On Standards for Mechanical Testing of Materials at Cryogenic Temperatures
Рассмотрены и проанализированы основные положения стандартов АSТМ, ISO и ГОСТ, которые регламентируют метод испытаний металлов на растяжение при температуре жидкого гелия. Определены основные факторы, обусловливающие параметры деформирования, нагружения и размеры образцов при испытаниях металлов и...
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Інститут проблем міцності ім. Г.С. Писаренко НАН України
2010
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irk-123456789-1119792017-01-17T03:03:05Z On Standards for Mechanical Testing of Materials at Cryogenic Temperatures Novogrudskii, L.S. Strizhalo, V.A. Научно-технический раздел Рассмотрены и проанализированы основные положения стандартов АSТМ, ISO и ГОСТ, которые регламентируют метод испытаний металлов на растяжение при температуре жидкого гелия. Определены основные факторы, обусловливающие параметры деформирования, нагружения и размеры образцов при испытаниях металлов и сплавов в указанных температурных условиях. Представлены рекомендации по дополнению и изменению положений стандартов. Розглянуто i проаналізовано основні положення стандартів ASTM, ISO та ГОСТ, що регламентують метод випробувань матеріалів на розтяг при температурі рідкого гелію. Виявлено головні фактори, що обумовлюють параметри деформування, навантажування та розміри зразків при випробуваннях металів і сплавів в умовах указаної температури. Подано рекомендації щодо доповнень положень стандартів. 2010 Article On Standards for Mechanical Testing of Materials at Cryogenic Temperatures / L.S. Novogrudskii, V.A. Strizhalo // Проблемы прочности. — 2010. — № 3. — С. 47-56. — Бібліогр.: 12 назв. — англ. 0556-171X http://dspace.nbuv.gov.ua/handle/123456789/111979 669.01: 620.172 en Проблемы прочности Інститут проблем міцності ім. Г.С. Писаренко НАН України |
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Научно-технический раздел Научно-технический раздел |
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Научно-технический раздел Научно-технический раздел Novogrudskii, L.S. Strizhalo, V.A. On Standards for Mechanical Testing of Materials at Cryogenic Temperatures Проблемы прочности |
| description |
Рассмотрены и проанализированы основные положения стандартов АSТМ, ISO и ГОСТ,
которые регламентируют метод испытаний металлов на растяжение при температуре
жидкого гелия. Определены основные факторы, обусловливающие параметры деформирования, нагружения и размеры образцов при испытаниях металлов и сплавов в указанных
температурных условиях. Представлены рекомендации по дополнению и изменению положений стандартов. |
| format |
Article |
| author |
Novogrudskii, L.S. Strizhalo, V.A. |
| author_facet |
Novogrudskii, L.S. Strizhalo, V.A. |
| author_sort |
Novogrudskii, L.S. |
| title |
On Standards for Mechanical Testing of Materials at Cryogenic Temperatures |
| title_short |
On Standards for Mechanical Testing of Materials at Cryogenic Temperatures |
| title_full |
On Standards for Mechanical Testing of Materials at Cryogenic Temperatures |
| title_fullStr |
On Standards for Mechanical Testing of Materials at Cryogenic Temperatures |
| title_full_unstemmed |
On Standards for Mechanical Testing of Materials at Cryogenic Temperatures |
| title_sort |
on standards for mechanical testing of materials at cryogenic temperatures |
| publisher |
Інститут проблем міцності ім. Г.С. Писаренко НАН України |
| publishDate |
2010 |
| topic_facet |
Научно-технический раздел |
| url |
http://dspace.nbuv.gov.ua/handle/123456789/111979 |
| citation_txt |
On Standards for Mechanical Testing of Materials at Cryogenic Temperatures / L.S. Novogrudskii, V.A. Strizhalo // Проблемы прочности. — 2010. — № 3. — С. 47-56. — Бібліогр.: 12 назв. — англ. |
| series |
Проблемы прочности |
| work_keys_str_mv |
