A Method to Determine the Effect of Microscale Heterogeneities on Macroscopic Web Mechanics

Abstract

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.