Failure analysis

Failure Analysis Skill

Purpose

The Failure Analysis skill provides systematic methodology for investigating mechanical component failures, enabling root cause identification through fractography, metallography, stress analysis, and structured problem-solving approaches.

Capabilities

• Fractography interpretation (SEM, optical)
• Metallographic examination guidance
• Root cause analysis frameworks (5-Why, Fishbone)
• Failure mode identification (fatigue, corrosion, overload)
• Stress analysis correlation to failure location
• Chemical analysis interpretation
• Corrective action development
• Failure analysis report generation

Usage Guidelines

Investigation Process

Phase 1: Evidence Preservation

1. Documentation

   • Photograph failed components as-received
   • Document orientation and assembly position
   • Record operating conditions at failure
   • Preserve all fragments

2. Chain of Custody

   • Log all handling
   • Secure storage
   • Controlled access
   • Document any cleaning or cutting

Phase 2: Visual Examination

1. Macroscopic Features

   Feature	Indication
   Beach marks	Fatigue
   Chevron marks	Brittle fracture
   Shear lips	Ductile overload
   Corrosion products	Environmental attack
   Wear patterns	Tribological failure

2. Fracture Origin

   • Identify initiation site
   • Look for stress concentrations
   • Check for material defects
   • Document surface conditions

Phase 3: Fractography

1. Optical Microscopy

   • Low magnification overview
   • Document fracture features
   • Identify regions of interest

2. Scanning Electron Microscopy (SEM)

   Fracture Feature	Failure Mode
   Striations	Fatigue crack growth
   Dimples	Ductile overload
   Cleavage facets	Brittle fracture
   Intergranular	Creep, SCC, hydrogen
   Quasi-cleavage	Mixed mode

3. EDS Analysis

   • Identify corrosion products
   • Detect contamination
   • Verify material composition

Phase 4: Metallography

1. Sample Preparation

   • Section perpendicular to fracture
   • Mount in appropriate media
   • Grind and polish
   • Select appropriate etchant

2. Examination

   • Grain structure
   • Heat treatment condition
   • Inclusions and defects
   • Microcracking
   • Decarburization

Failure Mode Identification

Fatigue Failure

Characteristics:
- Beach marks (macroscopic)
- Striations (microscopic)
- Origin at stress concentration
- Minimal plastic deformation
- Flat fracture surface

Contributing Factors:
- Cyclic loading
- Stress concentration
- Residual stress
- Material defects
- Environmental effects

Overload Failure

Ductile:
- Significant plastic deformation
- Cup-and-cone fracture (tensile)
- Shear lips
- Dimpled fracture surface

Brittle:
- Little plastic deformation
- Flat fracture surface
- Chevron marks pointing to origin
- Cleavage or intergranular fracture

Corrosion Failures

Type	Characteristics	Environment
Uniform	General metal loss	Acids, bases
Pitting	Localized attack	Chlorides
SCC	Branching cracks	Specific ion + stress
Corrosion fatigue	Accelerated fatigue	Cyclic + corrosive
Hydrogen embrittlement	Intergranular fracture	Hydrogen source

Wear Failures

Type	Mechanism	Evidence
Adhesive	Material transfer	Galling, scoring
Abrasive	Hard particle cutting	Grooves, scratches
Erosive	Fluid/particle impact	Surface damage pattern
Fretting	Small amplitude motion	Oxide debris, pitting

Root Cause Analysis

5-Why Method

Problem: Shaft failure
Why 1: Fatigue fracture
Why 2: High stress concentration at keyway
Why 3: Sharp corner radius
Why 4: Drawing did not specify radius
Why 5: Design review did not catch omission

Root Cause: Inadequate design review process

Fishbone Diagram Categories

• Material: Composition, defects, properties
• Machine: Equipment condition, maintenance
• Method: Process, procedure, design
• Man: Training, error, supervision
• Environment: Temperature, humidity, contamination
• Measurement: Calibration, accuracy

Process Integration

• ME-016: Failure Analysis Investigation

Input Schema

{
  "failed_component": {
    "part_number": "string",
    "material": "string",
    "service_history": "string",
    "failure_date": "date"
  },
  "operating_conditions": {
    "loads": "string",
    "environment": "string",
    "temperature": "number (C)",
    "cycles_or_hours": "number"
  },
  "available_evidence": {
    "fracture_surfaces": "boolean",
    "mating_parts": "boolean",
    "lubricant_samples": "boolean",
    "maintenance_records": "boolean"
  },
  "analysis_scope": "preliminary|comprehensive"
}

Output Schema

{
  "failure_mode": "fatigue|overload|corrosion|wear|other",
  "root_cause": "string",
  "contributing_factors": "array",
  "evidence_summary": {
    "visual": "string",
    "fractography": "string",
    "metallography": "string",
    "chemical": "string"
  },
  "corrective_actions": [
    {
      "action": "string",
      "category": "design|material|process|maintenance",
      "priority": "high|medium|low"
    }
  ],
  "preventive_recommendations": "array",
  "report_reference": "string"
}

Best Practices

1. Preserve evidence before any destructive examination
2. Document all observations photographically
3. Follow systematic investigation process
4. Consider multiple failure mechanisms
5. Correlate fracture features with stress analysis
6. Validate root cause with evidence

Integration Points

• Connects with FEA Structural for stress analysis
• Feeds into Material Selection for improved materials
• Supports Design Review for lessons learned
• Integrates with Quality for corrective actions