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TRANSPORT
ISSN 1648-4142 / eISSN 1648-3480
2018 Volume 331: 231241
doi:10.3846/16484142.2017.1301549
INFLUENCE OF DYNAMIC NON-EQUILIBRIUM PROCESSES ON STRENGTH
AND PLASTICITY OF MATERIALS OF TRANSPORTATION SYSTEMS
Mykola Chausov1, Andriy Pylypenko2, Valentyn Berezin3, Kateryna Volyanska4,
Pavlo Maruschak5, Volodymyr Hutsaylyuk6, Lyudmila Markashova7,
Stanislav Nedoseka8, Abdellah Menou9
1–4Dept of Mechanics, National University of Life and Environmental Sciences
of Ukraine, Kyiv, Ukraine
5Dept of Industrial Automation, Ternopil Ivan Pul’uj National Technical University, Ternopil, Ukraine
6Dept of Machine Design, Military University of Technology, Warsaw, Poland
7, 8Dept of Physical and Chemical Research of Materials, E.O.Paton Electric Welding Institute
of the National Academy of Sciences of Ukraine, Kyiv, Ukraine
9International Academy of Civil Aviation, Casablanca, Morocco
Submitted 23 August 2015; resubmitted 6 July 2016; accepted 15 September 2016;
published online 10 May 2017
Abstract. New experimental results on the eect of additional force impulse loading on the variation of the initial
structure of the aircra material (alloys D16, 2024-T3, VT22) at various stages of deformation are presented and a
signicant enhancement of its initial plasticity is achieved. Complex investigations into the material properties aer a
dynamic non-equilibrium process made it possible to describe the main regularities in the nature of deformation and
fracture of materials, which allowed proposing general recommendations on using the revealed physical and mechani-
cal regularities in the evaluation of strength of aircra structures.
Keywords: aircra material; deformation; fracture; strength of aircra structures; failure analysis.
Corresponding author: Pavlo Maruschak
E-mail: maruschak.tu.edu@gmail.com
Copyright © 2017 Vilnius Gediminas Technical University (VGTU) Press
http://www.tandfonline.com/TRAN
_________
A preliminary version of this paper was presented at the 4th International Conference ‘In-Service Damage of Materials, its Diagnostics and Predic-
ti on’ on 21–24 of September 2015 (Ternopil, Ukraine).
Introduction
An indispensable component of aircra construction is
the performance of endurance eld tests and laboratory
tests of structural elements and materials (Starke, Staley
1996; Ostash etal. 2006). Structural materials used in
the production of planting of the aircra fuselage should
be resistant to depletion of plasticity and aging (Merati
2005). e same is true about the need to ensure dura-
bility (taking into account plastic qualities and strength
of materials) of rocket and aircra structures, as well as
chemical, petrochemical and transport structures, oper-
ated under heavy inuences of dierent physical nature,
including local loads and contact interactions (Merati
2005; Smith etal. 2000; Lo etal. 2009).
Therefore, the development of new methods for
enhancing the mechanical properties of materials is
very important. One of them is the modification of
their properties using additional force impulse loading,
and the implementation of Dynamic Non-equilibrium
Processes (DNP) (Zasimchuk etal. 2009; Chausov etal.
2015a).
In DNP, the interaction of structural elements of
materials with energy fields causes self-organized pro-
cess in materials, leading to the formation of new space-
dissipative structures that cause significant changes in
the initial mechanical properties of materials.
In this case, the essential parameters of the DNP
process are time and speed of the energy introduction
into the material. As it was shown earlier (Zasimchuk
etal. 2009; Chausov etal. 2015a), under additional force
impulse loading of materials, with the preset speed and
frequency of loading (in particular, the preset range of
loading is 1–60 1/sec, and the preset range of loading
frequencies is 1–2 kHz), structural reorganization begins
232 M. Chausov et al. Inuence of dynamic non-equilibrium processes on strength and plasticity of materials ...
in materials, which is due to variation of the energy ex-
change mode in the medium, when the medium absorbs
the impulse brought by the impulse wave, but has not
enough time to pass it directly to the microscopic level
and transform heat energy.
Thus, there is a situation when a large part of the
energy from the additional impulse loading is transmit-
ted not to the microscopic level, but to some interme-
diate mesoscopic level, where it is spent on the struc-
tural reorganization and heterogenization of the material
(Khantuleva, Meshcheryakov 2016).
This mode of processing allows obtaining a num-
ber of specific properties of the material, which manifest
themselves, first of all, in a significant plastification due
to the formation of dissipative structures with the pres-
ervation of strength properties (Chausov etal. 2015b).
This is associated with self-organization mechanisms of
the material structure in case of a sudden variation of
action of the external force.
