ISSN 10683666, Journal of Friction and Wear, 2010, Vol. 31, No. 3, pp. 208–213. © Allerton Press, Inc., 2010.
Original Russian Text © A.A. Semenets, V. N. Anisimov, 2010, published in Trenie i Iznos, 2010, Vol. 31, No. 3, pp. 282–288.

208

INTRODUCTION

Progress in modern machinery is closely linked to

the development of new types of composite materials
without which we can not imagine any branch of
industry. Novel polymeric materials for the base for the
creation of new designs and various goods. They also
promote weight reduction of these goods, reduction of
service and transport cost, and optimization of quality
and appearance. The application of new composite
materials in mechanical engineering provides a num
ber of advantages by ensuring high wear resistance,
reduced friction coefficient, extended durability, and
capacity of operation in hostile media [1–3].

One of the acute problems of today is protection of

components and mechanisms against abrasive wear.
The industries of building materials, dressing works,
metallurgy of ferrous and nonferrous metals, and
mining employ in their work pneumatic pipelines;
crushers; ball and rod mills; sieve and spiral classifiers;
cyclones; sandblasters; flotation, sand and dredging
pumps; compressors; ventilators; and other equip
ment. The low wear resistance of parts working in
abrasive media gives an impetus to the development of
more efficient methods of increasing abrasive resis
tance [4, 5].

The traditional procedures aimed at enhancing the

wear resistance of working components by raising the
hardness of materials to a maximum (highalloyed
materials and hard alloys, facing, corundum, stone
casting, etc.) may in some cases solve this problem.
However, it becomes necessary under some operating
conditions to increase not the hardness but the elastic
compliance of the surface to raise its wear resistance [5].

The method of gumming is extensively used today,

although special rubber grades and vulcanization pro
cedures make it inapplicable for a wide range of equip
ment. It has become possible to solve this problem
with a wide usage of PU that are devoid of above dis
advantages. They possess a unique complex of proper
ties—high strength and elasticity; high vibration resis
tance and impact strength; resistance to various non
polar solvents, oils, and fuels; and manufacturability
by highly productive technologies [6]. Nevertheless,
not all materials of this spectrum display the ability to
resist abrasive affects, while the related data are very
scarce in the scientific literature. One of the reasons
why we are still lacking scientifically substantiated
methods of developing highperformance materials is
the limited number of investigations into the structure
and properties of the named polymers in conditions of
gasoabrasive wear.

The aim of the work is to establish the relationship

between the conditions of synthesis and processing of
thermoplastic polyurethanes (TPU) and their struc
ture, physicomechanical, and triboengineering char
acteristics. In addition, we have undertaken to develop
methods of predicting the wear of TPU in a flow of
abrasive particles with consideration of their structural
parameters (concentration of rigid blocks, molecular
mass), the nature and type of the initial components,
and the operating parameters (flow velocity of abrasive
particles, angle of attack); to elaborate means of
enhancing the abrasive resistance of TPU via synthe
sizing initial ingredients with preset properties; and to
advance practical recommendations on the usage of

Development of Triboengineering Composite Materials

Based on Thermoplastic Polyurethanes

A. A. Semenets* and V. N. Anisimov

Ukrainian University of Chemical Technology, pr. Gagarina 8, Dnepropetrovsk, 49005 Ukraine

*email: semenetzdp@.ukr.net

Received June 10, 2009

Abstract—The work presents results of study of gasoabrasive wear of a wide range of thermoplastic polymers.
A relationship is found between the conditions of synthesis of thermoplastic polyurethanes and their struc
ture, physicomechanical, and triboengineering characteristics. Methods of predicting wear of polyurethane
thermoplastics in a flow of abrasive particles are developed with account of varying structural parameters
(concentration of rigid blocks, molecular mass), origin and type of initial components, and service charac
teristics (flow velocity of abrasive particles, angle of attack). Recommendations are given for enhancing abra
sive resistance by synthesizing initial materials with preset properties.

Key words: abrasive resistance, polyurethanes, structure, wear rate, gumming, angle of attack.

DOI: 10.3103/S1068366610030098

JOURNAL OF FRICTION AND WEAR

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DEVELOPMENT OF TRIBOENGINEERING COMPOSITE MATERIALS

209

PU resistant to abrasives in conditions of gasoabrasive
wear.

