Indentation crack profiles of cordierite materials under mechanical and thermal biaxial stresses

The indentation crack profiles under mechanical and thermal stresses of cordierite materials obtained from a commercial powder were studied. Disks were prepared by slip casting and sintering, and they were indented (Vickers; 44.1 N; 15 s) at the center of one of their surfaces to be subjected to flexion in the mechanical test or to a sudden temperature change in the thermal shock test. Indented specimens were fractured in biaxial flexure (BF) or thermal shock (TS) tests. Some indented disks were thermally treated following two different schedules that involve exposures at high temperatures without (T1) and with a sudden cooling (T2). These specimens were fractured in biaxial flexure to observe the fracture surfaces. In all specimens (BF, TS, T1 and T2), the evolution of the indentation crack profiles was fractographically analyzed by SEM. In order to study the crack shape and the profile evolution, both the length and the depth of the indentation cracks were measured.