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.
The special spring steel material must be high strength, high rigidity, high fatigue limit
and acceptable plasticity and tenacity.
The plotted lines represent the median S-N curves which were calculated according to the random fatigue limit
(RFL) model [4, 15].
for steel = 0.5 x 460 = 230 MN/[m.sup.2] (33,358.7 psi)
where [DELTA][[sigma].sub.f] is the fatigue limit
, c represents the surface crack length, and F represents the boundary correction factor.
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
The result of processing fatigue test dataset using models of fatigue curve with random fatigue limit
is presented in paper (Pascual, Meeker 1999).