Modulus matters.
Beam theory.
Stiff designs.
Material selection for stiff structures. Modulus × moment of inertia = stiffness. High-modulus materials enable thinner stiff structures.
Key principles.
Reference modulus
Carbon steel highest common modulus.
Vibration damping
Cast iron good damping plus reasonable stiffness.
Stiffness + light
Titanium 55% steel modulus, 56% steel density.
Light, less stiff
Aluminum 35% steel modulus.
Lightest, low E
Lowest density but low modulus too.
Anisotropic
Composite stiffness per fiber direction.
Stiffest plastic
PEEK among stiffest engineering plastics.
E=8-12 GPa
Glass fibers triple plastic modulus.
Construction
Construction-scale stiff material.
FAQ
Stiff material rankings?
By modulus: ceramic > steel > titanium > cast iron > aluminum > magnesium > engineering plastics > commodity plastics.
Specific modulus (E/ρ)?
Stiffness-per-mass measure. Steel and aluminum nearly equal. Beryllium and composites highest.
Geometry vs material for stiffness?
Cube of dimension dominates over linear in modulus. Doubling thickness 8× stiffness. Material change 3× max effect.
Composite anisotropy?
Carbon fiber stiff along fibers, weak across. Lay up at 45° + 0/90° for balanced. Premium application.
Stiff plastics?
PEEK, PEI, PSU among stiffest unfilled. Glass-filled boost 3-5×. Carbon-fiber-filled even stiffer.
Cost vs stiffness?
Steel cheapest stiff metal. Aluminum cheaper but less stiff. Composites premium but high specific modulus.
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