Rotational Stiffness

Stiffness

Stiffness (k) is the relationship between an applied force and the displacement the force produces. This relationship can be defined for two common cases:

In the linear case, the applied force (F) is proportional to the linear displacement (x) of one end of the "spring" with respect to the other (i.e. the amount of stretch or compression of the spring).

F = k * x

In the rotational case, the applied torque (T) is proportional to the angular displacement (theta) of one side/end with respect to the other.

T = k * theta

In both cases, the relationship can be non-linear, however a linear relationship is easier to work with.

Linear Spring

Extension springs avaiable through Ganga Spring Industries

A linear extension spring is generally a coil, usually made of a tempered steel. The thickness of the wire used to make the spring and the number and diameter of the coils determines the stiffness. Over the elastic extension range for the spring, the relationship between the extension of the spring and the force required to attain that extension is linear. This type of spring obeys Hook's Law:

F = k * x

Torque/Moment

A torque (or moment) is a