ULTRASONIC IMPACT TREATMENT.
PHYSICS OF THE PROCESS. APPLICATION. RESULTS.
DESIGN FEATURES. EQUIPMENT.
E.S. Statnikov
Applied Ultrasonics, P.O. Box 100422, Birmingham, Alabama, 35210, USA
Northern Scientific and Technology Company
6 Voronin St., Severodvinsk, Arkhangelsk Region, 164500, Russia
ABSTRACT
Considerable recent attention has been given to post-weld and concurrent treatments
of welded joints. These treatment methods are intended to increase the quality,
reliability and life of welded structures. Ultrasonic impact treatment (UIT) has a
particular place among them.
Independent expert assessments of this method obtained from the laboratories in
Russia, Ukraine, France, Norway, Sweden, USA and Japan pointed out the
effectiveness of this technology.
The paper covers the information on the design features of the UIT process systems,
physics of UIT, equipment and areas of application, and UIT effect on the fatigue
resistance.
1. INTRODUCTION
The paper presents the results of the development [1] and study of UIT benefits for
increasing the fatigue limit of welded joints. The UIT technology and equipment
have been developed at NSTC (Severodvinsk, Russia). At different times, the UIT
method was adapted and studied at the E.O. Paton Electric Welding Institute, Ukraine
together with NSTC and based on the orders of NSTC. The results of the UIT study
performed at the Norwegian University of Science and Technology, Trondheim,
Norway and SSAB, Sweden are presented.
2. METHOD FOR ULTRASONIC IMPACT TREATMENT OF WELDED
JOINTS [2]
The method is based on the instrumental conversion of harmonic oscillations of the
ultrasonic transducer into peening impulses of ultrasonic frequency and their further
conversion into harmonic oscillations of a treated surface and a structure element at an
excitation frequency.
In the course of the method development we achieved the optimization of an active
element being a part of the ultrasonic tool which allowed us for minimization of sizes
and 4 times increase in specific power as compared to the conventional manual tools
[3].
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The UIT zones of action are shown in Fig. 1 in a cross-sectional view of the surface
layer of the welded joint metal being treated.
ULTRASONIC RELAXATION (10-:-12mm)
IMPULSE RELAXATION (3-:-5mm)
“WHITE LAYER”
(0.02-:-0.1 mm)
PLASTIC DEFORMATION (1-:-1.5mm)
imp. = (1.2-:-1..5)t
Ах=Аоexp(-x)
imp. = 0.5
Ах=Аоsin(t-kx)
[Symbolic presentation in
polarization plane, no scale
cycles = (0.1-:-0.3)
Zones
"White layer"
Plastic
deformation
Impulse
relaxation
Ultrasound
relaxation
EFFECT
Wear-resistance, corrosion resistance
Cyclic endurance, compensation of deformation, corrosionfatigue strength
Reduction in residual welded stress and strain of up to 70% of
the initial state
Reduction in residual welded stress and strain of up to 50% of
the initial state
Fig. 1 UIT action physical zones
Figure 1 and the accompanying table represent the UIT study results. The results
define the topical areas of UIT application in production, maintenance and repair of
welded structures. Only one area of application is addressed below, namely the
fatigue resistance of the welded joint metal.
3. UIT EFFECT ON FATIGUE STRENGTH OF WELDED STEEL
JOINTS [4]
Presented here are the fatigue test results for welded joints from steel WELDOX 420
made at SSAB, Sweden. The results were obtained at the E.O. Paton Electric
Welding Institute of the NAS of Ukraine in cooperation with NSTC and to the order
of NSTC. The intention was to compare the effectiveness of UIT with that of wellknown methods of shot peening, hammer peening and TIG dressing of weld toes. The
tests were in accordance with IIW Collaborative Test Program on Improvement
Methods (Doc. XIII-WG2-30-94).
3.1.
Material and Specimen Fabrication
Specimens were fabricated from WELDOX 420 steel 20mm in thickness made at
SSAB, Sweden. Mechanical properties of the steel as determined during study are
given in Table 1.
