In a creep curve, which stage represents a near-steady-state creep rate?

In a creep curve, which stage represents a near-steady-state creep rate?

• A. Primary creep is steady-state.
• B. Secondary (steady-state) creep is the stage of near-constant creep rate.
• C. Tertiary creep is the stage of near-constant creep rate.
• D. There is no steady-state phase.

Answer: (B)

The concept tested is how creep rate evolves with time under a sustained load at high temperature. When a material is held under constant stress and temperature, it goes through three stages. In the early phase the creep rate is high but slows down as work hardening makes dislocation motion harder. The middle phase shows a nearly constant creep rate because the hardening and recovery processes balance each other; this is the steady-state, or secondary, creep. In the final phase, damage accumulates—microvoids and cracks grow and the material can no longer relieve deformation effectively—so the creep rate accelerates until failure. So the near-steady-state creep rate is observed in the secondary (steady-state) stage.

The concept tested is how creep rate evolves with time under a sustained load at high temperature. When a material is held under constant stress and temperature, it goes through three stages. In the early phase the creep rate is high but slows down as work hardening makes dislocation motion harder. The middle phase shows a nearly constant creep rate because the hardening and recovery processes balance each other; this is the steady-state, or secondary, creep. In the final phase, damage accumulates—microvoids and cracks grow and the material can no longer relieve deformation effectively—so the creep rate accelerates until failure. So the near-steady-state creep rate is observed in the secondary (steady-state) stage.