Temperatuursinvloed op de impactweerstand van composieten voertuigonderdelen

143 Pages·2006·4.39 MB·English

UNIVERSITEIT GENT
Faculteit der Ingenieurswetenschappen

Vakgroep Mechanische constructie en productie
Directeur : Prof. dr. ir. J. Degrieck

Temperatuursinvloed op de impactweerstand van
composieten voertuigonderdelen.

door Vicky De Bruyne

Promotoren: Prof. dr. ir. J. Degrieck en Prof. dr.ir. W. Van Paepegem
Scriptiebegeleider: ir. F. Van den Abeele

Scriptie ingediend tot het
behalen van de graad van
burgerlijk materiaalkundig ingenieur
optie: metaalkunde

Academiejaar 2005-2006
Toelating tot bruikleen

De auteur geeft toelating deze scriptie voor consultatie beschikbaar te stellen en delen van de scriptie
te kopiëren voor persoonlijk gebruik.
Elk ander gebruik valt onder de beperking van het auteursrecht, in het bijzonder met betrekking tot de
verplichting de bron uitdrukkelijk te vermelden bij het aanhalen van resultaten uit deze scriptie.

Gent, juni 2006-06-04

Vicky De Bruyne
i
Woord vooraf

Bij het tot stand komen van deze scriptie kon ik steeds rekenen op de nodige hulp van vele mensen.
Graag zou ik iedereen willen bedanken die mij geholpen en gesteund heeft bij het verwezenlijken van
deze scriptie.

In de eerste plaats wens ik Professor dr. ir. Joris Degrieck en Prof. dr.ir. Wim van Paepegem,
promotoren van dit afstudeerwerk, te bedanken voor de opvolging en het verschaffen van het
onderwerp van deze thesis. Bedankt voor de tips, vooral op die momenten dat we geen oplossing
voor ogen hadden.

Een bijzonder woord van dank gaat uit naar ir. Filip Van den Abeele voor de dagelijkse begeleiding en
opvolging van dit afstudeerwerk. Bedankt, niet in het minst, voor de medewerking bij de proeven, het
aandachtig nalezen en het beantwoorden van mijn vele vragen.

Verder wens ik alle medewerkers en technici van het Laboratorium Soete te bedanken voor de vele
praktische hulp. In het bijzonder wens ik Luc te bedanken die, zelfs in drukke tijden, altijd bereid was
om te helpen of informatie te geven.

Tenslotte wens ik mijn familie en vrienden, in het bijzonder Gert, te bedanken. Zonder hun steun, zou
ik nu niet op de drempel staan van het afronden van deze studies.
ii
Overzicht

Temperatuursinvloed op de impactweerstand van composieten
voertuigonderdelen.

door
Vicky De Bruyne

Scriptie ingediend tot het behalen van de graad van burgerlijk materiaalkundig ingenieur -
optie: metaalkunde

Academiejaar 2005-2006

Promotoren: Prof. dr. ir. J. Degrieck en Prof. dr.ir. W. Van Paepegem
Scriptiebegeleider: ir. F. Van den Abeele
Faculteit Toegepaste Wetenschappen
Universiteit Gent

Vakgroep Mechanische Constructie en Productie
Directeur : Prof. Dr. Ir. J. Degrieck

iii
Samenvatting

Dit afstudeerwerk kadert in een lopend onderzoek naar het gebruik van composieten als
bumpermateriaal. Voor deze toepassing is de impactweerstand van het materiaal cruciaal. In deze
scriptie wordt de nadruk gelegd op de invloed van de temperatuur op de eigenschappen van GMT40
al dan niet verstevigd met een staalkoord.

Na de inleiding, overlopen we in het tweede hoofdstuk de componenten waaruit het gebruikte
composiet is opgebouwd.

Om een idee te krijgen van de karakteristieken van het materiaal, voeren we uitgebreid trek- en
buigproeven uit (hoofdstuk 3 en 4) bij variërende temperatuur en testsnelheid.

