Method of Prevention of Fracture of Welded Metal Structural Elements Subjected to Single Dynamic Loads
Method of assessment of fracture toughness of structural materials and their welded joints under the conditions of a single dynamic loading has been suggested on the basis of criterion of a non-linear fracture mechanics δcr^D(CTOD). The regularities of effect of loading rate, determined by parameter...
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Інститут проблем міцності ім. Г.С. Писаренко НАН України
2002
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irk-123456789-467632013-07-07T12:13:37Z Method of Prevention of Fracture of Welded Metal Structural Elements Subjected to Single Dynamic Loads Kir’yan, V.I. Shamanovskii, S.V. Научно-технический раздел Method of assessment of fracture toughness of structural materials and their welded joints under the conditions of a single dynamic loading has been suggested on the basis of criterion of a non-linear fracture mechanics δcr^D(CTOD). The regularities of effect of loading rate, determined by parameter δ' (rate of crack tip opening) on the fracture toughness were established. Procedure of prevention of fracture of welded structure elements at a high-strength deforming was recommended. На основе критерия нелинейной механики разрушения δcr^D (CTOD) предложена методика оценки вязкости разрушения конструкционных материалов и их сварных соединений в условиях однократного динамического нагружения. Установлены закономерности влияния скорости нагружения, определяемой параметром δ' (скорость раскрытия вершины трещины), на вязкость разрушения. Рекомендована методика предупреждения разрушений элементов сварных конструкций при высокоскоростном деформировании. На основі критерію нелінійної механіки руйнування δcr^D (CTOD) запропоновано методику оцінки в’язкості руйнування конструкційних матеріалів і 'їхніх зварних з’єднань в умовах одноразового динамічного навантаження. Установлено закономірності впливу швидкості навантаження, що визначається параметром δ' (швидкість розкриття вістря тріщини), на в’язкість руйнування. Рекомендовано методику попередження руйнування елементів зварних конструкцій за високошвидкісного деформування. 2002 Article Method of Prevention of Fracture of Welded Metal Structural Elements Subjected to Single Dynamic Loads / V.I. Kir’yan, S.V. Shamanovskii // Проблемы прочности. — 2002. — № 3. — С. 62-68. — Бібліогр.: 6 назв. — англ. 0556-171X http://dspace.nbuv.gov.ua/handle/123456789/46763 539.4 en Проблемы прочности Інститут проблем міцності ім. Г.С. Писаренко НАН України |
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Научно-технический раздел Научно-технический раздел Kir’yan, V.I. Shamanovskii, S.V. Method of Prevention of Fracture of Welded Metal Structural Elements Subjected to Single Dynamic Loads Проблемы прочности |
| description |
Method of assessment of fracture toughness of structural materials and their welded joints under the conditions of a single dynamic loading has been suggested on the basis of criterion of a non-linear fracture mechanics δcr^D(CTOD). The regularities of effect of loading rate, determined by parameter δ' (rate of crack tip opening) on the fracture toughness were established. Procedure of prevention of fracture of welded structure elements at a high-strength deforming was recommended. |
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Article |
| author |
Kir’yan, V.I. Shamanovskii, S.V. |
| author_facet |
Kir’yan, V.I. Shamanovskii, S.V. |
| author_sort |
Kir’yan, V.I. |
| title |
Method of Prevention of Fracture of Welded Metal Structural Elements Subjected to Single Dynamic Loads |
| title_short |
Method of Prevention of Fracture of Welded Metal Structural Elements Subjected to Single Dynamic Loads |
| title_full |
Method of Prevention of Fracture of Welded Metal Structural Elements Subjected to Single Dynamic Loads |
| title_fullStr |
Method of Prevention of Fracture of Welded Metal Structural Elements Subjected to Single Dynamic Loads |
| title_full_unstemmed |
Method of Prevention of Fracture of Welded Metal Structural Elements Subjected to Single Dynamic Loads |
| title_sort |
method of prevention of fracture of welded metal structural elements subjected to single dynamic loads |
| publisher |
Інститут проблем міцності ім. Г.С. Писаренко НАН України |
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2002 |
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Научно-технический раздел |
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http://dspace.nbuv.gov.ua/handle/123456789/46763 |
