Balancing between Fold-crack Resistance and Stiffness

Abstract

This article is a summary of computational research conducted to assess the relationship between fold-crack resistance and bending stiffness in coated papers. Though this article is based on theoretical research, an experimental pilot coating program was undertaken in conjunction with the modeling. The objective of the computational work was to suggest ways in which coated paper could be optimized to maximize fold-crack resistance as well as bending stiffness, both of which are inversely related. Models were developed to calculate the bending stiffness, to predict the onset of failure, and based on this prediction, to calculate the residual load-carrying capacity of coated paper composites. Optimization of the coated paper composite was taken as a function of the number of coating layers used, the individual layer thickness, and the mechanical properties of the coating layers during 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. But the elastic moduli of the coatings were varied independently, though failure stress values were kept constant in order to vary the strain to failure stress and stiffness simultaneously. The optimal coating lay-up as per the hypothesis was a triple coating comprising of a thin, stiff inner coating layer; a thick, low-stiffness middle coating; and a thin, low-stiffness outer coating. The hypothesis was confirmed by the pilot coating trials.