Question: Explain in detail Andrades analysis of creep curve.

Subject: Material Technology

Topic: Failure Mechanisms

Difficulty: High

mt(63) • 203 views
modified 12 months ago  • written 12 months ago by gravatar for Atharv Inamdar Atharv Inamdar650

Basic observations for creep loading done on metal is as follows:

  • An initial steep rate that is at least partly of elastic origin, from point "0" to point "A"
  • This is followed by a region in which the elongation or deformation rate decreases with time, the so-called transient or primary creep, from region "A" to "B". The portion from point "0" to point "B" occurs fairly quickly. Here the creep rate is slow as strain hardening is more.
  • The next portion of the creep curve is the area of engineering interest, where the creep rate is almost constant. The portion from "B" to "C" is nearly linear and predictable. Depending on the load or stress, the time can be very long; two years in a test and several decades in service, here the strain hardening is balanced and hence we get uniform creep rate.
  • The fourth portion of the creep curve, beyond the constant-creep-rate or linear region, shows a rapidly increasing creep rate which culminates in failure. Even under constant-load test conditions, the effective stress may actually increase due to the damage that forms within the microstructure.
written 12 months ago by gravatar for Atharv Inamdar Atharv Inamdar650
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