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March 2017
AFRICAN FUSION
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Figure 2: A schematic view of the welded sample used in fatigue testing.
Figure 4. Drawings of the welded specimens for fatigue testing at different
conditions: W: As-welded condition; R: Repair by gouging and welding; R/UP:
Repair by gouging, welding and UP.
Figure 3: Fatigue curves of welded elements (transverse non-load carrying
attachment). 1: In the as welded condition; 2: UP was applied before fatigue
testing; 3: UP was applied after fatigue loading with the number of cycles
corresponding to 50% of expected fatigue life of samples in as-welded
condition.
Mechanical Properties
σ
y
(MPa)
σ
u
(MPa)
δ
(%)
Ψ
(%)
260
450
37.6
63
Table 1: The mechanical properties of base material.
Chemical composition (%)
C
Si
Mn
S
0.210
0.205
0.520
0.019
P
Cr
Ni
Cu
0.007
0.040
0.040
<0.010
Table 2: The data on chemical composition of base material
the mechanical properties of the material used, the type of
welded joints, the cyclic loading parameters and other factors.
For the effective application of the UP, depending on the
above-mentioned factors, a software package for optimum
application of ultrasonic peeningwas developed that is based
on an original predictive model. In the optimum application,
a maximum possible increase in fatigue life of welded ele-
ments with minimum time, labour and power consumption
is predicted [4].
Manufacturing and rehabilitation
The effectiveness of UP treatment applications to as-manu-
factured parts and in rehabilitation of parts that have already
served a considerable amount of their useful fatigue life was
studied. Rehabilitation is considered as the prevention of pos-
sible fatigue crack initiation in existing welded elements and
structures that are in service. UPwas applied to newparts and
to parts after 50% of their expected fatigue life.
Three series of large-scale welded samples imitating the
transverse non-load-carrying attachments (Figure 2) were
subjected to fatigue testing in 1: The as welded condition; 2:
After UP was applied before fatigue testing; and 3: After UP
was applied after fatigue loading with the number of cycles
corresponding to 50% of the expected fatigue life of samples
in the as-welded condition [8].
Tables 1 and 2 present themechanical and chemical prop-
erties of the materials used for preparation of the samples.
The results of the conducted fatigue testing with UP applied
to specimens in the as-welded condition and also after 50%
of expected fatigue life are presented in Figure 3.
As can be seen from Figure 3, UP caused a significant
increase in fatigue strength of the welded elements for both
series of UP treated samples. The increase in the limit stress
range at N=2×10
6
cycles of welded samples is 49% (from
119 MPa to 177 MPa) for UP treated samples before fatigue
loading; and 66% (from 119 MPa to 197 MPa) for UP treated
samples after fatigue loading – with the number of cycles cor-
responding to 50% of the expected fatigue life of the samples
in the as-welded condition.
The higher increase of fatigue life of UP treated welded
elements for fatigue curve No 3 could be explained by a more
beneficial redistribution of residual stresses and/or ‘healing’
of fatigue-damaged material by UP in comparison with the
fatigue curve No 2.
Use of UIT/UP for weld repair
UP could also be effectively used during the weld repair of
fatigue cracks [3, 5]. Figure 4 shows the drawings of large-scale
welded specimens containing non-load carrying longitudinal
attachments for fatigue testing [3]. These specimens were