A number of works are known, which describe in-
dividual aspects of the material self-organization under
additional impulse loading and DNP (Hutsaylyuk etal.
2013, 2014). There have been some attempts to describe
mathematically the processes of self-organization of the
material surface, predict the formation of topography on
the surface, which occurs due to morphological changes
in the material (Lytvynenko, Maruschak 2015). Howev-
er, most of these works consider simplified conditions
of deformation or other groups of materials (Chausov
etal. 2012; Lebedev, Chausov 2004). This suggests that,
on the whole, insufficient attention has been given to the
comprehensive study of the problem of the DNP in the
materials used in transport and petrochemical machine
building.
This necessitates the analysis of strain localization
processes, systematization of the DNP influence on the
properties of materials of transport systems. Also im-
portant is the establishment of interconnection between
transient changes in the temperature and force modes of
specimen loading, and the methods of additional treat-
ment of specimens with cold, taking into account their
influence on the material characteristics and physical in-
terpretation of the revealed effects. The practical value
of such approaches is that the results obtained can be
used for further development of the theory of weaken-
ing environments in the development of methods for
the modification of structural materials of aircrafts and
spaceships. This will allow using the effect of plastifica-
tion to ensure a more complete use of the existing re-
source and create the additional resource of the materi-
als of transport systems, which, in turn, will enhance the
structural reliability (Lebedev, Chausov 2004).
The objective of this work is to reveal characteristic
changes in the structures of materials of different classes
after the DNP implementation, using new methods, and
systematize additional force loading to ensure maximum
increase in the initial plasticity.
Aircraft materials. In this paper, the most com-
mon groups of materials for the production of aircrafts
are considered (Gantois, Morris 2004; Kaufmann 2008),
Fig.1. Although there is a tendency for a widespread
use of composite materials in aircraft production, a sig-
nificant part of present-day aircrafts is made of metallic
materials. There is a problem of improving the structural
characteristics and durability (Jones etal. 2005; Warren
2004), Fig.1. Decreasing the material damageability, in-
creasing its durability, and reducing the number of de-
fects can significantly lower the cost of the aircraft main-
tenance. Aluminum and titanium alloys are traditional
aircraft materials, but with the emergence of composite
materials with similar mechanical properties, their use
has declined slightly.
1. Research Technique
e objects of research were the materials of transport
systems, in particular:
–Alloy D16 (GOST 4784-97, Al = 90.9–94.7%;
Cu= 3.8–4.9%; Mg= 1.2–1.8%; Fe and Si ≤ 0.5%;
Mn = 0.3–0.9%; Cr ≤ 0.1%; Ti ≤ 0.15%; Zn ≤
0.25%; admixture ≤ 0.15%), used in the produc-
tion of plating, framing, stringers, longerons of
Fig.1. Combination of materials used in Boeing aircras: a, b– Boeing-747; c, d– Boeing-777
(Dursun, Soutis 2014; Jones etal. 2005)
Aluminium
Steel
Titanium
Composite
Other
81%
13%
1%
4%
1%
11%
7%
11%
70%
1%
a) b)
c) d)
Maruschak-1
Transport, 2018, 33(1): 231–241 233
aircras and car bodies (Ostash etal. 2006; Leb-
edev, Chausov 2004);
–Alloy 2024-T3 (ASTM B209-14, Cu = 4.35%;
Mg= 1.50%; Fe= 0.50%; Si= 0.50%; Zn= 0.25%;
Ti= 0.15%; Cr= 0.10%; others ≤ 0.20), which is
widely used for the outer covering, in particu-
lar, of civil aircra fuselages (Merati 2005; Smith
etal. 2000);
–Alloy VT22 (GOST 19807-91, Fe = 0.5–1.5%;
C= up to 0.1%; Si ≤ 0.15%; Cr= 0.5–1.5%; Mo=
4–5.5%; V= 4–5.5%; N ≤ 0.05%; Ti= 79.4–86.3%;
Al= 4.4%; Zr ≤ 0.3%; O ≤ 0.18%; H ≤ 0.015%;
others ≤ 0.3%), which is traditionally used for the
production of vital components of the airframe
and chassis of the passenger and heavy transport
aircras, in particular, Il-96Т, Il-114 (Shakleina,
Zamyatin 2010; Moiseev 2000; Zherebtsov 2012);
these alloys ensure reliability of aircras, a reduc-
tion in their mass, and a long service life of their
vital components operated under complex modes
of loading (tension, bending, etc.);
–Another test material was steel 04Kh18N10
(GOST 5632-72, C ≤ 0.04%; Si ≤ 0.8%; Mn ≤
2%; Ni= 9–11%; S ≤ 0.02%; P ≤ 0.035%; Cr=
17–19%), which is used in the production of
seamless pipes for chemical and petrochemical
industry (Lo etal. 2009; Zholud etal. 2012).
