The concentration of internal force, that is, the internal force per unit area, is called "stress". Stress can be decomposed into components perpendicular to the section (shear plane), which are called "normal stress" or "normal stress". The component tangent to the section (shear plane) is called "shear stress".
Extended data
Under the action of shear stress, the cross section of the material is relatively dislocated and deformed along the direction of external force. The force that can cause shear deformation of materials is called shear force or shear force. A section with shear deformation is called a shear plane.
The key to judge whether it is "shearing" is whether the cross section of the material is relatively misaligned. Therefore, cutting vegetables with a kitchen knife is not a shearing phenomenon (because the cross section of vegetables does not move relatively), but cutting nails with scissors is (the cross section of nails moves relatively). Note: Nail clippers can cut nails, but it is not a phenomenon.