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| Failure Mechanisms | ||||||||||||||||||
| ·
The
lifetime to fatigue failure is dependent on the mean stress acting on the
sample.
· Lifetime is decreased if the mean stress is tensile, and increased if the mean stress is compressive. |
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| From: Hertzberg, "Deformation & Fracture Mechanics of Engineering Materials," Wiley (1976) | ||||||||||||||||||
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The
S-N curves for several mean stress levels are shown, also three models
for estimating the reduced lifetime under tensile values of the mean stress.
* Goodman: σa = σN(1 - {σm /σUTS} ) * Gerber: σa = σN(1 - {σm /σUTS}2 ) * Soderberg: σa = σN(1 - {σm /σy} ) |
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