ASTM B406 Test Fixtures & Test Systems Model: G-ASTM-B406

The Rigidity Requirement: ASTM B406 measures the transverse rupture strength of cemented carbides. Given the extreme hardness of these materials (often exceeding 1500 HV), the fixture rollers must be made of a material even harder than the specimen—typically high-grade tungsten carbide themselves—to prevent indentation of the rollers. The mechanical challenge here is the Stiffness Budget. If the UTM frame or the fixture base exhibits any compliance, the energy stored in the machine squish will be released into the specimen at the moment of crack initiation, resulting in a violent shattering that makes it impossible to analyze the fracture origin. The rollers must be free-rolling to eliminate longitudinal constraints, but they must also be constrained laterally to prevent wandering under high loads. From an engineering standpoint, even a 0.05mm misalignment in the span will propagate a massive error in the TRS calculation due to the extremely high modulus of the carbide. MTO’s fixtures utilize a self-aligning top roller to compensate for minor specimen non-parallelism, ensuring the force is distributed as a uniform line load across the specimen width, which is the only way to get a repeatable, statistically valid B-value for carbide quality control.