ISO 21712:2020 Fine ceramics (advanced ceramics, advanced technical ceramics) — Test method for flexural bond strength of ceramics.
5.1 Testing machine
A suitable testing machine capable or applying a unitorm crosshead speed shall be usea. The testing machine shall have the function for recording the peak load applied to the test specimen. The testing machine shall fulfil the requirements of ISO 7500-1, Class 1, with an accuracy of 1 % of the indicated load at fracture.
5.2 Test fixture
The test adopts four-point flexure configurations, as illustrated in Figure 1. The four-point 1/4 point configuration is recommended. The fixture shall have bearings that are free to roll, as described in 5.2.2, in order to eliminate frictional constraints when the specimen surfaces expand or contract during loading. In addition, the fixture shall he designed so that it can articulate or tilt to ensure uniform loading to the specimen. The articulation is designed so that bearing parts of the fixture can rotate, as shown in ISO 14704:2016, Figure B.1. The bearing parts should also provide articulation to ensure that all bearing contacts can apply uniform load to the specimen surfaces. Semi-articulated fixtures, which have pairs of upper and lower bearings articulating to match the specimen surfaces, may be used with specimens that have flat and parallel surfaces, as illustrated in ISO 14704:2016, Figures B.2 a) and 8.3 a). Fully articulated fixtures have more moving parts and are necessary for specimens that do not have flat and parallel surfaces, as illustrated in ISO 14704:2016, Figures 8.2 b) and B.3 b).
The loading and supporting bearings of specimens may be cylindrical rollers or cylindrical bearings.
The specifications for bearings shall be as given in ISO 14704.
5.2.3 Positioning of bearings
The requirements for the positioning of bearings shall be as given in ISO 14704. In addition, the joining interfaces should be positioned at the centre of the inner bearings to within ± 0,1 mm.
5.2.4 Fixture material
The fixture should not be permanently deformed by hearings. The requirements and recommendations for fixture materials shall be as given in ISO 14704.
A micrometer, as described in ISO 3611 but with a resolution of 0,002 mm, shall be used to measure the specimen dimensions (see ISO 14704). Alternative dimension-measuring instruments may be used, provided that they have a resolution of 0,002 mm or finer.ISO 21712 pdf download.