Failure Mechanism: Creep

Creep is a diffusion controlled mechanism where grain boundaries slide past each other.

  • Creep is dependant on time, temperature and the load/force applied. If all these factors are increased then creep will be more severe.
  • Creep also accelerates fatigue.
  • To design against creep, limit the number of grain boundaries.

Demonstration

It is possible to see from the large poly-crystal that the separate crystals can move when force is applied: it is like wobbly teeth.

Polycrystalline structure

Polycrystalline structure

Compare the creep process for a single crystal with one grain and a poly-crystal with lots of grains and thus grain boundaries. There is no slip/creep in the single crystal whereas you can feel and see the slip in the large poly-crystal.

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