An Indirect Method to Determine Friction Coefficient in the OSU Punch Stretch Test

An indirect method to determine friction coefficient under punch stretching conditions has been developed. The methodology involves correlation of experimental draw-in measurements to FEA predictions for a range of assumed friction coefficients. Initial evaluation with a ferritic stainless steel (SS 439) shows that the proposed indirect method to determine the effective friction coefficient during punch stretching is feasible. Friction coefficient (μ) estimate based on the indirect method was 0.15 for the sample with residual mill oil (dry), 0.12 with excess mill oil (wet), and 0.03 with polyethylene sheets between the sample blank and tooling. The importance of prescribing accurate material hardening behavior beyond uniform elongation to obtain good correlation between simulation and experimental punch loads and to better tune the model is highlighted in the paper.