shot peening residual stress - Metal Improvement Company

C H A P T E R T W O
RESPONSE OF METALS
10
H I G H S T R E N G T H S T E E L S
The residual compressive stress induced by shot peening is a percentage of the ultimate tensile strength
and this percentage increases as the strength/hardness increases. Higher strength/hardness metals
tend to be brittle and sensitive to surface notches. These conditions can be overcome by shot peening
permitting the use of
high strength metals in
fatigue prone
applications. Aircraft
landing gear are often
designed to strength
levels of 300 ksi (2068
MPa) that incorporate
shot peening. Figure 2-
1 shows the relationship
between shot peening
and use of higher
strength materials.
Without shot peening,
optimal fatigue
Figure 2-1 Fatigue Strength vs. Ultimate Tensile Strength
properties for machined
steel components are obtained at approximately 30 HRC. At higher strength/hardness levels, materials
lose fatigue strength due to increased notch sensitivity and brittleness. With the addition of compressive
stresses, fatigue strength increases proportionately to increasing strength/hardness. At 52 HRC, the
fatigue strength of the shot peened specimen is 144 ksi (993 MPa), more than twice the fatigue strength
of the unpeened, smooth specimen [Ref 2.1].
Typical applications that take advantage of high strength/hardness and excellent fatigue properties with
shot peening are impact wrenches and percussion tools. In addition, the fatigue strength of peened
parts is not impaired by shallow scratches that could otherwise be detrimental to unpeened high
strength steel [Ref 2.2].
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