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.
Transverse Shear Strain
Shear Angle
Relative sliding displacement between the parallel fiber planes of a paperboard sheet across its thickness under a bending load defines the intensity of the shear stress acting on the internal bond of the material. This transverse shear strain is a primary driver of ply delamination in heavy multi-ply cartonboard during folding operations. Measuring this strain allows engineers to predict where the internal fiber bonds of the board are most likely to fail under load.
Ply Delamination
When a thick paperboard sheet is folded or creased, the high bending force creates a gradient of shear stress that reaches its maximum at the neutral axis of the sheet. If this transverse shear strain exceeds the elastic limit of the fiber matrix, the fiber-to-fiber bonds within the core layer will rupture. This localized failure is necessary for forming a clean crease but must be controlled to prevent the cracks from propagating into the outer surface plies of the board.
Stacking Stability
Uncontrolled shear straining during transit causes carton panels to bow outward under the weight of upper boxes. Specifying paperboard with high resistance to shear strain ensures that the final packaging maintains its shape and stackability throughout the logistics chain.