Shot peening is
a cold working process in which small spherical media
called shot bombard the surface of a part. During the shot peening process, each piece of
shot that strikes the material acts as a tiny peening
hammer, imparting to the surface a small indentation
or dimple. To create the dimple, the surface of the
material must yield in tension. Below the surface, the
material tries to restore its original shape, thereby
producing below the dimple, a hemisphere of cold-worked
material highly stressed in compression.
Nearly all fatigue and stress corrosion failures originate at the surface of a part, but cracks will not initiate or propagate in a compressively stressed zone. Because the overlapping dimples from shot peening create a uniform layer of compressive stress at metal surfaces, shot peening provides considerable increases in part life. Compressive stresses are beneficial in increasing resistance to fatigue failures, corrosion fatigue, stress corrosion cracking, hydrogen assisted cracking, fretting, galling and erosion caused by cavitation. The maximum compressive residual stress produced just below the surface of a part by shot peening is at least as great as one-half the yield strength of the material being shot peened.
most modes of long-term failure, the common
denominator is tensile stress. Tensile stresses attempt
to stretch or pull the surface apart and may eventually
lead to crack initiation. Because crack growth is slowed
significantly in a compressive layer, increasing the
depth of this layer increases crack resistance. Shot
peening is the most economical and practical
method of ensuring surface residual compressive stresses.
For applications that require deeper residual compressive
stresses than those provided by shot peening, Metal
Improvement Company's laser peening process imparts
a layer of beneficial compressive stress that is four
times deeper than that attainable from conventional shot peening treatments.
Shot peening also can induce the aerodynamic curvature in metallic wing skins used in advanced aircraft designs. Additional applications for shot peening include work hardening through cold work to improve wear characteristics, closing of porosity, improving resistance to intergranular corrosion, straightening of distorted parts, surface texturing and testing the bond strength of coatings.
Metal Improvement Company engineering specialists
can help you best address the fatigue, forming and distortion
correction challenges that manufacturers of fabricated
metal parts face every day. Metal Improvement Company's
shot peening facilities employ the latest state-of-the-art
processing capabilities for shot peening components
of diverse shapes, sizes and materials under rigidly