Abstract: In order to solve the problems in the fracture prediction of incremental sheet forming of metals，in which the prediction strongly depends on the strain path and a real-time prediction cannot be achieved， a numerical model has been built. To perform that， the Yu Zhongqi ductile fracture criterion was firstly added into ABAQUS software through the interface subroutine of the VUMAT for DC56D+Z steel. Then， the uniaxial tensile and incremental forming processes were simulated by the new user-defined model and ABAQUS built-in Von Mises model， respectively. Finally， according to the results of finite element simulation， the critical fracture integral value I of the incremental forming model under the Yu Zhongqi ductile fracture criterion can be reduced reversely based on the actual experimental results. The results show that the calculated stress and strain from the two models have the same order of magnitude and similar distribution， which prove the validity of the subroutine. The maximum fracture integral value I in the simulated sheet forming process appears on the side wall of the workpiece， which is consistent with the experimental ones. The critical fracture integral value I=17 can be used as an effective way to predict the fracture in the incremental sheet metal forming process.

Key words: incremental forming, finite element analysis, Yu Zhongqi ductile fracture criterion, critical fracture integral value, fracture prediction