| citation_txt |
Method of Prevention of Fracture of Welded Metal Structural
Elements Subjected to Single Dynamic Loads / V.I. Kir’yan, S.V. Shamanovskii // Проблемы прочности. — 2002. — № 3. — С. 62-68. — Бібліогр.: 6 назв. — англ. |
| series |
Проблемы прочности |
| work_keys_str_mv |
AT kiryanvi methodofpreventionoffractureofweldedmetalstructuralelementssubjectedtosingledynamicloads AT shamanovskiisv methodofpreventionoffractureofweldedmetalstructuralelementssubjectedtosingledynamicloads |
| first_indexed |
2025-07-04T06:13:18Z |
| last_indexed |
2025-07-04T06:13:18Z |
| _version_ |
1836695787159945216 |
| fulltext |
UDC 539.4
Method of Prevention of Fracture of Welded Metal Structural
Elements Subjected to Single Dynamic Loads
V. I. Kir’yan and S. V. Shamanovskii
Paton Electric Welding Institute, National Academy of Sciences of Ukraine, Kiev,
Ukraine
УДК 539.4
М етодика предупреждения разрушений элементов сварных
м е т а л л о к о н с т р у к ц и й при о д н о к р а т н о м д и н а м и ч е с к о м
нагружении
В. И. Кирьян, С. В. Шамановский
Институт электросварки им. Е. О. Патона НАН Украины, Киев, Украина
На основе критерия нелинейной механики разрушения dfr (CTOD) предложена методика
оценки вязкости разрушения конструкционных материалов и их сварных соединений в
условиях однократного динамического нагружения. Установлены закономерности влияния
скорости нагружения, определяемой параметром & (скорость раскрытия вершины тре
щины), на вязкость разрушения. Рекомендована методика предупреждения разрушений эле
ментов сварных конструкций при высокоскоростном деформировании.
Ключевые слова: конструкционные стали, сварные соединения, однократ
ное динамическое нагружение, вязкость разрушения, методика, предупреж
дение разрушений.
Introduction. Under dynamic loading conditions, the level of nominal
stresses increases relative to design static stresses due to forces of inertia and
transformation of kinetic energy of moving bodies to the potential energy of
deformation. To make allowance for this effect, the dynamic coefficient Kd is
introduced during designing of metal structures. As a result, the nominal dynamic
tensile stresses aD are determined by design static stresses as (aD = Kdas ).
The coefficient Kd is set theoretically or experimentally depending on the type
of loading of a definite design element. In this case, the condition of strength
design takes a form a s < [ad ]/Kd , if the allowable values of normal stresses at
dynamic [aD ] and static [as ] loading are assumed to be equal ([aD ]= [as ]).
Thus, the dynamic design of strength is replaced by a static design.
In addition to increasing the nominal stresses, the dynamic loading leads to
changes in the mechanical properties of metal, caused by its plastic deformation.
This is stipulated by the material improved resistance to plastic deformations due
to the inertia factor. As the investigations showed, with increase of a loading rate
on flat structural steel specimens, the yield strength a yS is significantly
increased, while the ultimate strength aus is increased to a less degree [1]. This
© V. I. KIRYAN, S. V. SHAMANOVSKII, 2002
62 ISSN 0556-171X. Проблемы прочности, 2002, N 3
Method o f Prevention o f Fracture
leads to the decrease in the relation a yS /a us ■ As to the characteristics of
plasticity (such as elongation and cross-section area reduction), these change even
less noticeably and not always adequately. It is quite evident that the change in
elongation and reduction in area of the specimens, as well as in a us , is
determined not only by the resistance to a plastic deformation, but to the fracture
as well. The fracture resistance depends, in turn, on the level of stress
concentration, degree of restriction and localizing of plastic deformations, metal
microstructure, fracture mechanism, etc. The cases of fractures of welded metal
structures described in literature, which occurred under the extreme conditions of
a dynamic loading (earthquake), proved the hazard of stress concentrators, which
were not critical at static loading [2, 3]. Hence, to prevent fractures under the
conditions of a high-rate deformation, the selection of a proper design of
connections, type and shape of welded joints from the point of view of reduction
of stress concentrations has a primary importance. The butt-welded joints are
preferable in this case. The next step in the way of prevention of fractures is the
application of the “fitness-for-purpose” concept based on the fracture mechanics
approaches and criteria.
