PROBLEM: A couple of forces, each having magnitude F, keep a cuboid at rest.Mathematically, action of this couple can be represented by two collinear vectors as shown in the figure.

Calculate normal nominal stress acting on the cross-section A located in the middle of the plate length. The cross-section A is parallel to the base of the cuboid.

SOLUTION: One simple way of calculating the required stress is to assume that the cuboid(i) is stiff enough to prevent any deflection due to the action of gravity on its mass,(ii) is made of continuous, isotropic and homogeneous material, and(iii) geometry allows for ideally equal distribution of stress within the cross-section A.