JEC COMPOSITES MAGAZINE - Issue #36 - October 2007 - 65

KNOW-HOW Measurement A high-level permeability measurement technique Since it was founded in 1990, the Institut für Verbundwerkstoffe GmbH (IVW) has made its reputation in the world of composites. Besides basic research projects, the institute’s employees work each year on 130 projects directly funded by industry. Liquid composite moulding (LCM ) is only one of several research fields. LCM is now one of the most commonly used processes for fibre-reinforced polymers. G. RIEBER RESEARCH ASSOCIATE, PROF. MITSCHANG, RESEARCH DIRECTOR MANUFACTURING SCIENCE INSTITUT FÜR VERBUNDWERKSTOFFE GMBH pressure gradient ΔP over a given length ΔL. As most re-inforcement textiles show an orthotropic behaviour, permeability has to be determined in the x and y directions. When a point-inlet is chosen, the permeability can be determined in both the x (K1) and y (K2) directions in one trial. eing able to determine permeability contributes to a better understanding of the LCM process, which facilitates process simulation and the optimization of process parameter and tool design [1,2]. The Cell for the Online Measurement of in-plane Permeability (2D-COMP) is a tool for measuring permeability continuously under industrial process parameters. The tool is cool, heatable up to 180°C, and resin resistant, and it shows less than 0.01 mm deflection at an injection pressure of 10 bar. Fig. 2: Darcy’s Law – flow front propagation for 1D and 2D measurements Advantages of determining permeability Knowing the permeability of the reinforcement textile benefits the whole process chain: - the reinforcement textile manufacturer can provide quality assurance (a variation in permeability indicates fluctuations in the textile) and develop easy-to-impregnate textiles; - the resin producer can determine the influence of resin on the impregnation process at industrial boundary conditions (interaction to the fibre geometry and sizing); - the manufacturer of fibre-reinforced plastic components can simulate the design process for components and tools, and determine process parameters; he can spot manufacturing-related issues in the early stage of product development and better understand the process; and he benefits from greater process reliability and improved documentation, resulting in fewer rejects. It also becomes easier to change material suppliers, as the process can be adapted to the new textile with known permeability. Fig. 1: The LCM process The LCM process (figure 1) is being used more and more for medium-volume parts. At the same time, part quality and process reliability requirements are becoming stricter. This can be addressed by using simulation software (RTM-Worx, LIMS, PAM-RTM), which can also help to cut development costs and time. Different configurations can be tested on the computer instead of using expensive tools and carrying out experiments. What is permeability? Permeability is a pore structure parameter that describes the ability of the resin to flow through the fabric. The resin injection process cannot be simulated without knowledge of the reinforcement permeability. The flow of a fluid through a porous material was first described by Darcy in 1856 (figure 2). The velocity of the resin flow front is determined by the permeability Κ, the viscosity η , and the Requirements for a permeability measurement cell A permeability measurement cell has to fulfil several requirements: - pressure inside the tool up to 30 bar (mould deflection lower No36 October - November 2007 / JEC Composites Magazine

JEC COMPOSITES MAGAZINE - Issue #36 - October 2007

Table of Contents for the Digital Edition of JEC COMPOSITES MAGAZINE - Issue #36 - October 2007