Parameter identification of normalized cockcroft & latham elevated temperature damage model for 35CrMo steel using inverse optimization method

The impact ring of extra-large forgings, a core component of large marine hydraulic pile drivers, requires fracture defect control in its forging process. Therefore, considering the influence of temperature and strain rate, a coupled Normalized Cockcroft & Latham elevated temperature damage model was proposed to predict cracking in 35CrMo steel during hot forging process. Firstly, the Gleeble-1500D thermal simulation tester was used to conduct elevated temperature tensile tests on 35CrMo steel under deformation conditions of a temperature range of 900-1200 degrees C and a strain rate range of 0.01-5 s-1. Based on experimental data, a Normalized Cockcroft & Latham elevated temperature damage model on 35CrMo steel was established by introducing Zener-Hollomon parameter which accounted for temperature and strain rate. To obtain an elevated temperature damage model with high prediction accuracy, an inverse optimization method was put forward to determine model parameters. The genetic algorithm was employed as optimization algorithm, the critical damage value was used as optimization parameter, and the mean square error between the actual and simulated fracture displacement was used as objective function. The established model was modified through a subroutine modification and was embedded into the finite element code Forge (R) to simulate the process of elevated temperature tensile. The experimental and simulated fracture displacements were compared to verify the accuracy, the correlation coefficient R was 0.9706, and the root mean square error was 1.0305. The result showed that the proposed elevated temperature damage model could accurately predict the fracture behavior in elevated temperature forging process of 35CrMo steel.