Uncertainties in the Swift Hardening Law Parameters and Their Influence on the Flow Stress and the Hole Expansion Behavior of Dual-Phase (DP600) Steel Specimens

Swift hardening law is one of the widely used phenomenological model to describe the stress–strain behavior in sheet metal forming simulations. In the present study, a statistical approach was used to investigate the effect of the variation in material model parameters on estimated values of the stress–strain data obtained using Swift hardening law. This estimation employed values of the Swift hardening law parameters as reported in the literature and those from three uniaxial tensile tests conducted in this study. Uncertainties in the flow stress were estimated using Monte Carlo (MC) simulations. A detailed sensitivity analysis was performed to determine the most sensitive parameter influencing the flow stress estimation. It was found that the sensitivity coefficients of the Swift hardening parameters are dependent on the true plastic strain. At lower plastic strains, ϵ was found to be most sensitive parameter whereas at larger pre-strains K was observed to be the critical parameter affecting the flow stress estimation. Further, computed hardening curves were used to simulate the deformation in hole expansion tests (HET) of dual phase steel (DP600) steel specimens using an explicit finite element analysis (FEA) technique. The effects of the material property variation on the thinning rate of the sheet with punch displacement were estimated with a mean (μ) and standard deviations (σ) for determining (± 1 ± 2σ) statistical limits. FEA predictions were compared with measured data obtained from HET conducted using specimens with holes fabricated with both drilling and boring processes. A reasonable agreement was achieved. Furthermore, the experimental values of the final sheet thicknesses were found to lie within the statistical limits using finite element simulations.