Study to Uncover the Microstructural Basis for the Intrinsic Toughness of Interfaces and Its Relation to the Plastic Work That Accompanies Interface

摘要

A fundamental relationship between intrinsic and total toughness of tantalum/sapphire, Al/epoxy, and Si/epoxy joints is established using several novel interface characterization tools. The focus of research was to understand issues related to size effects, energy absorption capacity, and reliability, of joints. A double cantilever beam experiment equipped with a cryogenic cell, and a lasergenerated stress wave technique was used to measure the strength and toughness of interfaces, respectively. Although not part of the original proposal, experimental procedures to determine interfacial moisture content were established and then related to the measured interface strength. This was demonstrated for a polymer/nitride interface. This allows quantitative prediction of the durability of epoxy joints in service. The experimental procedures are general and applicable to epoxy/Al joints of direct interest to the Army. In addition, a novel application of laser-generated stress waves was developed which involved their use in releasing stiction in MEMS devices. Finally, during the execution of the above research objectives, discovery of glass modified stress waves with rarefaction shocks was made. The technological importance of such waves in measuring the interfacial tensile strength of ultrathin films was demonstrated. The ability of the glass to modify the rise time of the stress pulse from 1-2 ns to almost 50 ns points to an interesting effect that is worthy of further inquiry for defeating shock fronts for the purposes of designing armors.