ECCOMAS 2024

The Phase-Field Modeling of Fracture Evolution in Ductile Materials with Application to Paperboard Mechanics

  • Marengo, Alessandro (Tetra Pak)

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Paperboard is a widely employed material in the food package industry with the purpose of providing the mechanical properties to the final package. The yearly production of such packages amounts at several hundred billion units. This number motivates the intense research activity aimed at waste reduction. The current work aims at extending the state-of-the-art modeling of paperboard material, currently limited to the elastoplastic regime, to describe the onset of damage and crack evolution using the phase-field approach to fracture mechanics. Starting from established variational statements of finite-step elastoplasticity for generalized standard materials, a variational formulation is consistently derived, incorporating a rigorous finite-step update for both the elastoplastic and the phase-field dissipations. The interaction between ductile and brittle dissipation mechanisms is modeled by assuming a plasticity-driven crack evolution. A non-variational function of the plastic deformation is then introduced to modulate the fracture dissipation based on the developed plastic strains. At small strains, a gradient-extended plasticity framework has been proposed to prevent the mesh-dependence due to the softening response. Specific care has been devoted to the algorithmic aspects of gradient plasticity (e.g., the consistent Newton-Raphson scheme with a global return mapping and line-search). The resulting solution procedure has demonstrated to be robust and computationally effective. The ductile fracture model has been then extended to orthotropic materials, being ductility and orthotropy the fundamental features of the paperboard mechanical response. The resulting orthotropic ductile fracture framework, based on the state-of-the-art elastoplastic in-plane model, has been applied to simulate physical experimental tests on paperboard samples until failure, with excellent results in terms of accuracy and scale independence.