Improved process stability in three-dimensional paper forming due to numerical modeling of the material inhomogeneity

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The aim of the research project is to improve the design and control of paper forming processes by taking into account the existing material inhomogeneity. To this end, the influence of the locally different properties on the macroscopic mechanical behavior of the material is to be investigated and numerically modeled. The applicants of TU Dresden (VM/VT) and TU Darmstadt (PtU) are cooperating on this project. They benefit from the complementary expertise, whereby they have focused on conventional (VM/VT) and active media-based (PtU) paper forming processes, so far. The applicants' approaches to numerical process mapping are based on micromechanical models (VM/VT) and the transfer of established models of metal forming to paper forming (PtU). The state of the art provides inconsistent information on the influence of locally inhomogeneously distributed material properties, such as density, on global mechanical properties. The work in the proposed project is intended to clarify which fluctuations in material properties have a significant influence on macroscopic behavior. For this purpose, different measurement methods such as formation measurement, digital image correlation and thermography are planned. These are integrated into classical material characterization methods such as the tensile test to observe the local mechanical behavior. When impressing different load scenarios, elastic and plastic strain components can also be separated from each other.The numerical modeling and parameterization of inhomogeneous material properties at element level represents the second part of the research project. The previously determined data is used and a numerical model is developed in three levels. In addition to the part that overlays the globally determined characteristic values with an inhomogeneous distribution at element level, a model for modeling delamination and damage (crack start) is developed. The three model levels are validated by comparison with example tests such as the tensile test and the bulge test. Finally, the model is integrated into three-dimensional, complete forming simulations to investigate the influence of material and process parameters on the forming result. The complementary experiences of the applicants from the fields of paper forming are used here. This makes it possible to derive specifications for forming-compatible paper production, robust process design and process control. Within the scope of this project, the question is clarified which property fluctuations in the material are responsible for the dispersion of the macroscopic characteristic values. Based on these results, numerical methods help to develop design guidelines for semi-finished products and paper forming processes.