Numerical and experimental investigation of paperboard creasing and folding

Abstract:  This licentiate thesis aims to increase the understanding of deformation and damage mechanisms of paperboard during converting, especially creasing and folding will be analyzed. A simple two dimensional creasing simulation was performed. In this model, paperboard was modeled as a combination of an anisotropic elastic-plastic continuum model with isotropic hardening and a softening cohesive interface model. The paperboard was composed of four plies with uniform material parameters. Creasing simulations were done on both machine direction (MD) and cross machine direction (CD) samples to two crease depths 0.0 mm and 0.2 mm, respectively. The simulation results showed good agreement with experimental results. The out-of-plane shear properties are dominating factors for creasing and folding. Therefore, a test method to determine shear properties was proposed. This part of the work is based on the most recently proposed test method, the laminated double notch shear test. To improve the technique, double notches with declined slopes, called tilted double notch shear test, were used instead of uniform depth double notches. The influence of shear zone length was also investigated. The results reveal the short shear zone lengths gave higher shear strength and more pronounced shear strength profile. The results from the rst two analyses were utilized to study folding of paperboard. The simulation model was the same as in the creasing simulations. However, to improve the model and better account the actual micro structure of paperboard a new material mapping method was proposed. The continuum properties of the plies were assumed to vary in the thickness direction. The shear strengths of the interfaces were determined by using the tilted double notch shear test using a short shear zone length, L= 5 mm. The agreement between simulation results and experiment results was good, and most of the folding properties were captured.