- Location
- Billings MT/Rapid City SD
Ok this is gonna be long. Excerpts taken from Carroll Smith book Engineer To Win
"Grain Boundaries and dislocations within the metallic crystal lattice serve as barriers which prevent ( or atleast discourage) the propagation of cracks. Thin surface layers of highly compressed metals also serve as highly effective crack propagation barriers. Almost all fatique and stress corrosion cracks orginate at the surface of a part, there fore if we can introduce a highly compressed layer of material at the surface of the part, the fatigue life of the part will be notably improved.
Shot Peening is a cold working process designed to both increase the fatigue life and discourage stress corrosion cracking of highly stressed metal parts. The surface of a part is heavily and continously bombarded with round steel shot under prescisely controlled conditons. Each ball acts as a tiny peening hammer, compressing a small area of the surface layer of the metal. When then complete surface has been evenly peened the result is a residual compression stress of predetermined depth and stress level in the surface of the part. This layer is permanent and will discourage the fromation of both fatique and stress corrosion cracks. The treatment is universally applied to highly stressed parts in the aerospace industry and should be in motor sports. The chief reason it is not is ignorance.
Shot Peening is not:
Sand Blasting
Glass bead blasting
Peening with steel shot in your in shop blasting cabinet. The control is not possible to obtain.
Example:
The effects of various blasting and peening process on E4130 tube.
Condition Fatigue Limit
As received...............................45 ks
Sand Blasted with round sand..42 ksi
Sand Blasted ith sand dust........44 ksi
Blasted with steel grit.................45 ksi
Shot Peened...............................55 ksi
What to Peen:
Springs: coil, leaf, and or torsion bars/ And reputable spring maker will have already shot peened his springs. Detroit does. The lack of shot peening give you one more reason not to buy them. "
There are a few more example on how shot peening increase fatigue life but I'm not going to mention them unless someone wants to see them. This is to clear up any ideas and to give you a clear idea of what shot peening is and whats it's designed to do.
"Grain Boundaries and dislocations within the metallic crystal lattice serve as barriers which prevent ( or atleast discourage) the propagation of cracks. Thin surface layers of highly compressed metals also serve as highly effective crack propagation barriers. Almost all fatique and stress corrosion cracks orginate at the surface of a part, there fore if we can introduce a highly compressed layer of material at the surface of the part, the fatigue life of the part will be notably improved.
Shot Peening is a cold working process designed to both increase the fatigue life and discourage stress corrosion cracking of highly stressed metal parts. The surface of a part is heavily and continously bombarded with round steel shot under prescisely controlled conditons. Each ball acts as a tiny peening hammer, compressing a small area of the surface layer of the metal. When then complete surface has been evenly peened the result is a residual compression stress of predetermined depth and stress level in the surface of the part. This layer is permanent and will discourage the fromation of both fatique and stress corrosion cracks. The treatment is universally applied to highly stressed parts in the aerospace industry and should be in motor sports. The chief reason it is not is ignorance.
Shot Peening is not:
Sand Blasting
Glass bead blasting
Peening with steel shot in your in shop blasting cabinet. The control is not possible to obtain.
Example:
The effects of various blasting and peening process on E4130 tube.
Condition Fatigue Limit
As received...............................45 ks
Sand Blasted with round sand..42 ksi
Sand Blasted ith sand dust........44 ksi
Blasted with steel grit.................45 ksi
Shot Peened...............................55 ksi
What to Peen:
Springs: coil, leaf, and or torsion bars/ And reputable spring maker will have already shot peened his springs. Detroit does. The lack of shot peening give you one more reason not to buy them. "
There are a few more example on how shot peening increase fatigue life but I'm not going to mention them unless someone wants to see them. This is to clear up any ideas and to give you a clear idea of what shot peening is and whats it's designed to do.