AT novogrudskiils onstandardsformechanicaltestingofmaterialsatcryogenictemperatures AT strizhalova onstandardsformechanicaltestingofmaterialsatcryogenictemperatures |
| first_indexed |
2025-07-08T03:07:33Z |
| last_indexed |
2025-07-08T03:07:33Z |
| _version_ |
1837046490321649664 |
| fulltext |
UDC 669.01: 620.172
On Standards for Mechanical Testing of Materials at Cryogenic
Temperatures
L. S. Novogrudskii and V. A. Strizhalo
Pisarenko Institute of Problems of Strength of the National Academy of Sciences of
Ukraine, Kiev, Ukraine
ÓÄÊ 669.01: 620.172
Î ñòàíäàðòàõ íà ìåõàíè÷åñêèå èñïûòàíèÿ ìàòåðèàëîâ ïðè
êðèîãåííûõ òåìïåðàòóðàõ
Ë. Ñ. Íîâîãðóäñêèé, Â. À. Ñòðèæàëî
Èíñòèòóò ïðîáëåì ïðî÷íîñòè èì. Ã. Ñ. Ïèñàðåíêî ÍÀÍ Óêðàèíû, Êèåâ, Óêðàèíà
Ðàññìîòðåíû è ïðîàíàëèçèðîâàíû îñíîâíûå ïîëîæåíèÿ ñòàíäàðòîâ ÀSÒÌ, ISO è ÃÎÑÒ,
êîòîðûå ðåãëàìåíòèðóþò ìåòîä èñïûòàíèé ìåòàëëîâ íà ðàñòÿæåíèå ïðè òåìïåðàòóðå
æèäêîãî ãåëèÿ. Îïðåäåëåíû îñíîâíûå ôàêòîðû, îáóñëîâëèâàþùèå ïàðàìåòðû äåôîðìèðî-
âàíèÿ, íàãðóæåíèÿ è ðàçìåðû îáðàçöîâ ïðè èñïûòàíèÿõ ìåòàëëîâ è ñïëàâîâ â óêàçàííûõ
òåìïåðàòóðíûõ óñëîâèÿõ. Ïðåäñòàâëåíû ðåêîìåíäàöèè ïî äîïîëíåíèþ è èçìåíåíèþ ïîëî-
æåíèé ñòàíäàðòîâ.
Êëþ÷åâûå ñëîâà: íîðìàòèâíûé äîêóìåíò, ïðåðûâèñòîå òå÷åíèå, ïîäàòëè-
âîñòü ìàøèíû, ýíåðãîåìêîñòü ìàòåðèàëà, òåìïåðàòóðà æèäêîãî ãåëèÿ, ñêîðîñòü
äåôîðìèðîâàíèÿ, ñêîðîñòü íàãðóæåíèÿ.
Introduction. Investigations on mechanical properties of structural metallic
materials at temperatures close to absolute zero, which were developed extensively
in the 60th–80th of the last century, have not lost their importance up to now as
evidenced by numerous publications of both Ukrainian and foreign researchers
[1–7]. This interest in the problem, which would, as it might seem, concern only
experts specializing in particular, quite narrow, and even specific fields of human
activity (space exploration, defense industry), is connected with the fact that
cryogenic temperatures have already been used since some time and will be
introduced even faster in certain spheres of our day-to-day life (power engineering,
medicine, agriculture, electronic engineering). The range of devices whose units
should be in operation at very low temperatures is expanding accordingly. The
carrying capacity of these units is ensured by metallic materials. The immediate
interest in such investigations is emphasized by the fact that ASTM E 1450
standard (2003) and ISO 19819 standard (2004), which regulate the methods for
testing metallic materials in liquid helium, have been recently developed in the
USA and the European Union. The State Standard of the USSR GOST 22706-77
“Metals. Methods for Tensile Testing at Temperatures Ranging from �100 to
� �269 C” was developed in the USSR in 1977 and brought into effect in 1978 in
© L. S. NOVOGRUDSKII, V. A. STRIZHALO, 2010
ISSN 0556-171X. Ïðîáëåìû ïðî÷íîñòè, 2010, ¹ 3 47
order to unify the methods for determining mechanical characteristics of metallic
materials at cryogenic temperatures. This normative document as amended has
been effective in Ukraine up to now. Essentially GOST 22706-77 is a version of
the State Standard GOST 1497-73 “Metals. Methods for Tensile Testing” (next
wording of which STSEV 471-77 appeared in 1984) that was extended to include
the procedure of cooling down to temperatures of 77 and 4.2 K. Its original version
regulates testing at a temperature of 293 K and practically does not consider the
peculiarities of the development of the elastic-plastic deformation of metallic
materials at the temperature of liquid helium. These peculiarities, namely, the
unstable accumulation of plastic strain by metals and alloys loaded under the above
temperature conditions (the so-called discontinuous yielding, see Figs. 1 and 2),
determine basic requirements for the parameters and modes of tensile testing of
metallic materials at a temperature of 4.2 K.
