Laboratory experiments and numerical simulations are performed to determine the accuracy and reproducibility of the falling-ball test for viscosity determination in Newtonian fluids. The results explore the wall and end effects of the containing cylinder and other possible sources that affect the accuracy and reproducibility of the falling ball tests. A formal error analysis of the falling-ball method, an evaluation of the relative merits of calibration and individual measurements, and an analysis of reproducibility in the falling-ball test are performed. Recommendations based on this study for improving both the accuracy and reproducibility of the falling-ball test are presented.

The effect of a spatially heterogeneous density distribution on the development of defects during the transport of nonwoven webs through roller systems has been investigated numerically. A modeling approach has been developed by which the spatial heterogeneity in web mechanical properties can be characterized statistically and recreated for use in finite element simulations. The approach has been applied to model the transport of a carded nonwoven web, consisting of an agglomeration of polypropylene fibers bound together by a regular array of thermal bond points. The web was scanned optically to obtain a gray scale light distribution representing the local material density. Analysis of the local density distribution permitted the generation of “virtual webs” for use in heterogeneous finite element models, in which local mechanical properties were governed by local density. Virtual web response was investigated under two loading configurations; simple tensile testing, and web transport under tension through a three-roller system. The modeling approach provided results that were in good agreement with experimentally observed web mechanics, failure mechanisms, and processing instabilities. Spatial heterogeneity in material properties was found to strongly influence both general web behavior and the tendency for the web to incur manufacturing defects during transport through roller systems.