To attain these aims, we have formulated the fol

lowing main tasks:

⎯development of the methods of monitoring

structure and properties of TPU in order to enhance
their abrasive resistance;

⎯experimental study of gasoabrasive wear of TPU

as dependent on their chemical structure and consid
eration of the polymer molecular mass, concentration
of rigid blocks, nature and type of ingredients;

⎯elaboration of a mathematical model of the wear

process in the form of analytic equations interrelating
the structural parameters (concentration of rigid
blocks and molecular mass) and service characteristics
(stream velocity of abrasive particles, angle of attack)
of PU thermoplastics.

OBJECTS AND METHODS OF RESEARCH

The research objects were TPU synthesized at

OAO “Polimersintez” (Vladimir, Russia). The systems
under study differed in the use of polyester or poly
ether, in molecular mass (which varied according to
recommendations from 500 to 2000), and in the
nature of the initial components. We used polyesters
for synthesis, namely, polyethylene glycol adipinate
(PEGA), polybutylene glycol adipinate (PBGA),
polyethylene butylene glycol adipinate (PEBGA), and
a polyether polyoxytetramethylene glycol (POTMG).
The isocyanates were 4,4

1

diphenylmethanediisocy

anate (MDI) and 2,4toluylene diisocyanate(TDI).
As the chain elongation agents we used ethanediol
(ethylene glycol, EG) and 1,4butanediol (butylene
glycol) (BD). The initial samples of TPU were
obtained by a onestage synthesis in oil at a parity of
isocyanate and hydroxyl groups (NCO/OH = 1).

Analysis of spatial models for the PU obtained with

account of the type and share of components showed
that these materials represent block copolymers of the
(AB)

n

type whose molecules consist of blocks (seg

ments) of flexible and rigid chains. The flexible blocks
include both polyesters and polyethers. The rigid
blocks are formed as a result of interactions between
diisocyanates and lowmolecular glycols. Since the
blocks have low solubility, a biphase structure is
formed in the PU with rather high heterogeneity. The
presence of structural inhomogeneities in the TPU
bulk in the form of microphases of the rigid and flexi
ble blocks interconnected via chemical links governs
the main peculiarities of these polymeric materials [7].
The characteristics of the PU can be controlled both
by varying the concentration of the rigid blocks and by
changing the molecular mass of the polymer.

The Xray diffraction analysis of the phase compo

sition of the developed materials was carried out by
using a DRON2 diffractometer. The pictures were
taken in copper (CuK

α

) radiation using a crystal

monochromator under the following operating condi
tions: voltage—20 kV; current strength—10 mA;
measurement range—1000. The curves of the inten
sity distribution were recorded on a chart strip of the
potentiometer. The diffraction maxima were recorded
within the interval of the double angles (5–150

°). The

angles were determined from the position of the peak
of the diffraction maximum, after which the interpla
nar spacing

d, nm, was found by the angle of reflection

θ based on Wolf–Bragg’s equation.

The physicomechanical characteristics of the PU

(conventional stress at elongation, f

300

; relative elon

gation,

ε

p

; residual elongation,

ε; conventional

strength at tension,

f

p

) were determined according to

GOST (State Standard) 270–75 on an INSTRON1122
universal machine. The conventional stress at elonga
tion,

f

300

, of the TPU was measured under 293 K tem

perature in the region of linear viscoelasticity (

f < f

k

,

where

f

k

is the elasticity threshold of the TPU of the

given composition). The coefficient of mechanical
hysteresis losses

χ was measured at a 50 mm/min ten

sion rate of the movable grip and 100% deformation
degree. The hysteresis losses were found both in the
first loading cycle (loading–unloading) and in the fifth
cycle (

χ values stabilize by the fifth cycle).

Thermomechanical investigations were carried out

on a TMK2 instrument using the integral method
with automatic recording of the strain–temperature
dependence under 1 MPa load and 2 K/min tempera
ture rise intensity.

For the investigations on gasoabrasive wear we used

a TUK3M centrifugal accelerator. The geometric and
kinematic parameters of the accelerator meet the
requirements of

GOST 23.201–78 “Provision of Wear

Resistance of Goods. A Method of Gasoabrasive Wear
Testing of Materials and Coatings Using a Centrifugal
Accelerator”. The investigations were conducted with
the angle of attack

α = 15, 30, 45, 60, and 90°. The

flow velocity of the abrasive particles was 38, 57, and
76 m/s. The abrasive material was river sand with grain
size up to 1 mm and relative moisture content below
0.15%.

