The stress vector f which describes the state of stress of a deformable body subjected to external loads is defined as [1]:

where is the average force per unit area over an increment of surface area . The state of stress drives the response of bodies subjected to static and dynamic loads.

The state of stress of a deformable body may be determined either numerically or experimentally [2]. However, the term "stress analysis" as presently used generally refers to the numerical solution of the state of stress using the displacement method of finite elements.