The bilinear S-N curve has a certain inclination (usually m = 3) to the point that fits the constant amplitude
fatigue limit (CA, Figure 3.).
The sharp boundaries of primary type I graphite nucleated in pearlitic matrix drastically reduces the notch toughness of material and prematurely failed against safe life stress based design philosophy under
fatigue limit. The higher hardness on failed cross sectional area reveals cyclic hardening during fatigue crack propagation.
Instead, the fatigue life prediction, ignoring the
fatigue limit [DELTA][[sigma].sub.D], is directly looked at and compared.
Fatigue limit for steel = 0.5 x 460 = 230 MN/[m.sup.2] (33,358.7 psi)
Among the topics are calculating thermal dissipation, the effects of stress concentration on fiber reinforced composites, estimating
fatigue limit in interior inclusion induced fracture mode for bearing steel in rotating bending, failure mechanism of high strength steels, and the influence of high-cycle fatigue on crater wear characteristics of cemented carbide tool.
This
fatigue limit is around a third to a half of the tensile strength, depending on the alloy.
For the VW nylon materials and composites studied, the
fatigue limit in terms of maximum stress at R = 0.1 was reported to be 0.33 of the tensile strength.
The drawback of the Miners rule is the hypothesis that damage accumulation has nothing to do with the load conditions, the load sequences, the interaction between various loads, and the damage induced by stresses below the
fatigue limit [3].
The result of processing fatigue test dataset using models of fatigue curve with random
fatigue limit is presented in paper (Pascual, Meeker 1999).