A cantilever effect for cracks with mismatching crack faces?

摘要

It is often assumed in alternating fatigue tests of ceramics that a cantilever effect may exist which is able to transform global compressive stresses to local crack-tip tensile stresses. Fig. I shows a typical situation which is commonly referred to in advancing simple arguments. A positive stress intensity factor resulting in positive stresses in front of the crack tip and in positive COD at the crack tip is assumed to occur during application of negative external loading as a consequence of a mismatch of the crack faces. Single grains dissolved from the bulk material during fatigue, fragments of grains, and even single molecules are sometimes considered in the literature to be responsible for such a local mismatch.