In this work, a choice of test materials was pre-
conditioned by a need to compare the kinetics of de-
formation fields of materials with a pronounced wave
process of plastic deformation– aluminum alloys D16
and 2024-T3, and materials with relatively uniform and
proportional process of plastic deformation– titanium
alloy VT22 and stainless steel 04Kh18N10.
Investigations were carried out on specimens from
plastic sheet materials with a thickness of 1.5 and 3 mm
and a width of 10.2 and 25 mm. The gauge length of
specimens varied from 18.5 to 75 mm depending on the
selected width.
Specimens of the material were tested on the ZD-
100Pu modified hydraulic setup for static tests. The
modified version of the setup consists of two contours–
the external (load frame of the setup) and the internal
ones, respectively. The internal contour represents the
simplest statically undetermined structure in the form of
three parallel elements, which are loaded simultaneous-
ly– the central specimen and two symmetrical satellite
specimens (‘brittle samples’) of different cross-section,
prepared from tampered steels 65G or U8-U12. During
loading of this structure, satellite specimens get broken
(under preset loading or deformation), and the impulse
introduction of energy into the material of the test speci-
men is performed at the frequency of 1–2 kHz (Fig.2).
By changing the load that is necessary for the
specimens-satellites failure (given high force impulse)
and changing the degree of prior static of the materials
sample at which the short-term loadings are performed
(15–45ms), it is possible to study the effect of these pa-
rameters on the subsequent mechanical behaviour of the
material specimens until its fracture.
Moreover, with a view to localization of the dis-
sipative structure, a special methodology was used with
regard to the gauge length of the test specimen, which
consisted in the application and drying of the concen-
trated colloid solution of tungsten nanoparticles on the
separate gauge length of specimens (Chausov, Volianska
2011).
To investigate fracture toughness in the gauge
length of specimens with a width of 20 mm, an opening
with diameter of 1.4 mm was made in the middle and
then a ‘natural’ macrocrack of preset size was ‘grown’ in
the zone of concentrator for further Static Tensioning
(ST) and the DNP. The colloid solution was also applied
to the crack tip and in the zone of its potential propaga-
tion in accordance with the above technique. Specimens
with cracks were tested using the method of complete
curves, which provided for the stability of the processes
of deformation and fracture at different stages, includ-
ing at the stage of macrofracture (Lebedev et al. 1996;
Lebedev, Chausov 2004).
The Acoustic Emission (AE) method was also used,
which consists in scanning by contemporary AE devices
ЕМА-3 (Vasyl’jev etal. 2012) in a special temperature
mode of loading (Holding specimens in the medium of
Liquid Nitrogen (HLN) after the DNP implementation
at a room temperature) for the evaluation of the non-
uniformity of the mechanical properties of materials
after the formation of dissipative structures.
2. Metal Properties
2.1. Aluminum Alloys D16 and 2024-T3
In case of one-time impulse loading of materials, there
are two main factors, which have a significant effect on
the variation of the mechanical properties of materials
under subsequent ST:
–the level of the preliminary static deformation, at
which impulse force loading was performed, and
the amplitude of loading;
–the eect of variation of the temperature mode
of loading.
Fig.2. General view of the inner-contour
of the loading system
234 M. Chausov et al. Inuence of dynamic non-equilibrium processes on strength and plasticity of materials ...
In fact, depending on the values of these factors, a
multitude of new mechanical conditions of the material
may occur under the DNP. Therefore, it is important to
know when the mechanical properties of the material
improve to the maximum, and when they worsen to the
maximum. At first, the structure of the material after
the DNP at a room temperature was ‘frozen’ in the me-
dium of liquid nitrogen. After warming at a room tem-
perature, the specimens were subjected to static loading
again, and their work to embrittlement was evaluated.
Alloy D16. Typical stress–strain curves of alu-
minum alloy D16 subjected to static deformation by
the scheme ST+ DNP+ ST are given in Fig. 3. One
of the main effects associated with the influence of the
DNP on aluminum alloy D16 is the formation of the
yield plateau, whose length can be regulated by the ini-
tial conditions of additional force loading. If the initial
plasticity of aluminum alloy D16 was 14%, the length
of such plateau in the alloy reached 10–12% (Fig.3) in
our investigations, indicating a significant influence of
the DNP on the enhancement of the general plasticity
of alloy D16.
Alloy 2024-T3. In the course of previous investiga-
tions of specimens from alloy 2024-T3 (Zasimchuk etal.
2009), the deformation of alloys 2024-T3 and D16 was
found to be similar under the DNP. Let us consider the
effect of different test patterns on the regularities in the
deformation of alloy 2024-T3 (Fig.4):
–HLN, warming up to 20оС+ ST (curve 2, Fig.4)
has practically no eect on the mechanical prop-
erties of alloy 2024-T3;
–ST+ DNP (Fimp = 90.4 kN), HLN, warming up
to 20ºС+ ST does not lead to an improvement of
the mechanical properties of the material (curve
3), since damage or defects that appeared during
the DNP does not disappear, causing a depletion
of the material plasticity;
–ST+ DNP (Fimp= 111.8 kN), HLN, warming up
to 20ºС + ST also deteriorates the mechanical
properties of the material (curve 4, Fig.4).
–It should be noted that under the above modes of
loading, specimens got broken practically in the
quasi-brittle manner (curve 4, Fig.4).
Thus, it is proven experimentally that self-organi-
zation of structures of aluminum alloys at a room tem-
perature due to additional force loading leads to a sig-
nificant increase in plasticity (up to 60–70%), practically
without any depletion of strength of the alloy 2024-T3.
However, with a decrease in temperature, a newly
created dissipative structure of aluminum alloys used in
aviation is prone to embrittlement, which should be tak-
en into account in operation of real products. Therefore,
it is important to consider the influence of additional
compressive temperature stresses on an increase in the
volume of damage in the dissipative structure.
The obtained experimental results indicate that the
volume of the newly formed dissipative structure in the
material should be referred to one of the key parameters,
which have a significant effect on the variation of the
mechanical properties during the repeated ST (Zasim-
chuk etal. 2009; Hutsaylyuk etal. 2014).
We should also note a stable, although insignificant
decrease in strength by ~10–30 MPa in aluminum alloy
D16 after the DNP. In this case, a decrease in strength
of the alloy 2024-T3 is not observed. The fact that an
increase in the material plasticity after the DNP im-
plementation is associated with the structural self-or-
ganization was time and again proved by the authors
using direct physical methods of research (Zasimchuk
etal. 2009; Hutsaylyuk etal. 2013, 2014; Chausov etal.
2015b, 2012). In case of the DNP implementation in the
plastic area of the material deformation, self-organiza-
tion occurs in the form of newly formed finely banded
structures interconnected at different structural levels.
Moreover, the density of these structures is less than that
of the base material.
2.2. Stainless Steel 04Kh18N10
e DNP implementation in the plastic area of stain-
less steel also leads to the formation of spatial narrow-
banded dissipative structures (Chausov, Volianska 2011).
e DNP implementation under initially low strain was
chosen specically to decrease the inuence of the ma-
terial damage on the process character. Fig.5 shows the
experimental results in the case when impulse load-
ing was applied practically within the elastic section of
deformation. e results were obtained in accordance
Fig.4. Stress–strain curve of aluminum alloy 2024-T3: 1– ST
at 20ºС; 2– HLN, warming up to 20ºС+ ST; 3– ST+ DNP
(Fimp=90.4 kN), HLN, warming up to 20ºС+ ST; 4– ST+
DNP (Fimp=111.8 kN), HLN, warming up to 20ºС+ ST
Fig.3. Stress–strain curves of aluminum alloy D16:
1– ST; 2– ST+DNP (Fimp=89.6 kN)+ST
e
[%]
s [MPa]
12
0510 15 20 25
0
100
200
300
400
500
e
[%]
s [MPa]
12
3
4
0510 15 20
0
50
100
150
200
250
300
350
400
450
500
Transport, 2018, 33(1): 231–241 235
with the technique, which allows localizing the dissipa-
tive structure on the preset gauge length of the specimen
(Chausov, Volianska 2011).
Two sequential impulse loads (DNP) were imple-
mented, and, additionally, a change in the temperature
mode of loading (after each impulse loading, specimens
were held for 1 hour in the medium of liquid nitrogen).
Under the above complex preliminary mode of loading
during the repeated ST of the specimen at a room tem-
perature, the test steel moved to the yield plateau with
the length of more than 14% (curve 1, Fig.5) practi-
cally immediately. However, the manifestation of such a
specific plastic behaviour of the steel leads to a notice-
able decrease in its general plasticity as compared to the
initial condition (curve 2, Fig.5). As is seen, the yield
point of the material increases after the DNP, and the
material hardens (Fig.5). Under such conditions, the
metal grains change their orientation in the direction of
force application, a resistance to deformation increases,
and the plasticity of the steel decreases. The experiments
with stainless steel confirm previous results obtained
for aluminum alloys, according to which a dissipative
structure formed at a room temperature becomes brittle
during its subsequent tensioning at a low temperature,
the effect of which must be taken into account while
constructing the models of material behaviour under
such complex modes of loading and evaluating safety
margins.
Fig.6 shows some characteristic experimental re-
sults for the embrittlement of dissipative structures in
stainless steels after HLN for one hour. In the process
of investigations, a significant influence of deformation
hardening on the variation of the mechanical properties
of stainless steel 04Kh18N10 during subsequent ST was
observed.
The analysis of curves (Fig.6) shows that the com-
plex mode of loading of steel 04Kh18N10 does not lead
to an improvement of the mechanical properties of the
material, since positive qualities of the dissipative struc-
ture disappear due to relaxation, but damage or defects
obtained after the DNP remain.
Let us consider the effect of the DNP on fracture
toughness of steel 04Kh18N10 (Fig.7). The results ob-
tained indicate a possibility to enhance fracture tough-
ness of materials after the DNP within the local area in
the vicinity of the macrocrack tip.
Attention should be paid to (curve 1, Fig.7), which
corresponds to the self-pressing growth of a macrocrack
from the initial concentrator in the form of an opening.
A slope of this curve at the stage of growth of a macroc-
rack (section І) characterizes energy expenditures on the
macrocrack propagation across the width of the sheet
steel. A complete unloading of the specimen at a pre-
set length of the macrocrack and impulse loading up to
point K in curve 2 increases energy expenditures on the
growth of a macrocrack significantly (the dashed part in
Fig.7). Even greater energy expenditures on the growth
of a macrocrack were achieved when concentrated col-
loid solution of nanoparticles was applied to the mac-
rocrack tip and to the zone of its propagation prior to
impulse loading (curve 3, Fig.7).
In the process of the DNP implementation, nano-
particles of tungsten were ‘coined’ into the specimen
surface, because the density of newly formed dissipative
structures was lower than that of the base material, and
they extruded to the surface (Chausov, Volianska 2011).
As a result, the hardness of the surface layer of the ma-
terial within different sections of the specimen differed
significantly, and possibilities were created for a sharp
localization of the dissipative structure within the given
working section of the material sample.
Fig.5. Stress–strain curves for stainless steel 04Kh18N10:
1– ST+ DNP (Fimp= 103.9 kN)+ HLN+ DNP (Fimp=
109.3 kN)+ HLN+ ST; 2– ST
Fig.6. Stress–strain curve for stainless steel 04Kh18N10: 1 –
DNP (Fimp=68.5 kN)+ST; 2– HLN+ DNP (Fimp=59.9kN)+
ST; 3– ST in the initial condition at t= 20ºС
Fig.7. Curves of macrocrack growth in specimens from
stainless steel 04Kh18N10 with openings: 1– ST, 2– ST+
DNP (Fimp=7.4 kN); 3– ST+ DNP (Fimp=12.7 kN)
with the application of colloid solution
s [MPa]
e
[%]
12
0
100
200
300
400
500
0510 15 20
25
–5
12
3
e [%]
s [MPa]
5 15 25 35 45–5
0
100
200
300
400
500
s [MPa]
e
[%]
1
2
3
I
K
0
100
200
300
400
500
0510 15 20 25 30 35
236 M. Chausov et al. Inuence of dynamic non-equilibrium processes on strength and plasticity of materials ...
2.3. Titanium Alloy VT22
In the course of testing aluminum alloys D16, 2024-T3
and stainless steel 04Kh18N10, the DNP was imple-
mented in the plastic area of the statically pre-strained
specimens. e major experiments with the DNP imple-
mentation in the heavy-duty titanium alloy VT22 were
performed within the elastic section of the stress–strain
curve. In this case, the total stress in the alloy caused by
static pre-straining and impulse loading did not exceed
the yield point of the alloy (Fig.8).
Let us consider the regularities in deformation and
failure of alloy VT22:
–ST (curve 1, Fig.8). e form of the curve indi-
cates that the material has a high strength and
low plasticity. Failure occurred at the longitudinal
strain of 6.5%;
–ST+ DNP+ ST (curve 2, Fig. 8) causes an in-
crease in the longitudinal strain to 13.4% during
failure;
–preliminary HLN of the alloy VT22 with subse-
quent warming up to 20оС leads to an increase in
plasticity of the alloy, the failure strain is 14.2%
(curve 3, Fig.8);
–HLN aer the DNP implementation within the
elastic section of the stress–strain curve also en-
hances plasticity of the alloy, the failure strain is
13.8%. However, the strength characteristics of
the alloy decrease signicantly (curve4, Fig. 8).
is can be associated with certain structural
damage of the alloy and relevant residual increase
in the volume aer fragmentation (Zasimchuk
etal. 2009; Hutsaylyuk etal. 2014).
Individual investigations into fracture surfaces of
the alloy under different test patterns confirm that, in
the case of formation of dissipative structures, the metal
becomes non-uniform, i.e. some kind of a composite, in
which there is alternation between soft zones (dissipa-
tive structure), hard zones (base material), and relevant
layers between them. It is natural that energy expendi-
tures on the growth of a macrocrack in such a hybrid
material, as well as in the above-mentioned cases, must
increase, which was observed in this work.
Thus, we were the first to achieve a significant
increase in the initial plasticity of the material (alloy
VT22) (practically by 2.75 times) due to the DNP im-
plementation (Fig.8).
3. Discussion and Generalization
To interpret the results obtained and describe the regu-
larities obtained, we used additional methods of control
of the material condition with a view to conrming the
relationship between physical and mechanical phenom-
ena that occur in the aviation alloys and stainless steels
under investigation. Dierences between the mecha-
nisms of material deformation under the DNP are as-
sociated with signicant uctuations of the injection rate
of energy into the material, due to which the specimen
becomes agitated, and the surplus dissipates in local
weakened zones.
3.1. Using the AE
e condition of steel 04Kh18N10 was investigated
using the method of AE under various test patterns
(Vasyl’jev etal. 2012). A sensor-imitator, which emits
AE signals of the preset shape and amplitude, was in-
stalled on the wide part of the at test portion, and a
similar sensor, which accepts AE signals, was installed
at a xed distance from the sensor-imitator. e signal
velocity between the sensors was recorded along the at
surface of the specimen. At least 25–30identical tests
were performed for each condition of the material.
The results, which were obtained and general-
ized, are presented in Fig.9 in the form of dependence
of signal velocity imitated by the sensor-imitator on the
degree of plastic deformation under the DNP implemen-
tation. The results obtained for steel 04Kh18N10 con-
firm the data obtained previously on a lower density of
the dissipative structure formed after the DNP as com-
pared to the base material.
The dissipative structure was found to extrude on
the surface, and the elastic properties of the surface layer
were found to be less than those of the initial material.
In addition, the wave velocity decreased depending on
the degree of plastic deformation under the DNP imple-
Fig.8. Stress–strain curves for titanium alloy VT22: 1– ST;
2– ST+ DNP (Fimp= 60 kN)+ ST; 3– HLN+ ST; 4–DNP
(Fimp= 60 kN) before the yield point of the alloy HLN+ ST
e [%]
1
2
3
4
s [MPa]
0510 15 20
0
200
400
600
800
1000
1200
Fig.9. Dependence of signal velocity of steel 04Kh18N10
emitted by the sensor-imitator on the degree of plastic
deformation under the implementation of the DNP
e
[%]
3.3
3.4
3.5
3.6
3.7
3.8
3.9
4.0
4.1
v [km/s]
y = –0.0575x + 4.0066
R = 0.9952
0 2 468 10 12
Transport, 2018, 33(1): 231–241 237
mentation. Moreover, the greater the degree of plastic
deformation under the DNP implementation, the great-
er the volume of a newly formed dissipative structure.
However, variations of the thin structure of the material
are possible, as well as the accumulation of microdefects
with an increase in the volume and localization of strain.
A change in the strain rate from ST to DNP and the
effect of HLN cause changes in relaxation processes in
the metal structure and can lead to an increase in plas-
tic deformation during further loading, or a coalescence
of newly formed defects and subsequent failure of the
specimen. The presence of inclusions and strengthen-
ing phases in the structure of steel 04Kh18N10 causes
a decrease in the material plasticity after the DNP, i.e.
a reverse effect.
3.2. Aluminum Alloys D16 and 2024-T3
Aluminum and titanium alloys are inclined to short-
term plastication with simultaneous ‘abnormal’ weak-
ening due to the formation of amorphous dissipative
structure in the form of localized bands volume bound
at dierent scale levels, at which hydrodynamic yield-
ing of the material occurs. However, shear strains in
structural elements of the material are accompanied by
changes in volume and depend on the DNP conditions.
Thus, a dissipative structure is formed due to the
impulse injection of energy; moreover, the greatest part
of the material within this new structure is subjected to
the intensive compression (Chausov etal. 2015a). Most
sensitive to such structural reconstructions of the mate-
rial are the thermal capacity and the electrical resistance
of the material (Omari, Sevostianov 2013; Sevostianov
etal. 2010).
Structural changes, defect formation, and grain
grinding affect the thermal capacity of the material, which
will manifest itself indirectly while comparing the width
of the initial specimens to those subjected to the DNP.
Fig.10 presents the results of the width measurements
of specimens from the aluminum alloy 2024-T3 stud-
ied under different test patterns (Chausov etal. 2015a).
