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Fatigue crack closure concept has been used to extend fatigue life of cracked
components via slowing down or halting crack propagation by introducing a
variety of artificial closure materials into the crack. This necessitated the
consideration of deformation characteristics of the closure materials. The
previously proposed elastic wedge closure model along with a modified partial
crack closure concept was briefly reviewed. The elastic wedge model was then
extended to integrate with the plastic deformation characteristics of the wedge
based on the Ramberg-Osgood type relationship. The occurrence of wedge
plasticity was observed to cause a non-linear concave variation in the applied
stress-crack opening displacement (COD) response and the slope became
smaller in comparison with the elastic wedge. This resulted in a greater
effective stress range Δσeff due to a larger COD range experienced by the
fatigue crack tip for a given cyclic loading condition.