Stiffness

Stiffness is the resistance of an elastic body to deflection by an applied force. The stiffness k of a body that deflects a distance δ under an applied force P is:

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:k=rac {P} {delta}

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Stiffness is typically measured in newtons per metre.

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As both the applied force and displacement are vectors (respectively P and δ), in general their relationship is characterised by a stiffness matrix, k where:

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:P = k δ.

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The displacement can, in general, refer to a point distinct from that where the force is applied and a complicated structure will not deflect purely in the same direction as an applied force. The stiffness matrix enables such systems to be characterised in straightforward terms.

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The inverse of stiffness is compliance, typically measured in units of metres per newton.

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