Method of Assessment of Fracture Toughness under the Dynamic
Loading Conditions. This method has been developed at the Paton Electric
Welding Institute of National Academy of Sciences of Ukraine [1, 4]. It is based
on the determination of a critical crack tip opening displacement (CTOD) - dD -
This selection of the criterion was due to the necessity in establishment of fracture
toughness within the wide range of its variation, including brittle, quasi-brittle and
tough states of the material. Moreover, in this case it is not necessary to record
and calculate the actual forces acting on the specimen which are difficult to
realize at dynamic tests from the point of view of procedure. In accordance with
the procedure developed, the tests of standard specimens under the conditions of a
three-point bending at the rates of loading A' up to 10 m/s are performed in a
vertical drop-weight impact machine. The preset rate A' is attained by an
appropriate height of lifting of the loading hammer head, and its relative
constancy during all the stage of the specimen deforming is reached by a selection
of a weight mass using the following condition: the impact energy should exceed
the energy required for the specimen deformation by more than three times. The
significant increase in the loading rate A' (approximately up to 120 m/s) is
attained by a shock wave of a cumulative charge of an explosive in a special
device. To determine d D, a series (5 or 6) of specimens is tested at a preset
temperature T and rate A' up to different levels of bending. This is provided by
a stop of the loading head in fixed positions during the process of the specimen
deforming. It is noteworthy that this procedure makes it possible to arrest the
propagation of both brittle and tough cracks. The plastic constituent of the current
opening of the crack tip d p, for which the specimen was deformed, is determined
by varying the distance between the crack lips near its tip. The elastic constituent
d e was approximately in accordance with the relation “opening during loading d
- opening after loading d p,” plotted at static loading for the test specimen,
similar by sizes and mechanical properties with allowance for the dynamics:
(d e = d — dp). After the complete fracture of specimens with a changeover in its
ISSN 0556-171X. npoôëeubi npounocmu, 2002, № 3 63
V. I. Kiryan and S. V. Shamanovskii
mode, the value of crack growth I' formed at the preliminary deformation is
measured. Relation &D — I' is plotted from these data and CTOD is determined
at the stage of initiating of the brittle (quasi-brittle) fracture &D (Fig. 1a) or
tough fracture ôD (Fig. 1b).
<5 D, mm
0.6
0.4
0.2
0
1
/ 0 8
0 0
2 0
0 0
?
0
ô D, mm
0.6
0.4
0.2
H ,<
k
f 3
V, mm o 1 l', mm
Fig. 1. R elationship betw een the initial crack tip opening &' and increm ent o f its length I' at
quasi-brittle (a) and tough (b) states o f the m aterial: 1 - line o f b lunting o f the crack tip (I' = 0.5& );
2 - critical crack tip opening at the stage o f initiation o f a quasi-brittle fracture &D ; 3 - the sam e for
the tough fracture &D and &;; 4 - &R -curve; ▼ ■ A ' — 1 n—5
• - A ' = 9.7 m/s.
A ' = 10 m /s (static loading); O - A ' = 5 m/s;
For comparison of results of dynamic tests, and their application for the
prediction of serviceability of structure elements, it is important to associate the
loading conditions with the parameters controlling the rate of metal deforming in
the region of a crack tip (pre-fracture). The rate of deformation has a decisive
impact on the metal resistance to the fracture initiation and depends on the rate of
loading, geometry and dimensions of the test specimens. In the given case, the
rate of crack tip opening &' is used as such parameter. It is calculated as a mean
value of rate of the crack lips displacement in its tip for the time r cr from the beginning of the specimen deforming until the moment of fracture initiation
&' = &DJ r cr, r cr = Acr/A', where Acr is the critical displacement of the
specimen in the direction of the force action. Using characteristics &' and &̂, it
is possible to calculate directly the rate of deformation e' in the contour of a
blunted crack tip [5].
