Investigation of fracture prediction in hydraulic continuous rotary bending low-stress cropping based on modified damage model

Due to the complexity of the near-net shape forming mechanism in the low-stress cropping(LSC) process, it was a challenge to accurately predict the process of fracture separation. A shear modified GTN model was proposed to study the fracture mechanism of hydraulic continuous rotary bending low-stress cropping(HCRB-LSC), and was applied to simulate the material damage evolution and predict the fracture behavior of HCRB-LSC. Moreover, the rationality and validity of simulation results were verified by precision cropping experiments. Combined with the proposed evaluation method and evaluation index of the cross-section, the quality of cross-section obtained by cropping was quantitatively evaluated. It was found that this cropping method could increase the accuracy of the cross-section and the efficiency of cropping, and could efficiently achieve reasonable sectional accuracy and flatness at 338 mm loading position. Additionally, the crack initiation zone was the quasi-cleavage fracture, and the predominant fracture mechanism involved micro-crack initiation and propagation induced by the void damage evolution under the complex three-dimensional stress. The crack propagation zone and instantaneous fracture zone were the dimple fracture caused by the shear stress, and deeper and larger dimples were produced in the loading position 338 mm. Precise prediction of near-net-shape forming damage evolution and fracture in HCRB-LSC provided an important basis for subsequent optimization of the precision cropping process.