rotatingbending

Rotating bending, or rotating bending fatigue testing, is a mechanical testing method used to evaluate the fatigue properties of materials under cyclic bending. In a typical setup, a cylindrical specimen is held so that it experiences a bending moment as it is rotated by a motor. The combination of rotation and bending produces alternating tensile and compressive stresses on the specimen surface, which drives crack initiation and growth under cyclic loading.

The test yields data on how many cycles a material can endure at a given stress amplitude, allowing the construction of an S-N curve (stress versus number of cycles). A related concept is the endurance or fatigue limit, the stress level below which the material can theoretically endure an unlimited number of cycles for certain alloys. Because bending stresses dominate the failure mode in this test, rotating bending is especially relevant for shaft-like components and other parts where bending fatigue is critical. The results are influenced by specimen geometry, surface finish, notch sensitivity, and heat treatment.

Advantages of rotating bending include simplicity, relatively low cost, and the ability to produce high-cycle bending fatigue data without large axial loads. Limitations include the restriction to predominantly bending-dominated stress states, potential sensitivity to misalignment, and difficulties in translating results to multi-axial service conditions.

Applications span ferrous and nonferrous alloys used in shafts, gears, and other rotating components. Standards and guidelines from various standards organizations describe procedures and reporting practices for rotating bending fatigue tests.