ISO 23242:2020 pdf free.Fine ceramics [advanced ceramics,advanced technical ceramics)一Test method for flexural strength of monolithic ceramic thin plates at room temperature by three-point or
four-point bending.
5 Apparatus
5.1 Bend testing machine
A suitable testing machine capable of applying a uniform crosshead speed shall be used. The testing machine shall be in accordance with ISO 7500-1, with an accuracy of 1 % of the indicated force at fracture. The test load of ceramic thin samples ranges roughly between 20 N and 200 N. A load cell shall be selected so that the fracture load of thin plates is not close to the limits of load capacity interval, i.e. the lower limit for high-load cell capacity and the upper limit for low-load cell capacity.
5.2 Bend test fixture
5.2.1 General
Three- or four-point flexure configurations shall be used, as illustrated in Figure 1 and Table 1. 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 be designed so that parts “articulate” or tilt to ensure uniform loading to the specimen. The articulation shall be designed so that parts of the fixture can rotate, as specified in ISO 14704:2016, Figure B.1, to ensure even loading on the left and right bearings. An articulation is also needed to ensure that all the bearings contact the specimen surfaces evenly and apply a uniform load. Semi-articulated fixtures have some articulating or tilting capabilities and may be used with specimens that have flat and parallel surfaces, such as those of machined specimens. A semi-articulating fixture shall have pairs of upper and lower bearings that articulate to match the specimen surfaces, as specified in ISO 14704:2016, Figures B.2 and B.3. Fully articulated fixtures have more moving parts and shall be used for specimens that do not have flat and parallel surfaces. They allow independent articulation of the bearings. Fully articulated fixtures are often necessary for as-fired, heat-treated or oxidized specimens, since uneven loading can cause twisting and severe errors. A fully articulating fixture may also be used with machined specimens. For further detail on both semi-articulating and fully articulating fixtures, refer to ISO 14704.
5.2.2 Bearings
Specimens shall be loaded and supported by bearings. The bearings may be cylindrical rollers or cylindrical pins. The bearings shall he made of a steel which has a hardness of no less than HRC 40 for specimen strengths up to 1 400 MPa, or no less than HRC 46 for specimen strengths up to 2 000 MPa. Alternatively, the bearing may be made of a ceramic or a hard metal with an elastic modulus between 200 GPa and 500 GPa and a flexural strength greater than 275 MPa. The bearing length shall be greater than or equal to 35 mm. The bearing diameter shall be between 4,5 mm and 5 mm, except that samples with a thickness of less than 0,5 mm are bent in a four-point bending. When samples with a thickness of less than 0,5 mm are bent in a four-point configuration, the bearing diameter shall be between 2,5 mm and 3 mm. The bearings shall have a smooth surface and shall have a diameter that is uniform to ± 0,015 mm. The bearings shall be free to roll in order to eliminate friction, as shown in Figure 2. In four-point flexure, the two inner bearings shall be free to roll inward, and the two outer bearings shall be free to roll outward. In three-point flexure, the two outer bearings shall be free to roll outward, and the inner (middle) hearing shall not roll.
5.2.3 Positioning of bearings
Bearings shall be positioned so that their spans are accurate to within ± 0,1 mm. The middle bearing in a three-point fixture shall be positioned midway between the outer bearings to within ± 0,1 mm. The inner bearings in a four-point fixture shall be centred over the outer bearings to within ± 0,1 mm.
NOTE The positions of the bearings can be defined either by the use of captive bearings or by appropriate stops against which the bearings are held at the commencement of a test. The spans can be measured to the nearest 0,1 mm using a travelling microscope or other suitable device. The spans can also be verified by measuring the distances between bearing stops and adding (outer span) or subtracting (inner span) the radii of the bearing cylinders.ISO 23242 pdf download.