Evaluation of the three-dimensional region around a crack tip by caustics

摘要

A study of the extent of the three-dimensionalregion around the border of a straight though-crack in mode-Iloading was undertaken by the method of caustics. A series ofexperiments were performed in single edge-notched specimensmade of PMMA (Plexiglas). It was found that the state of stressvery close to the crack tip can be approximated as plane strain.Following this region, three-dimensional stress conditions holdin the neighborhood of the crack tip, up to a critical distancewhich depend on the thickness of the plate and the crack length.Beyond this critical distance plane stress conditions dominate.Results were obtained for the extent of the three-dimensionalregion as a function of the specimen thickness. The presentinvestigation illuminates the complicated problem of thechanging state of stress around cracks and establishes the limitsof applicability of the method of caustics for the determinationstress intensity factors.