Blade cutting of thin walled structures by explicit dynamics finite elements

In cohesive crack propagation induced by blade cutting, it is necessary to consider the blade radius of curvature as a characteristic length additional to the shell thickness and to the cohesive process zone length, which usually characterize crack propagation in thin walled structures. When the finite element simulation of a blade cutting process is considered, these three lengths need to be properly resolved. The blade radius of curvature can be orders of magnitude smaller than the shell thickness and the cohesive process zone. Furthermore, the transition from a continuous mesh to a mesh containing a crack with a cohesive interface is well known to be critical for solution accuracy. Nodal equilibrium is in general violated during the transition, with subsequent generation of spurious stress oscillations that, in view of the non-reversible nature of the problem, can lead to significant inaccuracies in the stress response. The smallest length, i.e. the blade radius of curvature, is here resolved using the so called directional cohesive element model as in Pagani and Perego (CMAME 285:515–541, 2015), while the structural thickness is modeled using solid-shell elements. The concept of directional cohesive elements is here extended for application to the case of cutting by scissors. As for the cohesive process zone length, different modeling options are discussed in terms of their capability to reduce the spurious oscillations and to provide an accurate estimate of the cutting parameters. Numerical tests are presented to validate the proposed modeling strategies. © 2017, Springer Science+Business Media B.V.