In het daaropvolgende hoofdstuk (hoofdstuk 5) komen enkele impactproeven op een valopstelling aan
bod.

Vervolgens wordt de aanloop genomen naar een uitgebreid onderzoek betreffende het correct
simuleren in een eindig elementenpakket (hoofdstuk 6).

Aangezien de temperatuursinvloed een cruciale rol speelt in deze scriptie, is er tot slot onderzoek
verricht naar de thermische expansie van het materiaal en de methodes die hiervoor gebruikt kunnen
worden (hoofdstuk 7).

Trefwoorden: composieten, GMT40, staalkoord, impact, temperatuur.

iv
Temperature influence on the impact resistance of
composite materials used for automotive applications
Vicky De Bruyne
Promoters: Prof. dr. ir. Joris Degrieck and Prof. dr. ir. Wim Van Paepegem

Abstract-Composite material is widely used in many industrial III. TESTING PROGRAM
structures including automotive, aviation and civil applications A. Tensile tests
due to their lower weights compared to metal structures. Full- To get an idea of the mechanical behaviour of the basis
composite body structures, especially in automotive and aviation
material (GMT40), a testing program is carried out on this
applications are becoming important replacement materials for
material. The program is focused on the influence of the
metal. For this reason, damage of such structures subjected to
temperature and the test velocity on some properties, namely
impact is a crucial case study in current research[1]. Materials
tensile strength, Young’s modulus and the ability to absorb
used in cars and airplanes, are subjected to various and
sometimes even extreme weather conditions. Knowledge of the energy. To investigate the temperature influence, tensile tests
mechanical behaviour of the materials under this conditions is are carried out at four temperatures: -20°C, room temperature,
essential. In this project the focus is set on the influence of the +60°C, +100°C. At every temperature the specimens are tested
temperature conditions on the material properties. at three test velocities: 2 mm/min, 45 mm/min and 1000
Keywords- GMT40, steelcord, impact, mechanical testing mm/min. A statistical analysis is made on all test values. To

get the specimen on the appropriate temperature a climate case
I. INTRODUCTION
and a heating/cooling element is used. Graph 1 gives a typical
During the last years, steel in vehicles is more and more being
result : the strength is shown in function of the test velocities
replaced by composite material. The main reason to use
for the different temperatures. The diagram shows that when
composites instead of steel is to obtain higher mechanical
the monster specimen is heated, the material loses a part of his
properties in comparison with the specific mass. A reduction
tensile strength. In none of the cases the test velocity has a
of the fuel and the lower impact on the environment, is the
significant influence.
main driving force of this change-over.

