Discrete Element Method to Model Tension and Bending for Single Layer 3-Dimension Systems with Bimodal and Pseudo-Full Particle Size Distributions of Spherical Particles

The mechanical properties of paper coating layers are important in converting operations such as calendering, printing and, folding. While a number of experimental and theoretical studies have advanced our knowledge of these systems, a good particle level understanding of issues like crack-at-the-fold are lacking. In this paper, the three-dimensional version of the discrete element method (DEM) model of Varney et al. (2019) has been modified. The particles used in the model have been expanded from the standard monodisperse packing of spherical particles to bimodal distributions of spherical particles and also to pseudo-full particle size distributions of spherical particles. In making this upgrade to the model, the impact of particle size distribution on the mechanical properties of the coating layer could be studied. Simulations were run for both in-line tension and for three-point bending of single coating layer systems. As with past models, inputs to the 3D version include properties of the pure binder film and the binder concentration. The model predicts crack formation as a function of these parameters and can also calculate the modulus, the maximum stress, and the strain-at-failure. The simulation results were compared to the work of Zhu et al. (2014) and of Hashemi-Najafi et al. (2018). Reasonable predictions were obtained for both tensile and bending for a range of latex-starch ratios and at various pigment concentrations. In addition, the model predicted the correct trends and order of magnitude relative to the experimental data.