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Table 1 Mechanical properties of steel
Specimen No. Yield strength, MPa Ultimate tensile strength, MPa Elongation, %
1
457,1
571,9
28,0
2
463,7
571,5
28,8
3
462,7
575,5
29,6
Average
461,2
573,0
28,8
Plates for specimen fabrication were welded at SSAB by the SAW process. ESAB
welding materials were used: OK 12.32 / OK Flux 10.71.
The welding conditions were as follows:
Interpass temperature: 150 – 170ºC, DC+
Pass No. 1: side 1, 925A, 34V, speed = 39 cm/min ; HI = 4,8 kJ/mm
Pass No. 2: side 1, 720A, 30V, speed = 49 cm/min; HI = 5,8 kJ/mm
Pass No. 3: side 1, 720A, 30V, speed = 49 cm/min; HI = 5,8 kJ/mm
Pass No. 4: side 2, 925A, 34V, speed = 39 cm/min; HI = 4,8 kJ/mm
Pass No. 5: side 2, 720A, 30V, speed = 39 cm/min; HI = 4,8 kJ/mm
Pass No. 6: side 2, 720A, 30V, speed = 39 cm/min; HI = 4,8 kJ/mm
A total of three plates were welded to the sizes shown in Fig. 2.
1 – as-welded specimens; 2 – UIT treated specimens; 3 – hammer peened specimens;
4 – shot peened specimens; 5 – TIG dressed specimens; 6 – specimens subjected to
TIG dressing followed by UIT;
Fig. 2
Geometry of welded plates for fabrication of as-welded and improved
specimens
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The plates were cold sawn into specimen widths and then milled to finished sizes, as
shown in Fig. 3. 54 fatigue test specimens were made in the as-welded condition (1
series) and improved by various treatments (5 series). Each series was made up of 9
specimens.
Fig. 3 Fatigue test specimen geometry
3.2.
Fatigue Test Results
Based on the results, the benefits of hammer peening, shot peening, TIG dressing and
combined treatment of TIG dressing and UIT were virtually the same. These
improvement treatments increased the fatigue strength at 2 x 10 6 cycles by 41-51%.
The considerable improvement, 65%, was obtained from the UIT treated joints with
treatment performed using the 3mm multi-pin tool. Comparison of fatigue curves for
the as-welded joints and welded joints treated by UIT using various parameters
(including 5mm diameter pins) shows that the maximum effect is obtained by
treatment with a 3mm multi-pin tool which produces a groove (up to 0,8mm in this
particular case) at the weld toe.
3.3.
Conclusion
Comparison of all the fatigue curves obtained, shown in Fig. 4, indicates that UIT
gives the great benefit as against other improvement techniques. It should be noted
that the benefit from UIT depends on the treatment parameters.
707


,
M
P
a
4
5
0
57 6
4
0
0
2
3
5
0
4
3
0
0
3
2
5
0
1
2
0
0
1
e
+
4
1
e
+
5
1
e
+
6
N
,
c
y
c
l
e
s
Linear regression :
Series 1 – as welded (m = -5,6867);
Series 2 – UIT treated (m = -17,5413), 5 and 3mm pin diameter;
Series 3 – hammer peened (m = -8,3701);
Series 4 – shot peened (m = -8,1321);
Series 5 – TIG dressed (m = -6,5539);
Series 6 – TIG dressed and UIT treated (m = -6,2090);
Series 7 – UIT treated (m = -9,7799), additional series, 3mm pin diameter.
Series No.
1
2
3
4
5
6
7
Δ
(N=2000000 cycles), MPa
198,2789
327,5881
278,9457
280,6418
286,7175
293,2463
341,9457
Results of approximation
lgN=19,3650-5,6867*lg
lgN=50,4231-17,5413*lg
lgN=26,7702-8,3701*lg
lgN=26,2096-8,1321*lg
lgN=22,4068-6,5539*lg
lgN=19,3650-6,2090*lg
lgN=31,0829-9,7799*lg
After treatment increase of Δ,
%
65
41
42
44
51
73
Fig. 4 Fatigue curves for WELDOX 420 welded joint in the as-welded and improved
conditions
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4. UIT EFFECT ON FATIGUE STRENGTH OF WELDED ALUMINUM
PLATES [5]
Two types of aluminum specimens were tested in the as-welded condition and
improved by ultrasonic impact treatment at the Norwegian University of Science and
Technology, Trondheim, Norway in collaboration with SSAB, Sweden.