The most common used composite material in vehicles is
GMT (glass mat thermoplastic). The industrial use of this
-20°C
material raises 10% every year. In this project the properties of 110 +24°C
GMT and GMT strengthened with steelcord are studied. +60°C
A lot of research has already been done on this complex Pa]100 -20°C +100°C
M
material. In none of the cases, the influence of the temperature h [ 90 +24°C
gt
on the material properties were taken into account. In order to en 80
design safer and efficient crash components, knowledge and str +60°C
e 70
understanding of the material behaviour under different sil
n
temperature conditions is important. Te 60 +100°C
50
II. MATERIAL AND USE 0 200 400 600 800 1000
Test velocity [mm/min]
The material used for this research program is called GMT401.
It is a glass mat thermoplastic composed of a matrix of Graph 1: Tensile strength in function of the test velocity for different
polypropylene reinforced with 40 weight procent of chopped temperatures.
glassfibres . In a later stage this material is reinforced with a
sink coated steelcord2 composed of nine filaments. After calculating the Young’s modulus, the conclusion is that
The test program of this material is focused on the properties the higher the temperature, the lower the Young’s modulus.
necessary for the application of bumpers for cars. A bumper For a testing velocity of 1000 mm/min, the modulus has the
is a part of the car that has to absorb the impact during a crash lowest value. For the other test velocities no clear conclusion
as good as possible. This means on one side that the impact is can be made.
slowed down and on the other side that the energy is dissipated For the energy absorption, only the value at 100°C shows a
in a controlled way. A good material choice with the significant difference with the other temperatures.
appropriate properties is essential: a strong material with a
good impact resistance and the ability of absorbing a lot of B. Three point bending tests
energy is needed [2]. An extra property that is desirable for The testing program for bending on GMT40 is analogue with
safety, is the structural integrity. that of the tensile tests. Experiments are carried out at four
temperatures and three test velocities. Not only the base
1 The GM T40 used for this research is produced by Quadrant Plastic m a terial is tested in bending, also the material reinforced with
compo sites. steelcord. These experiments don’t show a difference in
2 The steelcord used for this research is produced by Bekaert.
temperature. They are all carried out at room temperature. The
Extended Abstract v
influence of the place of the steelcord is also investigated. It’s
important to emphasize that in none of the tests, the steelcord V. TEMPERATURE EXPANSION
was broken. When testing the material at high velocities, the When testing materials at different temperatures, the
matrix is broken over the total height, followed by a pull-out of temperature expansion of the material becomes important.
the steel cord. There are different methods to investigate the temperature
For the base material, the temperature has an influence on the expansion coefficient of a material. Strain gages or an
bending strength: the higher the temperature, the lower the extensometer are used when the strains are not too little.
strength. A similar conclusion can be drawn for the bending Interferometry, moiré or bragg rasters, and dilatometry are
modulus. The influence of the test velocity on the different used for high precision measurements. Tests with an
properties is not significant. extensometer and a dilatometer on GMT40 are already done,
When using GMT40 with steelcord in stead of the base but without achieving of the expected results.
material, we obtain characteristics that are ideal for using in
bumpers. The bending strength is higher with higher test VI. CONCLUSION
velocities. Also the energy-absorption capacity has a much By introducing a steelcord in GMT40, the properties of the
higher value, as shown in Graph 2. It’s striking that, by material become more suited for the use in bumpers. Not only
introducing a steelcord, half of the total energy absorption the strength raises, also the energy absorption becomes
capacity is obtained after the maximal force. The value of the significantly higher. Temperature has especially an influence
bending modulus on the other hand, is lower. For this on the strength and the Young’s modulus, but a far much lower
application however, a higher bending modulus is better. The influence on the ability to absorb energy. The loss in strength
use of a cord in the tensile zone (at the bottom) of the matrix is increases with increasing temperature.
the best choice.
VII. PERSPECTIVES
A further investigation of the dynamical impact response of
70 the composite material at different temperatures is needed. To
65
achieve this goal not only experiments, but also the further
n [J]556050 at the bottom development of the simulations with ABAQUS are necessary.
ptio45 in the middle Another point which can be further investigated, is the
or40 at the top at the top research on the thermal expansion of the basis material:
s35
b in the middle
a30 GMT40.
y-25 at the bottom
erg20 no steelcord
En15 no steelcord REFERENCES
10
5 [1] Ramin Hosseinzadeh, Mahmood Mehrdad Shokrieh, Larry Lessard,
0 Damage behavior of fiber reinforced composite plates subjected to drop weight
0 200 400 600 800 1000 impacts, Composites Science and Technology 66 (2006), 61-68.
Test velocity [mm/min] [2] Ignace Proot, Dynamical characterizing of a composite

strengthened with a steel cord, Final work, Faculty of engineering sciences,
Graph 2: Energy-absorption in function of the test velocity for
Department mechanical construction and production, UGent (2003).
GMT40 with and without steelcord.

C. Impact tests
To get a better view on the behaviour of a material under
different circumstances, it’s important to carry out not only
(quasi-)static but also dynamical tests. A dynamic three point
bending test is performed using a drop weight impact
apparatus. The impactor of 5,07 kg falls down from six
different heights between 1 m and 2, 25 m. The impact
velocity is measured by two lasers and photodiodes. Next to
the fall down height, the influence of the temperature of the
material is investigated. The material used for the impact
experiments is GMT40 with a steelcord at the bottom.
The conclusion which can be drawn from this tests, is that the
damage on the specimen is greater with increasing impact
velocity. In some cases, for high impact velocities, the matrix
breaks first, followed by a pull-out of the steel cord. This
pulling-out is responsible for a part of the energy absorption.
The steelcord itself didn’t break at any time. The influence of
the material is not clear yet.

