Analytical Discipline
Analysis of multi-layer structures such as coated paperboards or laminated packaging foils focuses on the initiation and propagation of cracks along the boundary between dissimilar materials. The framework of interfacial fracture mechanics provides the mathematical tools to evaluate these crack-tip behaviors under various loading modes. It focuses on the energy required to separate the bonded layers rather than the stress levels alone.
This approach assumes that a pre-existing flaw or defect lies along the boundary between the substrate and the coating. This method enables packaging engineers to predict the risk of laminate peel under high-stress processing conditions.
Energy Release
Calculation of the crack driving force utilizes the energy release rate, which is the change in potential energy per unit of new crack area. If this rate exceeds the critical energy release rate of the interface, the crack will propagate unstably. This energy threshold depends on the adhesive properties and the thickness of the joined layers.
It dictates whether the layers will stay together during die-cutting.
Delamination Resistance
Experimental testing often employs peel tests or double cantilever beam tests to measure the toughness of the interface. This measurement defines the resistance of the laminated structure to peeling and separation. It helps converting operations select the correct surface treatments for plastic films before gluing them to paperboard.
The test cycle concludes when the layers are completely parted.
