Normal Stress Differences in Suspensions of Rigid Fibers

Measurements and simulations of normal stress differences are reported for suspensions of rigid, non-Brownian fibers over a range of concentrations and aspect ratios.  For the experiments, the deformation of the interface in two free surface flows is measured and related to the the first and second normal stress differences.  The free surface deformation in a tilted trough gives the second normal stress difference and the surface deformation in the rotating rod, or Weissenberg geometry, gives a linear combination of the first and second normal stress differences.  The results are compared with normal stress differences calculated from simulations and are found to be in agreement.  The second normal stress difference is negative and the magnitude increases as the concentration is raised and the aspect ratio is lowered. The first normal stress difference is positive and the magnitude is approximately twice that of the second normal stress difference.  Comparison of the measurements with other, published results indicate a strong dependence of the stresses on confinement; stresses calculated from the simulations likewise indicate a dependence on confinement.