Numerical Modelling and Analysis of Ductile Crack Propagation in Blanking Process Using Modified Nodal Release Method

摘要

Ductile fracture processes for discrete crack propagation using nodal release approach is well established for modelling crack in metal sheet. In this method, the crack is assumed to initiate or propagate along the element edges; hence, a new crack is implemented in the FE mesh. In Blanking process, the crack trajectory is unknown; therefore a very fine mesh is required to simulate a realistic crack propagation using the nodal release method. Consequently, the nodal release method has to be modified in which first the direction of crack extension is calculated and then, accordingly, the local element topology near the crack-tip is modified such that the nodes of elements are moved to predicted crack-tip in order to accommodate the crack extension. The advantage of this method is that it is possible to model the predicted crack with only slight modification in the local mesh near to the crack tip. However, it is necessary to transfer history variables from old local elements of previous increment to the new local elements of the current increment at the vicinity of crack-tip. But this method can lead to slight loss of accuracy to predict the subsequent crack extension due to interpolations. However, the advantage of this method is that remeshing can be either completely eliminated or reduced to a greater extend during the simulation. Therefore, in this paper, modified nodal release method for modelling ductile crack propagation in blanking process with the uncoupled damage approach is presented, and is further implemented in commercial FE software - MSC.Marc~R together with predefined user-subroutines