Measurement of Elastic Properties Related to the R-Curve-Behavior of Ceramics

We measured the reduction of the elastic modulus due to material damage in Al2O3- and SiC/TiB2- ceramics occurring during steady and stable crack growth. V(z)-curves were obtained with an acoustic microscope. The results support the microcrack model assuming a formation of microcracks inside a frontal process zone around a macrocrack. From the measurements the microcrack density parameter and the size of the process zone are obtained. The increase of the crack resistance is deduced as well as the shielding effect of the microcracks around the macrocrack. However, the calculated increase of the crack resistance is about two times smaller than the measured one. For the crack resistance, it is shown that the influence of residual compressive stress must be taken into account and that wake effects play an important role as well.