Damage and fracture propagationmodelling of thin packaging materiallayers : Experimental Characterization and Numerical Modelling of Damage and Fracture in Thin LDPE Films

Sammanfattning

Thin polymer used in packaging must balance flexibility with adequate resistance to damage and fracture, especially in areas without structural support. At the same time, they need to protect printed surfaces and prevent fluids from reaching the paper. This master’s thesis investigates the mechanical behavior and properties of low-density polyethylene (LDPE) and the subsequent damage initiation and fracture propagation through a combined experimental and numerical approach. The work is motivated by the need to optimize packaging material usage while maintaining mechanical performance, with a specific focus on simulating fracture behavior in thin polymer layers. An experimental test program included smooth (undamaged geometry) uniaxial tensile tests, Single Edge Notch Tension (SENT) tests, Double Edge Notch Tension (DENT) tests, and a trouser tear test. Smooth tensile tests were used to characterize the linear and non-linearmaterial response, while notched tests enabled the investigation of damage initiation, stable crack growth, and fracture energy under different stress states, due to controlled damage initiation and fracture path growth in a specific region. The Essential Work of Fracture (EWF) method was applied to DENT tests to extract a geometry‑independent fracture energy parameter governing damage evolution. A constitutive material model was defined and implemented in Abaqus/Explicit using shell elements under plane stress assumptions. Elastic-plastic behavior was assumed and calibratedusing experimental tensile data, while damage initiation was defined in terms of equivalent plastic strain and stress triaxiality. Damage evolution was governed by an energy‑based formulation with element deletion to simulate crack propagation. Special attention was given to numerical stability, mesh design, mass scaling, and quasi‑static loading conditions. The results show that uniaxial tensile tests alone are insufficient to describe fracture behavior in thin LDPE films, as damage initiation and crack propagation are highly sensitive to stress state and could not be measured in a controlled way using uniaxial test. A well‑defined relationship between fracture strain and stress triaxiality is essential to obtain physically realistic simulations (Fracture locus). The developed numerical framework successfully reproduces the global mechanical response and fracture behavior observed experimentally for both smooth and notched specimens. The study demonstrates that reliable fracture modelling of thin polymer films requires a combination of targeted experiments and informed modelling assumptions, providing a useful basis for future simulation of packaging components.