Pulse Current Treatment Effect on the Strength of Reinforcing Steel and Its Weld Joint under Impact Loading
Приведены результаты испытаний на статическое и ударное растяжение образцов из строительной арматурной стали в состоянии поставки, образцов со стыковым сварным соединением в рабочей части, а также образцов, предварительно обработанных пропусканием импульсного электрического тока высокой плотно...
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Інститут проблем міцності ім. Г.С. Писаренко НАН України
2009
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| Назва видання: | Проблемы прочности |
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| Цитувати: | Pulse Current Treatment Effect on the Strength of Reinforcing Steel and Its Weld Joint under Impact Loading / L. Kruszka, G.V. Stepanov, V.I. Zubov, A.I. Babutskiib // Проблемы прочности. — 2009. — № 3. — С. 89-96. — Бібліогр.: 4 назв. — англ. |
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irk-123456789-483882013-08-19T13:31:07Z Pulse Current Treatment Effect on the Strength of Reinforcing Steel and Its Weld Joint under Impact Loading Kruszka, L. Stepanov, G.V. Zubov, V.I. Babutskiib, A.I. Научно-технический раздел Приведены результаты испытаний на статическое и ударное растяжение образцов из строительной арматурной стали в состоянии поставки, образцов со стыковым сварным соединением в рабочей части, а также образцов, предварительно обработанных пропусканием импульсного электрического тока высокой плотности. Показано, что повышенная скорость деформации вызывает увеличение прочности, а обработка импульсным электрическим током существенно влияет на прочность и пластичность металла с дефектами в области сварного шва как при статическом, так и при ударном растяжении. Наведено результати випробувань на статичний та ударний розтяг зразків із будівельної сталі у стані поставки, зразків зі стиковим зварним з’єднанням у робочій частині та зразків, що попередньо обробляли пропусканням імпульсного електричного струму високої густини. Показано, що підвищена швидкість деформації призводить до збільшення міцності, а обробка імпульсним електричним струмом суттєво впливає на міцність і пластичність металу з дефектами в області зварного шва як за статичного, так і ударного розтягу. We present results o f static and impact tension tests o f as-received reinforcing steel specimens, specimens with weld joints in their test portion, as well as specimens pretreated by high-density pulse current. As test results demonstrate, an increased strain rate enhances strength, and the pulse current treatment greatly influences the strength and plasticity o f a defect-containing weld metal under static and impact tension. 2009 Article Pulse Current Treatment Effect on the Strength of Reinforcing Steel and Its Weld Joint under Impact Loading / L. Kruszka, G.V. Stepanov, V.I. Zubov, A.I. Babutskiib // Проблемы прочности. — 2009. — № 3. — С. 89-96. — Бібліогр.: 4 назв. — англ. 0556-171X http://dspace.nbuv.gov.ua/handle/123456789/48388 539.4 en Проблемы прочности Інститут проблем міцності ім. Г.С. Писаренко НАН України |
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Научно-технический раздел Научно-технический раздел Kruszka, L. Stepanov, G.V. Zubov, V.I. Babutskiib, A.I. Pulse Current Treatment Effect on the Strength of Reinforcing Steel and Its Weld Joint under Impact Loading Проблемы прочности |
| description |
Приведены результаты испытаний на статическое и ударное растяжение образцов из строительной арматурной стали в состоянии поставки, образцов со стыковым сварным соединением в рабочей части, а также образцов, предварительно обработанных пропусканием импульсного электрического тока высокой плотности. Показано, что повышенная скорость деформации вызывает увеличение прочности, а обработка импульсным электрическим током существенно влияет на прочность и пластичность металла с дефектами в области сварного шва как при статическом, так и при ударном растяжении. |
| format |
Article |
| author |
Kruszka, L. Stepanov, G.V. Zubov, V.I. Babutskiib, A.I. |
| author_facet |
Kruszka, L. Stepanov, G.V. Zubov, V.I. Babutskiib, A.I. |
| author_sort |
Kruszka, L. |
| title |
Pulse Current Treatment Effect on the Strength of Reinforcing Steel and Its Weld Joint under Impact Loading |
| title_short |
Pulse Current Treatment Effect on the Strength of Reinforcing Steel and Its Weld Joint under Impact Loading |
| title_full |
