Critical evaluation of SEVNP-method to measure fracture toughness of ceramic thin plates

Abstract

The fracture toughness of ceramic substrates made of alumina, ZTA and silicon nitride was determined using the single edge V-notched plate method. In order to make a statement about the measurement precision, not only 5, as required by the standard, but 30 specimens per material type were tested. In addition, a much more practical and less error-prone holding and testing device for the ceramic plates was used, which is presented in the paper. For all materials, including the comparatively fine-grained ZTA, the material-typical KIc values could be determined. However, the range of variation of the measured values is comparatively high with coefficients of variance up to 7.8 %. It is shown that a standard-compliant test on Al2O3 substrates can exhibit a fluctuation range of 0.5 MPa m0.5 without the material showing any differences. It is important to be aware of this when using the method. Especially for quality assurance, where deviations in the range of a few tenths of MPa∙m0.5 are considered problematic, the method should therefore be regarded as critical. An increase in the number of specimens should be considered, as well as the inclusion of a statement on the precision of the measurement method in the standard.