Calibration of the Johnson–Cook Model for Sub-Size Charpy Impact Tests on AISI 304 Steel

Accurate numerical reproduction of Charpy impact tests requires constitutive and damage models capable of representing material behavior under dynamic loading conditions. This study presents an experimental–numerical investigation of the impact response of sub-size AISI 304 stainless-steel Charpy specimens characterized by different thicknesses and notch depths. Instrumented tests were performed using a 50 J pendulum impact system at an impact velocity of 3.458 m/s. The experimental force, displacement, velocity, and absorbed-energy histories were used as reference data for explicit finite element simulations developed in LS-DYNA using the Johnson–Cook constitutive and damage model. A two-level full factorial Design of Experiments, comprising 64 simulations, was conducted by varying six Johnson–Cook parameters—A, B, n, D1, D2, and D3—by ±20% relative to their baseline values. The effects of these parameters on the peak impact force were evaluated using a General Linear Model and the Analysis of Variance. Then, the sensitivity results were used to guide the calibration of the most influential parameters, and the resulting parameter set was assessed across the different specimen geometries. Overall, the calibrated model reproduced the initial loading stage, peak-force magnitude, and energy-absorption trends with reasonable accuracy. The largest discrepancies occurred during the post-peak and fracture stages, including differences between the experimentally observed and numerically predicted fracture conditions. The results demonstrate that DOE-guided sensitivity analysis can reduce parameter space and support a more systematic calibration process. However, they also show that calibration based primarily on peak force is insufficient to ensure an accurate prediction of post-peak behavior and fracture conditions across different sub-size specimen geometries.