The surface topography of the surfaces worn out by

the abrasive stream was studied using an MBS9 ste
reoscopic microscope with artificial illumination in
reflected light.

The investigation results were processed by the

Mathcad applied software package. The equation for
wear was found as the linear combination of functions
giving the best approximation of the data. The arith
metic mean of the investigation results

x; the mean

square deviation

S; the variation factor

ν, %; the con

fidence interval

γ; and the relative deviation β were

found according to

GOST 269–91.

210

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2010

SEMENETS, ANISIMOV

EFFECT OF POLYMER MOLECULAR MASS

ON GASOABRASIVE WEAR RATE

For the present investigations we chose the TPU of

synthesized polyester PBGA with molecular mass 500
and BD and MDI with the ratio of ingredients in each
series 1 : 0.5 : 1.5 and 1 : 1.5 : 2.5 and 1 : 3 : 4, corre
spondingly. The molecular mass M was controlled by
the criterion of characteristic viscosity [

η] of the TPU

solutions in dimethyl formamide at 303 K.

Proceeding from the investigation results we estab

lished that the molecular mass is a critical characteris
tic that defines both the processing and service proper
ties of PU thermoplastics. The dependence of the wear
rate of the polyurethanes under study on the charac
teristic viscosity index [

η] is of extreme character.

Depending on the [

η] value, we can isolate three char

acteristic regions (Fig. 1).

The materials having [

η] within 0.52–0.90, 0.42–

0.80, and 0.6–1.0 dl/g for the TPU with correspond
ing BD content 0.5, 1.5, and 3 mol show a high wear
rate. The features of the TPU in these regions are the
fast lowering of the wear rate, even with only slight
increase in the characteristic viscosity, as well as abrupt
growth of the strength characteristics. The TPU con
taining 0.5, 1.5, and 3.0 mole BD show the maximal
resistance to the abrasive stream in the region [

η] =

0.9–1.0 dl/g (Fig. 1a), 0.8–0.9 (Fig. 1b), and 1.0–1.1
(Fig. 1c), correspondingly. The materials of the third
region having [

η] > 1.0 gl/g (Fig. 1a), >0.9 dl/g

(Fig. 1b), and > 1.1 dl/g (M > 75 000) (Fig. 1c), respec
tively, display wear rate growth. This can be explained
by a low resistance of the surface layers to gasoabrasive
effects due to impaired physicomechanical character
istics such as relative elongation, bending strength,
and conventional strength at tension.

The wear rate dependence of the angle of attack

also bears an extreme character. This dependence
becomes more pronounced upon transition from the
materials with BD content 0.5 mol to that of 3.0 mol.
We can observe here a shift of the region of extreme
wear to the region of large angles of attack (for the
materials with BD content 0.5 mol

α

max

= 25

°, for

those with 1.5 BD content

α

max

= 30

°, and for those

with 3.0 BD content

α

max

= 35

°). When α > 70°, the

wear rate of all the materials is found in the negative
region. This is connected with abrasive saturation of
the surface layers since these angles create the condi
tions when the particles collide with the surface by
close to a frontal impact. During collision, the abrasive
particles overcome the forces of macromolecular
interactions on the TPU surface layer thanks to ele
vated stresses that appear in the contact zone between
the particle’s sharp edge and the surface layer, thus
embedding into the PU sample. In the case that a par
ticle either lacks the kinetic energy of impact for
embedding or contacts the surface not by a sharp edge,
it rebounds from the surface. We cannot rule out the
possibility of conditions when the surface layer of the
embedded particles may behave like a specific protec
tive screen against wear.

Analysis of the radiograms has shown that increas

ing the characteristic viscosity index to 9–1.1 dl/g
induces growth of structural formations. The crystal
line lattice parameters are 0.36–0.48 nm under the
fixed scattering angles 2

θ = 19–24°, which is indica

tive of perfected structural ordering. We have also
established an abrupt rise of the softening temperature
within the same range.

