Experimental Analysis of the Influence of Structural Parameters on the Behavior of Glass-Fiber Reinforced Polypropylene Composites
In a composite material reinforced by short random fibers, damage results from different elementary failure mechanisms such as matrix micro-cracking, fiber pull out, failure of fiber/matrix interface, failure of fibers, etc. These damages have a large influence on the macroscopic behavior of c...
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| Published in: | Проблемы прочности |
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| Date: | 2001 |
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Інститут проблем міцності ім. Г.С. Писаренко НАН України
2001
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| Cite this: | Experimental Analysis of the Influence of Structural Parameters on the Behavior of Glass-Fiber Reinforced Polypropylene Composites / L. Bounouas, S. Benmedakhene, A. Laksimi, F. Neumann, A. Imad, Z. Azari // Проблемы прочности. — 2001. — № 1. — С. 68-82. — Бібліогр.: 15 назв. — англ. |
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Digital Library of Periodicals of National Academy of Sciences of Ukraine| _version_ | 1859744674099494912 |
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| author | Bounouas, L. Benmedakhene, S. Laksimi, A. Neumann, F. Imad, A. Azari, Z. |
| author_facet | Bounouas, L. Benmedakhene, S. Laksimi, A. Neumann, F. Imad, A. Azari, Z. |
| citation_txt | Experimental Analysis of the Influence of Structural Parameters on the Behavior of Glass-Fiber Reinforced Polypropylene Composites / L. Bounouas, S. Benmedakhene, A. Laksimi, F. Neumann, A. Imad, Z. Azari // Проблемы прочности. — 2001. — № 1. — С. 68-82. — Бібліогр.: 15 назв. — англ. |
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| container_title | Проблемы прочности |
| description | In a composite material reinforced by short
random fibers, damage results from different
elementary failure mechanisms such as matrix
micro-cracking, fiber pull out, failure of
fiber/matrix interface, failure of fibers, etc.
These damages have a large influence on the
macroscopic behavior of composite materials.
To obtain a good mechanical performance of a
composite material, it is important to optimize
the fiber ratio and the quality of the
fiber/matrix interface, which have a direct
influence on the damage mentioned above. The
main objective of this study is to determine the
influence of structural parameters on the
evolution of damage for two types of polypropylene
glass-fiber reinforced composites. In
parallel with a classical approach of the
mechanical theory of damage, which consists in
load-unload tensile tests, the use of acoustic
emission allows one to follow in real time the
character and the importance of damage
mechanisms in the course of loading. In
addition, fractographic analysis makes it
possible to confirm different assumptions and
conclusions from this study.
В композитном материале, армированном случайно расположенными короткими волокнами,
повреждения при механическом нагружении возникают в результате действия разных
элементарных механизмов, таких как микрорастрескивание матрицы, выдергивание волокон,
разрушение межфазной границы волокно-матрица, разрушение волокон. Эти повреждения
оказывают большое влияние на макроскопические свойства композитного материала.
Для получения приемлемых механических характеристик композитного материала важно
оптимизировать концентрацию волокон, а также качество межфазной границы волокно-
матрица, которые оказывают непосредственное влияние на перечисленные выше повреждения.
Главной целью статьи является определение влияния структурных параметров на
эволюцию повреждаемости двух типов стеклопластиков на основе полипропилена. Одновременно
с классическим подходом к механической теории повреждаемости, основанной на
испытаниях на растяжение с периодической разгрузкой, использование метода акустической
эмиссии дает возможность изучать в реальном времени природу и важность
механизмов повреждений в процессе нагружения. В дополнение к этому фрактографический
анализ позволяет подтвердить различные предпосылки и заключения настоящего исследования.
У композитному матеріалі, що армований випадково розташованими короткими
волокнами, пошкодження при механічному навантаженні виникають
внаслідок дії різних елементарних механізмів, таких як мікророзтріскування
матриці, висмикування волокон, руйнування міжфазової границі волокно-
матриця, руйнування волокон. Ці пошкодження зумовлюють значний вплив
на макроскопічні властивості композитного матеріалу. Щоб отримати прийнятні
механічні характеристики композитного матеріалу, важливо оптимі-
зувати концентрацію волокон, а також якість міжфазової границі волокно-
матриця, які безпосередньо впливають на ці пошкодження. Головна мета
роботи - визначення впливу структурних параметрів на еволюцію пошкодження
двох типів склопластиків на основі поліпропілену. Одночасно з
класичним підходом до механічної теорії пошкодження, що заснована на
випробуваннях на розтяг із періодичним розвантаженням, використання
методу акустичної емісії дає змогу вивчати в реальному часі природу і
важливість механізмів пошкоджень у процесі навантаження. Додатково до
цього фрактографічний аналіз дозволяє підтвердити різні передумови і
висновки даного дослідження.
