The stress–strain behavior for Al2O3of different grain size, for three different Mg‐PSZ grades, and for various differently composed duplex structures is investigated and compared with their flaw resistance,KR‐curve behavior, and thermal shock behavior measured in previous works. The experimental results seem to reveal that, for most materials, quasi ductility increases with increasing flaw resistance, increasingly pronouncedKR‐curve behavior, and increasing thermal shock retained strength. However, brittle ceramics can exhibit risingKR‐curves, whereas pronounced quasiductile materials can exhibit flatKR‐curves. An explanation for the apparent pseudo relationship between quasi ductility andKR‐curve behavior may be that, apart from genuine transformation ductility, most quasi‐ductile effects such as microcracking have only a minor contribution to risingR‐curve behavior, but require the existence of strong residual stresses, which are, on the other hand, responsible for the occurrence of most toughening mechanisms. Also discussed is the influence of microcracking on flaw resistance and thermal shock str