Cohesive Zone Modelling of a Mode I Crack in an Elastic-Plastic Sheet - Comparison of Different Fracture Mechanics Approaches for ..., 1999 International Paper Physics Conference Proceedings

Petri Mäkelä, Sören Östlund

Paper in general exhibits an anisotropic non-linear mechanical material behaviour. It is further observed that a narrow band of damage, characterised by fibre fractures and breaking of bonds, is formed ahead of a crack tip in a paper web containing a mode I crack. In this work, an elastic-plastic model with a softening cohesive zone formulation that accounts for the damage evolution ahead of the crack tip was suggested. The model was applied in a numerical study of copy paper strips containing centre cracks of varying sizes. A verifying experimental study of copy paper test pieces containing centre cracks was also performed. The results from the analyses were compared with the corresponding results from the experiments and with the results from three other in-plane fracture mechanics approaches frequently adopted for paper, i.e. linear elastic fracture mechanics, the J-integral method, and a linear elastic cohesive zone formulation. The comparison showed that a treatment of paper as a linear elastic material in general yields poor results in fracture mechanics analyses. Furthermore, the study showed that the J-integral method predicted accurate results for medium and large crack sizes. The suggested elastic-plastic cohesive zone approach, however, yielded close correspondence between the predictions and the experimental results, for all the crack sizes that were included in the investigation.