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  • 1. Andersson, Magnus
    Vacuum infusion of polymer composites2001Licentiate thesis, comprehensive summary (Other academic)
    Abstract [en]

    The current trend towards an increased use of vacuum infusion for manufacturing of high performance fibre reinforced polymer composites has stressed the necessity of an advanced modelling of the process. Until recent years development in this area has mainly been based on trial and error and the behaviour of the method is therefore not fully understood. The basic principle of the vacuum infusion process is that a stack of dry fabrics is placed between a stiff mould half and a flexible and airtight bag. The bag is sealed to the mould expect at certain positions being open for resin supplies and outlets. Liquid resin then penetrates the stack by a reduction of the pressure at one or several positions in the formed cavity. After complete filling the pressure in the cavity is evened out by retaining the vacuum level at the outlets throughout curing of the resin. The overall goal of this research is to develop tools that ensure optimum and secure processing in practical work with vacuum infusion. The means to achieve this goal has so far been industry scale experiments, simple analysis and numerical simulations. The experimental part comprises full-scale impregnations where thickness variations are measured with an advanced optical metrology system and the out-of-plane flow front is monitored by means of colour marks in the reinforcement stack. Experimental findings are then incorporated in a numerical model including moving boundaries and two-phase flow through porous media based on a commercial software for computational fluid dynamics.

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  • 2. Andersson, Magnus
    Visualisation of composites manufacturing2003Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    The five papers in this thesis demonstrate five unique ways to monitor composite manufacturing. They also clarify several phenomena that take place during composite manufacturing. Of particular interest are two manufacturing methods, namely vacuum infusion (Paper A-D) and compression moulding of SMC (Paper E). The former process is, for instance, used for large surface area parts such as wind-turbine blades. The concept is that a dry reinforcement is placed on a stiff mould half and covered with a flexible and airtight bag. The bag is then sealed to the mould except at certain positions being open for resin supplies and outlets. By keeping the pressure atmospheric at the resin inlets and reducing the pressure at one or several positions in the formed cavity, liquid resin is forced to impregnate the stack. A further result of the difference between the ambient pressure and the pressure within the cavity is a compaction force and a corresponding compression of the elastic stack. In compression moulding of SMC a charge consisting of a polymer, fillers and chopped fibres is placed in a heated and open mould. When the mould is closed, the charged material will fill the mould. This is a rapid process and it is therefore suitable for parts to the automotive industry. Exclusively, this thesis presents optical measurements of the full 3D position of the flow front during vacuum infusion moulding. Equally exceptional are field measurements made with a stereoscopic digital speckle photography system of the movement of the bag during moulding by the same manufacturing process. The actual results from these two measuring techniques are also very interesting. First of all is it clarified that there can be rather large gradients in the flow front with respect to the thickness direction enabling the formation of voids. Secondly it is shown that certain permeability measurements could be used to predict the flow front position during vacuum infusion while others fail. Thirdly it is confirmed that a ditch is formed at the resin flow front and that there can be a considerable and seemingly perpetual compaction after complete filling. Special attention has also been given to the advancing flow front during compression moulding of SMC. In this case the full complexity is captured by means of continuous high resolution close-up monitoring. From these visualisations three phases are defined, namely pitch, floating, and boiling. In the initial phase, pitch, outer layers do not remain outer layers, the actual flow is very complex and air is likely to be entrapped. In the second phase, floating, the flow is stable and seemingly viscous. In the last phase, boiling, bubbles are observed in the low pressure region at the flow front, favouring the formation of void both internally and on the surface. For vacuum infusion it is also essential to develop and evaluate new numerical visualisation tools. This is rather challenging since the impregnation is characterized by a full three-dimensional flow in a porous medium having an anisotropic, spatial- and time-dependent permeability. The new approach taken here is to implement such models in an all-purpose and commercial computational fluid dynamics software through custom written subroutines. The strategy has been to first verify and validate the modifications by 2D simulations and then demonstrate the full 3D capacity through one demonstrator.