Analysis of the main factors set forth or omitted in the clauses of the ASTM Å
1450:03, ISO 19819:04 and GOST 22706-77 standards, which determine the kinetics
of discontinuous yielding in materials and alloys and, as a consequence, the values
of their mechanical characteristics, will be presented hereafter.
Discussion. Table [7] gives the values of the mechanical characteristics of
steels and aluminum alloys obtained under similar temperature conditions (in
liquid helium) but on specimens of different geometry and dimensions, under
different loading conditions (constant cross-head speed or constant loading rate),
and at different ratios of the energy absorbed by the specimen and the elastic
energy accumulated by the loading system of the testing facility (hereinafter
referred to as the machine).
As we can see, the extent to which the above factors influence the values of
the characteristics is ambiguous. By the extent of this effect the above factors can
be placed in the following order: specimen shape, specimen dimensions; loading
L. S. Novogrudskii and V. A. Strizhalo
48 ISSN 0556-171X. Ïðîáëåìû ïðî÷íîñòè, 2010, ¹ 3
Fig. 1. Load–elongation diagrams for steels 12Kh18N10T (a) and 03Kh20N16AG6 (b) at a
temperature of 4.2 K: (1) constant strain rate; (2) constant loading rate (within the elastic region);
specimen � �0 4 mm, l0 20� mm.
a b
rate and conditions; the relation between the energy absorbed by the specimen and
the amount of the elastic energy accumulated in the machine. The shape of the
specimen cross-section (either circular or rectangular) under conditions of
discontinuous yielding must ensure maximum approximation to the linear stress
state. Dimensions of the specimens determine the requirements for the systems of
loading, cooling, mechanical force exciter, etc., on the one hand, and, on the other
hand, regulate the development of elastic-plastic deformation, i.e., the number and
amplitude of the load jumps and the energy absorbed by a specimen. According to
references [3, 8], the strain rate below 7 10 4� � s�1 has no effect on the parameters
of discontinuous yielding in metals and alloys. At the same time, the effect of the
strain rate on the discontinuous yielding alone has been considered, i.e., the
number of jumps, their amplitude and shape. There are no systematic data on how
the mechanical characteristics of metals and commercial alloys change in response
to changing the strain rate.
Nevertheless, since the discontinuous yielding kinetics also determines the
values of the material strength and plasticity characteristics, it can be stated that at
a strain rate of ��� �10 3 s�1, as put forth in ASTM 1450 and ISO 19819 standards,
the values of the mechanical characteristics will be independent of the strain rate as
well. All the standards analyzed in this paper regulate the strain rate alone
(cross-head displacement). This is specifically emphasized in the ASTM standard.
Nevertheless, at a sufficient rigidity of testing facilities the values of the mechanical
characteristics obtained at a constant loading rate agree closely with analogous
values obtained at a constant strain rate [9]. That is, the standards must also set the
regimes of specimen loading at a constant rate of load application for a given
rigidity (compliance) of a testing machine.
On Standards for Mechanical Testing of Materials ...