|
| first_indexed | 2025-12-01T20:17:25Z |
| format | Article |
| fulltext |
UDC 539.4
Experimental Analysis of the Influence of Structural Parameters on
the Behavior of Glass-Fiber Reinforced Polypropylene Composites
L. Bounouasab, S. Benm edakhenea, A. Laksim ia, F. Neum anna, A. Im adc,
and Z. A zarid
a Université de Technologie de Compiègne (UTC), Compiègne, France
b Université Hassan II, Faculté des Sciences Ben M’sick-sidi othman, Casablanca, Maroc
c HEI Laboratoire d’Études des Structures, Lille, France
d Faculté de Mathématique et d’informatique, Université de Picardie, Amiens, France
УДК 539.4
Э к сп ер и м ен тал ь н ое и ссл ед ов ан и е влияния п ар ам етров
структуры на свойства стеклопластика на основе полипропилена
Л. Бунуааб, С. Бенмедахена, А. Л аксим иа, Ф. Н ью мана, А. Имадв,
3. Азариг
а Технологический университет Компьеня, Компьень, Франция
6 Университет Хасана II, Факультет естественных наук, Касабланка, Марокко
в Лаборатория изучения структуры, Лилль, Франция
г Университет Пикарди, Факультет математики и информатики, Амьен, Франция
В композитном материале, армированном случайно расположенными короткими волокнами,
повреждения при механическом нагружении возникают в результате действия разных
элементарных механизмов, таких как микрорастрескивание матрицы, выдергивание воло
кон, разрушение межфазной границы волокно-матрица, разрушение волокон. Эти повреж
дения оказывают большое влияние на макроскопические свойства композитного материала.
Для получения приемлемых механических характеристик композитного материала важно
оптимизировать концентрацию волокон, а также качество межфазной границы волокно-
матрица, которые оказывают непосредственное влияние на перечисленные выше повреж
дения. Главной целью статьи является определение влияния структурных параметров на
эволюцию повреждаемости двух типов стеклопластиков на основе полипропилена. Одно
временно с классическим подходом к механической теории повреждаемости, основанной на
испытаниях на растяжение с периодической разгрузкой, использование метода акусти
ческой эмиссии дает возможность изучать в реальном времени природу и важность
механизмов повреждений в процессе нагружения. В дополнение к этому фрактографический
анализ позволяет подтвердить различные предпосылки и заключения настоящего иссле
дования.
К л ю ч е в ы е с л о в а : композит, полипропилен, стеклопластик, акустическая
эмиссия, повреждение.
In troduction . Composite materials offer several advantages over the
conventional ones. In fact, they have higher rigidity and specific strength, higher
© L. BOUNOUAS, S. BENMEDAKHENE, A. LAKSIMI, F. NEUMANN, A. IMAD, Z. AZARI, 2001
68 ISSN 0556-171X. Проблемы прочности, 2001, N 1
Experimental Analysis o f the Influence
oxidation resistance and improved flexibility in application. However, they often
involve long manufacturing cycles that result in high fabrication costs. Moreover,
their high sensitivity to damage is often inconvenient for their structural
applications. A solution to overcome this sensitivity to damage is the use of
thermoplastic-matrix composites. One of the thermoplastics most often used as a
matrix in this new type of composites is polypropylene (PP), which is prepared by
a continuous process of injection moulding. In fact, glass-fiber reinforced
po lypropylene offers very in te resting m echanical and environm ental
performances. The use of these materials in automobile industry is in expanding
continuously. However, their application is still limited due to the lack of data
concerning their behavior and damage resistance. Thus, much research work has
to be done in this field in order to optimize and extend their application.
Damage initiation in composites may often be initiated at low-energy
interactions during service life, such as drop of tools or parts, impacts during
transport and/or due to environmental agents (such as hail-stones). This has been
considered a serious problem encountered during the use of composite materials
and consequently it has attracted increasing attention in recent years, assuming
that damage results in a more or less appreciable reduction in mechanical
properties depending on the loading conditions. As for conventional composites, a
complete study is required in order to understand damage resistance and behavior
of thermoplastic composite materials.
The literature presents several studies conducted in this area. In fact, many
studies are concerned mainly with the influence of structural parameters such as
fibers, volume ratio and the quality of fiber/matrix interface. However, the
majority of the authors limit their investigations to the theory of mechanical
damage. In this study, an effort has been made to implement the classical
approach of the theory of mechanical damage through the load-unload tensile
tests combined with a nondestructive method to follow the material behavior in
real time.
The latter is an acoustic emission method, which allows one to obtain precise
information on the chronology and damage intensity during loading. In addition,
fractographic analysis is used to confirm different hypotheses and conclusions.
Thus, the aim of this work is the identification of damages in glass-fiber/
polypropylene composites and determination o f the influence of different
structural parameters on damage behavior of composites. Both acoustic emission
and microscopic observations have been used for the identification of damage
mechanisms.
Experim ental Procedure.
