Viscoelastic Creep Compliance and Interfacial Fracture Energy in Paperboard Laminates
Creep compliance dictates long-term carton deformation, while interfacial fracture energy governs delamination under score bending and pallet loads.
Mode Mixity
Fracture Tension
Multi-axial stress fields act on glue joints and laminated layers, causing cracks to propagate under combined peeling and shearing forces. The level of mode mixity describes the ratio of tensile opening to shear sliding that occurs along the fracture front. This parameter dictates how a paperboard laminate or glued carton seam will fail under complex loads.
Stress Ratio
Peeling forces pull the material apart perpendicular to the bond line, while shearing forces slide the layers parallel to each other. During the opening of a carton or the bending of a crease, the adhesive layer experiences a variable mode mixity that alters its apparent toughness. Fiber tear and adhesive failure modes are highly sensitive to this ratio.
This transition point affects whether the board tears cleanly or the glue separates.
Adhesive Failure
Durable adhesive bonds must withstand both peel and shear stress during mechanical handling. When mode mixity is dominated by shear forces, the bond resists failure much more effectively than under peel-dominated stress. Engineers measure these critical strain energy release rates across different load angles to map the failure envelope of the packaging material.
This characterisation helps in formulating hot-melt adhesives that resist sudden pops when filled cartons are dropped or stacked. Accurate mapping of this boundary reduces shipping damage across the supply chain.