ISSN 0556-171X. Ïðîáëåìû ïðî÷íîñòè, 2010, ¹ 3 49
Fig. 2. Load–elongation diagrams for aluminum alloy ÀÌg6 (a) and titanium alloy 19 (b) at a
temperature of 4.2 Ê and a constant strain rate: (1) specimen � �0 4 mm, l0 20� mm; (2) specimen
12 20 mm, l0 80� mm.
a b
By far and large, the development of discontinuous yielding depends on the
elastic energies accumulated in the force excitation and load transmission systems
of the testing machine during the specimen loading, or, more specifically, on the
ratio of the specimen energy capacity to the total elastic energy accumulated in the
force excitation and load transmission systems, and on the rate of this elastic
energy reproduction. For instance, in steel 03Kh20N16ÀG6 with a stable austenite
structure, the number of the load jumps decreases from 22 at a constant strain rate
(insufficient amount of the machine elastic energy) to 1 at an uncontrolled increase
in the loading rate (considerable amount of the machine elastic energy and high
speed of its reproduction) during the jump. Accordingly, the determined ultimate
strength of the steel decreases 1.20 times, relative elongation after fracture 1.34
times, and relative necking after fracture due to strain localization increases 1.40
times.
The elastic energy Wm accumulated by the force excitation and the load
transmission systems of the testing machine during the specimen loading can be
presented in the general form as follows:
W W L F E P W Pm i i i i
i
n
f�
�
� ( , , , ) ( ),
1
(1)
where Wi is the elastic energy accumulated by the ith element in the load
transmission system during its loading to the load level P , Ei is the material
elastic modulus, Li is the length, Fi is the area of the element cross section, n is
the number of elements in the force excitation system, and W f is the elastic
energy of the force excitation system accumulated during loading to the P level.
The capacity of an element to accumulate elastic energy is characterized by its
compliance, C i , i.e., the ratio of the element absolute elastic elongation � i
e to the
load value P that induces this elongation:
C
Pi
i
e
�
�
. (2)
The higher the system compliance, the higher the amount of the elastic energy
accumulated in the system at equal loads. The element energy during tension is
W
P
C
P
i
i
e
i� �
�
2 2
2
. (3)
The influence of the amount of the accumulated elastic energy shows itself
mainly after a decrease in the material resistance to deformation, or, as stated by
the authors of [10], at the supercritical stage. Discontinuous yielding of metallic
materials at a temperature of 4.2 K is formed by a number of consecutive events of
local deformation of some parts and the gauge length of a specimen, each bringing
about local reduction in the cross section area – necking. Throughout this process,
the elastic energy accumulated by the machine, Eq. (1), and in the specimen region
50 ISSN 0556-171X. Ïðîáëåìû ïðî÷íîñòè, 2010, ¹ 3
L. S. Novogrudskii and V. A. Strizhalo
beyond the neck is released. This energy maintains local deformation. That is,
every event of discontinuous yielding can be considered as the material transition
to the supercritical stage. The development of the local deformation at the
supercritical stage can discontinue only if the residual elastic energy of the
machine–specimen system (after one event of discontinuous yielding) corresponds
to the residual energy capacity of the specimen material:
� � � �W W Wres m nds , (4)
where �Wres is the residual energy capacity of the specimen in a local zone, �Wm is
the residual elastic energy of the machine, and Wnds is the residual elastic energy
of the plastically non-deformed part of the specimen.
The residual energy capacity of the specimen material decreases after every
event of discontinuous yielding. That is why the smaller the total compliance of the
elements of the load transmission and force excitation systems, the smaller the
probability of premature specimen fracture after the next strain jump. At Wm �0
(C m �0) it is possible to determine the total deformability of the material of
specimens of certain dimensions. In testing specimens with the same dimensions
on a machine with a greater compliance, fracture will occur earlier. The extent of
premature fracture depends on the specimen dimensions, material properties
(energy capacity), compliance of the load transmission and force excitation
systems, and the rate of supplying mechanical energy to the specimen. As
emphasized above, the development of discontinuous yielding determines the
values of the metallic material strength and plasticity characteristics, therefore,
when setting the requirements for testing equipment, it is necessary to consider not
only the strain rate, as it was done in the documents considered in this paper, but
also the machine compliance, Eq. (4). In doing so it is also necessary to take into
account the fact that standard machines used for static tensile tests of metals at a
temperature of 4.2 K have three types of the load excitation systems: mechanical,
hydraulic, and servohydraulic ones. Machines equipped with a mechanical load
excitation system ensure deformation mostly at a constant rate, those with hydraulic
ones – at a constant loading rate (usually the constancy is provided within the zone
of the specimen elastic deformation), and those with servohydraulic load excitation
system realize both regimes of load application (yet modern machines of this type
with a small compliance ensure the constancy of the loading rate practically up to
the moment of the specimen fracture). The main accumulators of the elastic energy
in the machines of the first and the third types are the elements of the machine load
transmission system. The energy accumulated by the force excitation system is
insignificant and, as a rule, W Wf i
i
n
��
�
�
1
. In hydraulic machines, especially of a
direct action, this value is significant and can be far above Wi
i
n
�
�
1
. This proceeds
from the following considerations.
