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| Creep
involves time dependent plastic deformation under constant stress conditions.
The diagram shows three creep curves for the same material measured at
different temperatures or different applied stress levels.
The lower curve represents a stable creep condition. After the application of the stress, the material continues to deform but with a decreasing deformation rate that goes to zero at long times. The other two curves show unstable creep processes that end in fracture. During primary creep (de/dt) decreases with increasing time. Secondary creep is a steady state process for which (de/dt) is constant. In tertiary creep (de/dt) increases with time and the material fails by ductile fracture. |
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| From:
Newey and Weaver,
"Materials in Action" Butterworth (1990) |
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