Wind Turbine Blade Fatigue: Haigh Diagram (2D)

Load Conditions

Mean wind speed 11 m/s

Rotor speed 14 rpm

Turbulence intensity 14%

Fatigue-clock speed 200×

Root Stress Cycle

Stress amplitude Sₐ

— MPa

Mean stress Sₘ

— MPa

Cycles to failure at this load, N_f (Basquin)

—

Miner's-Rule Damage Accumulator

D = 0.0%0 cycles

Elapsed service life

0.0 yr

Projected life at D=1

— yr

How it works

This is the 2D-native counterpart to the 3D rotating-turbine fatigue simulator. Instead of orbiting a rendered rotor, it draws the three things that actually generate the physics: the live root-stress waveform, a Haigh (Goodman) diagram with constant-life boundaries, and the material's own Basquin S-N curve. Same load and damage model underneath:

σ(θ,t) = [M_g0·cosθ + M_w(t)] / Z          (root section modulus Z)
Sₐ = (σ_max − σ_min)/2,  Sₘ = (σ_max + σ_min)/2   per revolution
Goodman mean-stress correction:  Sₐ_eq = Sₐ / (1 − Sₘ/Sᵤ)
Basquin S-N curve:  N_f = N_ref · (Sₐ_eq / S_ref)^(−m)
Miner's rule:  D = Σ (nᵢ / N_fᵢ) → failure predicted at D = 1

Stress waveform (top strip) — the actual root stress trace at real time, combining the gravity-driven cos θ reversal with the rotationally-sampled turbulent gust; this is the signal the cycle counter measures directly, not an inferred colour.
Haigh diagram — plots each completed cycle's (mean stress, amplitude) point live. The diagonal lines are constant-life boundaries: any point crossing further out than a given line has consumed at least that many allowable cycles at this load. Turbulence intensity widens each cycle's swing, pushing points up (higher Sₐ); wind speed raises the mean aerodynamic moment, pushing points right (higher Sₘ).
Basquin S-N curve — log-log life curve; the marker is the current cycle's Goodman-corrected amplitude and its resulting N_f. Because N_f falls with roughly the 10th power of amplitude for composite laminates (m≈10), a modest rise in turbulence-driven amplitude collapses the allowable life far more than the same relative rise in mean wind.
Fatigue-clock speed only fast-forwards the damage integrator so a multi-decade design life is visible in seconds; the stress waveform panel always runs at the real rotor speed and is unaffected by it.

Real-world relevance: this exact bookkeeping — Goodman-corrected amplitude against a Basquin S-N curve, summed with Miner's rule — is what structural engineers use to certify a wind-turbine blade's design life before it is ever built.

Root stress σ(t) Constant-life boundary Current cycle

Wind Turbine Blade Fatigue Loading: Haigh Diagram (2D)