Journal
JOURNAL OF MATERIALS SCIENCE
Volume 47, Issue 6, Pages 2695-2699Publisher
SPRINGER
DOI: 10.1007/s10853-011-6095-2
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- Federal Ministry of Economics and Technology via the MEM-OXYCOAL [0327803]
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The temperature-dependent fracture toughness of brittle ceramics can be conveniently assessed from bending tests of specimens with defined cracks introduced by indentation. However, the validity of this indentation strength in bending method (ISM) depends critically on the correct consideration of the residual stress induced by the indentation process. The ISM has been applied to La0.58Sr0.4Co0.2Fe0.8O3-delta (LSCF) and, for comparison, on Ba0.5Sr0.5Co0.2Fe0.8O3-delta (BSCF) perovskite. LSCF with rhombohedral phase exhibits ferro-elastic behavior at ambient temperature, whereas BSCF deforms linear-elastically. Pre-indented specimens of both perovskites were fractured at room temperature in biaxial bending, some of them after an additional annealing step. The fracture toughness values of BSCF match reasonably well when determined with equations which consider the presence or absence of residual indentation stress. Interestingly, annealing has little influence on the apparent toughness results obtained for rhombohedral LSCF, which appears to be related with stress relaxation by ferro-elastic deformation.
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