3.1 This test method is used as a means of determining the quality of cemented carbide grade powders by measuring their sintered strength. It is performed on test specimens prepared to specified shape, dimensions, and surface finish; test specimens may be prepared from finished parts if size permits. There is no known standard material for this test method. The transverse rupture strength of cemented carbides is not a design value.

3.1.1 Most commercial cemented carbides have mechanical behavior that is best classified as brittle (negligible ductility). Fracture strengths are dependent on internal or surface flaws. Examples of incoherent internal flaws are macropores, Type B porosity (see Test Method B276), and inclusions of foreign particles. Such flaws are randomly distributed spatially and in size within the sintered material. This imparts a statistical nature to any transverse rupture strength measurement.

3.1.2 The stress distribution in a beam in three-point loading is non-uniform. It increases linearly along the span to a maximum at the center, and varies linearly through any section from compression on the top to tension on the bottom. The maximum tensile stress therefore occurs at center span in the bottom most fibers of the sample, and is defined as the transverse rupture strength at failure. Failure is initiated at a random flaw site, which is most probably not coincident with the maximum stress. This imparts an additional statistical nature to transverse rupture strength measurements.