The value of the elastic energy accumulated by a hydraulic force excitation
system is proportionate to the condensability of the liquid � used as a working
ISSN 0556-171X. Ïðîáëåìû ïðî÷íîñòè, 2010, ¹ 3 51
On Standards for Mechanical Testing of Materials ...
medium of the force excitation system. The condensability � is a reciprocal of the
bulk modulus of elasticity of the material K . For steel at a temperature of 293 K
the bulk modulus of elasticity is
K
E
� �
�
� �
1
3 1
152 106
� �( )
. kg/cm2 .
Here E and � is the elasticity modulus and Poisson’s ratio, respectively. That is
�� � �0 66 10 6. atm�1.
The condensability of oil used in the force excitation systems of hydraulic
machines with the pressure scale from 1 to 10 atm is within the range of
(47.2–63.3)� �10 6 atm�1. Thus, the oil compliance is from 60 to 100 times greater
than that of steel. The elastic energy accumulated accordingly by a hydraulic load
excitation system will be ~ (60–100) times higher as compared to metallic elements
of the load transmission system, all other conditions being equal (temperature,
material volume, etc.). Availability of such considerable amounts of the elastic
energy accumulated in the machine systems does not mean that they cannot be
used for tensile testing of metals and alloys at a temperature of 4.2 K. It is
generally known that some structures, for instance, pressure vessels, operate under
non-steady-state loading. In order to carry out strength calculations for such
structures operated at temperatures close to 4.2 K, to evaluate their load carrying
capacity, life, etc., the mechanical characteristics of materials should be determined
when the testing machine systems have accumulated certain amounts of the elastic
energy.
Thus, standards should regulate not only the strain rates or loads (which none
of those being analyzed does) but also the testing machine compliance.
Specimens. In tests in the medium of liquid helium, the specimen size and
geometry determine not only the design peculiarities of the cooling systems,
cryostat, grips, the maximum load capacity of the testing machine but also the
kinetics of the material deformation thus defining the strain rate, the rigidity of the
stress state in the necks, and the ratio of the elastic energies accumulated in the
machine–specimen system, i.e., the values of the material mechanical characteristics
that are determined in the course of testing (see Table 1).
As seen from the data presented here, the number of events of discontinuous
yielding and their amplitude and, as a consequence, the values of the material
strength and plasticity characteristics also depend considerably on the size and
shape of the specimen, even if it meets the requirements of the State Standard
GOST 22706-77. Therefore, it is reasonable that the dimensions of specimens for
tests at the temperatures of liquid helium should be limited (in contrast to GOST
22706-77) by the requirements of normative documents. To obtain reliable values
of the mechanical characteristics and for their comparability, the normative
documents should regulate one basic standard size of a cylindrical specimen. This
can be a small standard specimen recommended by ASTM E 1450:03. For sheet
materials of small thickness, from which the manufacture of this specimen by
orienting it across the direction of rolling is impossible, it is advisable to use a
plane specimen described in ISO 19819. It is the values of the mechanical
52 ISSN 0556-171X. Ïðîáëåìû ïðî÷íîñòè, 2010, ¹ 3
L. S. Novogrudskii and V. A. Strizhalo
characteristics obtained using these unified specimens that should be included in
handbooks and it is such values that should be the object of comparison. In order to
minimize the influence of the energy accumulated in the machine on the deformation
kinetics of a specimen, its dimensions should be selected in such a way as to ensure
a certain ratio between the energy absorbed by the specimen and the elastic energy
accumulated by the machine:
W
W
n
sp
m
� , n�1. (5)
The greater the value of n, the smaller (when going to a supercritical phase) the
effect of the elastic energy accumulated by the machine on the kinetics of further
specimen deformation. If, with the use of unified specimens, requirement (5) is not
met, the compliance of the machine elements should be adjusted.