It was similarly found that the PU thermoplastics

whose molecular mass responds to the characteristic
viscosity index [

η] = 0.9–1.1 dl/g displays minimal

gasoabrasive wear rate. The systems with the index
[

η] > 1.1 dl/g turn out to be inappropriate for synthe

sizing since their most important physicomechanical
characteristics tend to decline.

A mathematical model of the wear process has been

derived based on experimental results; using this
model, one can determine the wear of the sought
material proceeding from the known parameters of
characteristic viscosity and service characteristics
(abrasive stream velocity, angle of attack).

CONCENTRATION EFFECT

OF RIGID BLOCKS ON GASOABRASIVE

WEAR RATE OF TPU

The structure and properties of the TPU were con

trolled by varying the ratio of the initial ingredients
within a wide range. The materials synthesized with dif

40
20

0

–20

15

40

65

90 1.48

1.16

0.84

0.52

(a)

α, degrees

Kg, 10

3

g/kg

[

η], dl/g

(b)

(c)

60

40
20

0

–20

15

40

65

90 1.23

0.96

0.69

0.42

[

η], dl/g

α, degrees

Kg, 10

3

g/kg

100

50

0

15

40

65

90 1.65

1.30

0.95

0.60

[

η], dl/g

α, degrees

Kg, 10

3

g/kg

Fig. 1. Wear rate dependence of TPU based on PBGA:BD:MDI with BD content 0.5 mol (a), 1.5 mol (b), and 3 mol (c) upon
characteristic viscosity and angle of attack at flow velocity of gasoabrasive stream 76 m/s.

JOURNAL OF FRICTION AND WEAR

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DEVELOPMENT OF TRIBOENGINEERING COMPOSITE MATERIALS

211

ferent polyesters (simple and complex) of molecular
mass 500, 1000, 2000 and [

η] in the range 0.9–1.1 dl/g

were subjected to investigations. The agent for chain
lengthening was 1,4butanediol. To obtain a better
estimate of the triboengineering characteristics of the
TPU we analyzed their abrasive resistance in relation
to 1,4butanediol content during synthesis and to that
of the rigid block concentration,

ϕ

r

. The use of PU

thermoplastics having

ϕ

r

from 10 to 60 wt % has made

it possible to study materials with a wide spectrum of
physicomechanical properties.

The changes in the TPU properties were found to

result from the formation of a continuous microphase
of rigid blocks (MPRB). Three characteristic regions
can be conditionally isolated on the dependences of
the wear rate on the concentration of rigid blocks. Let
us consider an example of the materials based on
POTMG

1000

: BD : MDI (Fig. 2).

The first region with low

ϕ

r

values (up to 32 wt %)

represents the rigid blocks of the material in the form
of separate structural formations and aggregates. The
material consists mostly of elastic polyester blocks
with a low glass transition temperature, so that it is
unable to withstand external effects. In spite of the
minimal gasoabrasive wear rate of TPU in this region,
all the samples show a pronounced tendency of transi
tion to the region of negative values (Fig. 2). This is
because the materials with

ϕ

r

up to 32 wt % cannot

resist external effects and due to the embedding of
abrasive particles into the sample.

The second region (

ϕ

r

= 32–48 wt %) displays con

siderable changes in concentration of the rigid blocks
along with insignificant variation of the wear rate and
signs of stabilization. There appears a specific plateau
on the dependences. When

ϕ

r

= 32 wt % one can see

either an apparent kink on the dependences of the
physicomechanical characteristics on the concentra
tion of rigid blocks or an optimum. The described

character of the concentration dependences in this
region corresponds to the formation of a binding
structure based on MPRB. The working surface of the
TPU is characterized by the presence of fine rounded
undulated peaks, which is a proof of the joint effect of
the abrasive and fatigue wear mechanisms. In the case
where the angles of attack are

α = 45, 60, and 90° in

this region, the negative value of K

g

demonstrates that

the binding MPRB structure lacks rigidity.

The third region with concentration

ϕ

r

> 48 wt % is

characterized by an abrupt growth of resistance to gas
oabrasive wear. This regularity is observed with all
angles of attack and all stream velocities of abrasive
particles. There appears another kink on most physi
comechanical dependences. The elasticity of the
material drops and its hardness increases together with
hysteresis losses, while the share of the elastoplastic
strain reduces. The formation of a rigid structure
owing to MPRB takes place with increasing concen
tration of the rigid blocks. This hypothesis is supported
by Xray diffraction analysis, which confirms that

ϕ

r

growth promotes the formation of clearly expressed
ordered formations in the structure of the PU under
study.

