Characterization of paperboard for creasing and folding

To form a package with desired properties, paperboard is creased and folded. Creasing creates delamination cracks which during folding cause the plies to buckle and form a permanent corner. The delamination cracks facilitate folding but reduce the load-bearing capacity of the packaging. The processes must therefore be controlled. The result is affected both by the constituent material properties and by the actual creasing and folding processes. A good understanding of these processes create opportunities to resource-efficiently create packaging that meets high standards. Evaluation and development of processes and paperboard is facilitated by models and simulation with correct material properties. Material data for delamination have been difficult to obtain because the test methods are often unstable. In recent years, we have developed a new experimental method for paperboard. The results look promising but some critical properties are not fully captured. This leads to the question: What mechanical properties of paperboard are lacking in the current models to better capture the creasing and folding processes in simulations?

In this project, we will investigate two factors that probably have a substantial influence:

1) Effects of in-plane stresses in the paperboard. During creasing, the paperboard is exposed to combined tensile and shear loading. How the loads interact and how this affects subsequent folding is currently unknown;

2) Volume increase of the paperboard during delamination. From previous studies of cracking in other materials under shear load, volume increase has been observed.