Predicting Delamination Behaviour in Multi Layer Paperboard Creasing
Predicting paperboard delamination requires balancing Z-direction shear strength to permit core separation while preventing outer liner tensile fracture.
Mode II Fracture Energy
Shear Resistance
Strain energy release rate required to propagate an in-plane shear or sliding crack through the fiber matrix of a paperboard sheet governs the resistance of the material to delamination under bending loads. This mode ii fracture energy determines how well the individual plies of a multi-ply board hold together when subjected to severe folding or scoring. If this energy threshold is too low, the plies will slide and separate easily, reducing the structural stiffness of the folded carton.
Internal Shear
Bending a multi-ply board induces high shear stresses along the central plane of the sheet, where the fiber-to-fiber bonds are most vulnerable to sliding failure. Enhancing the mode ii fracture energy in this zone prevents premature failure of the board during the converting process. Papermakers control this by adjusting the refining of the fibers in the inner plies or by applying specialty bonding agents between the layers.
This treatment allows the sheet to absorb the intense shear strains generated during high-speed folding on automated packaging lines.
Failure Prevention
Low fracture energy in shear leads to bulging cartons and weak corners that cannot support vertical stacking loads. Ensuring a high shear resistance in the board grade is therefore necessary for maintaining carton stability throughout the transport and retail display cycles.