It follows that in addition to molecular mass, abra

sive resistance of PU thermoplastics is affected greatly
by the ratio of initial ingredients, whose targeted vari
ation during synthesis may yield materials with a wide
span of properties, triboengineering included.

One of the most important parameters that charac

terizes the chemical composition of the TPU and
defines its physicomechanical properties is the con
centration of rigid blocks in macromolecules (

ϕ

r

).

Variations in the TPU properties depending on

ϕ

r

are

connected, first of all, with the formation of a contin
uous rigid phase in the material. When the BD content
is low during synthesis and the

ϕ

r

values are also low

(24–32 wt %), the rigid phase of the material displays

3.75

2.50

1.25

0

–1.25

–2.50

20

30

40

50

60

70

1

2

3

4

5

(a)

Kg, 10

3

g/kg

(b)

15

10

5

0

–5

20 30

40

50

60

70

(c)

30

20

10

0

–10

20 30

40

50

60

ϕ

r

, wt %

5

4

3

2

1

5

4

3

2

1

Fig. 2. Wear rate dependence of TPU (by way of example of materials based on POTMG

1000

: BD : MDI) upon concentration of

rigid blocks at flow velocity of abrasive particles 38 m/s (a), 57 m/s (b) and 76 m/s (c), and different angles of attack: (1)

α = 15°;

(2) 30; (3) 45; (4) 60; (5) 90

°.

212

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SEMENETS, ANISIMOV

separate structural formations or aggregates. The
increasing diol content in the matrix leads to the for
mation of a rigidphase lattice that bears the main load
and provides for high physicomechanical properties of
the material. The density of this lattice increases with
increasing mass share of diol in the mixture. The pres
ence of this lattice explains the changes in the tri
boengineering characteristics of the PU under study
and their wear mechanism.

Thus, it has been demonstrated for the first time

that the TPU resistant to gasoabrasive wear with con
centrations of rigid blocks in the range bounded by
critical points

ϕ

r1

= 20–40 wt % and

ϕ

r2

= 40–50 wt %

characteristic for all studied PU compositions are rec
ommended for use as materials resisting a stream of
abrasive particles.

Processing of the study results has given a mathe

matical model of the wear process:

where K

g

is the gasoabrasive wear rate;

ϕ

r

is the con

centration of rigid blocks, wt %;

α is the angle of

attack, degrees; V is the flow velocity of abrasive parti
cles, m/s; and D1

i

, K1

i

, R1

i

, N1

i

, D2

i

, K2

i

, R2

i

, N2

i

,

D3

i

, K3

i

, R3

i

, N3

i

, D4

i

, K4

i

, R4

i

, N4

i

are approximation

factors that account for wear conditions variation (i =
1, 2).

The general type of the mathematical model con

tains a linear combination of the functions with poly
nomial factors ensuring the best approximation of the
data.

THE EFFECT OF NATURE AND TYPE

OF COMPONENTS ON GASOABRASIVE

WEAR RATE OF POLYURETHANE

THERMOPLASTICS

In the previous cases, we used MDI and BD to

obtain the rigid blocks. It was interesting from the sci
entific and practical viewpoints to substitute MDI in
the rigid block composition for TDI, which, together
with the former, is widely used in synthesizing molded
thermoplastics. It is not appropriate to study PU of the
named composition with

ϕ

r

< 48 wt % since these

materials lose their shape and undergo deformations

K

g

ϕ

r

α V

, ,

(

)

D1

1

D1

2

V

+

(

)

K1

1

K1

2

V

+

(

)α

+

[

=

+ R1

1

R1

2

V

+

(

)α

2

N1

1

N1

2

V

+

(

)α

3

]

+

+

D2

1

D2

2

V

+

(

)

[

K2

1

K2

2

V

+

(

)α

R2

1

R2

2

V

+

(

)α

2

+

+

+ N2

1

N2

2

V

+

(

)α

3

]ϕ

r

D3

1

D3

2

V

+

(

)

[

+

+ K3

1

K3

2

V

+

(

)α

R3

1

R3

2

V

+

(

)α

2

+

+ N3

1

N3

2

V

+

(

)α

3

]ϕ

r

2

D4

1

D4

2

V

+

(

)

[

+

+ K4

1

K4

2

V

+

(

)α

R4

1

R4

2

V

+

(

)α

2

+

+ N4

1

N4

2

V

+

(

)α

3

]ϕ

r

3

,

under normal conditions due to very poor physicome
chanical characteristics.

