Fracture Toughness of Ceramics Using the SEVNB Method: First Results of a Joint VAMAS/ESIS Round Robin

Abstract

Fracture toughness was measured on five ceramics by the Single Edge V-Notched Beam (SEVNB) method in a joint VAMAS / ESIS round robin with over 30 participants. The method measures the fracture toughness for a notch smaller than 30 μm. To date, very consistent results have been obtained for a cold pressed alumina-998 with KIc3.57 ±0.22 MPa √m and a gas-pressure sintered silicon nitride (GPSSN) with KIc 5.35 ± 0.33 MPa √m. (The tests for the remaining three materials in the round robin are still being evaluated.) In the round robin the within-lab repeatability coefficient of variation for the alumina-998 was 4.6 % and the between-lab reproducibility coefficient of variation 6.1 %. For the GPSSN the results were 5.3 % and 6.3 %, respectively. Contrary to the alumina-998, the fracture toughness measured for the GPSSN with the SEVNB method compared well with values from the SEPB, CN and SCF methods. The reason for the lack of agreement found for the alumina-998 is not clear yet. In general, the polishing procedure worked well for both materials and most participants were able to polish V-notches with a width smaller than 30 μm. At least for these two ceramics, the SEVNB method proved to be user-friendly and easy to conduct and therefore might be a potential standard test method. However, final conclusions can not be made before the results of all five ceramics used in the round robin are analysed and understood.