Fatigue behavior of powder metallurgy high-speed steels: fatigue limit prediction using a crack growth threshold-based approach

Based on the well-known fact that fatigue lifetime of powder metallurgy high speed steels (PM-HSSs) is given by subcritical crack growth of pre-existing defects, a linear elastic fracture mechanics (LEFM) approach is implemented by assessing a fatigue limit–fatigue crack growth (FCG) threshold correlation under infinite fatigue life conditions. In doing so, critical flaw size under cyclic loading is simply defined in terms of FCG threshold. Additionally, it is assumed that the fundamental LEFM correlation among defect size, strength and threshold conditions evaluated for large cracks applies for natural flaws too. Hence, the fatigue limit value for the PM-HSS studied is predicted using the experimentally measured fracture and FCG characteristics, provided that critical flaws are similar, in terms of nature, geometry and size, under monotonic and cyclic loading. The reliability of the applied LEFM approach is sustained through the excellent agreement observed between estimated and experimentally determined fatigue limit values.