shot peening residual stress - Metal Improvement Company

C H A P T E R T W O
RESPONSE OF METALS
14
T I T A N I U M
High Cycle Fatigue (HCF) - HCF of
titanium is illustrated by Figure 2-4 that
compares the capabilities of titanium
alloy connecting rods for a high
performance European sports car. The
rods are manufactured using various
processes. With shot peening, the
fatigue limit was increased by
approximately 20% while weight was
reduced by some 40% as compared to
steel connecting rods [Ref 2.12].
Low Cycle Fatigue (LCF) - As is typical
with other metals, the fatigue response
with shot peening increases with
higher cycle fatigue. Higher cycle
fatigue would be associated with lower
stresses whereas lower cycle fatigue
would be associated with higher stress
levels. This is demonstrated
graphically in the S-N Curve (Figure 1-4)
and also Figure 2-5.
Figure 2-5 shows the results of shot
peening titanium dovetail slots on a
rotating engine component [Ref 2.13].
There are two baseline load curves that
are not shot peened. When shot
peening is applied, the base line curve
that initially had more cycles to failure
responded significantly better. Note
that improvements in fatigue life are on
an exponential basis.
Figure 2-4 Comparison of Fatigue Strengths for Polished
and Shot Peened Titanium Ti6A14V
Figure 2-5 LCF Benefits from Shot Peening Notched Ti8-1-1
The most common application of LCF for titanium is the rotating turbine engine hardware (discs, spools,
& shafts) with the exception of blades. These components are shot peened to increase durability. Each
takeoff and landing is considered one load cycle.
M A G N E S I U M
Magnesium alloys are not commonly used in fatigue applications. However, when used for the benefit of
weight reduction, special peening techniques can be employed to achieve 25 - 35% improvement in
fatigue strength.
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