The shot peening is a modern technique of metal parts surface work hardening, widely spread in the aircraft and the car industries. This surfaces mechanical treatment should not be mixed up with the shot-blasting other usual applications which are all directed towards the surfaces cleaning, preparation or finishing. The shot peening must be considered as a real machining operation which will improve the parts life.
Object of the operation
The shot peening is a hammering technique with a spherical shot which aim is to create a residual stresses on the surface of metal or hammer-hardenable parts. It allows thus to increase their mechanical qualities..
The technique consists in shooting at high speed small steel, glass or ceramic beads on the surface of the parts to be treated. Under the action of the beads hammering, the surface which exceeded the tensile yield strength is bent out of shape and encloses a subjacent coat of compressive metal that has not reached its tensile yield strength. The contained force which requires to be released is opposed to the permanent strain of the surface coat.
The balance between these two forces generates surface tensions which improve thus: