Plasticity in the thickness direction of paperboard under combined shear and normal loading

Creasing and offset printing are both examples of paperboard converting ope rations where the stress state is multiaxial. and where elastic-plastic def ormation occurs in the thickness direction. Optimization of paperboard for such operations requires both advanced modeling and a better understanding of the mechanical behavior of the material. Today, our understanding and mo deling of the our-of-plane properties are nor as well established as our kn owledge of the in-plane behavior. In order to bridge this gap, a modificati on of the Arcan device, which is well known in other fields, was developed for the experimental characterization of the out-of-plane mechanical behavi or of paperboard. A fixture attached to the Arcan device was used to contro l the deformation in the test piece during loading. The test piece was glue d to the device with a high viscosity adhesive and left stress-free during curing to achieve an initial state free of stresses, The apparatus proved t o work well and to produce reliable results. Measurements of the mechanical behavior in combined normal and shear loading generated data points for th e determination of the yield surface in the stress space. The elastic-plast ic behavior in the thickness direction of paperboard was modeled assuming s mall-strain orthotropic linear elasticity and a quadratic yield function. S imulations using this yield function and an associative flow law showed goo d agreement with the rest results.