Although paper seems to be homogeneous to the human eye, an X-ray tomography (picture 1) reveals, that it has a fibrous structure on the microscale. To perform simulation of paper microstructure to predict paperboard properties represents a new approach to product and process development in paper industry.

To this aim we together with scientists from Albany International, Eka Chemicals, Stora Enso, Tetra Pak and Fraunhofer-Chalmers Centre (FCC) started the development of a new modular software ISOP based on enhancements of existing software packages. First, we extended GeoDict by a paper microstructure model (PaperGeo) which analytically describes the geometry of the fiber network. Secondly, we integrated beam models to simulate fiber deformations and sophisticated algorithms for the contact detection of huge fiber networks to the FEM elasticity solver FeelMath. The next step will be the combination of these tools with the FCC flow solver IBOFlow by the end of 2011, using the in parallel developed ISOP-interface. Then it will be possible to analyze and optimize the process of paper manufacturing as well as quality control with respect to paper composition. Due to the abstract approach, this technology can be also applied to any other fibrous products like textiles and nonwovens.

The first structural mechanical quality control that was simulated within the project is the bending resistance, described in detail by the Scandinavian pulp, paper and board testing committee (SCAN-P 29:95). To be more precise, the bending resistance of a paperboard is calculated in two steps: First, a stochastic geometry-model of the microstructure is generated with PaperGeo using parameters of the cellulose fiber (density, length distribution) and of the papermaking process (grammage, thickness of the paperboard). Secondly, with FeelMath the contacts between the cellulose fibers are detected and properly modeled. Afterwards, homogenization of the fiber geometry yields the tensile stiffness of the paperboard. This is used to calculate the bending resistance on a macroscopic level. Each step of this procedure has been validated by extensive measurements of the industrial partners.

The Fraunhofer ITWM developed advanced beam models to simulate the production of non-wovens (FIDYST - Fiber Dynamics Simulation Tool), fiber networks and together with FCC the structural dynamics of cables (IPS Cable Simulation).