Balancing between fold crack resistance and stiffness - Part 1: modelling and simulation

This paper is a summary of computational research conducted to assess the relationship between fold crack resistance and bending stiffness in coated papers. The objective of the work was to suggest ways in which coated paper could be optimised to maximise fold crack resistance as well as bending stiffness, both of which are inversely related. Models were developed to calculate bending stiffness, predict the onset of failure and based on this prediction, calculate the residual load carrying capacity of coated paper composites. Optimisation of the coated paper composite was undertaken as a function of the number of coating layers used, the individual layer thickness and the mechanical properties of the coating layers in both tension and compression. Simulations were conducted for single, double and triple coated papers keeping the properties and dimensions of the base paper substrate constant throughout. The elastic moduli of the coatings were nonetheless varied independently, though failure stress values were kept constant in order to vary the strain to failure and the stiffness simultaneously. The optimal coating lay-up hypothesised herein is a triple coating comprising a thin, stiff inner coating layer, a thick, lowered stiffness middle coating and a thin, low stiffness outer coating.