Indirect estimation of critical frontal process-zone size using a single-edge V-notched-beam technique

The size of the frontal process-zone at the crack tip of ceramics is an important factor to assess the toughening mechanisms operative in the material. An indirect technique is proposed here to estimate the critical size of the frontal process zone in ceramics using a single-edge Y-notched beam (SEVNB) method. A three-point flexure test was carried out on alumina specimens containing a sharp V-shaped notch whose depth was varied. Then, a critical local stress was calculated at a critical distance from the notch tip. The frontal process-zone size at the beginning of crack propagation, namely, the critical frontal process-zone size, was determined as the distance between the notch tip and the point where the critical local stress has the same value as the flexural strength of the specimen. This concept is based on a local fracture criterion. The calculated critical frontal process-zone size of alumina ceramics was 11.4 mum based on the linear elasticity, and 22.8 mum based on the Dugdale model.