Material Selection Skill Skill

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 |
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

Agent Skills: Material Selection Skill

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