The energy of interface adhesion between two elastic-plastic materials was directly evaluated as the mechanical work supplied exclusively to separate the interface. Interface crack extension was simulated by elastic plastic finite element models, where the nodes along the interface in the vicinity of crack tip were divided into two nodes and the nodal forces were gradually decreased to zero. While further plastic deformation takes place in the volume of materials during crack extension, the work done by these nodal forces against mutual displacement of crack surfaces should be consumed on the surfaces and thus equals to the interface adhesion energy. This technique was applied to a copper/polyimide system for flexible printed circuits in accordance with the new experimental results. In comparison to the results obtained by the conventional peel test, this technique yielded far smaller amount of interface energy successfully excluding the energy dissipated with bulk plastic deformation without any insertion of cohesive strip along the interface in the model.
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