  • 3. Andersson, Magnus
    Visualisation of the vacuum infusion process2003In: ICCM-14: 14th International Conference on Composite Materials : July 14-18, 2003, San Diego, California, USA, Dearborn, Mich: Society of Manufacturing Engineers, North American Manufacturing Research Institution, 2003Conference paper (Refereed)
  • 4. Andersson, Magnus
    et al.
    Gebart, Rikard
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Energy Science.
    Lundström, Staffan
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Fluid and Experimental Mechanics.
    Långström, R.
    Luleå University of Technology.
    Development of guidelines for the vacuum infusion process2000In: Proceedings of the 8th International Conference on Fibre Reinforced Composites, FRC 2000: Centre for Composite Materials Engineering, University of Newcastle, UK, 13 - 15 September 2000 / [ed] A. G. Gibson, Cambridge: Woodhead Publishing Materials , 2000, p. 113-120Conference paper (Refereed)
    Abstract [en]

    The current trend towards increased use of vacuum infusion moulding for large surface area parts has increased the interest for an advanced modelling of the process. This paper presents a detailed experimental investigation of laminate thickness and out-of-plane flow front shape during impregnation of high permeability reinforcement on top of a non-crimp fabric reinforcement lay-up. The goal with the experiments is to increase the understanding of the process and to provide accurate data that can later be used for validation of numerical models. The laminate thickness was measured during impregnation with a stereoscopic digital speckle photography system and the flow front shape was determined by tracking of colour marks in the stacking. The laminate lay-ups studied are different combinations of non-crimp fabrics and flow layers while the resin used was a polyester developed specifically for vacuum infusion moulding. Results are presented both for the instantaneous thickness and the flow front shape for several different material combinations. It was found that the skewness of the flow front became more pronounced with increasing number of flow layers when the number of non-crimp fabric layers was kept constant. As a first step towards a complete numerical model of the impregnation process a simplified model for the compressibility and a proven model for permeability was implemented in a commercial CFD package that can handle moving boundaries and moving flow fronts. Only a qualitative comparison with experiments was done but the conclusion was that the overall behaviour of the model was encouraging. A validation of the numerical model based on the measurements in this paper is under development.

  • 5. Andersson, Magnus
    et al.
    Lundström, Staffan
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Fluid and Experimental Mechanics.
    Gebart, Rikard
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Energy Science.
    Numerical model for vacuum infusion manufacturing of polymer composites2003In: International journal of numerical methods for heat & fluid flow, ISSN 0961-5539, E-ISSN 1758-6585, Vol. 13, no 3, p. 383-394Article in journal (Refereed)
    Abstract [en]

    The focus is set on the development and evaluation of a numerical mgodel describing the impregnation stage of a method to manufacture fibre reinforced polymer composites, namely the vacuum infusion process. Examples of items made with this process are hulls to sailing yachts and containers for the transportation industry. The impregnation is characterised by a full 3D flow in a porous medium having an anisotropic, spatial- and time-dependent permeability. The numerical model has been implemented in a general and commercial computational fluid dynamic software through custom written subroutines that: couple the flow equations to the equations describing the stiffness of the fibre reinforcement; modify the momentum equations to account for the porous medium flow; remesh the computational domain in each time step to account for the deformation by pressure change. The verification of the code showed excellent agreement with analytical solutions and very good agreement with experiments. The numerical model can easily be extended to more complex geometry and to other constitutive equations for the permeability and the compressibility of the reinforcement.

