Abstract
The Modified Rule of Mixtures has been verified to effectively predict the axial tensile strength of glass fiber reinforced injection molding compounds (IMC). Nylon, polypropylene, and polybutylene terephthalate (PBT) resins were molded with commercially available chopped strand fiberglass for parametric studies. The parameters which influence IMC strength were identified and test methods were developed for param eter measurements. The parameters included in the model are the fiber and resin strengths, their respective volume fractions, fiber orientation coefficient, fiber critical length, aver age fiber length, and a bonding efficiency factor. The fiber volume fraction and the fiber orientation were found to play a predominant role in controlling IMC strength. Even though the fiber critical length and average fiber length both varied between resin systems, the critical length ratio essentially remained constant. The Modified Rule of Mixtures showed a difference of under 2 % between the predicted and experimental values for nylon and PBT. A 15% difference between the predicted and experimental values was detected for polypropylene, which could be accounted for by poorer interfacial bonding and a higher void content. An efficiency factor was introduced into the equation to take these problems into account.
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