Results of Assessment of Fracture Toughness of Structural Steels and
Their Welded Joints. Typical relationship between the fracture toughness &
and the temperature T at different values of a rate parameter &'
(&' = 2.2 • 10—6-26.4 m/s) is given in Fig. 2. It is seen that in parallel with the level
of & Dr the temperature of transition from brittle (quasi-brittle) &D to the tough
& iD initiation of fracture Ti (determined as a temperature of beginning of the
stable crack growth) is an important characteristic from the point of view of the
fracture prevention. Above this temperature, the metal resistance to the initiation
of the tough fracture &D is invariant as to the temperature itself and also to the
rate of loading (straight line 5 in Fig. 2), i.e., &D =&t (&t is the fracture
64 ISSN 0556-171X. npoôëeubi npounocmu, 2002, N2 3
Method o f Prevention o f Fracture
toughness at static loading). In principle, the temperature curve of fracture
toughness is shifted equidistantly (parallel transfer) to the side of positive
temperatures with the increase in the rate of deforming 0'. Moreover, the
transition temperature T depends linearly on the logarithm of a rate parameter 0 '
T = k ln <5' + b. (1)
These relationships for the examined materials of different systems of alloying
and level of strength, and also their welded joints are presented in Fig. 3.
xD0 cr, mm
180 200 220 240 T , K
Fig. 2. Typical relationship betw een the resistance o f structural steels and their w elded jo in ts to the
initiation o f fracture and tem perature at d ifferent rates o f loading: 1 - 0 ' = 2 .2 -10_6 m /s; 2 -
0' = 1.1 m /s; 3 - 0 ' = 2.13 m /s; 4 - 0 ' = 26.4 m /s; 1-4 - 0'; 5 - 6D and 0 ; . A rrow s denote the
transition tem perature Tt.
Ti ,K
Fig. 3. T ransition tem perature Tt vs logarithm o f the crack-tip opening param eter 0': A - steel X46
(M n-S i), k = 6.60, b = 297; B - X 70 (M n -N i-M o -N b ), k = 4.86, b = 205; C - X 70 (M n-T i),
k = 3.04, b = 233; D - w elded jo in t o f steel C, k = 4.50, b = 270.
ISSN 0556-171X. npoôëeuu npouHocmu, 2002, № 3 65
V. I. Kiryan and S. V. Shamanovskii
Resistance of Structural Materials to the Initiation of Fracture ô i. It is
known that the important condition in assessment of the fracture toughness on the
basis of the nonlinear fracture mechanics criteria is an equality of the thickness t
of a standard specimen and the material examined. This is due to the fact that the
degree of restriction of the plastic deformation in the region of a pre-fracture and
its effect on the value ô t varies with thickness. The investigations showed that,
when the condition of a plane deformation t > ô E/Xo ys (where E is the elastic
modulus) is satisfied, ô t reaches its minimum value for the given material which
does not change with a thickness (Fig. 4). According to these data, the coefficient
X is equal to 4-5.
ô i , mm
u.t>
0.4
0.2
n
\V
o 4 8 12 16 20 t , mm
Fig. 4. V ariation o f steel X 52 (M n-V ) resistance to the initiation o f tough fracture &; w ith the
specim en thickness t.
The established boundary conditions for the metal resistance to the initiation
of the tough fracture & t to be independent of temperature, rate of loading and
specimen thickness allow to consider the parameter & { as a material
characteristic recommended to be applied in the assessment of “fitness-for-
purpose” criterion of welded structural elements.
Methodology of Fracture Prevention. Based of the above investigations,
the following approach to the assurance of serviceability of metal structural
elements subjected to the dynamic loading is proposed. The required condition of
selection of steels and welding technologies is Ts > Tt, where Ts is the minimum
service (design) temperature. The transition temperature T depending on the
service condition by the loading rate is determined by Eq. (1). Coefficients k and
b of this relation are established using the experimental data.
The sufficient condition consists in the assurance of the fracture toughness
&D of the parent material and metal of the welded joints at the level which
guarantees the non-fracture of structural elements from the most probable
crack-like defects &D >& t, where & t is the minimum required value of the
fracture toughness which is established from the “fitness-for-purpose” concept
with allowance for the coefficient KD and the dynamic values of the mechanical
properties.
