Study on Interfacial Strength between Dissimilar Materials with Micro-layered Structure

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Bonding dissimilar materials are widely used for engineering products and, hence, it is required to evaluate the reliability of those interfaces more precisely. Moreover, micro structures or layers are formed at interface. It is necessary to develop a strength law for those micro layered interfaces. The purpose of this study is to investigate parameters which govern the fracture criterion of the interface and develop the general criteria for interfacial strength for adhesive or bonding interface.First, stress singularity for multi-bonded wedge problem was discussed and the general solution for stress singularity was derived. Also, damage-based cohesive zone models were developed and the fracture criteria for interface by numerical simulation with cohesive zone model were investigated. Second, micro-structural change and its effect on interfacial strength were discussed. Interfacial oxide layers were observed and its growth model was proposed. Then, interfacial fatigue strength of lead-free solder joints after thermal aging was investigated and the relations between micro structural change and fatigue strength were discussed. The effects of ultraviolet irradiation on interfacial strength of ceramic thin film on polymer substrate were also investigated. Third, several testing methods for interfacial strength were proposed. Multi-stages peel test was proposed and applied to interfacial strength of copper thin film. Mixed mode fracture test method was proposed and applied to interfacial strength of thermal barrier coating. Testing method for MEMS thin films was also proposed. At last, non-destructive inspection method by Love wave propagation was investigated and its possibility to identify the interfacial condition was shown from both theoretical and experimental aspects.