M aterials. The material of the study is a polypropylene composite matrix
reinforced with short glass fibers approximately 4 mm in length and 10 jum in
diameter. The injection-moulded samples used in this study were prepared using a
computer-controlled Fast-Inject type injection machine. The operation conditions
such as injection speed, injection pressure, injection temperature and mould
temperature regulation are set by the operator and are chosen according to the ISO
R527 standard. Figure 1 summarizes the materials and the most essential
parameters considered in this study.
ISSN 0556-171X. npodneMbi npouuocmu, 2001, № 1 69
L. Bounouas, S. Benmedakhene, A. Laksimi, F. Neumann, A. Imad, Z. Azari
Fig. 1. Presentation of various materials studied.
In this study, the materials used will be designated as follows:
N20/100 (T20/100)
/ j_ \ .
N20/100 (T20/100)
T y p e o f f i b e r s / f \ M o u l d t e m p e r a t u r e
F i b e r s f r a c t i o n i n m a s s
T and N stand for treated and untreated glass fibers, respectively. For example,
T20/100 indicates a PP composite reinforced by 20% of treated glass fibers
injected at 100oC and N30/35 indicates a PP composite reinforced by 30% of
untreated glass fibers injected at 35oC.
Tensile Tests. Tensile tests are carried out on INSTRON 1186 static type
machine. In addition to the acoustic emission signals, the acquisition system
collects the data on the load applied to the specimen and the information from the
strain gauges.
The sample is instrumented with bidirectional gauges that allows the
measurement of longitudinal and transverse strains in the material (Fig. 2). After
testing, scanning electron microscope (SEM) observations are carried out on
fractured samples.
70
Fig. 2. Tensile specimen (dimensions in mm).
ISSN 0556-171X. Проблемы прочности, 2001, № 1
Experimental Analysis o f the Influence
Tensile Load-Unload Test. The load-unload tensile tests are carried out on
the same type of samples as used under simple tension. In this test, two levels of
unloading are chosen:
- partial unloading: in each sequence of loading, unloading is applied up to
30% of the previously reached load;
- complete unloading: in each loading sequence unloading is complete, i.e.,
the load is equal to zero.
Damage is quantified by the measurements of the elastic modulus using the
following relationship: D = 1— (E / E ), where D is the damage parameter, E is
Young’s modulus of an undamaged material, and E is Young’s modulus of a
damaged material.
The elastic parameters are measured within the linear part of the loading
phase. This phase generally shows a total absence of any reaction of acoustic
emission.
Acoustic Emission. Different studies have been accomplished using acoustic
emission as nondestructive method to follow damage in composite materials.
They involve different composites with different types of matrix and
reinforcements [1-7]. They all suggest that various damage mechanisms
encountered in the composites may be classified according to different ranges of
acoustic emission amplitudes (Fig. 3).
0 10 20 30 40 50 60 70 80 90 100
| I | I | 1...| I | I | I___| 1 | I | I | I |
Am plitude (dB)
Fig. 3. Typical amplitude distribution and areas definition (1 - matrix microcracking; 2 -
matrix/matrix friction; 3 - interface decohesion; 4 - fiber/matrix friction and fibre debonding; 5 -
fiber breakage and bundle shattering).
Thus, analysis of the amplitudes of acoustic emission signals generated
during the occurrence of different damage mechanisms facilitates the damage
growth detection during testing.
Processing of acoustic activity and data acquisition have been carried out by
means of an acoustic emission system (DUNEGANE/ENDEVCO 3000) with the
following physical characteristics:
preamplifier gain: 39 dB;
preamplifier filters: 450 B and 190 B;
AE threshold: selectable, fixed at 30 dB for the present study;
the range of amplitude channels is from 0 to 100 dB;
channel width (resolution): 1 dB;
dead time: 1 ms (emission by bursts).
Acoustic emission signals are detected using a piezoelectric transducer
(PAC-MICROPHONE 80) and have a large range of frequencies from 200 kHz to
1 MHz.
ISSN 0556-171X. npoGneMU npouwcmu, 2001, № 1 71
L. Bounouas, S. Benm.edak.hene, A. Laksimi, F. Neumann, A. Imad, Z. Azari
The AE investigation method is combined with microscopic observations
using a scanning electron microscope. This contributes to a better understanding
of the occurrence and evolution of the basic damage mechanisms.
Results and Discussion.
Tensile Test. The aim of tensile tests is to determine the influence of
structural and other parameters on the elastic behavior, damage and failure of the
materials.
Influence of the Interface. The following figures illustrate the difference in
the mechanical behavior between two glass-fiber reinforced polypropylene
materials with different interface qualities.
The stress-strain curve belonging to T20/100 material shows a better
mechanical performance. This is the result of improved interface quality due to
the addition of oiling. The stress-strain curve of N20/100 shows low mechanical
characteristics resulting from untreated fibers. In the case of T20/100 material
(Fig. 4), three significant phases are observed on the curve:
- The first linear elastic phase (phase A) without acoustic emission.