66 ISSN 0556-171X. npoôëeubi npounocmu, 2002, N2 3
Method o f Prevention o f Fracture
It should be noted in conclusion that, in order to select the materials meeting
the above-mentioned conditions, the widely used standard impact tests of the
V-notched Charpy-type specimens can be used. Here, the required level of the*impact strength Cv* is determined in accordance with the value 0 ,• on the basis
of the 0D - Cv correlation link. The test temperature Tc *, at which the preset
level of Cv * should be provided, is set depending on the service conditions by
the loading rate
Tcv * = ts -at- ,
where AT is the shift in the transition temperature caused by the high-rate
deformation. In accordance with Eq. (1), it is equal to
AT = kA ln0' = k(ln 01 - ln0'2).
Here, 01 is the parameter of the service loading rate, while 02 is the parameter
of the static loading rate.
C o n c l u s i o n s
1. The method developed makes it possible to determine the critical crack-tip
opening displacement (CTOD) at the stage of initiating of brittle (quasi-brittle)
0D and tough 0D fracture modes within the wide ranges of the temperature T
and loading rate A' variations.
2. The metal resistance to the initiation of tough fracture 0- is invariant to
the temperature (T = 120-330 K), rate of loading (A' = 10—5 ...120 m/s) and
thickness (t >0 El la yS). The value 0- can be considered as a critical
characteristic of material and used for the assessment of the “fitness-for-purpose”
criterion of the welded structural elements.
3. The temperature of transition from quasi-brittle to tough initiation of
fracture T is important for assurance of the serviceability of metal structures
under the conditions of the dynamic loading. Its shifting to the side of positive
temperatures depending on the logarithm of the rate parameter 0 ' has a linear
trend. This allows T to be determined for a wide range of rates 0' using a
limited scope of the experimental data.
4. In order to prevent fracture of the welded structural elements under
conditions of high-rate deformation, the metal should meet the requirements as to
the transition temperature T (Ts > T, where Ts is the design or minimum
service temperature) and to the resistance to initiation of tough fracture 0 - (set in
accordance with the “fitness-for-purpose” concept) in parallel with the selection
of the proper design of connections, type and shape of the welded joints aimed to
reduce the stress concentration.
5. In case of establishing the correlation link 0-- Cv (where Cv is the
energy in the Charpy-type specimen V-notch) and shift in the transition
temperature T caused by the high-rate deforming, the metal can be selected from
the results of testing the standard impact Charpy-type V-notched specimens.
ISSN 0556-171X. npoôëeubi npounocmu, 2002, N 3 67
V. I. Kiryan and S. V. Shamanovskii
Р е з ю м е
На основі критерію нелінійної механіки руйнування д Dr (CTOD) запропо
новано методику оцінки в’язкості руйнування конструкційних матеріалів і
'їхніх зварних з’єднань в умовах одноразового динамічного навантаження.
Установлено закономірності впливу швидкості навантаження, що визна
чається параметром д' (швидкість розкриття вістря тріщини), на в’язкість
руйнування. Рекомендовано методику попередження руйнування елементів
зварних конструкцій за високошвидкісного деформування.
1. J. L. Skiles and H. H. Campbell, “Why steel fractured in the northridge
earthquake,” Welding Journal, No. 11, 67 - 71 (1994).
2. Masao Toyoda, “How steel structures fared in Japan’s great earthquake,”
Ibid., No. 12, 32 - 42 (1995).
3. V. I. Kiryan and S.V. Shamanovskii, “Method of assessment of resistance of
materials and welded joints to the crack initiation at dynamic loading,”
Avtomat. Svarka, No. 5, 6 - 20 (1988).
4. V. I. Kiryan, A. P. Vashchenko, L. A. Volgin, and S. V. Shamanovskii,
“Assessment of fracture toughness of structural steels under the conditions of
a high-rate deformation,” Probl. Prochn., No. 5, 51 - 59 (1993).
5. V. I. Kiryan, “Calculated determination of a local plastic deformation in the
crack-like defect tip,” Avtomat. Svarka, No. 4, 6 - 9 (1985).
6. V. S. Girenko, and V. P. Dyadin, “Relationship between the impact strength
and criteria of fracture mechanics of structural materials and their welded
joints,” Ibid., No. 10, 61 - 62 (1986).
R eceived 14. 11. 2001
68 ISSN 0556-171X. Проблеми прочности, 2002, № 3
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