  • 6. Andersson, Magnus
    et al.
    Lundström, Staffan
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Fluid and Experimental Mechanics.
    Gebart, Rikard
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Energy Science.
    Långström, R.
    Swedish Institute of Composites, Piteå.
    Flow-enhancing layers in the vacuum infusion process2002In: Polymer Composites, ISSN 0272-8397, E-ISSN 1548-0569, Vol. 23, no 5, p. 895-901Article in journal (Refereed)
    Abstract [en]

    The current trend towards increased use of vacuum infusion molding for large surface-area parts has increased the interest in an advanced modeling of the process. Because the driving pressure is limited to 1 atmosphere, it is essential to evaluate possible ways to accelerate the impregnation. One way of doing this is to use layers of higher permeability within the reinforcing stack, i.e. flow-enhancing layers. We present an experimental investigation of the flow front shape when using such layers. The through-thickness flow front was observed by making a number of color marks on the glass-mats forming the reinforcing stack, which became visible when the resin reached their position. The in-plane flow front was derived from observations of the uppermost layer. It turned out that existing analytical models agree very well with the experiments if effective permeability data is used, that is, permeability obtained from vacuum infusions. However, the fill-time was nearly twice as long as predicted from permeability data obtained in a stiff tool. This rather large discrepancy may be due to certain features of a flexible mold half and is therefore a topic for further research. The lead-lag to final thickness ratio is dependent on the position of the flow front and ranges form 5 to 10 for the cases tested. Interestingly the lead-lag has a miximum close to the inlet.

  • 7. Andersson, Magnus
    et al.
    Lundström, Staffan
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Fluid and Experimental Mechanics.
    Langhans, N.
    EADS Military Aircraft, Munich.
    Computational fluid dynamics applied to the vacuum infusion process2005In: Polymer Composites, ISSN 0272-8397, E-ISSN 1548-0569, Vol. 26, no 2, p. 231-239Article in journal (Refereed)
    Abstract [en]

    An all-purpose computational fluid dynamics software is used for simulations of the vacuum infusion process. The study comprises simulations of a full three-dimensional two-phase flow through a porous medium. The medium that has an anisotropic, spatial- and time-dependent permeability is located in a complex mold with moving boundaries. With this generalization, different material combinations, processing conditions, and even other manufacturing techniques can be evaluated. The strength of the presented approach is exemplified by simulations of mold filling of a real part, using a typical vacuum infusion set-up. In addition to the overall development of the model, a number of specific aspects and phenomena are investigated and evaluated. Local lead of the flow front and a minor influence in overall flow front lead-lag, with no influence on the fill time, is the result of simulations of edge effects due to poor preform fitting.

  • 8. Andersson, Magnus
    et al.
    Lundström, Staffan
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Fluid and Experimental Mechanics.
    Langhans, N.
    Numerical simulation of the vacuum infusion process2006In: Experimental techniques and design in composite materials (ETDCM6): "Sixth International Seminar on Experimental Techniques and Design in Composite Materials" which was held at Padova in June 2003 / [ed] Marino Quaresimin, Amsterdam: Elsevier, 2006Conference paper (Refereed)
  • 9. Odenberger, Torbjörn
    et al.
    Andersson, Magnus
    Lundström, Staffan
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Fluid and Experimental Mechanics.
    Experimental flow-front visualisation in compression moulding of SMC2004In: Composites. Part A, Applied science and manufacturing, ISSN 1359-835X, E-ISSN 1878-5840, Vol. 35, no 10, p. 1125-1134Article in journal (Refereed)
    Abstract [en]

    This work is primarily focused on experimental visualisation of the flow during mould closure in compression moulding of sheet moulding compound. Circular plates are manufactured with industry scale equipment at close to production conditions. Special attention is given to the advancing flow front, for which the full complexity is captured by means of continuous high resolution close-up monitoring. From the experimental visualisation of the flow front, three phases are defined, namely squish, flow, and boiling. During the initial phase, squish, outer layers do not remain outer layers, the actual flow is very complex and air is likely to be entrapped. The governing process parameters during this phase are mould temperature, mould closing speed and amount of preheating in the mould. During the second phase, flow, the flow is stable and seemingly viscous. During the last phase, boiling, bubbles are observed in the low pressure region at the flow front, favouring the void content both internally and on the surface. Based on a chemical analysis including mass spectrometry and thermogravimetry, the gas is probably styrene.

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