is verified through environmental aging tests where the specimen is subjected to high humidity. This ensures that the interfacial fracture toughness remains sufficient to survive the thermal stresses of reflow soldering without internal separation.
Failure Threshold
Design thresholds are established by comparing the calculated stress intensity factors against the measured material capacity. Because interfacial fracture toughness depends on the mode mixity of the loading, a single value is rarely sufficient for complex geometries.
