Stress analysis of wedged rupture in surface layer of coated paperboard

This paper reports on deformation behavior of coated paperboard and the breaking stress in a surface layer during indentation with a trapezoidal center bevel cutter. The indentation was observed experimentally in the initial compression stage. By reviewing the compressive testing of paperboards in the thickness direction, an equivalent elastic deformation model was analyzed numerically without any cracks or fracture by using the finite element method analysis, by considering the orthotropic elasticity and the strain dependency. Through this simulation, it has been revealed that the out-of-plane modulus is a primary factor to characterize the load response of the cutter indentation when the tip thickness ww of the blade is sufficiently larger than 2% of the paperboard thickness t, while the in-plane tensile stress is a primary factor of the surface rupture at the first peak point. Regarding the surface layer breaking, it has been found that the in-plane mechanical strength should be considered and the pressure concentration at the edge of the trapezoidal blade tip can be explained by the suspension effect of the paperboard's surface layer. The proposed numerical analysis model, in which the orthotropic elasticity and the out-of-plane strain dependency are considered, enables to estimate the cutting resistance at the initial compression stage and also evaluate the breaking stress at the first peak point.