In-plane fracture of paperboard.
In order to prevent the occurrence of cracks in paper packages, the in-plane mechanical behavior for the full paperboard needs to be investigated. Further, it is of importance to understand also the in-plane behavior of the plies that build up the paperboard. In order to characterize the crack growth behavior, a normalized stress-widening model was developed, based on the minimum fracture energy, according to Tryding (2014). The model depends on the tensile strength, _t, and the maximum slope after peak stress in short-span tensile tests, Nmax. In this Master's thesis, it was investigated if the normalized stress-widening model is a true master curve, which describes the crack growth in full paperboards, and in their plies, respectively. To verify if the model is a true master curve, six paperboards from three di_erent suppliers were investigated. From short-span tensile tests, the properties needed for the stress-widening model were obtained.
The results indicate that the normalized stress-widening model is a true master curve, which also is valid for unloading. Furthermore, a linear relation between _t and Nmax was obtained, which means that the model might be reduced to be dependent of the tensile strength, _t, and a constant that will be de_ned empirically by the linear relation between _t and Nmax. All three-ply boards were based on sandwich construction theory, which was supported by the results, were two paperboards, Paperboard A and Paperboard C had signi_cantly larger tensile strength, in comparison to their density, than Paperboard D and Paperboard E, which indicates that Paperboard A and Paperboard C have better material distribution than Paperboard D and Paperboard E.
From the thesis, it can be concluded that, by performing short-span tensile tests, it is possible to normalize the post-peak stress behavior for paperboards into a master curve. Since all paperboards that have been investigated follow the master curve, it can be concluded that the fracture behavior can be characterized by the three parameters that a_ect the model, i.e. the tensile strength, _t, the maximum slope after peak stress, Nmax, and the tensile sti_ness, E.
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