Simulic
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Material selection chart – strength and stiffness against density

Design & TechnologyMechanical EngineeringAges 16–17

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An Ashby-style log–log chart places 24 materials (metals, polymers, timbers, GFRP and CFRP composites, ceramics and glass, foams) by strength or Young's modulus against density. Set a design brief for a tie or a cantilever beam: load, length, safety factor, maximum mass, maximum cost and carbon footprint, and widely recycled materials only. A mass-limit line based on the index σ/ρ or E/ρ shortlists the materials that pass, and a test panel compares the strength-to-weight ratio of CFRP, GFRP, aluminium and steel.

Lesson: Selecting materials by properties: strength, stiffness, density, cost and environmental impact; composite materials (GFRP, CFRP); performance indices σ/ρ and E/ρ

What it shows

Engineers rarely pick a material by one property. On an Ashby-style chart each material is a bubble spanning its typical range of strength or stiffness and density, and materials of a family cluster together. For a tie, the mass of the part is m = nFLρ/σ, so a light design needs a high strength-to-weight ratio σ/ρ; for a beam the index becomes σ^(2/3)/ρ or √E/ρ. The dashed line marks where the part reaches the mass limit; everything above it is light enough. Cost per kilogram, carbon footprint and recyclability narrow the shortlist further.

How to use

Choose Strength–density or Stiffness–density, and Tie or Cantilever beam. Set the load, length, safety factor and the limits for mass, cost and carbon footprint with the sliders, or tick Only widely recycled materials. Bright bubbles meet every requirement, faded ones fail. Click a bubble or use the Material list to read its data, see its part in the comparison test against CFRP, GFRP, aluminium and steel, and use the table to justify a choice. Colour by changes the overlay.

Parameters you can change

  • Chart Strength–density, Stiffness (E)–density
  • Component Tie (rod in tension), Square-section cantilever beam
  • Load F 0.1–50 kN
  • Length L 0.1–3 m
  • Safety factor n 1–4
  • Maximum mass of the part 0.01–100 kg
  • Maximum stretch or deflection δ 0.1–20 mm
  • Maximum cost of the part 0.1–500 USD
  • Maximum carbon footprint of the part 0.1–200 kg CO₂e
  • Only widely recycled materials
  • Colour by Material family, Price per kg, Carbon footprint per kg
  • Material shown Mild steel, Stainless steel, Cast iron, Aluminium alloy, Titanium alloy, Brass, Polyethylene (HDPE), Polypropylene (PP), Rigid PVC, Nylon (PA), Acrylic (PMMA), Epoxy resin, Rubber, Balsa, Pine, Oak, Plywood, Glass-fibre composite (GFRP), Carbon-fibre composite (CFRP), Glass, Alumina ceramic, Concrete, EPS foam, Rigid PU foam

Questions to explore

  1. Why does CFRP beat steel for a light tie, yet steel is still used for most building frames?
  2. How does the shortlist change when only widely recycled materials are allowed?
  3. Why do timbers do better as light beams than as light ties compared with metals?

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