RHEOLOGICAL PROPERTIES AND FIBER ORIENTATIONS OF SHORT-FIBER-REINFORCED PLASTICS

The effect of fiber orientation on the rheological properties of short glass fiber-reinforced composites was investigated by dynamic oscilla tory shearing with parallel plate fixtures. As an oscillatory shear am plitude and frequency applied to fiber-reinforced composites increased , more fibers in the composites were aligned in the flow direction, th us the complex viscosity gradually decreased. This phenomenon was conf irmed by observing the fiber orientations using optical photographs. T he complex viscosity depended upon the strain amplitude, and pre-oscil latory shearing frequency, and shearing time. Experimental results for fiber orientations and complex viscosity were compared with predictio ns available at the present time. The predictions of the dependence of fiber orientation upon strain amplitudes and fiber volume fractions a re in qualitative agreement with experimental data. However, there wer e effects of the magnitude of frequency and oscillatory shearing time on fiber orientation, thus complex viscosity could not be predicted su ccessfully although these effects were clearly demonstrated by the exp eriment. (C) 1997 The Society of Rheology.