Significant differences between variations of the
residual width of specimens were revealed, which are
directly associated with different volumes of the bro-
ken structural elements of the alloy held in the medium
of liquid nitrogen, and, respectively, different residual
volumes of the specimen material (the presence of dis-
persed damage) after holding.
VT22. Measurement results of variation of the
specimen width subjected to the DNP after HLN for one
hour (curve 1, Fig.11), as compared to the specimen in
the initial condition (curve 2, Fig.11), indicate a signifi-
cant structural non-uniformity of alloy VT22.
Sections of residual stresses caused by the struc-
tural and mechanical changes and thermal fields occur
in the material structure under the DNP. In the process
of cooling, thermoelastic vibrations caused by the dif-
ference between the thermal capacities of the initial and
modified layers are concentrated in them. The vibrations
have a complex spatial morphological structure, which
depicts the synergy of such collective self-organization
phenomena as the mechanical yielding of material, dis-
sipation processes, sharp changes in the dislocation den-
sity, etc. (Starke, Staley 1996).
The form of variation of the specimen width is one
of the parameters that allows evaluating the material
condition, since the newly created morphological struc-
tures are a result of the aggregation of the elementary
stress relaxation acts. However, a high-quality analysis
of the curve 1 (Fig.11) and a high amplitude of vibra-
tions indicate the presence of the zones with a signifi-
cant strain capacity in the material.
Fig.10. Width measurement of specimens from the alloy 2024-T3 during HLN for 1 hour: a– specimen in a bath with liquid
nitrogen; b– data on the specimen width variation (1– initial condition; 2– aer the DNP implementation)
0600 1200 1800 2400 3000 3600 4200 4800
t
[s]
m
5400 6000
1
2
–0.003
0.000
0.003
0.006
0.009
0.012
0.015
0.018
0.021
0.024
0.027
Dh [mm]
a) b)
Fig.11. Curves of variation of specimen width in the medium
of liquid nitrogen (explanations are given in the text)
0 500 1000 1500 2000 2500 3000 3500
–0.03
–0.01
0.01
0.03
0.05
0.07
0.09
Dh [mm]
1
2
t [s]
238 M. Chausov et al. Inuence of dynamic non-equilibrium processes on strength and plasticity of materials ...
3.3. Fractographic analysis
e comparative analysis of fracture surfaces of speci-
mens from the titanium alloy VT22 investigated under
dierent deformation modes testies to the following.
Regardless of the test pattern, a fracture surface has quite
a smooth, structureless view. Torn-out sections of the ma-
terial similar to ‘shear lips’ were found near the surface.
ST. The surface is formed by the ductile-brittle
mechanism; it is covered with band-like scars oriented
along the longest facet of the specimen, indicating the
localization of the deformation process (Fig.12а). The
microrelief is formed by shallow, but clear-cut pits with a
size of 1–3 µm. Side surfaces of the pits are smooth, brit-
tle, and have a view of spalling. Separation ridges have
Fig.12. Scanning Electron Microscope (SEM) images of fracture of alloy VT22 aer: a, b– ST; c, d– ST+ DNP
(Fimp= 60 kN)+ ST; e, f– HLN + ST; g, h– DNP (Fimp= 60 kN) before the yield point of the alloy+ HLN+ ST
a)
c)
e)
g)
b)
d)
f)
h)
Transport, 2018, 33(1): 231–241 239
sharp edges, which indicate a brittle component in the
process of material fracture (Fig.12b).
ST+ DNP+ ST. At the macrolevel, the fracture
surface is quite smooth and is covered with ‘terraces’ lo-
cated parallel to the longest of the side facets (Fig.12c).
At a high magnification, some clear-cut circular pits are
noticeable on the surface, which indicate a sufficient
ductility of the material and high energy efficiency of its
fracture. The size of pits is 5–7 µm, in addition, it should
be noted that they are all of nearly the same size, which
indicates the graded nature of their formation and prop-
agation, and a significant material plasticity (Fig.12d).
HLN + ST. At the macrolevel, the fracture sur-
face has two sections: a section of shear and a section
of separation. Some ‘banding’ is also noticeable on the
surface, indicating the presence of ridges located parallel
to the largest of the specimen facets. The ridges are cov-
ered with micropits of size 2–4 µm with rough contours.
The pits have a brittle view, and the mechanism of their
formation can be described as ductile-brittle (Fig.12e).
They have a shape of a polyhedron, whose facets are as-
sociated with the formation of angles, at which the pit
contours have the maximum thickness. Moreover, in
contrast to the previous example, pits are located at sev-
eral levels, i.e. on ridges and in valley sections (Fig.12f).
