Tension-shear multiaxial fatigue damage behavior of high-speed railway wheel rim steel. (April 2020) - Zhang, Qingsong
Highlights: Tension-shear multiaxial fatigue behavior is studied by a new self-designed multiaxial fatigue fixture. Surface temperature evolution divide into three stages, corresponding to rapid plastic work, micro-plastic deformation and crack initiation, and crack growth, respectively. Local brittleness features of multiaxial fatigue are more sensitive than that of uniaxial fatigue. Multiaxial fatigue failure mechanism happens to twinning, while slip is the dominant mechanism of uniaxial fatigue. Abstract: This work addresses the tension-shear multiaxial fatigue behavior of ER8 medium carbon steel, commonly used for the high-speed railway wheel. Making use of high-frequency fatigue tests with different applied loading angles, namely 0° (uniaxial), 30° and 45° (both multi-axial), the fatigue limit and its corresponding S-N curves were calculated. The results showed that as the loading angle increased, both the fatigue life and von Mises stress fatigue limit were dramatically reduced (more than 65% with respect to uniaxial loading). Temperature measurements were performed in the sample surface during the tests and the micro-structure of fatigue fractures were characterized. The surface temperature evolution tendency of the specimen in the multiaxial fatigue tests was similar to that in the uniaxial fatigue tests. Moreover, the surface temperature evolution can be divided into three stages: Rapid Increase Stage (RIS), Stability Stage (SS) and Mutation Stage (MS), corresponding to rapid plastic work, cyclic micro-plastic deformation and crack initiation, and crack growth, respectively. Although all tests showed brittle and ductile fractures, multiaxial fatigue lead to significant changes in the mode of cyclic micro-plastic strain and fatigue damage behavior. There was a change from the dislocation slip of the uniaxial fatigue, to deformation twinning of the multiaxial fatigue, owing to the larger shear stresses. We conclude that such large shear stresses induce profound changes in the fracture mode and deeply influences the fatigue behavior.