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