Directional cohesive elements for blade cutting simulations of layered shells

摘要

The blade cutting of thin layered shell involves three small geometrical scales, the scaleudof layer thicknesses, the scale of blade radius of curvature, the scale of fracture anduddelamination process zones, which need be resolved when a numerical simulation is carriedudout by means of a finite element discretization.udLarge deformations, material nonlinearity, contact, crack propagation and delaminationudmake the problem highly nonlinear, so that an explicit dynamics approach based on the useudof solid-shell elements is adopted to avoid convergence problems. A selective mass scalingudtechnique [1,2] is developed to overcome the critical time step limitation, dictated by theudlayers thickness.udThe prescribed blade trajectory drives crack propagation, so that it is possible to adjustudthe mesh with element edges along the expected crack path. To model crack propagationudaccounting for the interaction between the sharp blade and the cohesive process zone,udspecial “directional cohesive elements” [3] are placed between separating element edges.udCrack propagation and delamination can be characterized by very small process zoneudsizes, depending on the type of material and on the layer thickness. Discretizations that areudcoarse with respect to these lengths may give rise to spurious oscillations and accuracyudloss. Techniques for the mitigation of these problems are investigated.udNumerical applications to engineering problems are used to assess the effectiveness ofudthe proposed simulation approach.