Pulse Current Treatment Effect on the Strength of Reinforcing Steel and Its Weld Joint under Impact Loading |
| title_fullStr |
Pulse Current Treatment Effect on the Strength of Reinforcing Steel and Its Weld Joint under Impact Loading |
| title_full_unstemmed |
Pulse Current Treatment Effect on the Strength of Reinforcing Steel and Its Weld Joint under Impact Loading |
| title_sort |
pulse current treatment effect on the strength of reinforcing steel and its weld joint under impact loading |
| publisher |
Інститут проблем міцності ім. Г.С. Писаренко НАН України |
| publishDate |
2009 |
| topic_facet |
Научно-технический раздел |
| url |
http://dspace.nbuv.gov.ua/handle/123456789/48388 |
| citation_txt |
Pulse Current Treatment Effect on the Strength of Reinforcing Steel and Its Weld Joint under Impact Loading / L. Kruszka, G.V. Stepanov, V.I. Zubov, A.I. Babutskiib // Проблемы прочности. — 2009. — № 3. — С. 89-96. — Бібліогр.: 4 назв. — англ. |
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Проблемы прочности |
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2025-07-04T08:48:49Z |
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| fulltext |
UDC 539.4
Pulse Current Treatment Effect on the Strength of Reinforcing Steel
and Its Weld Joint under Impact Loading
L. K ruszka,a G. V. Stepanov,b V. I. Zubov,b and A. I. Babutskiib
a Military Technical Academy, Warsaw, Poland
b Pisarenko Institute of Problems of Strength, National Academy of Sciences of Ukraine,
Kiev, Ukraine
УДК 539.4
Влияние обработки импульсным электрическим током на
прочность арматурной стали и ее сварного соединения при
ударном нагружении
Л. К руш каа, Г. В. Степанов6, В. И. Зубов6, А. И. Бабуцкий6
а Военно-техническая академия, Варшава, Польша
6 Институт проблем прочности им. Г. С. Писаренко НАН Украины, Киев, Украина
П р и в е д е н ы р е з у л ь т а т ы и с п ы т а н и й н а с т а т и ч е с к о е и у д а р н о е р а с т я ж е н и е о б р а з ц о в и з
с т р о и т е л ь н о й а р м а т у р н о й с т а л и в с о с т о я н и и п о с т а в к и , о б р а з ц о в с о с т ы к о в ы м с в а р н ы м
с о е д и н е н и е м в р а б о ч е й ч а с т и , а т а к ж е о б р а з ц о в , п р е д в а р и т е л ь н о о б р а б о т а н н ы х п р о п у с
к а н и е м и м п у л ь с н о г о э л е к т р и ч е с к о г о т о к а в ы с о к о й п л о т н о с т и . П о к а з а н о , ч т о п о в ы ш е н н а я
с к о р о с т ь д е ф о р м а ц и и в ы з ы в а е т у в е л и ч е н и е п р о ч н о с т и , а о б р а б о т к а и м п у л ь с н ы м э л е к т р и
ч е с к и м т о к о м с у щ е с т в е н н о в л и я е т н а п р о ч н о с т ь и п л а с т и ч н о с т ь м е т а л л а с д е ф е к т а м и в
о б л а с т и с в а р н о г о ш в а к а к п р и с т а т и ч е с к о м , т а к и п р и у д а р н о м р а с т я ж е н и и .
Ключевые слова: импульсный электрический ток, ударное растяжение, арма
турная сталь, сварное соединение.
Introduction. Strength and performance of structural components are estimated
by calculation models with the account of material properties as well as influence
of loading conditions and manufacturing technology. One of the major parameters,
characterizing loading conditions, is a strain (or loading) rate, while weld technology
and further weld treatment are of primary importance for the strength of the
structure. Joint welding usually fails to avoid pores, slag inclusions, and other
defects [1], which exerts a considerable effect on the strength.
Quality of weld joints is one of the important factors, determining performance
and life of engineering structures. As is seen from the literature, this problem has
not been adequately investigated, which makes the development of these studies
currently central.
The present communication cites the results of experimental evaluation of the
strength and plasticity of as-received reinforcing steel specimens and steel specimens
with welds in their test portion under static and impact tension. The effect of
© L. KRUSZKA, G. V. STEPANOV, V. I. ZUBOV, A. I. BABUTSKII, 2009
ISSN 0556-171X. Проблемы прочности, 2009, № 3 89
L. Kruszka, G. V. Stepanov, V. I. Zubov, and A. I. Babutskii
high-density pulse current treatment on the strength and plasticity of the base metal
and weld joint was additionally investigated. It looks rather promising for enhancing
these characteristics [2].
Test Specimens. Test specimens were prepared from St3SX reinforcing steel
o f Polish production with the following chemical composition: C ~ 0.2%,
S i< 0.07%, P and S < 0.05%.
