Mechanical Characterization and Simulations of Laminated Pressboard.

Sammanfattning: Pressboard is a cellulose-based material, which is used in transformers as insulation as well as for providing structural support. The micro-structure of pressboard consists of networks of cellulose fibers, which has good mechanical properties as well as exceptional electrical insulation properties. Paper materials, such as pressboard, have anisotropic material properties due to events in the manufacturing process. Pressboard has been investigated earlier, but here laminated pressboard is studied. The objective of this study was to characterize the mechanical properties by means of experimental characterization and finite element simulations. The mechanical responses of laminated pressboard were studied under three- and four-pointbending (flexure) tests. In addition to the flexure tests, shear tests were performed on samples with asymmetric double notches under uniaxial tension. The objective of these tests was to calibrate model parameters related to through-thickness shear deformation. The finite element simulations of the shear tests captured the initial behavior of the experiments. At increasing strain levels there was a discrepancy between the experimental results and the results from the simulations. This can be explained by the evolution of damage in the material under the experiments and damage was not included in the present model. The simulations of the bending tests had a weaker response compared to the experiments for both three- and four-point bending. This could be explained by the penetration of glue into the pressboard, which makes the overall response of the laminated material stiffer.