Welding of Thermoplastic Matrix Composites: Prediction of Macromolecules Diffusion at the Interface Gilles Régnier, Célia Nicodeau, Jacques Verdu, Francisco Chinesta, Virginie Triquenaux, Jacques Cinquin
To cite this version:
Gilles Régnier, Célia Nicodeau, Jacques Verdu, Francisco Chinesta, Virginie Triquenaux, et al.. Weld- ing of Thermoplastic Matrix Composites: Prediction of Macromolecules Diffusion at the Interface. 8th ESAFORM Conference on Material Forming, 2005, Cluj-Napoca, Romania. hal-00020871
HAL Id: hal-00020871 https://hal.archives-ouvertes.fr/hal-00020871 Submitted on 12 Mar 2018
HAL is a multi-disciplinary open access L’archive ouverte pluridisciplinaire HAL, est archive for the deposit and dissemination of sci- destinée au dépôt et à la diffusion de documents entific research documents, whether they are pub- scientifiques de niveau recherche, publiés ou non, lished or not. The documents may come from émanant des établissements d’enseignement et de teaching and research institutions in France or recherche français ou étrangers, des laboratoires abroad, or from public or private research centers. publics ou privés. Welding of thermoplastic matrix composites: prediction of macromolecules’ diffusion at the interface
G. Régnier1, C. Nicodeau1, J. Verdu1, F. Chinesta2, V.Triquenaux3, J.Cinquin3
1Laboratoire de Transformation et de Vieillissement des Polymères ENSAM 151, Bd de l’Hôpital 75013 Paris e-mail: [email protected];
2Laboratoire de Mécanique des Systèmes et des Procédés, UMR CNRS 8106 ENSAM 151, Bd de l’Hôpital 75013 Paris e-mail: [email protected];
3EADS CCR 5, quai Marcel Dassault BP76 92152 Suresnes Cedex e-mail: [email protected];
ABSTRACT: The automated tow placement process allows to fabricate thermoplastic composite parts by welding of pre-impregnated plies. In order to describe the phenomenon of welding for a Carbon/PEEK composite by interdiffusion of polymer chains across the interface between two plies, a simulation of the process, which predicts the material thermal history, is done. The reptation time linked to chain diffusion is estimated by rheological experiments and extrapolated at high temperatures. Although the material only remains a very short time above its melting temperature, it is showed that, under appropriate process conditions, this welding process is promising.
Key words: in situ consolidation, thermoplastic composite tape, relaxation time, chains diffusion
whether or not the welding is possible under 1 INTRODUCTION industrial constraints. The optimisation of the process will eventually follow. Firstly, it is The automated tow placement process, developed in necessary to describe and model the physical the aircraft industry by EADS, Dassault Aviation phenomena taking place at the interplies. The APC-2 and Eurocopter, is an emerging technique for (UD Carbon/PEEK pre-impregnated) composite will manufacturing continuous fiber-reinforced be used for this study. thermoplastic parts. The consolidation is performed by the machine head, realising a welding phenomenon between the two plies as shown in 2 MACROMOLECULAR CHAINS DIFFUSION figure 1. Two torches first heat the incoming tape THEORY and the already-laid down substrate at a temperature greater than the resin melting temperature. Then a Once the intimate contact between plies is compaction roller applies a normal force in order to established, the interdiffusion of macromolecular improve the intimate contact between the plies. chains at the interface occurs as long as the matrix is
Roller (P,T) melt, i.e before crystallisation quenches movements. This achieved the adhesion phenomenon. Velocity v The reptation theory introduced by De Gennes [1]
Torches (T) and Doi & Edwards [2] models the motion of
v individual linear polymer chains in the bulk. In the model, a polymer chain of length L, is considered to Fig. 1. In situ consolidation process for thermoplastic tapes be confined in a tube, which represents the steric Process parameters such as lay-down velocity, effects of neighbourhood chains via entanglements torches and roller temperatures and compaction [3]. The chain can only move along the tube pressure will determine the interfacial bonding curvilinear length as shown in figure 2. The chain quality. The aim of this study is to determine moves within the tube in a Brownian motion
1 manner, and after a period of time t, the chain ends Viscoelastic phenomena are the consequence of escape from the original tube, forming the “minor chains intra- or intermolecular motions around their chains” of length l(t) [4]. During this process l(t) equilibrium configuration. The notion of “relaxation increases with time until it reaches L at the reptation time” describes the dependence of time -shear rate time tR. Beyond the reptation time, the entire or frequency- on viscoelastic properties. polymer chain is out of the tube, the interpenetration The longer the relaxation time is, the larger the and entanglement of all the polymer chain is fully spatial scale of possible motions [8]. If the frequency developed at the interface and the molecular is smaller than the transition frequency between the configuration is identical to that of the bulk material. rubbery plateau and the terminal zone, the minor observation period of time of macromolecular chains chain l(t) is greater than entanglements life time. Thus, the tube terminal zone -“long times” zone- describes the displacement along the entire polymer chain. For the chain description of the consolidation process, our aim is entanglement to evaluate this terminal relaxation time λ, referred Fig. 2. Reptation model as “long time”, which is the longest time for the De Gennes [5] represents chain motion by migration polymer chain. of certain “defects” along the chain. De Gennes 3 3.2 Dynamic tests showed that tR= M where M is the molecular weight of the linear chain. Doi and Edwards [6] showed the Experiments have been realised on pure PEEK same relation using a diffusion equation. However, it (G450; average molar mass in weight and in number is not possible in our case to determine a numerical Mw=106900g/mol and Mn=37000g/mol). reptation time from their theoretical expressions. Unfortunately, exact characteristics