Abstract
The bulk tensile viscosity of large arrays of aligned, high-modulus, high aspect-ratio, rod-like, cylindrical fibers is a constitutive figure useful to composite manufacturers interested in exploiting the axial extensibility of ordered staple-reinforced laminar preforms. These preforms, when embedded in a highly viscous coupling fluid, form a hyper-concentrated suspension for which little applicable modeling has been accomplished. Shear coupling between long fibers during bulk axial extension was studied using a series of tests that employ mechanically driven rods embedded in a viscous Newtonian fluid (40,000 cps). The local fluid velocity field created by an axially translating fiber and this field's screening by adjacent fibers was studied by measuring viscous shear tractions. A momentum flux-capture theory previously applied to elastic solids was reformulated for creepingregime composite deformation. The effectiveness of momentum screening for 4-, 5- and 6-neighbor cells of shear-coupled rods was measured at three different effective volume fractions and compared with this theory. Results of this comparison suggest that even at low volume fractions of around 0.15, a cell-type linear superposition model may suffice for describing bulk properties based on local shear-coupling interactions. At structural volume fractions of near 0.60, the cell-model approach should permit accurate modeling of bulk tensile viscosity.