Experimental Characterization of Orientation Formation in a Mold Cavity with Sudden Contraction

Orientation formation of short fibers suspended in a flow through a planar mold cavity is experimentally analyzed. The suspension of corn syrup mixed with short fibers is injected into the mold at constant flow rate through a narrow, planar inlet gate. The mold cavity contains a sudden expansion following the inlet gate, and a three-to-one sudden contraction downstream. Orientation data are obtained using computerized image analysis on photographs of thirteen zones of interest near the sudden contraction. The photographs are taken through the transparent top mold wall, thus collecting average planar orientation data through the mold thickness. Orientation distribution histograms are generated from the individual fiber orientations to graphically depict orientation microstructure. These histograms reveal bimodal fiber orientations in nearly all zones of interest. Experiments performed at different volume flow rates and viscosities also confirmed the bimodal orientation distribution observed through the top mold wall. Orientation results are observed to be more random compared to those predicted using Jeffery's theory (He et al., 1997). Fiber size or wall effects may contribute to the formation of a more random orientation field.