A Novel “Fiber-Spacing” Model of Tensile Modulus Enhancement by Shortening Fibers to Sub-Millimeter in an Injection-Molded Glass Fiber Reinforced Polymer Bulk Molding Compound (GFRP-BMC)

Abstract

Up to now, increasing modulus of fiber reinforced polymers (FRPs) by shortening fibers has not been reported however, shortening fiber length from commercial 6.4 to 0.44mm by additional mixing of paste prior to injection molding was found to increase initial and maximum tensile modulus 5 to 25% in a 3-phase system of highly CaCO3 filled 20mass% E-glass fiber reinforced thermoset polyester/styrene-butadiene polymer bulk-molding compound (GFRP-BMC). The increased number of spaces between fibers appears to allow for action of coefficient of thermal expansion (CTE) difference between fibers and matrix to increase thermal compressive residual stress sites during shrink and cool-down. A novel “fiber-spacing” model incorporating the “rule of mixtures” is constructed based on physical meaning to predict effect of fiber length (lf), fiber volume fraction (Vf), filled-matrix modulus (Em) fiber modulus (Ef), and nominal fiber diameter (d), valid for fiber orientation parameter (0.43 < ©o < 0.54) on tensile modulus (d·/d¾)o to be useful in BMC composite design. The “fiber-spacing” model exhibited a good fit with the experimental data of 20mass% fiber composite and predictions were made for 10, 30, and 40mass% fiber composite agreeing with data in the literature. [doi:10.2320/matertrans.M2014070]