Maximum flexural stress to rupture, as determined by a standardized flexural (or bending) test. Uses units of stress (force per unit area). The value for a material is determined as the maximum stress on the tensile side of a loaded beam just prior to failure. Also called modulus of rupture, typically in the context of ceramic materials.
Despite the fact that the underlying loading at the location of failure is tensile, flexural strength values tend to vary substantially from tensile strength values, due to substantial differences in the testing setup.
Like other "strength" type properties, flexural strength can be determined in ultimate and yield flavours. But since most of the materials for which flexural testing is preferred lack the ductility to produce meaningful yield strength values, flexural yield strength values are very rare.
ASTM testing standards include C133 for refractories at room temperature, C158 for glass, C583 for refractories at elevated temperature, C674 for ceramic whitewares, C880 for dimension stone, C1161 for advanced ceramics, D790 and D6272 for plastics, D1184 for laminar materials, and D7264 for polymeric-matrix composites.
ISO testing standards include 178 for plastics, 1209 for rigid polymeric foams, 3597 and 14125 for polymeric-matrix composites, 14704 for ceramics at room temperature, and 17565 for ceramics at elevated temperature.