The force-displacement curves of all notched bending tests show a similar trend (FIGURE ). First, there is a linear phase where the material deforms elastically. It is followed by a non-linear behaviour, where the load continues to increase with the displacement, but with a more irregular curve, sometimes with sudden small drops in load; this is due to the stable propagation of a crack in the specimen. Then the specimens break completely. AP ng compositions, with glass phase and alumina nanoparticles, seem to show a longer nonlinear phase. The curves in FIGURE have been normalized in load and displacement from the point where the curve leaves the elastic regime. Finally, these curves show that each sample presents reinforcement during crack propagation, a typical behaviour of nacre-like aluminas. Fracture properties, strength and toughness at initiation, vary greatly with the composition but also with the sintering cycle (FIGURE ). For samples prepared with a standard sintering cycle (maximum pressure of 40 MPa), the properties are better for AP ng compositions containing glass phase and alumina nanoparticules than for AP compositions. The zirconia-free sample AP and the sample with monoclinic zirconia AP-Zm have similar properties, i.e. an initation toughness of 3.7 ± 0.3 MPa.m 0.5 and 3.2 ± 0.3 MPa.m 0.5 , respectively, and a low strength of 144 ± 14 MPa and 85 ± 4 MPa, respectively. The AP-Zt specimen, although without glass phase and with the same sintering cycle, show higher properties with a KJ 0 of 5.5 ± 0.8 MPa.m 0.5 and a strength of 230 ± 62 MPa. The AP-Zt-HP specimen, with the same composition as AP-Zt but sintered at a higher maximum pressure of 80 MPa, has higher properties, with a KJ 0 of 6.6 ± 1.0 MPa.m 0.5 and a strength of 367 ± 55 MPa. For compositions with glass phase and alumina nano-particles, the zirconia-free sample AP ng and the sample with monoclinic zirconia AP ng -Zm have also similar properties; a KJ 0 of 6.4 ± 0.2 MPa.m 0.5 and 6.1 ± 0.6 MPa.m 0.5 , respectively, and a strength of 422 ± 48 MPa and 415 ± 29 MPa, respectively. When tetragonal zirconia is present (AP ng -Zt), the initation toughness is slightly lower, about 5.5 ± 0.8 MPa.m 0.5 , but the strength is 626 ± 39 MPa, i.e. about 50% higher. These differences in mechanical properties could be explained by different factors, in particular the differences in density between the samples, but also their microstructure. First of all, the sample relative densities of AP, AP-Zm and AP-Zt, around 93%, are clearly below the relative densities of AP ng , AP ng -Zm and AP ng -Zt, around 99% (TABLE ). For AP ng compositions, the alumina nanoparticles and the glass phase help the densification of the material. Moreover, when a higher pressure is applied during sintering of the sample without nanoparticles and glass phase, it shows the same relative density of composition with glass phase (99% for AP-Zt-HP), the increase in pressure improving the densification as compared to AP-Zt (TABLE ).