4.1.
Test Procedure
The aluminum specimens were fabricated from a typical ship plate material, AA5083
(or AlMg4.5Mn). The minimum specified yield and ultimate tensile strengths were
250 and 335 MPa, respectively, with a ductility of A5 = 10%.
Two basic types of aluminum specimens were tested. One is a lap type specimen
shown in Fig. 5.
t=8
Fig. 5 Aluminum lap joint fatigue test specimen
The second type of aluminum specimen is shown in Fig. 6.
140
8
8
Fig. 6 Aluminum specimen with longitudinal attachments
The specimens were fillet welded using standard shop practice at Kværner Fjellstrand
shipyard. The UIT was performed at Kvant in Severodvinsk according to standard
practice. The aluminum lap joints had good quality welds. The aluminum specimens
with longitudinal attachments, however, were weld at high production rates and had
welds of poor quality at the ends of the attachments. Ultrasonic Impact Treatment,
however, improved the shape of the end of the weld considerably.
All specimens were tested in axial loading, constant amplitude at R = 0.1 The test
frequency was in the range 3 to 10 Hz. Failure was defined to have taken place upon
complete separation of the specimen.
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4.2.
Results and discussion
The test results for as-welded specimens with longitudinal attachments and those
improved by UIT are plotted in Fig. 7. Although the untreated weld had a very
unfavorable shape at the stiffener ends the S-N curve for improved weld is quite high.
Two of the specimens treated by UIT failed outside the weld, the cracks initiated at
small defects on the plate. The improvement in fatigue strength at two million cycles
is more than 90%, corresponding to a factor on life of 20 over the entire range of the
data.
R =0.1
Fig. 7 Results on aluminum specimens with longitudinal attachments in the aswelded and UIT improved conditions.
The test results for aluminum lap joints are presented in Fig. 8. These joints were
tested in the as-welded and UIT improved condition.
SN-diagram
Stress Range[MPa]
200
 As-welded
 UIT
100
50
20
10
10
4
10
5
10
6
10
7
Number of Cycles [N]
Fig. 8 S-N data for aluminum lap joints in the as-welded condition and UIT improved
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The improvement due to UIT is somewhat lower than for the aluminum specimens
with longitudinal attachments. The reason is probably that the as-weld S-N curve is
quite high so further improvement is not possible. This assumption is substantiated by
the fact that several failures initiated on the plate.
4.3.
Conclusions
UIT gives consistently large increases in fatigue strength, particularly at long lives,
for welded AA5083 aluminum plates.
The improvements in fatigue strength at long lives due to UIT are 80 %.
5. DESIGN OF UIT PROCESS SYSTEMS [6]
The traditional approach to the design of the ultrasonic process systems more often
assumes the qualitative determination of the technical requirements to the selection of
the oscillating system type, frequency and power of the ultrasonic transducer and
generator.
In this case, the matching with the load, as a rule, is accomplished in the final stage of
the selection and adjustment of the generator components, and the ultrasonic
transducer is taken as a load. More rarely, the load includes the process object, i.e. the
object acted upon by the ultrasonic oscillating system.
At the same time, the object’s response to the ultrasonic oscillating system under high
dynamic and static forces, imparted to this system during the action, is the main
indicator of the effectiveness of the operational process, as well as of the optimum
matching and adjustment in the system object–transducer–generator. Here, by the
object’s response to the action is meant, on the one hand, the oscillations of the object
and on the other the structural changes in properties and stressed state of the object
material.
From this follows the development logic of ultrasonic specific-purpose systems.
Conclusion
During the development of the ultrasonic process systems, along with the traditional
approach to the selection of the oscillating system and generator parameters, it is
prudent to sequentially use the acoustic study results of the process load with the
conversion of this load into the form of the acouso-mechanic load applied to the
ultrasonic transducer, and then conversion of these loads into the form of the electric
load applied to the generator.