In view of (3), the energy accumulated by the machine at the load P can be
defined as
W W C
P
m i
i
n
i
i
n
� �
� �
� �
1
2
1
2
. (6)
ISSN 0556-171X. Ïðîáëåìû ïðî÷íîñòè, 2010, ¹ 3 53
T a b l e 1
Mechanical Properties of Steels and Alloys at a Temperature of 4.2 K
Material S0 0, ,�
mm
�0 2. ,
MPa
�u ,
MPa
�, % � , % n Jc ,
kJ/m2
AMg5 S0 12 0� . mm
� �0 4 0. mm
192
170
(170)
465
540
(405)
11.0
41.5
(32.0)
10.0
28.5
(40.0)
235
93
17.0*
AMg6 S0 12 5� . mm
� �0 4 0. mm
197
135
(135)
517
547
(470)
18.5
24.0
(22.5)
14.5
15.5
(27.2)
203
74
5.0*
AMtsS S0 10 0� . mm
� �0 4 0. mm
150
147
(140)
400
425
(340)
32.0
29.0
(28.0)
33.0
27.0
(30.0)
272
103
44.5
03Kh20N16AG6 S0 9 0� . mm
� �0 4 0. mm
1150
1290
(1293)
1620
1640
(1305)
34.0
35.5
(22.5)
40.0
36.0
(51.0)
34
22
(1)
150.0*
0N9 S0 10 0� . mm
� �0 4 0. mm
1040
1230
(1240)
1481
1560
(1300)
19.5
20.0
(16.0)
48.0
51.5
(67.5)
21
14
(1)
18.0**
12Kh18N10T � �0 4 0. mm 770
(775)
1680
(1415)
44.5
(39.0)
34.5
(60.5)
49
(11)
101.0
Notes. The magnitude of the characteristic at W Wm sp� is given in brackets; * correspond J cI
(critical value of J-integral); ** correspond to the value of Jc calculated with the account taken of
K cI ; S0 and �0 are specimen thickness and diameter, respectively; �0 2. is offset yield stress; �u is
ultimate strength; � is relative elongation after fracture; � is relative necking after fracture; n is the
number of discontinuous yielding events.
On Standards for Mechanical Testing of Materials ...
Here C i is the compliance of the machine elements, i.e., the components of the
load transmission system, their coupling, and the load excitation system.
Since after each event of discontinuous yielding the specimen is deformed in
an elastic manner, in order to meet requirement (5), it is sufficient to fulfill the
following condition to a first approximation:
C Cm sp� , (7)
where C Cm i
i
n
�
�
�
1
.
If the gauge length of the specimen is a geometrically uniform rod, then
C
P
l
F Esp
sp
� �
�
0
0
, (8)
where l0 and F0 are the initial calculated gauge length and the cross-section area
of the specimen, respectively, E is the modulus of elasticity of the material at the
test temperature, and � sp is the absolute elastic elongation of the specimen at the
load P.
It is obvious that a change in the specimen dimensions results in a change in
its compliance, i.e., the ratio between the elastic energies of the machine and the
specimen can be violated, therefore, condition (7) should be written as
C
l
F Em �
0
0
.
One must also consider that, in the case of discontinuous yielding, the value
of l0 corresponds to a part of the initial calculated specimen length
l0 that is
deformed at every event of deformation. Using the approach presented in [11], it is
possible to show that for a five-fold cylindrical specimen
�l l0 0
2
15
. The remaining
13/15 of the initial calculated specimen length is the source of the elastic energy
that contributes to the material yielding in a localized zone
l0 . That is, the
compliance of the specimen is defined only by a part of its gauge length. It is in the
volume of this part of the specimen during the event of discontinuous yielding that
the elastic energy accumulated by the machine and the specimen outside this part is
released. In the final form, condition (7) for cylindrical five-fold specimens can be
written as
C
l
F Em �
2
15
0
0
.
