CAE Simulation

Fatigue & Life Cycle Prediction: Engineering for Longevity

A product that survives a single load test is not necessarily a reliable product. Edelweis implements Fatigue & Life Cycle Prediction to understand how components behave under repetitive stress. By calculating the "damage accumulation" over time, we ensure systems meet their intended service life, preventing catastrophic failures due to material exhaustion.

1. Fatigue Analysis Methodologies

We select the mathematical approach based on expected stress levels and material ductility, matching the simulation to physical failure modes:

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Stress-Life (S-N): For high-cycle fatigue (HCF) where stresses remain elastic (e.g., rotating shafts). Logic follows Basquin’s equation.
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Strain-Life (ε-N): For low-cycle fatigue (LCF) involving plastic deformation (e.g., thermal cycling). Uses the Coffin-Manson relation.
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Fracture Mechanics (LEFM): Critical crack growth analysis predicting how fast existing microscopic flaws propagate under load.

2. Variable Amplitude & Mission Profiles

Rainflow Counting

Decomposing complex, erratic loading histories into discrete stress cycles for total damage calculation.

Palmgren-Miner Rule

Aggregating damage from various levels. Failure is predicted when the cumulative damage ratio (D) reaches 1.0.

Mean Stress Correction

Utilizing Goodman, Gerber, or Morrow theories to account for system pre-tension and accelerated failure.

3. Environmental & Surface Factors

Factor Type	Technical Adjustment	Impact on Life
Surface Finish	Adjusting for ground vs as-cast surfaces.	Rough surfaces act as stress risers, reducing life.
Size Factor	Accounting for flaw probability in volume.	Larger parts have lower fatigue limits statistically.
Corrosion	Simulating chemical attack + cyclic stress.	Humidity can reduce fatigue life by over 50%.
Temperature	Mapping fatigue across thermal envelope.	High heat accelerates creep-fatigue interaction.

4. Life Cycle Deliverables

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Life Plots (Total Cycles): Contour maps showing predicted cycles until first crack initiation.
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Damage Heatmaps: Identifying "Hot Spots" for targeted structural reinforcement.
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Maintenance Intervals: Data-driven inspection recommendations based on crack propagation rates.

Technical Directives

Directive	Protocol
Stress Concentration (Kt)	All geometric discontinuities must be analyzed with refined mesh to capture local peak stresses.
Infinite Life Target	Non-weight-sensitive parts are designed below the Endurance Limit (>10⁷ cycles).
Residual Stress	Analysis must account for internal stresses from welding or cold-forming which alter performance.