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Gokul43201

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The number of cycles to failure (N) is related to the cycle amplitude through an exponential relation [itex]N = A \cdot S^{-k} [/itex] which is typically plotted as a linear fit on a half-log plot, known as an S-N curve. (google "S-N curve fatigue" and look at images). The exponent in the relation is highly material dependent. Also, this behavior is only one possible kind of fatigue known as high-cycle fatigue (where loading is essentially restricted to the elastic regime). If stresses, are much higher (into the plastic regime), you have low-cycle fatigue, for which the cycles to failure (N) is related to the amplitude of plastic strain (again, by an exponential plot), and you can not relate this to a stress amplitude without a stress-strain curve.

The actual frequency does not enter into S-N relationships, to a first order approximation. I expect, it will only enter as a factor (a term in the exponent) of the same order as the strain rate sensitivity index.

Moving this to Materials Engg ....

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