車輪鋼における転動疲労き裂進展挙動評価

抄録

Rolling contact fatigue cracks propagate in mode II or mixed mode of I and II owing to the cyclic shear stress under multiaxial compressive stress states at the subsurface. No standardized evaluation method for shear mode crack propagation has been established. A method to evaluate the rates and behaviors of rolling contact fatigue crack propagation was studied using twin disc type rolling contact fatigue tests on railway wheel steels with artificial defects and finite element analyses (FEA) simulating the tests. The rolling contact fatigue test results indicated that the cracks initiated from the leading side of defects propagated in the depth direction, whereas those initiated from the trailing side propagated in the surface direction. Calculation results of the stress intensity factor (SIF) indicated that the cracks initiated from the leading side of defects propagated in the mixed mode, whereas those initiated from the trailing side propagated in only mode II. In addition, the crack propagation rates in the trailing side of defects accelerated with increasing number of cycles. This was because of the increase in the shear mode equivalent SIF during the crack propagation. Thus, the results of FEA corresponded to those of rolling contact fatigue tests. Therefore, the relationship between the rolling contact fatigue crack propagation rate and the shear mode SIF range could be evaluated by combining twin disc type rolling contact fatigue tests using test specimen with artificial defects and FEA.