The behavior of the wear curves at

ϕ

r

> 48 wt % is

like that of the aboveconsidered TPU dependences.
Specifically, an abrupt increase of the gasoabrasive
wear rate is observed for all angles of attack, confirm
ing the formation of a continuous lattice of rigid
blocks. As in other cases, the maximal wear rate is
observed for the dependences under any flow velocity
of abrasive particles at the angle of attack

α = 30°.

When the angles of attack are

α = 45, 15, 60, and 90°

the materials display a lower wear rate. With increasing
angles of attack, the wear rate tends to shift to the
region of negative values due to the additional mass of
abrasive particles embedded into the samples. Substi
tution of butanediol for ethylene glycol in the TPU
based on PBGA

2000

: BD : MDI does not result in any

significant deviation in the wear behavior indepen
dently of operating conditions. As in previous cases,
the initial effect on the wear rate is induced by the con
centration of rigid blocks.

CONCLUSIONS

It has been established that the defining effect on

the physicomechanical and triboengineering charac
teristics of polyurethane thermoplastics is exerted by
their chemical structure and origin; the type of the ini
tial components and their ratio during synthesis; and
the molecular mass.

PU thermoplastics with molecular mass corre

sponding to the characteristic viscosity value [

η] =

0.9–1.1 dl/g show the most favorable structural order
ing and the minimal gasoabrasive wear rate.

It is shown for the first time that PU thermoplastics

in which the concentration of rigid blocks is in the
region between the critical points

ϕ

r

= 20–40 wt % and

ϕ

r

= 40–50 wt % are recommended for use as wear

resistant materials in a stream of gasoabrasive particles.

The transition from a glancing impact (

α = 15°) to

a normal one (

α = 90°) has been found to result in

variation of the wear mechanism from abrasive to
fatigue independently of the flow velocity of abrasive
particles. As a consequence, this brings changes to the
gasoabrasive wear rate.

The mathematical models for the wear process of

TPU interrelating their structural parameters (con
centration of rigid blocks, molecular mass) and service
characteristics (velocity of abrasive particles, angle of
attack) have been elaborated. These models have
allowed us to predict the triboengineering properties of
the synthesized materials.

DESIGNATIONS

f

300

—conventional stress art elongation;

ε

r

—relative

elongation;

ε—residual elongation; f

t

—residual strength

at tension;

χ—coefficient of mechanical hysteresis

JOURNAL OF FRICTION AND WEAR

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2010

DEVELOPMENT OF TRIBOENGINEERING COMPOSITE MATERIALS

213

losses; x—mean arithmetic of research data; S—mean
square deviation;

ν—variation factor; γ—confidence

interval boundary;

β—relative deviation; [η]—char

acteristic viscosity index; 2

θ—angle of diffraction;

K

g

—gasoabrasive wear rate;

ϕ

r

—concentration of

rigid blocks;

α—angle of attack; V—flow velocity of

abrasive particles; D1

i

, K1

i

, R1

i

, N1

i

, D2

i

, K2

i

, R2

i

, N2

i

,

D3

i

, K3

i

, R3

i

, N3

i

, D4

i

, K4

i

, R4

i

, N4

i

—approximation

factors accounting for variations in wear conditions
(i = 1, 2).

REFERENCES

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tribologii i tribotekhniki: Uchebnoe posobie (Foundations
of Tribology and Tribological Engineering: Student’s
Book), Moscow: Mashinostroenie, 2008.

2. Pilipkovskii, Yu.L., Grudina, T.V., Sapozhnikova, A.B.,

et al., Kompozitsionnye materialy v mashinostroenii

(Composite Materials in Machinery Manufacturing),
Kiev: Tekhnika, 1990.

3. Buist, J.M., Kompozitsionnye materialy na osnove poli

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