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Effect of Fiber Orientation Anisotropies on the Structural Performance of Molded FRP Composite Parts

This paper focuses on the effects of fiber orientation anisotropies on the structural performance of FRP composite parts. The most important factors to consider when predicting fiber orientation are gate and initial charge location, as well as, part geometry. The structural performance of the part is greatly affected by the amount of fiber orientation. Taking an automotive headlamp housing and a truck front bumper as examples, this paper presents the structural effect that gate and charge location, as well as, choice of injection and/or compression molding have on performance of the final part. First a mold filling computer simulation is performed for each case. Then fiber orientation is computed and used to model the structural performance of the part under load. Results are compared to structural performance modeled without taking in consideration fiber orientation. The paper shows up to 100% difference on the final stress when fiber orientation is taken into account. These results demonstrate the importance of considering fiber orientation when modeling structural performance to design better FRP composite parts.

The increase use of composites in the automotive, electrical, aerospace, marine and household goods industries is predicted to increase for many years to come. This is mainly due to the excellent strength-to-weight ratios, damping characteristics, corrosion resistance and design freedom for sleek looking parts that composites have to offer.

Composite parts typically contain fibers that are made out of glass, carbon, and wood, among many others, which act as a reinforcement and increase mechanical properties. There is some freedom when choosing the polymeric-based matrix. Common thermoset matrices are phenolic, epoxies, polyesters or vinyl esters. Thermoplastic composites can be made from even a larger selection of resins, such as, polypropylene, nylon, and high density polyethylene, to name a few.

Fiber reinforcement is generally used to improve mechanical properties of the final part. However designing and molding composite parts offer some challenges and disadvantages. These disadvantages, when known and controlled, can be turn into advantages. When molding composite parts fibers will tend to orient in different directions. This orientation improves mechanical properties in the fiber direction while diminishing in the transverse direction. If fiber orientation can be predicted, and thus controlled, the designer can optimize the geometry and process to produce a lighter weight and lower cost product.

Current technologies permit fiber orientation to be predicted with molding simulation software [1-3]. This same software can be used for optimizing molding conditions to improve fiber orientation to strengthen the part. Combining the results of fiber orientation with structural analysis the molding process can be modified to adapt fiber orientation to strengthen the part in critical structural areas. Furthermore, location of ribs and thicker sections can be optimized to reduce weight, cost and improve performance of the part.

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Antoine Rios, Ph.D.

Dr. Rios is a Senior Managing Engineer and Partner at The Madison Group. Dr. Rios received his Ph.D. from the Polymer Engineering Center at the University of Wisconsin – Madison and he also holds an MBA from Edgewood College, Madison, Wisconsin. He specializes in forensic analysis, plastics part design, computer aided engineering (CAE), as well as failure analysis. His sound technical expertise has been called upon numerous times in a variety of litigations.