The strength and plasicity of as-received reinforcing steel under static tension
were determined by testing its specimens prepared according to GOST 1497-84
(test portion diameter and length are 6 mm and 35 mm), specimens with the weld
joint were cut in accordance with GOST 6996-66 (test portion diameter and length
are 6 mm and 70 mm).
The schemes of making steel specimens and specimens with the weld joint
from 20-mm-diameter bars are presented in Fig. 1. Bars for specimens with the
weld joint were welded by alternating current (100 A) in a CO2 protective
atmosphere with an SpG3S electrode wire (PN-88/M-69420).
Base metal specimens, specimens with the weld joint, and specimens pretreated by
_2 _1
pulse current were tested on a BISS universal machine at a strain rate of 10 s .
a
b
Fig. 1. Base metal specimen (a) and specimen with the weld joint (b) for standard tensile tests.
Experimental construction of true stress-strain relations under impact tension
is complicated by the fact that in the specimen with a short test portion, a
nonuniform stress-strain state develops, being the result of the wave nature of
specimen loading and loading of circuit elements (propagation, reflection, and
interaction of elastoplastic waves). The stress-strain state in the test portion close to
the uniform one (basic condition of plotting the stress-strain relation under impact
tension) is established after 3-5 paths of longitudinal waves along the specimen,
which requires specimens with a short test portion. The influence of radial
oscillations of the specimen is reduced by decreasing its diameter.
Therefore, investigations under impact tension made use of specimens with a
short test portion (diameter and length are 4 mm and 10 mm) that maintains the
stress-strain state uniformity in the volume of their test portion and undistorted
registration of stresses and strains in this volume. The deviation of the stress-strain
state from the uniform one is within allowable ranges [3, 4].
The scheme of impact tension (Fig. 2) is the modification of the Hopkinson
split pressure bar. The impact of free-falling striker 4 over anvil 5 fixed at the end
of loading rod 3 generates a longitudinal wave of elastic stresses, behind its front,
90 ISSN 0556-171X. npodxeMbi npounocmu, 2009, N 3
Pulse Current Treatment Effect on the Strength
the rate is approximately equal to the rate of the striker. The travel of an elastic
wave through the area of connection with the head of specimen 3 and further to the
dynamometer gives rise to the specimen tension.
The cross-section of the loading rod is much larger than the cross-section area
of the specimen test portion, which causes the displacement of the loaded specimen
head with a rate, being about two times higher than the striker rate.
I i I 1
Ж Г
a
Fig. 2. Scheme of impact tension, specimen (a) and bars for its preparation (b) and (c).
Scheme of Pulse C u rren t Treatment. The scheme of the generator used for
the treatment of specimens by pulse current passage is shown in Fig. 3. It includes
high-voltage source 1 (up to 5 kV), a bank of capacitors C (total capacity up to
1200 ^F), mechanical key P and ballast resistor R. The amplitude of pulse current
and its variation were registered by Rogovsky belt 3, its signal was fed to the
high-speed analog-digital converter of PC.
Specimen 2 was connected to the busline with one head, the second head was
connected to the cylinder bottom. The cylinder was connected to the discharge
cercuit with its end to provide symmetrical action of ponderomotive forces on the
specimen and prevents its flexure.
The characteristic diagram of discharge current variation with time is also
presented in Fig. 3.
Static Test Results for S tandard Specimens. The pulse current treatment
consisted in passage through the specimen one or three current pulses generated by
capacitor bank discharge (750 ^F). Discharge current was varied by changing the
initial voltage on capacitor bank terminals. In each pulse current treatment three
specimens were tested. Averaged test results are summarized in Table 1.
As follows from the results, passage of one current pulse results in an increase
in strength as compared to as-received steel within 4-6%. Three pulses give an
increase in this characteristic only by 2-5%.
ISSN 0556-171X. Проблемы прочности, 2009, N2 3 91
L. Kruszka, G. V. Stepanov, V. I. Zubov, and A. I. Babutskii
T a b l e 1
Results o f S tatic Tests
Metal state Pulse current treatment Yield stress,
MPa
Ultimate strength,
MPaCurrent I , kA Number o f pulses
As-received Without treatment 499 510
56 1/3 527/523 543/535
100 521/508 539/521
141 520/520 536/535
W eld joint Without treatment 232 282
56 1/3 290/331 334/406
100 340/324 453/400
141 242/- 273/-
I, A
4 0 0 0 0
20000
0
-20000
- 4 0 0 0 0
- 6 0 0 0 0
- 8 0 0 0 0
0
o — —H
I è
o - — Lj-«W X -
d \ r&><y
I \ r f °r
\ o j
v / V
\ o l
0.0002 0 . 0 0 0 4 0 . 0 0 0 6 t, s
Fig. 3. Scheme o f the pulse current treatment o f the specimen and characteristic discharge
current-tim e diagram (approximation - solid line, experiment - points).