of the PEEK That is the reason why we will approach this used for APC-2 cannot be known; however, relaxation time thanks to rheological experiments. according to the supplier, this grade G450 represents In order to study the diffusion phenomenon the highest boundary in terms of molecular weight. associated to this process, it is necessary to evaluate The dynamic shear measurements were performed the temperature field of a composite part during its on a rheometer (ARES Rheometric Scientific), with processing. A 2D model has been developed [7]. It is parallel plates geometry. Several isothermal tests based on an explicit numerical scheme that takes were made under nitrogen atmosphere at into account the heat transfer via conduction and temperatures in the range of 310°C to 410°C (glass convection as well as source terms due to material transition temperature Tg=140°C and melting crystallisation and melting. This calculation gives temperature Tm=330°C). A periodic strain with a the dependence of the temperature field in a multi- fixed amplitude (2% in order to be in the linear layered composite part -particularly the temperature viscoelastic zone) is imposed to the sample. The at a chosen interface- on the process parameters. An frequency sweep is performed between 100 and 0.01 experimental study is then carried out in order to rad/s. validate the numerical computation results. In the current study, we will focus on 3.3 Relaxation time & models macromolecular chains diffusion and other phenomena such as polymer crystallisation or Several analyses are possible to determine “long” thermal degradation won’t be discussed. relaxation time relative to reptation phenomenon We will use interfacial time-temperature history from experimental results: given by the model and we will explain the method • From intersection of G’ and G’’(elastic and which leads to conclusions on whether the welding viscous component of complex modulus) tangents phenomenon is possible or not. when ω tends to 0 [9]. However, in our case, complementary creep tests would be necessary to get G’ values at smaller frequencies. 3 EXPERIMENTAL STUDY • From the viscosity values; we consider 3.1 Introduction transition between newtonien state –characteristic of the intermolecular friction and which is obtained
2 when every molecule is relaxed- and the The dynamic measurements were performed on the rheofluidifiant regime -for which the viscosity rheometer at temperatures in the range of 310°C to follow the power law model- [10]. Yasuda and 410°C. We note that, for these temperatures Carreau’s equation applied to shear rate gives the conditions, the “long times” fit the Arrhenius’ law, relation of the viscosity η [11]: as the newtonian viscosity. Hence, Figure 4 shows
a (m-1)/a the extrapolation of long times at higher η = η0{1+ (λ ) } (1) temperatures typical of adhesion phenomenon on the with ηo(T) the newtonian viscosity, λ(T) the process. transition characteristic time between newtonien and pseudo-plastic regime, a a parameter relative to the 10 curvature of this transition and depending on the material polydispersity index and m the flow index. 1 0,001 0,0014 0,0018 The intersection point abscise of asymptotes defined 325°C at boundary frequencies gives hence the condition 0,1 600°C ω=1/λ and enables us to determine Carreau’s law 410°C relaxation time λ(T) as shown in figure 3. Here, for (s) time "long"relaxation example, the average “long” time at 360°C is 900 0,01 1/T (K-1) ms. ηo is given by the value of the plateau viscosity and Fig. 4. “Long time extrapolation” according to the Arrhenius’ fit the Arrhenius’ law. Parameters of Yasuda & law Carreau’s corresponding to our experimental values Our aim is to apply these results on time- are: a=0.7 and m=0.54. temperatures curves given by the model relative to
1,0E+04 the interface for different process parameters conditions given in figure 5.
800 a) b) c) 700
1,0E+03 600
l n* l (Pa.s) l n* l 500
400 exp. pts 300 Y&C law 200 Température (°C) Température 1,0E+02 0,01 0,1 1 10 100 100 w (1/s) 0 Fig. 3. Terminal relaxation time determination at 360°C 0 5 10 15 20 temps relatif (s) • From the maximum of the viscous component of complex viscosity η”. We can write a resonance Fig. 5. Temperature evolution relative to the interface for condition ω.λm=1 to define the characteristic different process parameters relaxation time λm. It has been showed We know that reptation time at a given temperature experimentally that these times are very close represents the period of time necessary for the chain from the Carreau’s law ones. to loose its initial configuration and to move of an • From generalised Maxwell’s model that generally average distance equal to its end-to-end distance. well describes the terminal zone comportment. The question is to determine how many times a The relaxation spectrum H(λ) can also be chain configuration renewal can happen during the deduced from the complex modulus [12]. temperature peak imposed by the process. However, in our case, with such a polydisperse The calculation principle introduced to our model is material, it is not easy to determine precisely the described below: terminal relaxation time of this relaxation The interdiffusion phenomenon takes place only spectrum. once the intimate contact between the two plies is achieved i.e once the roller applied the pressure. At this time ti, the interface temperature decreases. 4 APPLICATION TO THE PROCESS Thus, only the cooling part of the time-temperature
3 curves -limited at the temperature relative to the generally used for thermoplastic matrix composite beginning of the crystallisation tf – will be taken into parts. Indeed, with the on line process, it has been account. showed that the temperature seen by the material are Yang and Pitchumani [4] extended the far above its melting temperature while the material monodimensionnel diffusion equation derived from remains in a molten state for only a very short time the reptation model to the anisothermal case. (in the range of the second). The experimental Equation 2 gives the evolution of the minor chain for rheological study showed that relaxation time linked t
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