Stress‐Dependent Elastic Properties of Porous Microcracked Ceramics

Although ceramics are considered linear elastic materials, we have observed a non‐linear pseudo‐elastic behavior in porous cellular microcracked ceramics such as β‐eucryptite. This is attributed to the evolution of microstructure in these materials. This behavior is particularly different from that of non‐microcracked ceramics such as silicon carbide. It is shown that in microcracked materials two processes, namely stiffening and softening, always compete when a compressive external load is applied. The first regime is attributed to microcrack closure, and the second to microcracks opening, i.e. to a damage introduced by the applied stress. On the other hand rather a continuous damage is observed in the non‐microcracked case. A comparison has been done between the microscopic (as measured by neutron diffraction) and the macroscopic stress‐strain response. Also, it has been found that at constant load a significant strain relaxation occurs, which has two timescales, possibly driven by the two phenomena quoted above. Indeed, no such relaxation is observed for non‐microcracked SiC. Implications of these findings are discussed.