IV. SIMULATION
To get a better idea of the theoretical values of the mechanical
properties of GMT40 at different temperatures, a finite element
simulation would be appropriate. The finite element code used,
is ABAQUS. The first steps are already made to simulate a
static three point bending test on GMT40 at different
temperatures. A further investigation however is needed.
Extended Abstract vi
Inhoudstafel

Woord vooraf............................................................................................................................................ii
Overzicht.................................................................................................................................................iii
Extend Abstract…………………………………………………………………………………………………..v
Inhoudstafel............................................................................................................................................vii
Lijst met de figuren.................................................................................................................................xii
Lijst met de grafieken.............................................................................................................................xiii
Lijst met de tabellen..............................................................................................................................xiv
Lijst met de symbolen...........................................................................................................................xvi

Hoofdstuk 1: Inleiding...............................................................................................................................1

Hoofdstuk 2: Materiaaleigenschappen.....................................................................................................2
2.1 Definitie composieten................................................................................................................2
2.1.1 Gebruikte composiet..........................................................................................................2
2.1.2 Productie............................................................................................................................7

Hoofdstuk 3: Trekproeven........................................................................................................................9
3.1 Theoretische achtergrond..........................................................................................................9
3.2 Buigproeven op het basismateriaal.........................................................................................12
3.2.1 Voorbereiding proefstaven...............................................................................................12
3.2.2 Invloed van de testsnelheid op het trekgedrag van GMT40............................................17
3.2.2.1 Trekproeven op kamertemperatuur:........................................................................17
3.2.2.1.1 Algemeen............................................................................................................17
3.2.2.1.2 Treksterkte...........................................................................................................18
3.2.2.1.3 Energie-absorptie................................................................................................19
3.2.2.1.4 Elasticiteitsmodulus.............................................................................................20
3.2.2.2 Trekproeven bij –20°C.............................................................................................22
3.2.2.2.1 Algemeen............................................................................................................22
3.2.2.2.2 Treksterkte...........................................................................................................24
3.2.2.2.3 Energie-absorptie................................................................................................25
3.2.2.2.4 Elasticiteitsmodulus.............................................................................................25
3.2.2.3 Trekproeven bij +60°C.............................................................................................26
3.2.2.3.1 Algemeen............................................................................................................26
3.2.2.3.2 Treksterkte...........................................................................................................27
3.2.2.3.3 Energie-absorptie................................................................................................27
3.2.2.3.4 Elasticiteitsmodulus.............................................................................................28
vii
3.2.2.3.5 Thermografische camera....................................................................................28
3.2.2.4 Proeven bij +100°C..................................................................................................30
3.2.2.4.1 Algemeen............................................................................................................30
3.2.2.4.2 Treksterkte...........................................................................................................30
3.2.2.4.3 Energie-absorptie................................................................................................31
3.2.2.4.4 Elasticiteitsmodulus.............................................................................................31
3.2.2.4.5 Thermografische camera....................................................................................32
3.2.3 Vergelijking van de proefresultaten bij verschillende temperaturen:................................32
3.2.3.1 Treksterkte...............................................................................................................32
3.2.3.2 Energie-absorptie....................................................................................................34
3.2.3.3 Elasticiteitsmodulus.................................................................................................36
3.3 Besluit bij dit hoofdstuk............................................................................................................37

