SASTECH Journal 19 Volume 9, Issue 2, September 2010 STRUCTURAL ANALYSIS OF FIBER- FILLED PLASTICS WITH MOULDING PROCESS INDUCED ANISOTROPY P. Satheesh Kumar 1 , S. Srikari 2 , N. S. Mahesh 3 , S. Reddy 4 1 Student, M. Sc. [Engg.], 2 Professor, 3 Professor and Center Manager (AMT and EMM), M.S. Ramaiah School of Advanced Studies, Bangalore 560 054 4 Keywords: Fiber Filled Plastic, Fiber Orientation, Anisotropic, Orthotropic, Moldflow, ANSYS Senior Analyst, Schneider Electric India Pvt. Ltd. Abstract Thermoplastics have many advantages over metal parts, including lower mass and ease of fabrication. To further improve their elastic modulus, creep resistance, and dimensional stability, short fibers are added to polymers. Such composites find widespread use because they can be processed with techniques used for unfilled polymers, provided the fiber length is below a certain limit. However, the application of fiber-filled thermoplastic materials has been limited in many cases by the inability to accurately predict performance and durability. In this work, structural analysis capability of ANSYS is used in conjunction with flow simulation capability of Moldflow. The Moldflow fiber orientation simulation model allows significantly improved prediction of orientation of fibers in a molded component over a range of polymer materials and fiber contents. The ANSYS interface for Moldflow is used to translate this information to an input file for structural analysis using ANSYS. With effect of fiber orientation incorporated in the material properties, results of this structural analysis provide more realistic valuse of deformation and stresses in the formed part. Linear orthotropic analysis is carried out on ash tray door component by coupling Moldflow with ANSYS. A comparison is made between the results from linear isotropic and linear orthotropic analysis with different gating systems to understand the effect of these parameters on the mechanical performance of the part. Simulation results are able to predict the observed mechanical behaviour of short-fiber filled plastic components when the anisotropy of the material is taken into consideration. Traditional approach of treating the material property as isotropy overestimates the stiffness of the part. Also, modelling of flow is able to quantify the anisotropy generated in the part during its fabrication process. Abbreviations CAD Computer-Aided Design CAE Computer-Aided Engineering 1. INTRODUCTION The automotive industry is on the brink of a revolution, and the plastics industry is poised to play a major role. New technologies are enabling improvements in safety, comfort and savings in energy. Lightweight plastics allow automotive designers and engineers the freedom to deliver innovative concepts cost effectively. From an aesthetic perspective, plastics and plastic composites offer the automotive designers distinct advantages in many applications. Plastics provide versatile designs in electrical, electronic, and lighting applications, further enhancing new styling opportunities. Versatility is core to plastics' beauty, allowing for efficient design through consolidation of parts and their modularity, reducing parts manufacturing costs and enhancing vehicle affordability [1]. Short-fiber reinforced composites are widely used for their high strength to weight ratios and remarkably enhanced physical properties compared with pure polymer products. Compression molding, extrusion and injection molding are some of the processes often used for fabricating components of short-fiber reinforced composites. The fibers are suspended in the polymer matrix, and during manufacturing process orient themselves in response to the interactions among kinematics of the flow, other neighboring fibers and mold cavity. Fiber reinforced composites typically show anisotropic mechanical, thermal and rheological properties. Therefore, prediction of fiber orientation during the transient mold filling is important for the prediction of such anisotropic properties of final plastic part. One of the complicating factors for injection- molded plastic parts is the change in the properties of plastics during the manufacturing process. While this is not a problem in and of itself, problems can arise if the structural analyses are based on generic material data that does not accurately represent the actual properties of the molded part. This can lead to over engineering of components, resulting in increased costs and material usage, or under-engineering, which can result in premature failure of parts. When glass or carbon fibers are added to plastics, the elastic modulus can increase significantly with a negligible effect on part weight. This combination of low weight and high stiffness makes fiber-filled plastics ideal for high-performance applications. The orientation direction and the degree of orientation of the fibers determine the mechanical properties of the molded part. The material will have higher strength in the direction in which majority of the fibers are aligned, but will be relatively weak in the direction perpendicular to it (across the fibers). In areas where fibers are randomly oriented, the material will not achieve maximum strength and the material will exhibit isotropic behaviour. During injection molding process, the fibers in the plastic melt will orient in different directions under the influence of shear forces resulting from flow patterns. This will result in material properties being different at different locations of the part.