Material Selection Skill

Purpose

The Material Selection skill provides systematic capabilities for selecting materials using Ashby methodology and performance indices, enabling optimal material choices based on functional requirements, manufacturing constraints, and cost considerations.

Capabilities

• Ashby chart generation and interpretation
• Performance index derivation for design requirements
• Material property database access (MatWeb, CES)
• Environmental compatibility assessment
• Manufacturing process compatibility evaluation
• Cost and availability analysis
• Equivalent material identification
• Material specification documentation

Usage Guidelines

Ashby Methodology

Performance Indices

1. Stiffness-Limited Design

   Loading	Performance Index	Maximize
   Tie (tension)	E/rho	Specific stiffness
   Beam (bending)	E^(1/2)/rho	Flexural efficiency
   Panel (bending)	E^(1/3)/rho	Panel efficiency
   Shaft (torsion)	G^(1/2)/rho	Torsional efficiency

2. Strength-Limited Design

   Loading	Performance Index	Maximize
   Tie (tension)	sigma_y/rho	Specific strength
   Beam (bending)	sigma_y^(2/3)/rho	Flexural strength
   Panel (bending)	sigma_y^(1/2)/rho	Panel strength
   Shaft (torsion)	tau_y^(2/3)/rho	Torsional strength

3. Combined Objectives

   For minimum cost at required stiffness:
   M = E / (rho * C_m)
   
   Where:
   E = Young's modulus
   rho = density
   C_m = cost per unit mass
   

Material Selection Charts

1. Young's Modulus vs Density

   • Identify materials above target index line
   • Compare material families
   • Identify lightweight alternatives

2. Strength vs Density

   • Evaluate strength-to-weight ratio
   • Compare metallic and composite options
   • Identify high-performance materials

3. Thermal Conductivity vs Electrical Resistivity

   • Heat dissipation requirements
   • Electrical isolation needs
   • Combined thermal-electrical requirements

Property Requirements

Mechanical Properties

Property	Units	Considerations
Yield strength	MPa	Safety factors, fatigue
Ultimate strength	MPa	Failure modes
Young's modulus	GPa	Deflection limits
Fracture toughness	MPa.m^(1/2)	Damage tolerance
Fatigue strength	MPa	Cyclic loading
Hardness	HRC, HB	Wear resistance

Physical Properties

Property	Units	Considerations
Density	kg/m3	Weight constraints
Thermal expansion	10^-6/K	Dimensional stability
Thermal conductivity	W/m.K	Heat transfer
Electrical resistivity	ohm.m	Conductivity needs
Melting point	C	Operating temperature

Manufacturing Compatibility

Process-Material Matrix

Process	Metals	Polymers	Ceramics	Composites
Casting	Yes	Yes	Limited	No
Machining	Yes	Yes	Limited	Yes
Forging	Yes	No	No	No
Injection molding	No	Yes	No	Short fiber
Sheet forming	Yes	Limited	No	Limited
Additive	Yes	Yes	Limited	Yes

Environmental Considerations

1. Corrosion Resistance

   • Atmospheric exposure
   • Chemical exposure
   • Galvanic compatibility
   • Stress corrosion cracking

2. Temperature Effects

   • Property degradation
   • Creep behavior
   • Oxidation resistance
   • Cryogenic performance

3. Sustainability

   • Recyclability
   • Embodied energy
   • Toxicity
   • Lifecycle assessment

Process Integration

• ME-014: Material Selection Methodology

Input Schema

{
  "application": "string",
  "loading_conditions": {
    "type": "tension|bending|torsion|combined",
    "magnitude": "number",
    "cyclic": "boolean"
  },
  "constraints": {
    "max_weight": "number (kg)",
    "max_cost": "number ($/part)",
    "max_temperature": "number (C)",
    "corrosion_environment": "string"
  },
  "manufacturing_process": "machined|cast|molded|forged|additive",
  "current_material": "string (if replacement study)",
  "required_properties": {
    "min_yield": "number (MPa)",
    "min_stiffness": "number (GPa)",
    "max_density": "number (kg/m3)"
  }
}

Output Schema

{
  "recommended_materials": [
    {
      "name": "string",
      "specification": "string (e.g., ASTM, AMS)",
      "performance_index": "number",
      "properties": {
        "yield_strength": "number (MPa)",
        "modulus": "number (GPa)",
        "density": "number (kg/m3)"
      },
      "cost_estimate": "number ($/kg)",
      "availability": "string"
    }
  ],
  "selection_rationale": "string",
  "trade_off_analysis": {
    "primary_candidate": "string",
    "alternates": "array",
    "comparison_matrix": "object"
  },
  "manufacturing_notes": "string",
  "specification_recommendation": "string"
}

Best Practices

1. Define functional requirements before selecting material
2. Consider full lifecycle costs, not just material cost
3. Verify property data from reliable sources
4. Account for processing effects on properties
5. Evaluate galvanic compatibility in assemblies
6. Document selection rationale for traceability

Integration Points

• Connects with Requirements Flowdown for design constraints
• Feeds into FEA Structural for analysis properties
• Supports DFM Review for manufacturing feasibility
• Integrates with Material Testing for validation