Stress is a measure of the average amount of force exerted per unit area of a surface within a deformable body on which internal forces act. In other words, it is a measure of the intensity or internal distribution of the total internal forces acting within a deformable body across imaginary surfaces. These internal forces are produced between the particles in the body as a reaction to external forces applied on the body. Stress is defined as \({\rm{Stress}} = \frac{F}{A}\).