Blast/shot peening is a cold treatment process, the countless small circular called steel shot media continuous beat parts surface. Each star steel shot hit the metal parts, like a miniature great knocked on the surface, beating out small indentation or depression. In order to create a depression, metal surface will produce stretches. Below the surface, the grain trying to compress surface back to its original shape, so as to produce a highly compressed forces hemispheres. Numerous overlapping sag form even residual stress layer.
As is known to all, in a pressure stress area, crack is difficult to form or extending. Since almost all the exhaustion and stress corrosion failure occurs in parts surface or close to the surface of the place, and through the blast/shot peening guide into the compressive stress can greatly extend the life of parts. Strengthening the residual stress strength produced must achieve this parts material the tensile strength half.
A lot of metal fatigue failure of the transgressions is stress. The tensile stress may be caused by alternating load function or production process such as welding, grinding, machining form the residual stress. Stress tried to surface parts stretching or stretch, the ultimate cause of cracks occur. And pressure stress extrusion surface in grain, make the area of grain structure, laying the connection together, thus greatly delay fatigue crack formation. Stress layer, fine lines extend the slow, thus increasing the depth of stress, can effectively restrain the occurrence and development of cracks. This day, is shot/shot peening technology has been public thought that the most economic, effective prevention metal parts of the failure of early exhaustion technology.
Blast/shot peening mainly used for metal fatigue resistance. The following stress value and load times relationship figure with metal fatigue related LieShu several parameters points.
1. Fatigue load cycle by thousands of repeated loading a number, alternating load of the formation of the tensile stress in the parts of the surface up destructive tensile role
2. The tensile stress reduction in tired of life increase (load times) chart shows, such as stress reduce 32%, or 38 ksi (262 MPa), and the load life times can increase by 300%, or 150000 times.