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.
Elastic Plastic Fracture Mechanics
Material Characterisation
Non-linear structural analysis methods evaluate the crack resistance and tough tear behaviour of fibrous sheets that undergo permanent deformation before failing. The framework of elastic plastic fracture mechanics provides the mathematical tools to describe this behaviour in paperboard and polymer-coated paper packaging. Traditional linear models fail to capture the energy dissipation of these highly ductile materials.
Yield Behaviour
Stress concentration around a notch or pre-existing defect triggers localized plastic yielding rather than immediate brittle fracture. In paperboard, this yielding involves micro-delamination and fibre pull-out, which absorb substantial energy during folding and converting. The elastic plastic fracture mechanics methodology uses parameters like the J-integral to measure the energy required to grow a crack through this active process zone.
Failure Prediction
Predictive accuracy in carton performance depends on capturing these elastic and inelastic material responses. During the scoring and bending of heavy paperboard, the material must deform without tearing along the outer creases. Designers use the fracture toughness values derived from this approach to simulate the creasing process and optimise carton geometry for high-speed filling lines.
This prevents spontaneous structural failures in boxes when they are stacked under humid conditions. Refining these simulations helps converters select lighter board grades without compromising the load capacity of the final package. It ensures that the structural integrity of the paperboard remains intact during transport.