material-selection

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Systematic material selection using Ashby methodology and performance indices

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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

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

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

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

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

Young's Modulus vs Density
- Identify materials above target index line
- Compare material families
- Identify lightweight alternatives
Strength vs Density
- Evaluate strength-to-weight ratio
- Compare metallic and composite options
- Identify high-performance materials
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

Corrosion Resistance
- Atmospheric exposure
- Chemical exposure
- Galvanic compatibility
- Stress corrosion cracking
Temperature Effects
- Property degradation
- Creep behavior
- Oxidation resistance
- Cryogenic performance
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

Define functional requirements before selecting material
Consider full lifecycle costs, not just material cost
Verify property data from reliable sources
Account for processing effects on properties
Evaluate galvanic compatibility in assemblies
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

Other versions

Version 2 on GitHub

Version 3 on GitHub