MAT-26

Norton power-law creep

ε̇ = A σ^n. Secondary (steady) creep rate.

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CreepNorton 1929

Governing equation

\dot{\varepsilon}=A\sigma^n

where

A: Norton A (1/s/MPa^n)
\sigma: Stress (MPa)
n: Creep exponent (—)
\dot{\varepsilon}: Creep rate (1/s)

Lecture brief

Historical brief

Hooke (1678), Hall–Petch grain size, Arrhenius activation and Paris fatigue-crack growth are the spine of materials selection. The sheets relate stress, microstructure and life. This sheet (MAT-26 — Norton power-law creep) is the form associated with Norton 1929. Working symbols: $A$ , $\sigma$ , $n$ $\rightarrow$ $\dot{\varepsilon}$ . Norton fitted the steady creep rate of metals to a power of stress. Combined with Arrhenius it is the Norton–Bailey law.

Purpose

Purpose: compute

\dot{\varepsilon}

from

A

\sigma

n

in Materials via

\dot{\varepsilon}=A\sigma^n

ε̇ = A σ^n. Secondary (steady) creep rate. Use it when a real materials question must be answered in SI before a code check.

Live realistic example

In symbols

Live case. Given

A = 1.000e-16\,\mathrm{1/s/MPa^n}

\sigma = 80.000\,\mathrm{MPa}

n = 5.000\,\mathrm{—}

, the governing relation

\dot{\varepsilon}=A\sigma^n

yields

\dot{\varepsilon} = 3.277e-7\,\mathrm{1/s}

. A hot bar, a stress, a strain-rate arrow. Move a slider: the numbers are this situation, not a canned story.

Calculator

Inputs

Norton A A1e-16 1/s/MPa^nStress \sigma80 MPaCreep exponent n5 —

Outputs

Creep rate \dot{\varepsilon}0.000000 1/s

Reading speed

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Narration of this film

A hot bar, a stress, a strain-rate arrow.

Norton fitted the steady creep rate of metals to a power of stress. Combined with Arrhenius it is the Norton–Bailey law.

Reading speed

Watch on YouTube