At the same time, normative documents should allow defining the mechanical
characteristics of materials using specimens of other dimensions (according to
ASTM E8 or GOST 1497) either at the amount of the elastic energy accumulated
by the machine that differs from condition (7) or at other loading regimes if this is
54 ISSN 0556-171X. Ïðîáëåìû ïðî÷íîñòè, 2010, ¹ 3
L. S. Novogrudskii and V. A. Strizhalo
stipulated by the conditions of the material operation in structures or by the
requirements to metal products. These statements should be specified by separate
paragraphs of documentation.
Additional Remarks on the Standards. The strain rate in the interval indicated
in the standard should not influence the values of the characteristics determined in
accordance with the standardized procedure. Therefore, the statements of paragraphs
9.5.4 (ASTM 1450-03) and 8.3.3 (ISO 19819:2004) are subject to discussion. First,
if the strain rate variation in the regulated range leads to a change in the
deformation behavior or in the values of the mechanical characteristics, this means
that the selected range of rates does not ensure the identity of the testing
conditions. Second, the requirements of changing the strain rate for determining
the offset yield stress if the first event of the discontinuous yielding takes place at
the residual strain of less than 0.2%, which are stated in paragraphs 9.5.4 and 8.3.3
of the corresponding standards, are erroneous in essence. In our opinion, in this
case, the yield strength should be determined from the stress, which corresponds to
the onset of the first load jump. This manifestation of yielding is the property of
the material, i.e., the stress at which this jump takes place is the yield strength
under given test conditions, in particular, at a given strain rate.
In normative documents, it is reasonable to recommend that the compliance of
the force excitation and load transmission systems of the testing machine should be
determined experimentally. For this purpose it is necessary to use the method of a
low-compliance specimen [12]. Incidentally, the data on the machine compliance
obtained using this method make it possible to adjust the slope angle of the elastic
line of the tensile curves in the case of measuring the specimen elongation not
directly on its gauge length. This approach should also be included in the
recommendations of normative documents since measuring the specimen elongation
directly on the gauge length in the medium of liquid helium is a rather difficult
problem and when the amount of investigations is large it difficult to perform.
Conclusions. The normative documents that regulate the methods for testing
metallic materials at a temperature of liquid helium (ASTM E 1450-03, ISO 19819,
edition of 2004, GOSÒ-22706-77) have common essential drawbacks, which have
to be eliminated when developing an appropriate National Standard of Ukraine.
Among other things it is necessary:
(i) to regulate the compliance of the testing machine (the ratio of the
machine–specimen compliances);
(ii) to make it mandatory to test specimens of a unified standard size;
(iii) to determine the yield strength from the stress at which the first event of
discontinuous yielding begins or the offset yield stress from the stress that
corresponds to a normalized level of residual strain (the generally accepted level is
0.2%) for the selected standard strain rate.
Ð å ç þ ì å
Ðîçãëÿíóòî i ïðîàíàë³çîâàíî îñíîâí³ ïîëîæåííÿ ñòàíäàðò³â ASTM, ISO òà
ÃÎÑÒ, ùî ðåãëàìåíòóþòü ìåòîä âèïðîáóâàíü ìàòåð³àë³â íà ðîçòÿã ïðè òåìïå-
ðàòóð³ ð³äêîãî ãåë³þ. Âèÿâëåíî ãîëîâí³ ôàêòîðè, ùî îáóìîâëþþòü ïàðà-
ìåòðè äåôîðìóâàííÿ, íàâàíòàæóâàííÿ òà ðîçì³ðè çðàçê³â ïðè âèïðîáóâàííÿõ
ISSN 0556-171X. Ïðîáëåìû ïðî÷íîñòè, 2010, ¹ 3 55
On Standards for Mechanical Testing of Materials ...
ìåòàë³â ³ ñïëàâ³â â óìîâàõ óêàçàíî¿ òåìïåðàòóðè. Ïîäàíî ðåêîìåíäàö³¿ ùîäî
äîïîâíåíü ïîëîæåíü ñòàíäàðò³â.
1. T. J. Burns, “A simple criterion for the onset of discontinuous deformations in
metals at very low temperatures,” J. Mech. Phys. Solids, 42, No. 5, 897–811
(1994).
2. Ì. Ì. Krishtal, “Frequency sensitivity of the resistance to deformation and
strain macrorealization of during discontinuous yielding of Al–Mg alloys,”
Metalloved. Term. Obrab. Metal., No. 9, 26–30 (1997).
