Shear

If the forces applied on a material tend to slide one face of the material over an adjacent face, then the material is said to be in shear.

        In an aircraft structure, most load bearing members are subjected to a combination of tensile, compressive and shear forces. The structure is called as beam, when it is subjected to all these forces and middle part of the beam is called as shear web. The following figure shows a beam resting on two supports. A perpendicular force on a beam will create a shear force at the point of application. The beam tends to bend in the middle and gives complex stresses in these areas.

        In a flying aircraft, a compressive force is on the top surface, a tensile force is at the bottom and a shear force is in the middle. When on the ground, the wing will bow due to its own weight. In this case, the compressive and tensile forces will be reversed, but the shear web will still be in shear. The flanges are designed to withstand compressive and tensile forces while the web is designed to withstand shear forces.