- The second non-linear phase (phase B) related to the initiation of damage
mechanisms. During this phase, the first events of acoustic emission generated by
the material are observed.
- The third phase (phase C) characterized by a change of slope of the
stress-strain curve. This change is accompanied by a significant acoustic
emission. An exponential evolution is observed on the last portion of the acoustic
emission cumulative curve indicating the presence of large damage leading to
final failure of the material.
0 2 4 6 8 1 0 1 2 1 4 - 1 0 °
Fig. 4. Stress and acoustic emission versus strain (T20/100).
In the case of N20/100 material (Fig. 5), the behavior is characterized by
three phases different from those of T20/100:
- The first linear elastic phase (phase A ), which allows the measurement of
the elastic properties of the material without acoustic emission.
72 ISSN 0556-171X. npodmMbi nponnocmu, 2001, M 1
Experimental Analysis o f the Influence
T a b l e 1
Results of Tensile Testing of Composite Materials with Poor and Good Quality Interfaces
Mould T = 100oC Mould T = 35°C
Content of
glass fibers
20% 30% 20%
Fiber type treated untreated treated untreated treated untreated
E (GPa) 5.15
(0.30)
5.43
(0.49)
6.81
(0.41)
6.88
(0.64)
5.58
(0.15)
5.00
(0.23)
or (MPa) 62.87
(6.73)
33.09
(1.90)
70.46
(3.67)
32.70
(1.07)
73.35
(4.23)
32.83
(1.01)
£ r (%) 1.56
(0.36)
1.33
(0.25)
1.53
(0.25)
1.20
(0.60)
1.67
(0.63)
2.23
(0.25)
Note. Here E is Young’s modulus, or is the failure stress, and er is the failure strain (standard
deviations are given in parentheses).
Fig. 5. Stress and acoustic emission versus strain (N20/100).
- The second non-linear phase (phase B), wherein no acoustic emission is
detected. This phase indicates plastic deformation without damages.
- The third phase (phase C), wherein the stress-strain curve reaches a creep
plateau and deformation increases under constant stress. This phase is
characterized by a high acoustic emission activity. The creep plateau indicates the
absence of load transfer between the matrix and glass fibers beyond the elastic
field. Table 1 presents comparison between the elastic constant values and failure
characteristics of the two materials.
These results show that oiling of fibers allows us to double the failure stress
of the composite materials studied. However, it has no effect on the elastic
modulus. It is well established in both cases (with oiled and not oiled fibers) that
acoustic emission allows the initiation and evolution of damages taking place
after the elastic phase to be detected.
ISSN 0556-171X. npoôneMU npouHocmu, 2001, № 1 73
L. Bounouas, S. Benmedakhene, A. Laksimi, F. Neumann, A. Imad, Z. Azari
Influence of F iber Content Increase. The fraction of fibers has an
appreciable influence on the mechanical properties of the composite and
particularly on the elastic modulus. In fact, the increase of fibers ratio from 20%
(in weight) to 30% results in an increase in elastic modulus of 25% in the case of
treated fibers and 21% in the case of untreated fibers.
Damage Analysis. Through the study of the damage mechanisms, a
continuous correlation is established between the acoustic emission and
microscopic observations.
The distribution of events according to their amplitudes [8-13] has an
advantage. It allows the classification of damage mechanisms according to a
given range of amplitudes. This method also allows a chronological detection of
damages during loading.
Figures 6 and 7 present amplitude distributions during tensile loading in the
case of both oiled and not oiled fiber/matrix interfaces.
140
0 10 20 30 40 50 60 70 80 90 100
Amplitude (dB)
Fig. 6. Amplitude distribution for N20/100 for various stress levels.
0 1 0 2 0 3 0 4 0 5 0 6 0 7 0 8 0 9 0 1 0 0
Amplitude (dB)
Fig. 7. Amplitude distribution for T20/100 for various stress levels.
74 ISSN 0556-171X. npoOmMbi nponnocmu, 2001, № 1
Experimental Analysis o f the Influence
The evolution of amplitude distributions shows that the total number of
recorded events obtained in the case of treated fibers is more significant than that
obtained in the case of untreated ones. The results also show that for both oiled
and not oiled fibers the number of events decreases when the fiber content
increases. Figure 6 shows that for untreated fibers, the amplitude distribution is
very wide. This is an evidence of the presence of several types of damages such
as matrix cracking, microscopic crack coalescence, interface failures, matrix/fiber
friction and fiber failure. This is especially the case where the fiber content is low.
In the case of treated fibers, the amplitude distribution is narrow (Fig. 7). The
evolution of damages is less important between 60 and 80 dB, which indicates
that failure of the fiber/matrix interface and fiber pullout are not important. This is
the result of good matrix/fiber adherence that, consequently, ensures a better
mechanical behavior.
