In-plane fracture analysis of paperboard using x-ray tomography

Abstract: In this Master's Thesis x-ray tomography was used during tensile experiments on paperboard to study delamination and cohesive failure. Digital volume correlation of the x-ray tomograph images enabled quantitative analysis of strain fields. Tensile experiments on different specimen geometries were also conducted to investigate how the geometry affected the response of the specimens during loading. By analysing the size effects and by using normalisation it was found that the behaviour of the material during tensile experiments was independent of the geometry. Using x-ray tomography images, a thickness increase was measured, all the way from loading start to sample failure. It was found that right before the failure strength, the material experienced a higher dilation compared to during the rest of the experiment. It was further found, using digital volume correlation, that the normal strains in the loading direction localised in parabolic zones with higher strains between the notches in the test sample. From the shear strain fields it was also noted that in close proximity to the failure strength, shear strains increased. The thickness increase right before failure was probably caused by delamination of the paperboard. However, even though delamination results in dilation of the sample it was proven, by performing tensile tests on pre-delaminated samples, that it does not affect the cohesive failure. This means that delamination does not cause in-plane failure. From the analysis it was instead observed that the in-plane failure occurs at the zones with higher strains in the loading direction. During this Master's Thesis it was found that the combination of x-ray tomography and digital volume correlation is effective to gain more information about the internal structure and deformation of paperboard.