A compressible plasticity model for pulp fibers under transverse load

Abstract

In the progress of understanding the mechanical behavior of pulp fibers, advanced material models have to be developed alongside experimental investigations. The transverse behavior of pulp fibers is tested by atomic force microscopy (AFM)-based nanoindentation experiments to record both, the volume reduction and the force-displacement curve. Our measurements clearly indicate a compressible plastic behavior in conjunction with a highly nonlinear elastic behavior, both which are attributed to the nanoporous structure of pulp fibers. We therefore advocate a numerical model based on a compressible plastic model combined with a hyper-foam model. Our evaluation yields three key findings for the transverse behavior of pulp fibers: first, the compression behavior is dominated by plastic deformation and nonlinear elasticity, in agreement with the experimental indentation results; second, we found evidence that a compressible plasticity model is justified, with an estimated Poisson's ratio of 0.23; and third, a good agreement of our numerical model with out-of-plane compaction experiments from the literature for a sheet of paper was achieved.