It is important to predict the fatigue lives and endurance limits of metals under service loads,
i. e., complex stress histories. Although the modified Miner's law has been applied sometimes to predict the fatigue lives of metals under service loads in general, it is not adequate to do so accurately and can not predict the endurance limits under service loads. In the present study, a new prediction method for fatigue lives and endurance limits of metals under service loads was developed.
The fatigue damge
FN' produced in the
N'-th cycle of stress σ can be expressed as follows:
FN' =
Aσ
α·exp(-
mσ
pN'), where
Aσ
α is the basic fatigue damage and exp (-
mσ
pN') represents the change of fatigue damage due to strain aging and other factors, α,
A, m and
p being material constants. Then the fatigue lives of metals
N under service loads can be predicted by solving the equation: ∫
N0FN'dN'=1, applying the material constants which can be obtained from the data of
S-N curve.
The fatigue lives of 0.11%
C rimmed steel under programmed loading which included stresses lower than the fatigue endurance limit, were predicted by applying the new prediction methods. The material constants α,
A, m and
p were studied and the method of calculating α and
A obtained from the test results through
S-N curves was proposed. It was found that the predicted fatigue lives are in good agreement with the tested lives, when the adequate values of
m and
p are applied.
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