Computational Applied Mechanics

Modeling the anisotropic material response of paper accounting for damage progression coupled to plasticity

Anisotropy of paper in machine direction (MD), cross direction (CD) and thickness direction (ZD) as well as microscopic image of a torn paper

Paper is an multifunctional material and is therefore used in many areas of application. Mainly in the packaging industry it plays a major role, especially due to its recyclability and renewable raw materials. In particular, packaging manufacturers have a growing need for simulation tools that allow efficient structural calculation of cardboard packaging in order to predict durability and failure mechanisms.

The aim of the project is to investigate and simulate the damage mechanisms of paper, which are largely unknown so far. The difficulty in modeling lies in the fact that the macroscopic behavior of the material is predetermined by its intrinsic microstructure, which is a network consisting of interconnected fibers. On the macroscale, the elasto-plastic behavior of the individual fibers, the failure of individual fibers, and the possible debonding of fiber bonds lead on the one hand to elasto-plastic material behavior and on the other hand to the initiation and propagation of damage mechanisms. Due to the non-uniform distribution of the fibers, these phenomena must be considered as anisotropic. The damage behavior, which has not been understood so far, will be investigated by experimental tests to characterize the material behavior and modeling strategies for it will be developed. Overall, an anisotropic elasto-plastic material model for large deformations will therefore be developed, which will be extended by an anisotropic damage model after calibration based on experimental data. Furthermore, a novel cohesive zone formulation is constructed to describe delamination between individual layers of paper laminates. Finally, the material model is validated for forming processes relevant in practice.

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