Microscopic observations (Figs. 8-11) show the presence of matrix
microcracking in the T20/100 and N20/100 material. Figure 9 confirms the good
fiber/matrix adhesion for the same material.
■
ц з д и
_____ h a 1_ 0 J
X 1 , И Й 0 1 e t ' n W U 1 ?
> T S 0 1 0 / i
Fig. 8. Matrix microcracking and failure of fiber/matrix interface (T20/100).
— F 1 U 0 11 5KLI X 4 3 0 lEfJn , U D 3 3
М и д с T£0 1 a l e a c .
Fig. 9. SEM fractograph of the T20/100 material.
ISSN 0556-171X. Проблемы прочности, 2001, № 1 75
L. Bounouas, S. Benmedakhene, A. Laksimi, F. Neumann, A. Imad, Z. Azari
Fig. 10. SEM fractograph of the N20/100 material.
1 3KU
TRfi
> T E A C
Fig. 11. Matrix microcracking (N20/100 material).
Tensile Load-U nload. Quantitative estimation of the damage resulting from
load-unload tests is based on a comparison with the initial elastic characteristics
of an undamaged material. This type of test allows the determination and
quantification of the damage that cannot be measured in a simple tensile test.
The acoustic emission technique is used in order to show that damages are
not caused by unloading to which the material is subjected.
Iso tro p ic D am age. Damage is defined as a gradual deterioration
phenomenon leading to failure of the loaded material. Physically it results in the
appearance of microscopic defects within the material. These microdefects
influence the behavior of a specimen, particularly, in terms of the degradation of
macroscopic properties such as Young’s modulus.
The fact that the rigidity of the material is affected during the load-unload
tests makes the measurement of the elastic modulus essential in order to be able to
use a scalar D, which will permit us to quantify the damage mechanics. This
assumption of isotropy is confirmed in our case by the constancy of Poisson’s
ratio (as shown by the graphs in Fig. 12).
76 ISSN 0556-171X. npo6n.eubi npounocmu, 2001, № 1
Experimental Analysis o f the Influence
0 . 4 6
0 . 4 4
0 . 4 2
0 . 4
0 . 3 8
0 . 3 6
0 . 3 4
0 . 3 2
0 . 3
- . ■— x < r ^
v «
P " o
x xO X OAV
O N 2 0 / 1 0 0
X T 2 0 / 1 0 0
0
Fig.
0.2 0.4 0.6 0.8 1
Normalized strain (e/er)
12. Evolution of Poisson’s ratio v (oiled and not oiled samples)
The introduction of a variable damage parameter representing the surface
density of discontinuities is made using the concept of effective strain, i.e., the
strain, which takes into account the load-sustaining part of the specimen section
area [14, 15]. In the presence of isotropic damage of magnitude D, the load-
sustaining part of the specimen section area then becomes: in the case of simple
tension, the ratio between the applied force and the section of the representative
volume o = F / S gives the usual strain that satisfies the equilibrium conditions,
therefore
~ = S - S D = S ( 1 - D ).
Here S D is the damaged section.
The effective strain is expressed by
~ S ~ a
0 = 0 — ^ o = ------- .
S 1- D
In this formula, D is the damage parameter defined by
D = 1 - E ,
E
where E is Young’s modulus of the damaged material, E is Young’s modulus of
undamaged material.
The limits of this scalar can be defined as follows: when D = 0, the material
is undamaged and when D = 1, the material is fractured.
Evolution of the Damage P aram eter D. While following the load-unload
tensile mechanical tests, the damage phenomenon is characterized by means of an
indirect technique. The latter consists in the measurement of the Young’s modulus
of the damaged material from the stress-strain curves. The ratio between the
Young’s moduli of the damaged and undamaged materials quantifies the extent of
damage in the material at different stages of loading.
ISSN 0556-171X. npoôëeMbi nponnocmu, 2001, № 1 77
L. Bounouas, S. Benmedakhene, A. Laksimi, F. Neumann, A. Imad, Z. Azari
Microstrain
Fig. 13. Measurement of Young’s modulus (E) in the damaged material in the case of complete
unloading.
10
0 -------1-----------1-----------!----------- 1-----------1-----------1----------- 1-----------1----------- 1-----------1-----------1-----------1-----------1-----------1-----------1----------- 1-----------1----------- 1-----------1-----------
0 5 10 15 20-103
Microstrain (|xm/m)
Fig. 14. Measurement of Young’s modulus (E) in the damaged material in the case of unloading to
30% of the maximum load.
Figures 13 and 14 show the way of measuring the Young’s modulus in the
damaged material during the steps o f reloading.
Different situations are obtained depending on the mode of unloading and on
the interface quality. In the case of complete unloading (Fig. 15), the loss in
rigidity is rather low for all types of materials. This case is equivalent to the
situation, where the test was restarted from the beginning. This is related to the
total relaxation o f the material. In this case, when reloading, the measure of the
initial elastic modulus is related to a coupling of elasticity with damage. This can
be explained by the state of the majority of microcracks, which are rather closed,
and the material behaves almost as an undamaged one.
