Stiffness

Stiffness is the extent to which an object resists deformation in response to an applied force.

For an elastic body with a single degree of freedom (DOF) (for example, stretching or compression of a rod), the stiffness is defined as

In Imperial units, stiffness is typically measured in pounds (lbs) per inch.

For example, a point on a horizontal beam can undergo both a vertical displacement and a rotation relative to its undeformed axis.

The ratios between the reaction forces (or moments) and the produced deflection are the coupling stiffnesses.

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

In the SAE system, rotational stiffness is typically measured in inch-pounds per degree.

where Note that the torsional stiffness has dimensions [force] * [length] / [angle], so that its SI units are N*m/rad.

For the special case of unconstrained uniaxial tension or compression, Young's modulus can be thought of as a measure of the stiffness of a structure.

The stiffness of a structure is of principal importance in many engineering applications, so the modulus of elasticity is often one of the primary properties considered when selecting a material.

In biology, the stiffness of the extracellular matrix is important for guiding the migration of cells in a phenomenon called durotaxis.

The skin maintains its structure due to its intrinsic tension, contributed to by collagen, an extracellular protein that accounts for approximately 75% of its dry weight.

[5] The pliability of skin is a parameter of interest that represents its firmness and extensibility, encompassing characteristics such as elasticity, stiffness, and adherence.