6. UIT EQUIPMENT [7]
UIT of welded joints is performed with the equipment consisting of an ultrasonic tool
with operating frequency of 27, 36, 44 kHz and the associated ultrasonic generator
(Fig. 9).
711
Ultrasonic
generator
UIT tool
27 kHz
m=3.5 kg
Ultrasonic
transducer
27 kHz
UIT tool
36 kHz
m=1.2 kg
Ultrasonic
transducer
36 kHz
UIT tool
44 kHz
m=0.75 kg
Ultrasonic
transducer
44 kHz
Fig. 9 UIT equipment
5.1.
Specifications of Ultrasonic Tools
Operating frequency, kHz
Parameter
27*
Design
Rated consumed power, VA
Excitation voltage, V
Bias current, А
Oscillating amplitude of the waveguide
output end, micron
Treatment speed in manual mode,
m/min (m/h)
Treatment speed in automatic and semiautomatic mode, m/h
Overall dimensions of the manual tool, mm
Manual tool weight, kg
Cooling
Replaceable tool heads
Indenter diameter, mm
Hardness of the indenter work face
*Note:
27 kHz – production unit;
36 и 44 kHz – prototypes.
712
36*
44*
For manual treatment
For automatic treatment
600-1200
300-800
200-500
60-110
10-15
6-10
5-8
35-40
30-35
25-30
0,3 – 1,5 (18 – 90)
3 – 30
455х85х80
3,5
380х110х50
330х100х40
1,2
0,75
Liquid
Straight, angle
2-5
62-64 HRC
Manual ultrasonic tools installed on the welding machine travelers can be usable for
automatic UIT. Special tools can be designed based on the standardized ultrasonic
transducers developed and manufactured by NSTC (Fig. 9).
5.2.
Specifications of Ultrasonic Generator UIP MSP-5
Output power
Output power adjustment
Supply main voltage
Supply main frequency
Max output voltage
Operating frequency range
Overall dimensions
Weight: - generator
- power supply
Max cable length to connect generator and tool
Cooling
Automatic frequency adjustment
Mechanical resonance indication
Relative measurement of displacement amplitude
of the waveguide output end
600 – 1800 VA
stepped (4 ranges, 6 steps in each)
110/220 V
60/50 Hz
100 V
25 – 28,0 kHz
520 x 240x 470 mm
12,5 kg
19 kg
80 m
air
over the entire range
light
needle indicator
7. REFERENCES
1. Statnikov E S: Development and study of ultrasonic specific-purpose devices.
Thesis. Academy of Science of the USSR. Academic N.N Andreyev Acoustic
Institute, No. A-266, 1982.
2. Statnikov E S: ‘Increasing the life of welded joints by UIT’. Welding
Conference LUT JOIN’99. Int Conf on Efficient Welding in Industrial
Applications (ICEWIA), Lappeenranta, Acta Universitatis Lappeenrantaensis
85, 1999.
3. Statnikov E S, Kazantsev V F: ‘Design technological line of power acoustic
systems for technological purposes’. World Congress on Ultrasonics, Berlin,
1995.
4. Statnikov E S et al: 'Comparison of ultrasonic impact treatment (UIT) and
other fatigue life improvement methods'. IIW Doc. XIII-1817-00, Florence,
2000.
5. Haagensen P J, Statnikov E S and L Lopez-Martinez: 'Introductory fatigue
tests on welded joints in high strength steel and aluminium improved by
various methods including ultrasonic impact treatment (UIT)'. IIW Doc. XIII1748-98, Hamburg, 1998.
6. Statnikov E S: ‘Ultrasonic process systems for treating materials under high
dynamic and static forces imparted to oscillating system’. Int Conf Ultrasonic
Technological Processes-2000, Arkhangelsk, 2000.
7. Statnikov E S: 'Guide for application of ultrasonic impact treatment improving
fatigue life of welded structures’. IIW XIII-1757-99, Lisbon, 1999.
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