78 ISSN 0556-171X. npo6neMU npounocmu, 2001, № 1
Experimental Analysis o f the Influence
0.2 0.4 0.6
Normalized strain (£/£r)
Fig. 15. Damage parameter versus normalized strain for materials N30/100 and T30/100 in the case
of complete unloading.
Figure 16 shows that when unloading goes 30% below the maximum load,
the stress field during unloading remains high and maintains the material in the
state of significant damage. The graph in Fig. 16 illustrates this phenomenon.
According to the quality of the fiber/matrix interface, we can observe two
types of evolution of the damage parameter D. Thus, as shown in Fig. 16, in the
case of a good-quality interface, the damage grows in a regular way.
Fig. 16. Damage parameter versus normalized strain for materials N30/100 and T30/100 in the case
of partial unloading.
In the case of an untreated material, an irregular evolution of damage is
observed: first, a linear evolution of the behavior can be noted coupled with the
damage where the elastic modulus does not change significantly. In the second
stage, when the creep plateau is reached, the deformation grows at a constant
stress followed by a rapid increase in damage. The Kaiser effect is valid for
metallic materials, but for the composite structures it is replaced by the Felicity
effect. It consists in that the acoustic emission will start again before the
ISSN 0556-171X. npodneMbi nponnocmu, 2001, M 1 79
L. Bounouas, S. Benmedakhene, A. Laksimi, F. Neumann, A. Imad, Z. Azari
preceding maximum load has been reached. The Felicity ratio is equal to the ratio
between the stress corresponding to the acoustic emission and the stress reached
before unloading (Felicity ratio “R” is equal to P1/P2) (Fig. 17).
1 2 0 0 1 4 0 0 1 6 0 0 1 8 0 0 2 0 0 0 2 2 0 0 2 4 0 0 2 6 0 0
Load (N)
Fig 17. Measure of the Felicity ratio.
In general, the Felicity ratio decreases and tends to zero. Indeed, when this
ratio is equal to 1, the material is undamaged. When the Felicity ratio lies between
zero and 1, the material is damaged and when the ratio is equal to zero, the
material is fractured.
The graph below shows the evolution of the Felicity ratio according to the
quality of the fiber-matrix interface (Fig. 18).
Note that in the case o f an untreated sample, the ratio decreases sharply and
its values approach zero showing the weakness o f the interface.
Normalized strain
Fig. 18. Evolution of the Felicity ratio with the damage parameter.
80 ISSN 0556-171X. npoôneMU npoHHOcmu, 2001, № 1
Experimental Analysis o f the Influence
On the other hand, in the case of a treated sample, the Felicity ratio decreases
slowly and is much higher than in the case of the weak interface. This indicates
that the material undergoes weak damage owing to a good fiber/matrix interface.
Conclusions. An experimental study of damage of thermoplastic composites
was carried out according to two different approaches.
The first is a qualitative approach based on the acoustic emission technique
and scanning electron microscopy. It allowed the study of the global behavior of
the material. The use of the cumulated acoustic emission and the amplitude
distribution method allowed the identification and classification of various
damages according to the chronology of their occurrence.
Microscopic observations enabled the localization of damages and the
characterization of the fiber/matrix interface quality. In fact, the fiber pullout is
sudden and the surface of the fibers is smooth in the case of a weak interface.
The second is a quantitative approach, which involves a damage theory
based on the concept of the effective stress. This method uses the measure of the
level of damage reached in the material under cyclic loading such as load-unload
tension. The evolution of the material rigidity obtained through the measurements
of Young’s modulus at each step of successive loading makes it possible to
determine the damage parameter D and its evolution during loading.
The approach presented allowed a better understanding of the mechanical
behavior of the materials studied, their damage and failure in respect to structural
and moulding parameters.
Р е з ю м е
У композитному матеріалі, що армований випадково розташованими корот
кими волокнами, пошкодження при механічному навантаженні виникають
внаслідок дії різних елементарних механізмів, таких як мікророзтріскування
матриці, висмикування волокон, руйнування міжфазової границі волокно-
матриця, руйнування волокон. Ці пошкодження зумовлюють значний вплив
на макроскопічні властивості композитного матеріалу. Щоб отримати прий
нятні механічні характеристики композитного матеріалу, важливо оптимі-
зувати концентрацію волокон, а також якість міжфазової границі волокно-
матриця, які безпосередньо впливають на ці пошкодження. Головна мета
роботи - визначення впливу структурних параметрів на еволюцію пошкод
ження двох типів склопластиків на основі поліпропілену. Одночасно з
класичним підходом до механічної теорії пошкодження, що заснована на
випробуваннях на розтяг із періодичним розвантаженням, використання
методу акустичної емісії дає змогу вивчати в реальному часі природу і
важливість механізмів пошкоджень у процесі навантаження. Додатково до
цього фрактографічний аналіз дозволяє підтвердити різні передумови і
висновки даного дослідження.