The pulse current effect on the strength of the weld metal looks more
essential. Thus, passage of one current pulse leads to an increase in the yield stress
of the weld metal by 25-47% and in the ultimate strength by 18-61%. Three
current pulses result in an increase in the yield stress by 40-43% and the ultimate
strength by 42-44% depending on treatment conditions. One should note the wide
scatter in test results for the specimens with the weld joint, which is associated
with the presence of welding defects (Fig. 4). Probably, the pulse current treatment
leads to a decrease in the stress concentration factor in the vicinity of defects,
which increases the strength of a defect-containing weld.
92 ISSN 0556-171X. npoôëeMbi npounocmu, 2009, N 3
Pulse Current Treatment Effect on the Strength
Thus, the pulse current treatment of as-received reinforcing steel leads to an
inconsiderable increase (about 5%) in its strength under static tension. However,
the treatment of the weld joint considerably increases (up to 60%) strength,
bringing its values closer to the values for the as-received metal.
Welding Ductile "Neck"
defect fracture projection
Fig. 4. Fracture of the specimen with the weld joint (side view).
Test Results for the Specimens with a Short Test Portion. Comparison of
test results for identical specimens under static and impact tension permits
determining the effect of a strain rate on the strength and plasticity of materials in a
uniaxial stress state. The tests under impact tension were performed on a vertical
impact machine with a falling weight (nominal tension rate is 10 m/s, strain rate3 _ 1
£ = 10 s ). Static tension was effected by a screw loading device (Vo = 1.2
_3 _1
mm/min and £ = 10 s ) mounted on the vertical impact machine. Characteristic
diagrams under static and impact tension of as-received metal specimens and
specimens with the weld joint in their test portion, used to determine strength, are
shown in Fig. 5.
To estimate the pulse current effect on the strength and plasticity of steel,
identical as-received metal specimens and specimens with the weld joint in the test
portion were tested under static and impact tension. Identical specimens with a
short test portion (d = 4 mm and l = 10 mm) and thread-cutting heads made from
cylindrical bars of an as-received metal and bars with the weld joint, produced by
the above technology, were used for correct assessment of the metal strength under
static and impact tension (Fig. 1). Small sizes of the test portion provide the
stress-strain state close to the uniform one under static and impact tension at a rate
of 10 m/s.
The specimens were treated by pulse current passage with a capacitor bank
discharge (600 ^F) charged up to a preset voltage U 0 = 2-4 kV. The amplitude of
decaying sinusoidal current and period of oscillations (145 ^s) were measured by
the Rogovsky belt.
As numerical simulation results demonstrate, pulse current passage through
the specimen does not cause considerable nonuniformity of current distribution in a
homogeneous metal due to a skin effect. The calculated difference in a maximum
density of sinusoidal current on the surface and along the test portion axis of a
4-mm diameter specimen does not exceed 5%, which does not produce noticeable
temperature nonuniformity over the cross-section of the specimen.
ISSN 0556-171X. npoÖMeMbi npouHocmu, 2009, № 3 93
L. Kruszka, G. V. Stepanov, V. I. Zubov, and A. I. Babutskii
U, mV u, mV
0 100 200 300 t, s 0 200 D 4D00 t, [is
a b
Fig. 5. Characteristic electric signal-time diagrams under static (a) and impact (b) tension of
as-received metal specimens ( /) and specimens with the weld joint in the test portion (2).
Test Results and Discussion. As-Received Metal. For as-received metal
specimens with a short test portion, an averaged plastic extension and necking
under static tension (18.6 and 57.9%) are somewhat lower than under the impact
one (22.4 and 60%). The yield stress under impact tension (587 MPa) is 25%
higher than under the static one (465 MPa).
The pulse current pretreatment of specimens does not practically influence the
plasticity (relative extension d and relative necking \p after fracture), and the
yield stress a y increases by 12% with current density (Fig. 6).
a Y, MPa
600
500
400
300
0 2000 4000 6000 i, A/mm2
d, p ,
60
40
20 <
0 -
0 1000 2000 3000 4000 5000 6000 i, A/mm2
b
Fig. 6. Yield stress Oy (a) (open points - static tension and solid points - impact tension) and
plasticity (b) (d - open points and p - solid points) under impact tension vs current density for
as-received metal specimens.
Specimen with the Weld Joint. The plastic strain and yield stress of specimens
with the weld joint and a short test portion under static and impact tension are
much lower than those of as-received steel specimens. The wide scatter of
plasticity and strength values is probably caused by different effects of welding
defects present in all specimens with the weld joint.
