BS ISO 14704:2015 pdf download – Fine ceramics (advanced ceramics, advanced technical ceramics) — Test method for flexural strength of monolithic ceramics at room temperature
1 Scope
This International Standard specifies a test method for determining the flexural strength of monolithic fine ceramics, and whisker- or particulate-reinforced ceramic composites, at room temperature and applies to materials with grain size less than 200 µm. This test method may be used for materials development, quality control, characterization and design data-generation purposes.
NOTE Since fracture is due to tensile stress, flexural strength data can be used to calculate a uniaxial tensile strength considering the effect of the tested volume and Weibull-statistics. So, flexural strength is often used in substitute for uniaxial tensile strength.
2 Normative references
The following referenced documents are indispensable for the application of this document. For dated references, only the edition cited applies. For undated references, the latest edition of the referenced document (including any amendments) applies.
ISO 361 1 :1 978, Micrometer callipers for external measurement
ISO 7500-1 :2004, Metallic materials — Verification of static uniaxial testing machines — Part 1: Tension/compression testing machines — Verification and calibration of the force-measuring system
3 Terms and definitions
For the purposes of this document, the following terms and definitions apply.
flexural strength
maximum nominal stress at fracture of a specified elastic beam loaded in bending
four-point flexure
configuration of flexural strength testing where a specimen is loaded equally by two bearings symmetrically located between two support bearings
See Figure 1 a) and b).
NOTE The bearings may be cylindrical rollers or cylindrical bearings.
4 Principle A beam specimen with a rectangular cross-section is loaded in flexure until fracture. The load at fracture, the test fixture and specimen dimensions are used to compute the flexural strength which is often used in substitute for uniaxial tensile strength of a ceramic. The material is assumed to be isotropic and linearly elastic.
5 Apparatus
5.1 Testing machine The testing machine shall be capable of applying a force to the loading roller (three-point flexure) or equally to the loading rollers (four-point flexure) in order to stress the specimen. The machine shall be capable of applying the force at a constant loading or displacement rate. The test machine shall be equipped for recording the peak load applied to the specimen. The accuracy of the test machine shall be in accordance with ISO 7500-1 :2004, Class 1 , with an accuracy of 1 % of indicated load at fracture.
5.2 Test fixture
5.2.1 General Three- or four-point flexure configurations shall be used, 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 be designed so that parts “articulate” or tilt to ensure uniform loading to the specimen. The articulation is designed so that parts of the fixture can rotate, as shown in Figure B.1 , to ensure even loading on the left and right bearings. An articulation is also needed to ensure that all the bearings evenly contact the specimen surfaces and apply 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 on as- machined specimens. A semi-articulating fixture has pairs of upper and lower bearings that articulate to match the specimen surfaces, as shown in Figures B.2 and B.3. Fully articulated fixtures have more moving parts and are necessary for specimens that do not have flat and parallel surfaces. They allow independent articulation of the bearings. Fully articulated fixtures often are 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. BS ISO 14704 pdf download.