Automotive Automotive
Automotive Automotive parts must be predictable Material and flow models for natural fiber reinforced injection molding materials for practical use in the automotive industry By Erwin Baur M-Base Engineering + Software GmbH Aachen, Germany Fig. 1: Automotive part made from natural fiber reinforced PP with 30% Sisal (Source Ford) For many years natural fibers (NF) have been considered for reinforcement of plastics. They show good mechanical properties and the principle qualification has been demonstrated in many projects. However, natural fibers are a relatively new type of material, unknown to the classical plastics industry. The producers of natural fiber reinforced plastics and even more the producers of fibers have a hard time to match all expectations of potential users concerning product information, support in design and processing, and predictability of products. Very interesting high volume application fields, like in the automotive industry, can not be served due to this lack. Natural fibers can be processed in many different ways, but considering the actual use of plastics in the automotive industry, injection molding applications seem to be most promising. Polyproylene would be the most likely matrix material, because it is already broadly used in relevant applications and its thermal properties allow the compounding with natural fibers. Today the automotive producers are strongly interested in the use of materials from renewable sources and a reduction of the carbon footprint of their products. The willingness to use bio materials has increased, even against well established concerns towards unstable qualities, challenging processing and small processing windows. In one point, however, the automotive designers do not like to compromise: every part needs to be predictable, which means the material must allow simulation of performance during processing/manufacturing and in the final use. All components must show complete theoretical proof that they meet product safety requirements and are fit for purpose through using digital simulation. This is a fixed, established procedure in the automotive industry to meet today’s development times. So far injection moldable natural fiber reinforced thermoplastics could not offer the requested predictability. A new project, coordinated by M-Base Engineering + Software GmbH, Aachen, Germany has been started in order to bridge this gap. During a phase of three years relevant models for the simulation of natural fiber reinforced materials shall be developed, material parameters shall be measured and the validity of the new models shall be proofed with a realistic serial part. At the same time the basic simulation parameters shall be identified for as many different natural fibers as possible, so the results can be used for future projects. This project aims to open the way to enable natural fiber reinforced plastics to be designed theoretically and simulated in the automotive 20 bioplastics MAGAZINE [01/12] Vol. 7
Automotive i k Ti-1,i FHi Fig. 3: First results of flow simulation using specific mechanical properties of a natural fiber in a fountain flow. These patterns allow prediction of the most important effects during injection molding (Source: Tim Osswald, University of Wisconsin, Madison). Fig. 2: Mechanistic model for a single fiber (Source: Tim Osswald, University of Wisconsin, Madison) Fi-1,i THi Fc k,i Fi+1,i Ti+1,i industry and subsequently in other industries. This will give natural fiber reinforced plastics the same status as established conventional plastics when selecting materials and in the long term their use in the industry will grow. The project will consider all aspects of simulation, the mechanical calculations will focus on simulating crash response (including in total vehicle simulation), which is vital for most automotive applications. Meeting these aims means considering the process as a whole, especially the anisotropic mechanical properties have to be considered, which follow completely different laws, compared to classical glass fibers. The following tasks are necessary, in order to find an integrative solution, covering the complete process: • Establishing the micro-mechanical characteristics of natural fibers before and after processing • Deriving a suitable fiber orientation model • Modeling typical side-effects when using NF plastics (fiber damage, separation etc.) • Produce NF compounds and test pieces • Describing the rheological and thermal characteristics of NF compounds completely • Determining quasi-static and dynamic mechanical properties • Integrating the fiber orientation model with commercial flow simulation software • Scaling up compound production for selected materials to near-series level • Integrating material models with commercial CAE software, especially for processing and crash simulation purposes • Simulating a serial component • Producing the serial component and conducting extensive mechanical testing, including crash response During the project numerous combinations of several different PP matrix materials with natural fibers (Flax, Hamp, Sisal, Wood, Straw, Cellulose Regenerate) will be compounded and analyzed. The elementary mechanical properties of the fibers will be measured and incorporated into the flow models. Using special mechanistic models the flow behavior of the fibers during processing will be evaluated, including orientation, fiber damage and fiber matrix separation. Based on these first steps, new flow and orientation models will be incorporated into commercial injection molding simulation software, allowing prediction of the orientation in real parts. The orientation information will be used to determine the anisotropic mechanical properties of the parts. In addition to the fiber properties, the characteristic rheological and thermal properties for process simulation will also be measured for all compounds. Especially the viscosities curves will be challenging, due to fiber jamming in conventional capillary rheometers. The project partners offer a unique combination of expertise and equipment that is needed to fulfill these tasks efficiently: • Ford Research & Advanced Engineering, Aachen • IAC (International Automotive Components), Krefeld • LyondellBasell, Frankfurt • Kunststoffwerk Voerde Hueck & Schade GmbH & Co. KG, Ennepetal • Simcon Kunststofftechnische Software GmbH, Würselen • M-Base Engineering + Software GmbH, Aachen • University of Wisconsin-Madison, Madison • Hannover Technical College, Institute of bioplastics and biocomposites, Hannover • Hochschule Bremen, Bremen • Technical University Clausthal, Institute of polymer materials and plastics, Clausthal • Deutsches Kunststoff Institut (DKI), Darmstadt The project is funded by the Federal Ministry of Food, Agriculture and Consumer Protection (BMELV) via the Agency for Renewable Resources (FNR). www.m-base.de bioplastics MAGAZINE [01/12] Vol. 7 21
