Laminated paperboard is one of the most common packaging materials in industry. Its relatively low price, sustainability and straightforward manufacturing process make it an attractive packaging material. This material exhibits a highly anisotropic mechanical behavior due to its manufacturing process. Its elastic as well as its inelastic properties, such as initial yield point, strain hardening, and tensile failure, become direction dependent. To obtain an accurate prediction of paperboard packaging, it is essential to perform studies on two aspects, namely the paper sheet anisotropic behavior and the interface delamination between different layers. The aim of this study is to describe the anisotropic behavior of the paper sheet with an orthotropic elastic-plastic model and characterize the interface fracture behavior with a cohesive zone model. Paper is in general composed of a bonded fiber network. It is well known that the macroscopic mechanical properties of composites can be strongly influenced by the spatial distribution of the fiber orientation. In order to evaluate this influence, a microsphere-based homogenization approach was proposed, in which the passage from microstructural contributions to the macroscopic response was obtained by integration over the surface of a unit microsphere. The results illustrated the effects of the degree of fiber misalignment on the predicted overall properties.In order to further investigate the nonlinear anisotropic behavior of paper, a structural tensor-based approach was applied to model the elastic deformation, while a multi-surface based yield criterion was adopted to describe the yield behavior. The model incorporated nonlinear kinematic and isotropic hardening to capture the anisotropic hardening effect. In the experiment, the compressive yield stress was found to be insensitive to the previous tensile deformation. With the material parameters calibrated from a set of simple uniaxial tests in various directions, the model was shown to predict the stress-strain behavior for other orientations satisfactorily. The model was further validated with a punch test and found to capture the highly anisotropic, elastic-plastic behavior accurately.In order to experimentally and numerically investigate the interface fracture behavior in pure opening mode (mode I) and sliding mode (mode II), four experimental tests have been evaluated and compared to the numerical simulation, namely, the z-directional tensile test (ZDT), double-notch shear test (DNS), double-cantilever beam test (DCB) and end-notched flexure test (ENF). It was shown that, for the paperboard specimens tested, the ZDT test was sufficient to fully characterize the mode I crack growth response. However, the DNS and ENF tests were required to determine the maximum shear stress and the fracture toughness of pure mode II, respectively. The further mixed-mode investigation would enable the analysis of paperboard delamination behavior during the creasing and folding process.
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