Fiber orientation prediction in nylon-6 glass fiber composites using transient rheology and 3-dimensional x-ray computed tomography

In an attempt to relate transient rheology to 3-dimensional fiber orientation, experimental testing on compression molded Nylon-6 (PA-6) containing 30% by weight short glass fibers (PA6-30GF) and unfilled PA-6 were carried out. On applying steady shear, PA6-30GF samples displayed a transient viscosity overshoot while unfilled PA-6 did not. The overshoot behavior has been attributed to the reorientation of fibers from an initial orientation to a steady state orientation. Samples subjected to different shear strain units were obtained from the rheometer by rapid cooling for morphological analysis. X-ray Computed Tomography (X-CT) was used to image samples to obtain 3-dimensional fiber orientation and fiber concentration data. As the applied strain was increased, the second-order orientation tensor was found to increase in the shearing direction and reduce in the radial and thickness directions. Experimental fiber orientation evolution data were compared with simulations from the Reduced Strain Closure (RSC) orientation model which is based on Folgar-Tucker's orientation model. The interaction coefficient (C-i) and scalar reduction factor (K) which are parameters in the RSC model were fit using the experimental data. Currently available empirical expressions for determining the value of C-i were used to compare the experimental values. The experimental and predicted C-i values showed reasonable agreement which provided validation for the use of X-CT as an experimental technique to determine fiber orientation distribution. The added benefit of obtaining fiber concentration data from X-CT provides the opportunity to investigate the combined effects of fiber orientation and fiber concentration on transient rheological behavior of composites. POLYM. COMPOS., 40:E392-E398, 2019. (c) 2018 Society of Plastics Engineers