Abstract
We measured the reduction of the elastic modulus due to material damage in Al_2O3-and SiC/TiB_2- ceramics occurring during steady and stable crack growth by exploiting so-called V(z)-curves obtained with a scanning 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 contribution of the microcracks to the crack resistance is deduced as well as the their shielding effect around the macrocrack. However, the calculated increase of the crack resistance is about twice smaller than the measured one. For the prediction of 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.
