Fracture & Fatigue Simulators

How to Use

1. Select material class (steel, aluminum, composite) and input S-N curve parameters or fracture toughness K_IC value
2. Define cyclic load amplitude (σ_max, σ_min) and stress ratio R; enter initial crack length a₀ if performing crack growth analysis
3. Run simulation to compute fatigue life (N_f) via Miner's rule or Paris law crack propagation (da/dN = C·ΔK_m); review failure mode classification

Worked Example

7075-T73 aluminum plate: S-N exponent b = −0.087, σ_{fatigue limit} = 160 MPa, K_IC = 29 MPa√m. Applied stress range ΔS = 180 MPa, R = 0.1, initial surface crack a₀ = 0.5 mm. Paris law coefficients C = 1.2×10⁻¹⁰, m = 3.4 (SI units). Simulation predicts N_f ≈ 2.1×10⁵ cycles to fracture; final crack length a_f ≈ 12.3 mm. Stress intensity factor ΔK approaches K_IC at instability.

Practical Notes

1. Aircraft wing attachment points: use conservative R-ratio (R ≈ 0.5–0.8) and apply environmental knockdown factors (salt spray reduces K_IC by 10–20%)
2. Validate cat-filter selections against material spec sheets; notch sensitivity K_t elevates local stress concentration and reduces effective fatigue limit
3. Check Haigh diagram intersection for multiaxial loading; mean stress correction (Goodman/Morrow) becomes critical above R = −0.5
4. Use linear elastic fracture mechanics (LEFM) only if plastic zone r_p < 0.1 × crack length; switch to elastic-plastic or cohesive zone models for thick sections