Speaker
Description
Nonwovens are highly porous media, typically used in industrial applications to transport and absorb fluids and/or to insulate against heat and noise. Moreover, they should be mechanically stable, especially under high compression. In the current talk, Kimberly-Clark and Fraunhofer ITWM present their joint work on modelling the mechanical compression behavior of thin nonwoven and the impact on the resulting material properties.
The focus lies on thin nonwoven structures consisting of different fiber types. We generate virtual geometry models that possess the essential properties of a given reference medium. These properties comprise the caliper, the basis weight, fiber orientations and fiber composition. Furthermore, based on µCT images, the pore size distribution of the reference structure is determined. It turns out that the first virtual models have all desired properties except for the pore size distribution. The real medium shows larger pores. Hence, we established a two-step generation algorithm. First, a packing of spheres is created whose size distribution resembles the larger pores. In a second step, a non-overlapping fiber generator enters the desired fibers and, finally, deletes the spheres. By doing so, it is possible to validate the virtual medium against measured flow permeabilities.
Kimberly-Clark and Fraunhofer ITWM agreed on geometrical variations of the virtual reference medium to study the effects of changes in fiber diameters and fiber orientations. Moreover, based on this virtual models simulation studies of the mechanical compression behavior are performed. Of special interest is the impact of the number of bonding points between the fibers. In contrast to the number of fibers contained in the simulation box, the number of connection points between the fibers is not unique. Therefore, we present a procedure to compare the number of bond points in different structures.
The mechanical simulations are performed by ITWMs simulation tool FeelMath, which is also commercially available as the ElastoDict module in the software package GeoDict. This solver employs the Lippmann-Schwinger equations for elasticity in the Fourier space. Due to the voxel-based approach, large structures containing several thousands of highly resolved fibers and bonds are simulated. A further advantage of this method compared to Finite-Element approaches is the applicability to highly porous structures without the need of a mesh generation.
This effective approach allows for the numerical study of many virtual realizations, which are necessary to capture the variance of fiber networks with similar characteristics. In addition to the simulation of the mechanical effective stiffness of the nonwovens, the effective permeability is simulated and compared to experimental results.
| Time Block Preference | Time Block B (14:00-17:00 CET) |
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