Crack propagation in shells due to impact against sharp objects

The present paper is concerned with the development of an effective finite element tool for the simulation of crack propagation in thin structures, induced by contact or impact against sharp objects. In particular the purpose is the refinement and further development of a recently proposed finite element approach for the simulation of the blade cutting of thin membranes [1]. Standard cohesive interface elements are not suited for the simulation of this type of cutting, dominated by the blade sharpness and by large failure opening of the cohesive interface. The new concept of \directional" cohesive element, to be placed at the interface between adjacent shell elements, where the cohesive forces can have different directions on the two sides of the crack whenever the cohesive region is crossed by the cutting blade, was introduced in [1] for elastic 4-node full-integration shell elements with dissipation localized inside the interface elements, in the framework of an explicit dynamics formulation. In the present paper the computational effciency of the proposed approach is investigated by considering applications to different test problems, modifying the shell element kinematics. Some considerations about a reduced integration solid-shell element are here reported; the interaction between this kind of element and directional cohesive elements is under study.