Stress Mode
Mechanical separation of laminated paperboard layers occurs when concentrated tensile forces act perpendicularly at the edge of a rigid adhesive joint. Instances of cleavage failure propagate crack fronts along weak fiber interfaces or un-cured glue lines rather than distributing load across the entire bonded area. Standard peel testing and wedge insertion metrics measure the force required to initiate this localized fracture mode.
The boundary of this mechanism excludes uniform shear loads and pure compression forces that do not generate peel moments at substrate boundaries.
Interfacial Fracture
Asymmetrical stiffness between bonded plies amplifies prying forces at free boundaries during folding or converting operations. High-modulus synthetic coatings joined to low-density recycled paperboards concentrate bending stress at the adhesive line. When severe scoring or acute angle formation takes place, the stiff outer layer leverages open edges away from the flexible core.
Fiber tearing occurs when adhesive bond strength exceeds the z-direction tensile strength of the paperboard matrix. Polymer adhesive formulation choices dictate whether failure occurs cohesively within the glue layer or adhesively at the board surface.
Structural Boundary
Localized stress concentrations shorten the service life of heavy cartons subjected to corner impacts or top loads. Creasing profiles adjusted for board thickness reduce tensile strain during box erection.
