Stress (mechanical)

Description

Stress is a physical quantity that expresses the internal forces that neighboring particles of a continuous material exert on each other. Any strain (deformation) of a solid material generates an internal elastic stress, analogous to the reaction force of a spring, that tends to restore the material to its original non-deformed state. If the deformation is gradually changing with time, even in fluids, there will usually be some viscous stress, opposing that change. Elastic and viscous stresses are usually combined under the name mechanical stress. Stress is defined as the average force per unit area that some particle of a body exerts on an adjacent particle, across an imaginary surface that separates them. The stress that a particle applies on another particle perpendicular to the surface is the normal stress (compression or tension) and parallel to the surface is the shear stress.