Creep Rate Calculator
Secondary (steady-state) creep dominates the life of most high-temperature engineering components. Norton's power law models the steady-state creep strain rate as a function of applied stress and temperature. The strain rate is d(epsilon)/dt = A * sigma^n * exp(-Q/(R*T)), where A and n are material constants, Q is activation energy, R is the universal gas constant (8.314 J/(mol*K)), and T is absolute temperature. Enter your material's constants and service conditions to estimate the creep rate in strain per second.
Norton power-law creep formula
d(epsilon)/dt = A * sigma^n * exp(-Q / (R * T))
R = 8.314 J/(mol*K); T in Kelvin = T(C) + 273.15; Q in J/mol
Where A is the material pre-exponential constant, sigma is the applied stress (MPa), n is the stress exponent, Q is the activation energy (J/mol, input in kJ/mol and converted), R is the universal gas constant (8.314 J/(mol*K)), and T is absolute temperature in Kelvin.
Interpreting creep rate results
Typical acceptable secondary creep rates for power plant components are in the range of 10^-9 to 10^-11 per second, corresponding to 0.01 to 0.1 percent creep strain per 1,000 hours. Turbine blade alloys operate at higher creep rates but over much shorter replacement intervals. The calculated rate should be compared against the material's design allowable and the required component life to determine adequacy.
Creep rate: frequently asked questions
What is creep in materials science?
Creep is the time-dependent plastic deformation that occurs in materials subjected to sustained stress at elevated temperatures (generally above 30 to 50 percent of the absolute melting temperature). It is the primary life-limiting mechanism for turbine blades, boiler tubes, and other high-temperature components.
What is Norton's power law?
Norton's power law describes the steady-state (secondary) creep rate: d(epsilon)/dt = A * sigma^n * exp(-Q/(RT)), where A is a material constant, sigma is stress, n is the stress exponent (typically 3 to 8 for metals), Q is the activation energy, R is the gas constant, and T is absolute temperature.
What are typical values of the creep exponent n?
For most metals undergoing dislocation creep, n is between 3 and 8. n = 1 corresponds to diffusional (Newtonian) creep at low stresses. Superalloys used in turbine blades may show n = 5 to 10. The value is determined experimentally from creep tests at multiple stress levels.
What is the creep activation energy Q?
The activation energy Q for creep is often close to the activation energy for self-diffusion in the material. For pure aluminum, Q is approximately 142 kJ/mol. For austenitic stainless steels, Q is approximately 280 to 300 kJ/mol. Q is extracted from the temperature dependence of the creep rate using an Arrhenius plot.
How is creep rate used in design?
In high-temperature design, components are sized so that the accumulated creep strain over the design life does not exceed allowable values (often 1 percent in 100,000 hours for power plant components). The Larson-Miller parameter and Robinson's rule of linear damage accumulation are used to combine data from accelerated tests to predict behavior at service conditions.
Official sources
- ASTM E139, "Standard Test Methods for Conducting Creep, Creep-Rupture, and Stress-Rupture Tests": astm.org.
- ASM International, "ASM Handbook Vol. 8: Mechanical Testing and Evaluation": asminternational.org.
- NIST, "Mechanical Properties of Structural Materials at Elevated Temperatures": nist.gov.
Reviewed by the CalculatorHub team, edited by James Graham, 15 June 2026. See our methodology.