Hoofdstuk 4: Buigproeven......................................................................................................................38
4.1 Theoretische achtergrond........................................................................................................38
4.2 Buigproeven op basismateriaal...............................................................................................40
4.2.1 Algemeen.........................................................................................................................40
4.2.2 Invloed van de testsnelheid bij een bepaalde temperatuur..............................................41
4.2.2.1 Buigproeven op kamertemperatuur.........................................................................42
4.2.2.1.1 Algemeen............................................................................................................42
4.2.2.1.2 Buigsterkte...........................................................................................................43
4.2.2.1.3 Energie-absorptie................................................................................................45
4.2.2.1.4 Buigmodulus........................................................................................................46
4.2.2.2 Buigproeven bij –20°C.............................................................................................48
4.2.2.2.1 Algemeen............................................................................................................48
4.2.2.2.2 Buigsterkte...........................................................................................................50
4.2.2.2.3 Energie-absorptie................................................................................................50
4.2.2.2.4 Buigmodulus........................................................................................................51
4.2.2.3 Buigproeven bij +60°C.............................................................................................51
4.2.2.3.1 Algemeen............................................................................................................51
4.2.2.3.2 Buigsterkte...........................................................................................................52
4.2.2.3.3 Energie-absorptie................................................................................................53
4.2.2.3.4 Buigmodulus........................................................................................................53
4.2.2.4 Buigproeven bij +100°C...........................................................................................53
4.2.2.4.1 Algemeen............................................................................................................53
4.2.2.4.2 Buigsterkte...........................................................................................................54
4.2.2.4.3 Energie-absorptie................................................................................................54
4.2.2.4.4 Buigmodulus........................................................................................................55
4.2.3 Vergelijking proefresultaten bij verschillende temperaturen............................................55
4.2.3.1 Buigsterkte...............................................................................................................55
viii
4.2.3.2 Energie-absorptie....................................................................................................57
4.2.3.3 Buigmodulus............................................................................................................58
4.3 Buigproeven op basismateriaal met staalkoord......................................................................60
4.3.1 Invloed van de testsnelheid bij een bepaalde inbedhoogte van de staalkoord................60
4.3.1.2 Koord bovenaan......................................................................................................61
4.3.1.2.1 Waarnemingen....................................................................................................61
4.3.1.2.2 Buigsterkte...........................................................................................................63
4.3.1.2.3 Energie-absorptie................................................................................................63
4.3.1.2.4 Buigmodulus........................................................................................................64
4.3.1.3 Koord in het midden.................................................................................................64
4.3.1.3.1 Waarnemingen....................................................................................................64
4.3.1.3.2 Buigsterkte...........................................................................................................66
4.3.1.3.3 Energie-absorptie................................................................................................66
4.3.1.3.4 Buigmodulus........................................................................................................67
4.3.1.4 Koord onderaan.......................................................................................................67
4.3.1.4.1 Waarnemingen....................................................................................................67
4.3.1.4.2 Buigsterkte...........................................................................................................69
4.3.1.4.3 Energie-absorptie................................................................................................69
4.3.1.4.4 Buigmodulus........................................................................................................70
4.3.2 Invloed van de plaats van de staalkoord..........................................................................70
4.3.2.1 Buigsterkte...............................................................................................................70
4.3.2.2 Energie-absorptie....................................................................................................72
4.3.2.3 Buigmodulus............................................................................................................74
4.4 Besluit bij dit hoofdstuk............................................................................................................76

Hoofdstuk 5: Impactproeven..................................................................................................................77
5.1 Inleiding...................................................................................................................................77
5.2 Uitvoering proeven...................................................................................................................79
5.2.1 Opstelling..........................................................................................................................79
5.2.2 Uitvoering.........................................................................................................................80
5.2.3 Bespreking resultaten.......................................................................................................81
5.2.4 Waarnemingen na beproeving.........................................................................................83
5.2.4.1 Invloed van de valhoogte.........................................................................................83
5.2.4.1.1 Bij kamertemperatuur..........................................................................................83
5.2.4.1.2 Bij -20°C..............................................................................................................85
5.2.4.1.3 Bij +60°C.............................................................................................................85
5.2.4.1.4 Bij +100°C...........................................................................................................86
5.2.4.2 Invloed van de temperatuur op de proefresultaten..................................................87
5.3 Besluit bij dit hoofdstuk............................................................................................................88

ix