No abstract

Deformation tests combined with modern in situ acoustic emission (AE) and digital image correlation (DIC) techniques were applied to monitor low strain rate compressive behavior of illite‐based ceramics with controlled porosity (P). A strong effect of porosity on the mechanical performance was observed: Young's modulus decreased linearly from 29.4 ± 1.1 GPa (P = 14 vol%) to 3.0 ± 0.5 GPa (P = 55 vol%) and compressive strength decreased from 307 ± 13.6 MPa (P = 14 vol%) to 27.7 ± 1.0 MPa (P = 55 vol%). The AE and DIC techniques revealed a transition from brittle fracture to gradual localized crushing with increasing porosity. The AE signals possessed high‐energy burst‐like characteristics typical of brittle fracture and (micro)cracking. The AE data showed continuous activity from the beginning of loading, suggesting that true elasticity does not occur in this material. The combination of mechanical tests with in situ techniques, therefore, proved to be particularly effective in providing additional information on the deformation dynamics in ceramics.

The effect of elastic anisotropy on thermal diffusivity determination by transient grating spectroscopy (TGS) was studied. In experiments performed on a set of cubic single crystals, it was observed that TGS measurements may indicate anisotropy of thermal diffusivity in otherwise thermally isotropic materials, and that the strength of this apparent anisotropy is correlated with the strength of the elastic anisotropy. To find a source of the observed phenomenon, finite-element simulations of the TGS measurements were carried out. Time-domain TGS signals were generated from the simulations and processed identically to the experimental data. The simulation results revealed that the elastic anisotropy affects the detected time-domain signals. Consequently, the thermal diffusivity coefficients determined from them showed the artificial directional dependence. For the chosen set of cubic crystals, ranging from nearly isotropic to strongly anisotropic in terms of elastic constants, this simulated directional dependence was in full agreement with the one observed in the experiments.