Shot peening is a cold work process used to enhance the life of metal components, to prevent fatigue, stress corrosion failures and prolong the product life for the component part.

Fatigue is the weakening of a material caused by repeatedly applied loads.  It is the progressive and localised structural damage that occurs when a material is subjected to a cyclic loading.

Fatigue occurs when a material is subjected to repeated loading and unloading.   If the loads are above a certain threshold point microscopic cracks will begin to form at the stress concentration points, such as the surface, sharp points in the deviation in shape and the internal grain structure. Eventually a crack will reach a critical size, the crack will elongate suddenly, and the component will break.

The shape and structure of the component part will significantly affect its fatigue life.  Square holes or sharp corners, undercuts and swages, will lead to higher local stresses and this is where fatigue cracks can start.  Round holes, smooth transitions and fillets increase the fatigue strength of the component.

In the shot peening process, small round, spherical shot bombards the surface of the component.  The shot acts like a peening hammer, dimpling the surface and causing compression stresses under the dimple.   As the media continues to strike the part, it forms multiple overlapping dimples over the metal surface.

The surface compression stress strengthens the metal, ensuring that the component part will resist fatigue failures, corrosion fatigue, cracking, beading or galling of the surface and erosion from cavitation.

Shot peening is the most economical and effective method of producing and making surface residual compressive stresses to increase the product life of treated metal components. Shot peening is also used for work hardening to improve wear characteristics, straightening distortions, surface texturing and for creating aerodynamic curvatures for aerospace designs. The increased strength of treated parts allowsfor lighter-weight parts that exhibit high wear and fatigue resistance.

Typical applications include:

• Aircraft –  turbine components, aircraft frame components including stingers, ribs, flaps, wheels and landing gear components
• Automotive –  springs, valve  springs, cam shafts crankshafts, valves, valve seats, gears, splines, sprockets, steering components, clutches, manual and auto transmission parts, break discs, suspension, torsion bars and axle components, steel and alloy wheels, motor cycle handle bars
• Components for the oil and gas, electric, water and nuclear industries

Click on links to read

2 – Measurement Of Compressive Residual Stress Using X-ray Diffraction
3 – How to Measure Residual Stress
4 – MPa and Relationship to Almen Strips

For more information on shot peening please visit www.rosler.com

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Post written by
Haydn Kitchen
Shot Blasting Technical Manager