Fatigue failure is usually related to cyclic loading. Applied tensile
stress at the surface is most commonly from bending or torsion.
Residual tensile stress induced during manufacturing can also contribute
to failure.  Shot Peening is a cost effective and practical method of
improving metal fatigue properties through the use of beneficial compressive stress. This is proven to enhance protection against failures due to:

• Metal fatigue
• Stress Corrosion Cracking (SCC)
• Fretting
• Contact Fatigue
• Reduction of fatigue scatter from manufacturing processes – Manufacturing of highly loaded parts frequently involves multiple processes that modify either surface finish &/or residual stress which then has an effect on fatigue life. These processes include: aggressive machining, welding, heat treating, grinding, plating, etching, anodizing, & electro-discharge machining. Reduce fatigue scatter from manufacturing.
  When there is variability in surface finish &/or residual stress, there will be variability in fatigue performance. By incorporating shot peening, a uniform and predictable layer of residual compressive stress is imparted to the surface. In addition to increasing fatigue life, scatter in fatigue life will be reduced.