What is Norton's power law?

Norton's power law (also called the Norton-Bailey law) relates the steady-state creep strain rate to the applied stress and temperature: dot_epsilon = A * sigma^n * exp(-Q/(RT)). It is the most widely used empirical model for secondary creep in metals and alloys.

What are typical values for the stress exponent n?

For most metals, n ranges from 3 to 8. A value near 1 indicates diffusion (Newtonian) creep, values of 3-5 suggest dislocation climb, and values above 5 often indicate power-law breakdown at high stresses.

Where do I find material constants A and Q?

These constants are obtained from experimental creep tests (usually log-log plots of strain rate vs. stress at constant temperature) and are tabulated in materials handbooks, alloy datasheets, and research papers. Common sources include ASM Handbook Vol. 8 and NIMS databases.

What units should I use for activation energy Q?

This calculator accepts Q in kJ/mol, which is the most common unit in published creep data. The gas constant R is 8.314 J/(mol·K) = 0.008314 kJ/(mol·K), so the ratio Q/RT is dimensionless.

Why does the creep rate change so dramatically with temperature?

The Arrhenius exponential term exp(-Q/RT) is extremely sensitive to temperature. Even a small increase in T reduces Q/RT significantly, causing an exponential jump in creep rate. This is why high-temperature alloys are engineered to maximise Q.

Creep Rate Calculator

Name: Creep Rate Calculator
Availability: InStock
Author: Nham Vu

Enter the pre-exponential constant, stress, stress exponent, activation energy, and temperature to instantly compute the steady-state creep rate using Norton's power law.

Material & Test Parameters

All values from material datasheets or experimental tests.

Pre-exponential constant A (s^-1 MPa^-n)

Material-specific constant (from datasheets). Supports scientific notation.

Applied stress σ (MPa)

Stress exponent n (dimensionless)

Typically 3 to 8 for metals.

Activation energy Q (kJ/mol)

Enter in kJ/mol (not J/mol).

Temperature T

Enter temperature in °C — will be converted to Kelvin.

Enter parameters on the left and click Calculate.

Results and step-by-step breakdown will appear here.

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Summary

Enter the pre-exponential constant, stress, stress exponent, activation energy, and temperature to instantly compute the steady-state creep rate using Norton's power law.

How it works

The calculator evaluates Norton's power law: dot_epsilon = A * sigma^n * exp(-Q / (R * T)). You supply the four material/test parameters (A, sigma, n, Q) and the temperature. The tool converts Celsius to Kelvin if needed, substitutes all values into the formula, and displays the creep rate in s^-1 along with a step-by-step breakdown of each term.

Use cases

Estimating service life of turbine blades, boiler tubes, and high-temperature pressure vessels.
Comparing creep resistance of candidate alloys at elevated temperatures.
Validating FEA creep models by checking hand-calculation benchmarks.
Teaching materials science — demonstrating the sensitivity of creep rate to stress and temperature.

Frequently Asked Questions

Last updated: 2026-06-10 · Reviewed by Nham Vu