Directional Cohesive Elements for the Simulation of Blade Cutting of Thin Shells

This paper is concerned with the finite element simulation of a thin membrane cutting by a sharp blade. Smeared crack finite element approaches appear to be unsuitable for this purpose, since very small elements would be required to conform to the sharp edge of the cutter. Furthermore, when the membrane material is very ductile, classical interface cohesive elements, where the cohesive forces are transmitted in the direction of the crack opening displacement, cannot correctly reproduce situations where the blade crosses the process zone. A simplified approach, based on the new concept of “directional" cohesive elements, is here proposed for a computationally effective simulation of this type of problems. Whenever a crack is opening, cohesive “cable" elements are introduced between the separating nodes. These elements are geometric entities which can be monitored throughout the analysis to detect possible contact with the blade. When this happens, the cables transmit in a straightforward way cohesive forces to the crack flanks in different directions. The procedure has been tested against a real cutting process providing encouraging results with relatively coarse meshes. The calibration of the material properties of the cohesive cables is also briefly discussed.