Use of different damage models for simulating impact-driven spallation in metal plates

We have studied spallation in impact-loaded copper and mild steel plates, using one- and two-dimensional hydrodynamic simulations. Four different damage models have been used to determine the evolution of void volume, taking into account the effect of damage on material strength and the equation of state. The results obtained using the void growth and nucleation and growth models agree reasonably well with experimental observations described in a Russian spall database. The void growth model surprisingly yields a closer match with experiment, even though the nucleation and growth model includes more detailed physical effects. The two other models do not generally yield a good match. The Johnson–Cook model does not predict spall at all in the situations examined. The effect of impact pressure and tensile wave duration on spall parameters has been studied. For both kinds of targets, the computed spall thickness decreases monotonically with increase in flyer velocity, which is in accord with experimental observations in aluminum targets. For both copper and MS, the spall strength is found to generally increase monotonically with impact pressure, a feature reported in experiments with aluminum targets. However, for both materials, the computed increase is preceded by an initial drop, for which we have not found an explanation as yet. For a copper target, as the temperature increases from room temperature to approximately 80% of the melting point, the spall strength increases by a maximum of 20%. This matches experimental trends. Two-dimensional simulations have also been performed to study edge effects.