DNP before the yield point of the alloy+ HLN +
ST. The specimen surface has two clear-cut sections– a
section of ductile separation and a section of spalling
(Fig. 12g). In the zone of ductile separation, the sur-
face has a ‘fibrous structure’. The fracture surface was
formed in the ductile manner with the involvement of
significant sections of the material in the process of de-
formation, which caused shear and rotation processes in
the specimen cross-section. At the macrolevel, the frac-
ture surface can be characterized as ductile-brittle; the
fracture surface has a ‘smoothed-out’ view without any
clear-cut pits or spalling (Fig.12h).
The DNP implementation causes activation of the
mechanisms of transverse sliding in the zone of strain
localization, due to which even those phase compo-
nents became active, in which low values of the energy
of package defects impede the process of sliding (Yako-
vleva 2000; Maruschak etal. 2014; Okipnyi etal. 2014).
Using the methods of transmission electron mi-
croscopy, it was found that after additional force loading
there is a significant fragmentation of the alloy, due to
which small grains are formed in the base of the alloy
(β-phase), and the process of subgrain grinding takes
place. In particular, the initial size of the base grain,
which is 35–125 µm, decreased to 15–75 µm, and the
size of subgrains decreased from 1.3–3 µm to 0.6–3 µm.
In the authors’ opinion, it is the fine-grained structure
of the alloy (with a high volume content) under the ad-
ditional force loading that favours a significant increase
in the initial plasticity of the alloy during further ST.
Let us formulate general regularities and certain
technological recommendations, and technological pe-
culiarities of using the DNP mode:
–the application of additional force loading of
various classes during ST of specimens, as a rule,
enhances their plasticity; under optimal values of
the preliminary static deformation of a particular
material and intense additional force loading, it
is possible to achieve a signicant increase in the
initial plasticity of the material without any no-
ticeable decrease in the strength characteristics;
–if impulse loads are applied before the yield point
of the material, when the material damageability
is minimal, the newly formed dissipative struc-
ture in the material volume is more uniform as
compared to the dissipative structure, which is
formed in materials at a signicant level of plas-
tic deformation, when the degree of the material
damageability is much higher;
–to achieve an increase in plasticity, the presence
of the DNP is an indispensable condition, how-
ever, insucient; in this case, of paramount im-
portance is the initial condition of the processed
metal and the capacity of its structure for plastic
deformation without the accumulation of mul-
tiple structural microdefects; in particular, the
presence of inclusions and strengthening phases
in the metal structure, a typical example of which
is steel 04Kh18N10, causes a decrease in the ma-
terial plasticity and activates the accumulation of
structural damage aer the DNP, i.e. provides for
the reverse eect;
–uctuations of loads lead to quick changes in the
stress–strain state of the material, at which non-
elastic strains in the material are determined not
only by plastic deformation, but also by trans-
formational deformation associated with phase
transformations in the material; in addition, the
process of modication is aected by HLN; the
diusion of alloying elements and the uniform-
ity of their distribution depend, to a large extent,
on the temperature and force conditions aer
the DNP, and have a determining inuence on
the properties of the aircra materials (Nester-
enko,B., Nesterenko, G. 2013; Ignatovich etal.
2013).
Conclusions
A complex study of the DNP process allowed nding
the main regularities in the deformation behaviour of
aviation steels and the steel of petrochemical equipment,
as well as elaborating its mechanisms. In addition, an at-
tempt was made to use the methods of non-destructive
control and fractographic analysis to substantiate physi-
cal processes in the materials subjected to the DNP at
the stages of their deformation and failure.
The DNP implementation in the aviation materials
(alloys D16, 2024-Т3, V22) at various stages of defor-
mation causes a significant increase in their initial plas-
ticity. However, a reverse effect was obtained for steel
04Kh18N10, and its plasticity decreased after the DNP.
Using the method of АЕ-scanning in the course of
the DNP implementation, the previously obtained data
on the extrusion of the newly created dissipative struc-
240 M. Chausov et al. Inuence of dynamic non-equilibrium processes on strength and plasticity of materials ...
tures on the surface of flat specimens due to their lower
density, as compared to that of the base material, were
confirmed.
It is confirmed, that the hybrid structure formed in
the material in the course of the DNP implementation
at a room temperature increases the material fracture
toughness significantly at the same temperature. Howev-
er, a sudden cooling of the material specimens after the
formation of dissipative structures at a room tempera-
ture causes a significant concentration of defects on the
boundaries between dissipative structures and the base
material. This leads to the material embrittlement dur-
ing further testing at a room temperature after warming.
A new mechanism of the formation of dissipative
structures in the heavy-duty titanium alloy VT22 is
found, which is associated with a local fragmentation
of the initial structure under impact-oscillatory loading.
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