3. V. V. Pustovalov, “The effect of superconducting transition on the low-
temperature jump-like deformation of metals and alloys (Review),” Fiz. Nizk.
Temper., No. 6, 515–535 (2000).
4. À. Ê. Emaletdinov, “Unstable modes of plastic deformation of metals at
helium temperatures,” Fiz. Metal. Metalloved., 91, No. 4, 3–9 (2001).
5. S. À. Vologzhanina, Yu. P. Solntsev, Ò. V. Ermakova, “The effect of
structural changes on the reliability and service life of the material for
cryogenic equipment,” in: Strength of Materials and Structures at Low
Temperatures [in Russian], Collected Papers of the St. Petersburg State
University, St. Petersburg (2002), pp. 7–25.
6. Å. V. Vorob’ev and Ò. V. Anpilogova, “Peculiarities of manifestation of the
effect of low-temperature jump-like deformation,” in: Reliability and Life of
Machines and Structures [in Russian], Kiev (2006), Issue 26, pp. 166–174.
7. L. S. Novogrudskii, “Evaluation of low-temperature hardening of structural
materials at a temperature of 4.2 K,” in: Reliability and Life of Machines and
Structures [in Russian], Kiev (2006), Issue 26, pp. 319–325.
8. V. I. Startsev, V. Ya. Illichev, and V. V. Pustovalov, Plasticity and Strength of
Metals and Alloys at Low Temperatures [in Russian], Metallurgiya, Moscow
(1976).
9. V. À. Strizhalo, N. V. Filin, B. À. Kuranov, et al., Strength of Materials and
Structures at Cryogenic Temperatures [in Russian], Naukova Dumka, Kiev
(1988).
10. Ya. B. Fridman, Ò. K. Zilova, B. À. Drozdovskii, Kinetics of Deformation and
Fracture [in Russian], VÍNIIÀÌ, Ìoscow (1960).
11. V. I. Eremin, “Geometry of the zone of localized deformation in low-
temperature discontinuous yielding of metals,” Strength Mater., 19, No. 2,
181–184 (1987).
12. V. Î. Stryzhalo, L. S. Novogrudskyi, Ì. P. Zemtsov, Method to Determine
the Energy- and Strain-Based Characteristics of a Structural Material [in
Ukrainian], Ukraine Inventor’s Certificate 69351À, ÌK² G01N3/00 No.
20031212975. Bull. No. 8 (2004).
Received 28. 01. 2009
56 ISSN 0556-171X. Ïðîáëåìû ïðî÷íîñòè, 2010, ¹ 3
L. S. Novogrudskii and V. A. Strizhalo
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/CropImagesToFrames true
/ErrorControl /WarnAndContinue
/FlattenerIgnoreSpreadOverrides false
/IncludeGuidesGrids false
/IncludeNonPrinting false
/IncludeSlug false
/Namespace [
(Adobe)
(InDesign)
(4.0)
]
/OmitPlacedBitmaps false
/OmitPlacedEPS false
/OmitPlacedPDF false
/SimulateOverprint /Legacy
>>
<<
/AddBleedMarks false
/AddColorBars false
/AddCropMarks false
/AddPageInfo false
/AddRegMarks false
/ConvertColors /NoConversion
/DestinationProfileName ()
/DestinationProfileSelector /NA
/Downsample16BitImages true
/FlattenerPreset <<
/PresetSelector /MediumResolution
>>
/FormElements false
/GenerateStructure true
/IncludeBookmarks false
/IncludeHyperlinks false
/IncludeInteractive false
/IncludeLayers false
/IncludeProfiles true
/MultimediaHandling /UseObjectSettings
/Namespace [
(Adobe)
(CreativeSuite)
(2.0)
]
/PDFXOutputIntentProfileSelector /NA
/PreserveEditing true
/UntaggedCMYKHandling /LeaveUntagged
/UntaggedRGBHandling /LeaveUntagged
/UseDocumentBleed false
>>
]
>> setdistillerparams
<<
/HWResolution [2400 2400]
/PageSize [612.000 792.000]
>> setpagedevice
|