Creep Rate Calculator
Calculate steady-state creep rate using the Norton power law.
Find creep strain, time to failure, and Larson-Miller parameter for metals at high temperature.
What Is Creep? Creep is the slow, time-dependent plastic deformation of materials under constant stress below the yield strength. Significant above the homologous temperature T/T_m ≈ 0.3 to 0.4, with T and T_m in Kelvin. Room temperature creep: negligible for most metals (except lead, tin). Important in: gas turbine blades, nuclear fuel cladding, steam pipes, solder joints, polymers at room temperature.
Norton Power Law (Secondary/Steady-State Creep) ε̇ = A × σⁿ × exp(−Q / RT) Where: ε̇ = steady-state creep rate (s⁻¹) A = material constant σ = applied stress (MPa) n = stress exponent (typically 3 to 8 for metals, in the dislocation creep regime) Q = activation energy (kJ/mol) R = gas constant (8.314 J/mol·K) T = temperature (Kelvin)
Three Stages of Creep Primary (transient): decelerating creep rate: microstructure adjusting. Secondary (steady-state): minimum, constant creep rate. This is the main design region. Tertiary: accelerating creep leading to rupture, with necking and void coalescence. Design is based on secondary creep rate to set allowable service life.
Stress Exponent n n ≈ 1: diffusional creep (Nabarro-Herring or Coble), at very high T or low stress n = 3: viscous glide (some alloys) n = 4 to 5: dislocation climb, the most common case for metals n > 8: power-law breakdown, the high stress regime
Larson-Miller Parameter P_LM = T × (C + log₁₀ t_r) Where T = temperature (K), t_r = time to rupture (hours), and C ≈ 20 for steel, running 15 to 30 depending on the material. P_LM is material-specific and allows predicting rupture life at different T and σ combinations.
Typical Secondary Creep Rates A creep rate on its own means very little. Divide an allowable strain by it and it turns into something you can plan around. At 1% allowable strain, which is the figure this calculator uses, the bands work out like this:
| ε̇ (s⁻¹) | Time to 1% strain | What the calculator calls it |
|---|---|---|
| 10⁻¹² | ~320 years | Negligible |
| 10⁻¹¹ | ~32 years | Negligible |
| 10⁻¹⁰ | ~3.2 years (27,800 h) | Low |
| 10⁻⁹ | ~116 days (2,780 h) | Low |
| 10⁻⁸ | ~12 days (278 h) | Moderate |
| 10⁻⁷ | ~28 hours | Moderate |
| 10⁻⁶ | ~2.8 hours | High |
On the pre-exponential constant A. This is where people get burned, because A is not a small number. At 600 °C with Q = 280 kJ/mol the Arrhenius term exp(−Q/RT) is about 1.8 × 10⁻¹⁷, and σⁿ for 100 MPa at n = 4.5 is 10⁹. Those nearly cancel, so A has to be of order 0.1 to 10 to land on a physical creep rate. Feed in 10⁻¹⁰ because it looks like a plausible small constant and the calculator will faithfully report a life of a hundred million years.
A is also not portable. It is fitted alongside a specific n and Q for one material, and changing n by half a unit moves A by orders of magnitude. Always take all three from the same data set.
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