What is isotropic?
Isotropic means that a material has the same properties in all directions. This applies to strength, stiffness, heat conduction and expansion: for an isotropic material it does not matter at what angle you measure, the behaviour is the same. The opposite is anisotropic, where the properties do depend on direction.
Examples in construction
- Isotropic — steel is treated as isotropic in practice: it pulls, bends and conducts heat about equally in every direction. Unreinforced concrete and glass also approach isotropic behaviour.
- Anisotropic — wood is the best-known anisotropic building material: it is far stronger and stiffer along the grain than across it, and it moves (shrinks and swells) mainly across the grain. Layered or fibre-reinforced materials are also anisotropic.
Why it matters
Whether a material is isotropic or anisotropic determines how it is designed and used:
- Calculation — for an isotropic material one value for strength and stiffness often suffices; for an anisotropic material each direction must be calculated.
- Use of wood — beams are placed so that the load runs along the strong, lengthwise grain direction.
- Deformation — with anisotropic materials you must allow for direction-dependent shrinking, swelling and warping.
Many engineering materials are treated as isotropic for practical reasons, even though at the micro level they are never quite the same in all directions.
Related terms
- Material property
- Steel
- Concrete
- Wood
- Modulus of elasticity
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