94 ISSN 0556-171X. Проблемы прочности, 2009, N2 3
% a
------- *-
— *
о _o
— cr о
The relative extension and necking of specimens with the weld joint and a
short test portion after fracture under static tension (5.7 and 21.5%) are much lower
than under the impact one (8.6 and 26.9%). The yield stress under impact tension
(240 MPa) is 20% higher than under the static one (Fig. 7).
oy , MPa
6, p , %
’ 0
0
on
•
0 *
o T -----------------------
♦ C o
*
0 2000 4000 i, A/mm2
b
Fig. 7. Y ield stress Oy (a) (open points - static tension and solid points - impact tension) and
plasticity (b) (6 - solid points and p - open points) under impact tension vs current density for
specimens with the weld joint.
Plasticity and yield stress values increase during the pulse current treatment,
which can be the result of a positive local temperature growth effect that causes a
decrease of stress intensities in the vicinity of crack-like defects due to plastic
strains near them and other stress concentrators. The pulse current pretreatment of
2
a weld joint metal at a current density of about 5 kA/mm increases its dynamic
yield stress by about 1.5 times as compared to an untreated weld joint metal.
As follows from the analysis of test results, the level of strength and plasticity
of specimens with the weld joint decreases. Macrodefects (pores) are clearly
visible on the fracture surface, their effect is seen as strain localization in their
vicinity. The pulse current pretreatment of such specimens causes a considerable
increase in strength and plasticity. Under impact tension, the scatter in data is much
smaller than under the static one (Fig. 7).
An essential effect of the pulse current treatment on the strength and plasticity
over the area of the weld joint is most likely associated with local stress relaxation
and plastic strains reducing the local stress concentration factor at increased
localized heating in the vicinity of defects (average heating temperature does not
exceed 150°C, which cannot influence the yield stress). Localized heading is
effected by pulse current passage at the growth rate ensuring a temperature
ISSN 0556-171X. npo6n.eMH npounocmu, 2009, N 3 95
gradient in the vicinity of defects. At an insufficient current growth rate, the
temperature gradient decreases as a result of heat conduction effects.
Conclusions. As the rest results for standard specimens without the weld joint
demonstrated, pulse current passage leads to an inconsiderable increase in strength
(up to 6%) as compared to an as-received metal. Current passage through
specimens with the weld joint produces an increase in the yield stress (up to 47%)
and ultimate strength (up to 61%) of the weld joint metal.
An increase in a strain rate up to 1000 s 1 under impact tension of as-received
metal specimens with a short test portion causes an increase in the yield stress
without noticeable plasticity changes.
The pulse current treatment of as-received metal specimens causes an increase
in the yield stress under static tension, which is less significant under impact
tension without noticeable plasticity changes.
The pulse current treatment of specimens with a defect-containing weld joint
and a short test portion produces a considerable increase in the yield stress and
reduces the scatter of data under impact tension without a noticeable influence on
plasticity.
The pulse current effect on the strength and plasticity of the metal over the
area of the weld joint can be explained by stress relaxation and microstrains in the
vicinity of defects.
In the tests of specimens with a reduced cross-section area (increased relative
weld defect sizes) the influence of these defects becomes more pronounced.
Р е з ю м е
Наведено результати випробувань на статичний та ударний розтяг зразків із
будівельної сталі у стані поставки, зразків зі стиковим зварним з’єднанням у
робочій частині та зразків, що попередньо обробляли пропусканням імпульс
ного електричного струму високої густини. Показано, що підвищена швид
кість деформації призводить до збільшення міцності, а обробка імпульсним
електричним струмом суттєво впливає на міцність і пластичність металу з
дефектами в області зварного шва як за статичного, так і ударного розтягу.
1. G. P. Karzov, V. P. Leonov, and B. T. Timofeev, Welded High-Pressure
Vessels: Strength and Service Life [in Russian], Mashinostroenie, Leningrad
(1982).
2. G. Stepanov, A. Babutsky, and L. Kruszka, “Metals behavior under passage of
impulse electric current,” J. Phys. IV France, 110, 577-582 (2003).
3. G. V. Stepanov, Elastoplastic Deformation and Fracture o f Materials under
Pulse Loading [in Russian], Naukova Dumka, Kiev (1991).
4. G. V. Stepanov, “Strength of metals at high strain rates,” Strength Mater., 34,
No. 3, 214-218 (2002).
Received 24. 06. 2008
96 ISSN 0556-171X. Проблеми прочности, 2009, № 3
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