Interfacial mode, damage

Yasaee M, Bond LP, Trask RS, Greenhalgh ES. Mode II interfacial toughening through discontinuous interleaves for damage suppression and control. Compos Part A Appl Sci Manuf 2012 43 121-8. http //dx.doi.Org/10.1016/j.compositesa.2011.09.026. 

The durability of the bonded joints was greatly influenced by the nature of the adhesive the best performers in all climates were epoxy-novolak and nitrile-phenolic formulations. A tropical, hot-wet climate was the most damaging to bonded stmctures and the combination of high humidity and applied stress was particularly deleterious. During exposure to natural environments, the failure mode of aluminium joints was found to change gradually from wholly cohesive, within the adhesive, to include increasing amounts of interfacial failure (see Stress distribution mode of failure). 

In a properly made solder joint, the solder should always be the weakest link, deforming to relieve stresses so they are not transmitted beyond the terminal pads on either side of the joint. Additionally, this is the preferred failure mode because solder fails due to the accumulation of plastic strain damage and the failure behavior can be modeled and predicted. That is, the interfaces in a proper solder joint fail when the interfacial strength is degraded due to any number of mechanisms such as a phase change, impurities, void accumulation, etc. If the interfacial strength is reduced below the applied stress, the interface fails. This type of failure mode is more difficult to model and predict compared to the accumulation of plastic strain damage in the bulk solder. 

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