Determination of interfacial bonding strength using a cantilever bending method with in situ monitoring acoustic emission

A cantilever bending method with in situ monitoring acoustic emission (AE) is proposed to determine the interfacial bonding strength of joints and coatings on microscopic level. An interface may fail under a bending force when the resultant stress normal to the interface exceeds a critical value. Micro-cracking at an interface could be determined by monitoring AE. It was demonstrated that micro-cracking might occur in the interface, accompanied with acoustic emission signals prior to the complete failure of the interface as the load was increased. The critical load corresponding to initiation of micro-cracking can be used to determine the interfacial bonding strength. However, if the ratio of the length of a specimen to its thickness was sufficiently large, false AE signals could be released due to the slip between the sample surface and the loading head that was used to apply a force to bend the specimen. It was demonstrated that the false AE signals could be identified by monitoring variations in lateral force. An Al2O3/Al alloy interface was used as an example for the present study.