Continuum modeling of the mechanical properties of paperboard

Sammanfattning: Continuum based elasto-plastic models for paperboard have been established in the work herein. The thesis begins with an introductory section that describes some of the background of the problem and gives some more motivation for the modeling choices made in the appended papers. Some preliminary simulation results on the folding operation is also provided. The main part of the thesis consists of the two papers, A and B. The thermodynamical framework is established in Paper A and a model for the in-plane response is developed. The anisotropy is handled by introducing a set of director vectors directed in-plane and evolves together with the continuum. A yield surface with several internal variables is introduced, which hardens distortionally in the stress space. The effects of pre-straining a sample in e.g. first MD and then subsequently load the sample in CD is studied. The model is compared to measurements obtained with Digital Image Correlation. In Paper B, the weak out-of-plane properties is included in the model. A normal vector is utilized for the preferred direction in ZD. An expression for the plastic spin is determined, which is used to control the direction of the plastic flow. Simulations are performed on the line crease setup and compared to experimental measurments and the industrial rotation crease setup is studied in detail using the developed model.