1. D. Laroche, A c c u m u la tio n d 'E n d o m m a g e m e n t D a n s le C a rb o n e É p o x y d e
D é te c té p a r E m iss io n A c o u s tiq u e , Thèse de docteur-ingénieur de l’école de
mines de Paris, (1980).
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2. D. Valentin, E tu d e p a r É m is s io n A c o u s t iq u e d e l 'E n d o m m a g e m e n t
S o u sso llic ita tio n s M é c a n iq u e s d e s C o m p o site s C a r b o n e -R é s in e , Thèse de
Docteur-Ingénieur de l ’école des mines de Paris (1983).
3. M. Fuwa, A. R. Bunsell, and B. Harris, “Tensile failure mechanisms in
carbon-fiber-reinforced plastics,” J. M a ter . S c i., 10, 353-364 (1975).
4. B. Ponsot and D. Valentin, “Analyse qualitative et quantitative de
l ’endommagement de structures composites par émission acoustique,”
J N C 5 , Paris (1986), pp. 123-129.
5. Xl. Gong, A. Laksimi, and M. L. Benzeggagh, “Nouvelle approche de
l’émission acoustique et son application à l ’identification des mécanismes
d ’endommagement dans les m atériaux com posites,” in: R e v u e d e s
C o m p o site s e t d es M a té r ia u x A v a n c é s , 8, No. 1, 7-23 (1998).
6 . A. Laksimi, M. Cherfaoui, and C. Bathias, “Etude par émission acoustique
de l ’amorçage et de la propagation dans un composite verre-époxy,” J N C 5 ,
Paris (1986), pp. 625-637.
7. A. Laksimi, S. Benmedakhene, and L. Bounouas, “Monitoring of acoustic
emission during tensile loading of thermoplastic composite materials,” 12th
International Conference on Composite Materials, July 5-9, 1999, Paris.
8. J. M. Berthelot and J. Rhazi, “Caractérisation des mécanismes de rupture
dans les matériaux composites à l ’aide de l ’amplitude des signaux
d’émission acoustique,” J N C 5 , Paris (1986), pp. 230-238.
9. J. R. Wadim, A c o u s tic E m iss io n A p p lic a tio n s , Dunegan Endevco, San Juan
Capistrano CA (1978).
10. S. Barre, “Etude de l ’endommagement des matériaux composites à fibres
courtes et à matrice thermoplastique sous chargement statique et cyclique,”
DEA UTC, Compiègne (1991).
11. L. Bounouas, S. Benmedakhene, A. Laksimi, G. Villoutreix, and A. Ilidrissi,
“Etude de l’influence des paramètres structuraux et de mise en oeuvre sur le
comportement mécanique des matériaux composites,” in: R e v u e d e s
C o m p o site s e t d es M a té r ia u x A v a n c é s , 8, No. 2, 179-205 (1998).
12. F. Meraghni, S. Benmedakhene, and M. L. Benzeggagh, “Identification and
m odeling o f dam age m echanism s in short g lass-fiber-re in fo rced
polypropylene composites,” in: Proc. ICCM 10, Vancouver, Aug. 1995,
pp. 366-369.
13. S. Benmedekhene, E tu d e P h é n o m é n o lo g iq u e d u C o m p o r te m e n t à l 'Im p a c t
d es M a té r ia u x C o m p o sites , Thèse de doctorat UTC, Compiègne (1996).
14. L. M. Kachanov, “Time of the rupture process under creep conditions,” Izv.
A ka d . N a u k S S S R , 8, 26-31 (1958).
