--- name: fatigue-analysis-28f8bb2de05a description: Specialized skill for fatigue life assessment and durability prediction under cyclic loading conditions allowed-tools: - Read - Write - Glob - Grep - Bash metadata: specialization: mechanical-engineering domain: science category: structural-analysis priority: high phase: 5 tools-libraries: - nCode DesignLife - Fe-Safe - NASGRO - AFGROW - MATLAB graph: domains: [domain:mechanical-engineering] skillAreas: [skill-area:physics-simulation, skill-area:mathematical-reasoning, skill-area:motion-planning] roles: [role:systems-integration-engineer, role:research-engineer] --- # Fatigue Life Prediction Skill ## Purpose The Fatigue Life Prediction skill provides specialized capabilities for assessing fatigue life and durability under cyclic loading conditions, enabling systematic evaluation of component life using stress-life, strain-life, and fracture mechanics approaches. ## Capabilities - Stress-life (S-N) curve application and analysis - Strain-life (epsilon-N) methodology implementation - Fracture mechanics crack growth prediction (NASGRO, AFGROW) - Load spectrum development and cycle counting (rainflow) - Damage accumulation using Miner's rule - Mean stress correction methods (Goodman, Gerber, Soderberg) - Multiaxial fatigue assessment - Fatigue report generation with life predictions ## Usage Guidelines ### Fatigue Analysis Approaches #### Stress-Life Method (S-N) 1. **Application** - High-cycle fatigue (N > 10^4 cycles) - Elastic stress conditions - Rotating machinery, vibration loading 2. **S-N Curve Development** ``` S = A * N^b Where: S = stress amplitude N = cycles to failure A, b = material constants ``` 3. **Endurance Limit Modifiers** ``` Se = Se' * ka * kb * kc * kd * ke * kf Where: ka = surface factor kb = size factor kc = load factor kd = temperature factor ke = reliability factor kf = miscellaneous effects ``` #### Strain-Life Method (epsilon-N) 1. **Application** - Low-cycle fatigue (N < 10^4 cycles) - Plastic strain present - Notched components 2. **Coffin-Manson Equation** ``` epsilon_a = (sigma_f'/E) * (2Nf)^b + epsilon_f' * (2Nf)^c Where: epsilon_a = strain amplitude sigma_f' = fatigue strength coefficient b = fatigue strength exponent epsilon_f' = fatigue ductility coefficient c = fatigue ductility exponent ``` 3. **Neuber's Rule for Notches** ``` (Kt * S)^2 / E = sigma * epsilon ``` #### Fracture Mechanics 1. **Application** - Damage tolerance analysis - Crack growth life prediction - Inspection interval determination 2. **Paris Law** ``` da/dN = C * (delta_K)^m Where: da/dN = crack growth rate delta_K = stress intensity factor range C, m = material constants ``` 3. **Stress Intensity Factor** ``` K = beta * S * sqrt(pi * a) Where: beta = geometry factor S = remote stress a = crack length ``` ### Load Spectrum Development 1. **Rainflow Cycle Counting** - Extract cycles from complex load history - Identify cycle ranges and means - Generate cycle count matrix 2. **Damage Summation** ``` D = sum(ni/Ni) Failure when D >= 1.0 ``` 3. **Load Sequence Effects** - Consider overload retardation - Evaluate block loading effects - Apply appropriate interaction models ### Mean Stress Corrections | Method | Equation | Application | |--------|----------|-------------| | Goodman | Sa/Se + Sm/Su = 1 | Conservative, most common | | Gerber | Sa/Se + (Sm/Su)^2 = 1 | Less conservative | | Soderberg | Sa/Se + Sm/Sy = 1 | Very conservative | | Morrow | Sa/Se + Sm/sigma_f' = 1 | Strain-life approach | ## Process Integration - ME-008: Fatigue Life Prediction ## Input Schema ```json { "component": "string", "material": { "name": "string", "Su": "number (Pa)", "Sy": "number (Pa)", "Se_prime": "number (Pa)", "sigma_f_prime": "number (Pa)", "epsilon_f_prime": "number", "b": "number", "c": "number" }, "loading": { "type": "constant_amplitude|spectrum", "stress_amplitude": "number (Pa)", "mean_stress": "number (Pa)", "spectrum_file": "string (if spectrum)" }, "geometry": { "Kt": "number (stress concentration)", "surface_finish": "string", "size": "number (mm)" }, "target_life": "number (cycles)", "reliability": "number (0-1)" } ``` ## Output Schema ```json { "fatigue_life": { "predicted_cycles": "number", "safety_factor": "number", "critical_location": "string" }, "damage_summary": { "total_damage": "number", "damage_by_range": "array" }, "analysis_details": { "method_used": "string", "mean_stress_correction": "string", "modifying_factors": "object" }, "recommendations": { "design_changes": "array", "inspection_interval": "number (if applicable)" } } ``` ## Best Practices 1. Use appropriate method for expected life regime (HCF vs LCF) 2. Include all relevant modifying factors 3. Account for mean stress effects 4. Validate material properties from tested data 5. Consider multiaxial stress states for complex loading 6. Apply appropriate safety factors per industry standards ## Integration Points - Connects with FEA Structural for stress inputs - Feeds into Test Planning for validation requirements - Supports Material Selection for fatigue-resistant materials - Integrates with Design Review for life certification --- Source attribution: a5c-ai Original project: https://github.com/a5c-ai/babysitter/blob/feb68abe397acc14f32b34984975c48fedba2b33/library/specializations/domains/science/mechanical-engineering/skills/fatigue-analysis/SKILL.md License: MIT License information: https://opensource.org/license/mit Original upstream instructions; downloaded from Mega AI Hub. ## Upstream license notice # MIT License Copyright (c) 2025 A5C AI Permission is hereby granted, free of charge, to any person obtaining a copy of this software and associated documentation files (the "Software"), to deal in the Software without restriction, including without limitation the rights to use, copy, modify, merge, publish, distribute, sublicense, and/or sell copies of the Software, and to permit persons to whom the Software is furnished to do so, subject to the following conditions: The above copyright notice and this permission notice shall be included in all copies or substantial portions of the Software. THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE. # Mega AI Hub resource metadata Creator / publisher: a5c-ai Original project: https://github.com/a5c-ai/babysitter/blob/feb68abe397acc14f32b34984975c48fedba2b33/library/specializations/domains/science/mechanical-engineering/skills/fatigue-analysis/SKILL.md Attribution basis: Source repository record Fields of work: Data & Analytics, Development & Engineering, Education & Research, Product Management, Project & Program Management Roles: Data Scientist, ML / AI Engineer, Product Manager, Project Manager, Researcher Specialties: Specialty not specified Tools: Afgrow, Fe Safe, Matlab, Nasgro, Ncode Designlife Country applicability: Country not specified Classification basis: Source catalog labels Instruction SHA-256: d1ec61e78ec3a9c0f45cc97cf2d897fbe7ff6d251d8a17e5e661c9f36c36be9a