Creep Rate Calculator

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 ≈ 0.3–0.4 (T, 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 3–8 for metals; dislocation creep) 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 — main design region. Tertiary: accelerating creep leading to rupture — necking, 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) — very high T or low stress n = 3: viscous glide (some alloys) n = 4–5: dislocation climb — most common for metals n > 8: power-law breakdown — high stress regime

Larson-Miller Parameter P_LM = T × (C + log₁₀ t_r) Where T = temperature (K), t_r = time to rupture (hours), C ≈ 20 (steel), 15–30 depending on material. P_LM is material-specific and allows predicting rupture life at different T and σ combinations.

Typical Secondary Creep Rates (s⁻¹) Negligible service life concern: ε̇ < 10⁻¹¹ Acceptable for long-term (> 100,000 hours): ε̇ ≈ 10⁻¹⁰ to 10⁻¹¹ Problematic (failure in < 10,000 hours): ε̇ > 10⁻⁸