Prediction of fracture limits of Ni-Cr based alloy under warm forming condition using ductile damage models and numerical method

The stretch forming and the deep-drawing processes were carried out at 300 and 673 K to determine the safe forming and fracture limits of IN625 alloy. The experimentally obtained strain-based fracture forming limit diagram (FFLD) was transformed into a stress based (sigma-FFLD) and effective plastic strain (EPS) vs triaxiality (eta) plot to remove the excess dependency of fracture limits over the strains. For the prediction of fracture limits, seven different damage models were calibrated. The Oh model displayed the best ability to predict the fracture locus with the least absolute error. Though the experimentally obtained fracture limits have only been used for the numerical analysis, none of the considered damage models predicted the fracture strains over the entire considered range of stress triaxiality (0.33<0.66). The deep drawing process window helped to determine wrinkling, safe and fracture zones while drawing the cylindrical cups under different temperature and lubricating conditions. Further, the highest drawing ratio of 2 was achieved at 673 K under the lubricating condition. All the numerically predicted results of both stretch forming and deep drawing processes using the Hill 1948 anisotropic yielding function were found to be good within the acceptable range of error.

Automated summary

The stretch forming and deep-drawing processes were conducted at temperatures of 300 and 673 K to determine the safe forming and fracture limits of IN625 alloy. The experimentally obtained strain-based fracture forming limit diagram was transformed into a stress-based diagram to remove excess dependency. Various damage models were calibrated for prediction, with the Oh model showing the best accuracy. Despite the experimentally obtained fracture limits being used for numerical analysis, none of the considered models predicted fracture strains over the entire stress triaxiality range. The deep drawing process helped determine safe zones and achieve a drawing ratio of 2 at 673 K under lubrication conditions. Numerical predictions using the Hill 1948 anisotropic yielding function were found to be within an acceptable range of error.