15. J. L. Chaboche, “Sur l’utilisation des variables d’état internes pour la
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Received 28. 04. 2000
82 ISSN 0556-171X. npoôneMbi npounocmu, 2001, № 1
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| id | nasplib_isofts_kiev_ua-123456789-46557 |
| institution | Digital Library of Periodicals of National Academy of Sciences of Ukraine |
| issn | 0556-171X |
| language | English |
| last_indexed | 2025-12-01T20:17:25Z |
| publishDate | 2001 |
| publisher | Інститут проблем міцності ім. Г.С. Писаренко НАН України |
| record_format | dspace |
| spelling | Bounouas, L. Benmedakhene, S. Laksimi, A. Neumann, F. Imad, A. Azari, Z. 2013-06-30T20:08:04Z 2013-06-30T20:08:04Z 2001 Experimental Analysis of the Influence of Structural Parameters on the Behavior of Glass-Fiber Reinforced Polypropylene Composites / L. Bounouas, S. Benmedakhene, A. Laksimi, F. Neumann, A. Imad, Z. Azari // Проблемы прочности. — 2001. — № 1. — С. 68-82. — Бібліогр.: 15 назв. — англ. 0556-171X https://nasplib.isofts.kiev.ua/handle/123456789/46557 539.4 In a composite material reinforced by short random fibers, damage results from different elementary failure mechanisms such as matrix micro-cracking, fiber pull out, failure of fiber/matrix interface, failure of fibers, etc. These damages have a large influence on the macroscopic behavior of composite materials. To obtain a good mechanical performance of a composite material, it is important to optimize the fiber ratio and the quality of the fiber/matrix interface, which have a direct influence on the damage mentioned above. The main objective of this study is to determine the influence of structural parameters on the evolution of damage for two types of polypropylene glass-fiber reinforced composites. In parallel with a classical approach of the mechanical theory of damage, which consists in load-unload tensile tests, the use of acoustic emission allows one to follow in real time the character and the importance of damage mechanisms in the course of loading. In addition, fractographic analysis makes it possible to confirm different assumptions and conclusions from this study. В композитном материале, армированном случайно расположенными короткими волокнами, повреждения при механическом нагружении возникают в результате действия разных элементарных механизмов, таких как микрорастрескивание матрицы, выдергивание волокон, разрушение межфазной границы волокно-матрица, разрушение волокон. Эти повреждения оказывают большое влияние на макроскопические свойства композитного материала. Для получения приемлемых механических характеристик композитного материала важно оптимизировать концентрацию волокон, а также качество межфазной границы волокно- матрица, которые оказывают непосредственное влияние на перечисленные выше повреждения. Главной целью статьи является определение влияния структурных параметров на эволюцию повреждаемости двух типов стеклопластиков на основе полипропилена. Одновременно с классическим подходом к механической теории повреждаемости, основанной на испытаниях на растяжение с периодической разгрузкой, использование метода акустической эмиссии дает возможность изучать в реальном времени природу и важность механизмов повреждений в процессе нагружения. В дополнение к этому фрактографический анализ позволяет подтвердить различные предпосылки и заключения настоящего исследования. У композитному матеріалі, що армований випадково розташованими короткими волокнами, пошкодження при механічному навантаженні виникають внаслідок дії різних елементарних механізмів, таких як мікророзтріскування матриці, висмикування волокон, руйнування міжфазової границі волокно- матриця, руйнування волокон. Ці пошкодження зумовлюють значний вплив на макроскопічні властивості композитного матеріалу. Щоб отримати прийнятні механічні характеристики композитного матеріалу, важливо оптимі- зувати концентрацію волокон, а також якість міжфазової границі волокно- матриця, які безпосередньо впливають на ці пошкодження. Головна мета роботи - визначення впливу структурних параметрів на еволюцію пошкодження двох типів склопластиків на основі поліпропілену. Одночасно з класичним підходом до механічної теорії пошкодження, що заснована на випробуваннях на розтяг із періодичним розвантаженням, використання методу акустичної емісії дає змогу вивчати в реальному часі природу і важливість механізмів пошкоджень у процесі навантаження. Додатково до цього фрактографічний аналіз дозволяє підтвердити різні передумови і висновки даного дослідження. en Інститут проблем міцності ім. Г.С. Писаренко НАН України Проблемы прочности Научно-технический раздел Experimental Analysis of the Influence of Structural Parameters on the Behavior of Glass-Fiber Reinforced Polypropylene Composites Экспериментальное исследование влияния параметров структуры на свойства стеклопластика на основе полипропилена Article published earlier |
| spellingShingle | Experimental Analysis of the Influence of Structural Parameters on the Behavior of Glass-Fiber Reinforced Polypropylene Composites Bounouas, L. Benmedakhene, S. Laksimi, A. Neumann, F. Imad, A. Azari, Z. Научно-технический раздел |
| title | Experimental Analysis of the Influence of Structural Parameters on the Behavior of Glass-Fiber Reinforced Polypropylene Composites |
| title_alt | Экспериментальное исследование влияния параметров структуры на свойства стеклопластика на основе полипропилена |
| title_full | Experimental Analysis of the Influence of Structural Parameters on the Behavior of Glass-Fiber Reinforced Polypropylene Composites |
| title_fullStr | Experimental Analysis of the Influence of Structural Parameters on the Behavior of Glass-Fiber Reinforced Polypropylene Composites |
| title_full_unstemmed | Experimental Analysis of the Influence of Structural Parameters on the Behavior of Glass-Fiber Reinforced Polypropylene Composites |
| title_short | Experimental Analysis of the Influence of Structural Parameters on the Behavior of Glass-Fiber Reinforced Polypropylene Composites |
| title_sort | experimental analysis of the influence of structural parameters on the behavior of glass-fiber reinforced polypropylene composites |
| topic | Научно-технический раздел |
| topic_facet | Научно-технический раздел |
| url | https://nasplib.isofts.kiev.ua/handle/123456789/46557 |
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