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Article

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

[+] Author and Article Information
Lewis Thigpen

Department of Mechanical Engineering,  Howard University, 2300 Sixth Street NW, Washington, D.C. 20059thigpen@scs.howard.eduFellow ASME

Patrick T. Reardon

Material Science and Technology Division,  Los Alamos National Laboratory, P.O. Box 1663, MS P946, Los Alamos, NM 87545 reardon@lanl.govMember ASME

Jeremy W. Leggoe

Department of Chemical Engineering,  Texas Tech University, P.O. Box 43121, Lubbock, TX 79409-3121 Jeremy.Leggoe@ttu.edu

Alan L. Graham

Engineering Sciences and Applications Division,  Los Alamos National Laboratory, P.O. Box 1663, MS P946, Los Alamos, NM 87545 graham@lanl.gov

Mark Fitzgerald

Department of Mathematics,  University of Colorado at Denver, P.O. Box 173364, Campus Box 170, Denver, CO 80217-3364 fitz@carbon.cudenver.edu

J. Appl. Mech 72(3), 365-373 (Jul 20, 2004) (9 pages) doi:10.1115/1.1876396 History: Received March 11, 2003; Revised July 20, 2004

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.

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Copyright © 2005 by American Society of Mechanical Engineers
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Figures

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Figure 1

Secondary electron SEM micrograph illustrating typical web microstructure. The diamond-shaped dark regions are bond points, where fibers have fused together under temperature and pressure during calendaring.

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Figure 2

Gray scale TIFF image resulting from optically scanning a web sample

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Figure 3

Secondary electron SEM micrograph showing ruptured fibers in the vicinity of the nonwoven web fracture path

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Figure 4

Configuration and constraints for finite element models simulating tensile testing of heterogeneous nonwoven web specimens

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Figure 5

Schematic illustration of the geometry of a three-roller web transport model. The shaded rollers (1 and 2) are driven at a fixed angular velocities; the unshaded roller (3) is an idler. A tensile load of 20N is maintained at each end of the web to simulate line conditions.

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Figure 6

Tensile test results for 320×80mm “longitudinal” specimens, with load plotted in units of Newtons per meter specimen width

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Figure 7

Comparison of tensile responses of finite element models representing uniform and heterogeneous web specimens with experimental results obtained for “longitudinal” specimens

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Figure 8

(a) Plot showing contours of equivalent plastic strain at an applied displacement of 0.00625m (representing an overall applied strain of 0.02). (b) Plot showing contours of equivalent plastic strain at an applied displacement of 0.0112m (representing an overall applied strain of 0.035). Final necking of the web has initiated.

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Figure 9

Deformed mesh for a model representing a uniform web at an applied displacement of 0.0112 (representing an overall applied strain of 0.035). The web is constrained to zero lateral (x2) displacement at the ends to simulate being glued to loading plates. The shaded web illustrates the undeformed web path.

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Figure 10

Fracture path for a 320×80mm “longitudinal” specimen of the carded nonwoven. The irregular failure path is similar in form to that arising in the heterogeneous web model of Fig. 8.

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Figure 11

Deformation of a uniform web during transport through a three-roller system in which the idler roller (roller 3) is misaligned (model WEBHWD) after 1.0s of web motion. The shaded web illustrates the undeformed web path.

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Figure 12

Deformation of a spatially heterogeneous web during transport through a three-roller system in which the idler roller (roller 3) is misaligned after 0.8s of web motion, for a web having a mean density of 88.89kg∕m3 and standard deviation in element density of 9.31kg∕m3 (model WEBRWD1). The shaded web illustrates the undeformed web path.

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Figure 13

Deformation of a spatially heterogeneous web during transport through a three-roller system in which the idler roller (roller 3) is misaligned after 1.0s of web motion, for a web having a mean density of 112.27kg∕m3 and standard deviation in element density of 8.89kg∕m3 (model WEBRWD2). The shaded web illustrates the undeformed web path.

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