Prediction of fracture and deep drawing behavior of solution treated Inconel-718 sheets: Numerical modeling and experimental validation

In the present work, fracture forming limit diagram (FFLD) of two different solution treated i.e. 970 degrees C (HT970) and 1070 degrees C (HT1070) Inconel-718 sheets were evaluated by carrying out stretch forming experiments. The obtained failure limiting strains were then transformed into effective plastic strain versus triaxiality locus (eta EPS-FFLD) and major versus minor principal stress space (sigma-FFLD). It was observed that the HT1070 material possessed higher eta EPS-FFLD and lower sigma-FFLD indicating improved formability with reduced deformation load. In order to predict the fracture, six different ductile fracture models incorporating anisotropic properties were calibrated with experimental data. Among all the models, Oh model showed comparatively better prediction with an average absolute error of 10.2% and 10.1% for HT970 and HT1070 materials respectively. However, the model was not able to capture the fracture limits along complete triaxiality path (0.33 <= eta <= 0.66). Therefore, finite element (FE) analysis of deep drawing and stretch forming processes were performed incorporating experimentally evaluated eta EPS-FFLD and sigma-FFLD. The formability in terms of fracture location, limiting draw ratio, wrinkling evolution, thickness distribution, and limiting dome height were predicted successfully using Hills-48 plasticity theory. Also, the microhardness at critical regions of deformed cups was determined and the maximum hardness was found at cup junction of HT970 material especially in case of hemispherical dome cups. Thus, it was suggested that the deep drawn components of HT970 material have better part performance as compared to that of HT1070 material.