ISO 21618:2019 Fine ceramics (advanced ceramics, advanced technical ceramics)一Test method for fracture resistance of monolithic ceramics at room temperature by indentation fracture (IF) method

ISO 21618:2019 Fine ceramics (advanced ceramics, advanced technical ceramics)一Test method for fracture resistance of monolithic ceramics at room temperature by indentation fracture (IF) method. 5 Apparatus 5.1 Testing machine The testing machine shall be in accordance with ISO 6507-2. A suitable testing machine capable of applying an indentation force of 49,03 N up to 196,1 N shall be used. 5.2 Indenter The indenter shall meet the specification for Vickers indenters. See test method ISO 6507-2. The diamond should be examined before the test, and if it is loose in the mounting material, chipped or cracked it shall be replaced. 5.3 Verification by standard reference materials The reference materials which are in accordance with ISO 6507-3 shall be used to verify the testing machine and their Vickers hardness shall not vary from the hardness of the material to be measured by more than 20 %. 5.4 Metallurgical microscope or travelling microscope The metallurgical microscope equipped with calibrated stage movement or the travelling microscope shall be employed for both detection of the crack tips and measurement of the crack length. The magnification of the objective lens shall be 40 x or 50 x and the total magnification shall be 400 x or more. The travelling stage shall move both vertically and horizontally and the readout resolution of the table position shall be 1 pm or less. The coaxial vertical illumination with enough light intensity shall be used for the observation of the crack tips. 6 Test specimen 6.1 Thickness The thickness of the specimen shall be large enough so that the crack lengths are not affected by variations in the thickness. As long as the thickness of the specimen is more than five times the crack length (2c), the test will not be affected. In general, a specimen thickness of more than 3 mm is suitable. 6.2 Surface finish Specimens shall have a ground and polished surface so that the crack lengths can be measured accurately. The surface roughness, Ra, as defined in ISO 4287, shall be not more than 0,1 pm. Any grinding-induced damage layer at the surface shall be removed completely by polishing so that the crack lengths are not affected by any residual stress at the surface layer. The area fraction of tiny pits due to dropout of a grain or fragmentation shall be as small as possible to enable the precious crack- length measurement. NOTE Annex A provides...