Transverse mechanical properties of unidirectional hybrid fiber composites

Much experimental characterization and theoretical modeling on the mechanical properties of hybrid fiber composites in the fiber direction can be found in the literature. For the direction transverse to the fibers, theoretical models for the elastic properties of hybrid composites are available, but no experimental data could be found by the authors. Therefore, the objectives of the current investigation are to manufacture unidirectional carbon and E-glass hybrid fiber composites of various fiber proportions by a filament winding process, to characterize the elastic modulus and flexural strength of beam specimens tested transversely to the fibers, and to evaluate several analytical models for the transverse elastic modulus. The nominal compositions tested included 100% carbon, 75% carbon and 25% glass, 50% carbon and 50% glass with two differently shaped regions of carbon and glass fiber, 25% carbon and 75% glass, and 100% glass. The modulus increased monotonically with an increasing glass-to-carbon ratio. The tension-governed flexural strength was higher in the all-glass composite than the allcarbon composite, but the hybrids all had nearly the same strength halfway between the non-hybrids. A modified iso-stress model had the best correlation with the experimental modulus data and a modified Halpin Tsai model was second best. The conventional iso-stress model consistently under-predicted the experimental moduli, as expected for a lower bound model.