the external pressure which creates the interval force. The stress

the external pressure which creates the interval force. The stress

Stress (in a solid)

The force per unit area, acting on any surface within it, and variously expressed as pound or tons per square inch, or dynes or kilograms per square centimeter; also, by extension, the external pressure which creates the interval force. The stress at any point is mathematically defined by nine values: three to specify the normal components and six to specify the shear components, relative to three mutually perpendicular reference axes.

Stress is a tensor of second rank. The forces area thought to act on every one of the infinitesimal elements of area with different orientation, which can be imagined at one point. Only such forces are considered which are locally in equilibrium with equal and opposite forces: tensor is symmetrical.