Modelling of spalling in tantalum

Abstract
The present work deals with the description of ductile fracture during dynamic pressure loading. The two first stages of the process, i.e. nucleation and growth of voids, are investigated. Potential sites for nucleation are supposed statistically distributed within the material assumed initially free of voids. The nucleation stage is believed to be stress controlled: when the applied pressure overcomes the cavitation pressure a void appears and then grows by plastic deformation of the matrix material. Inertia effects, known as refraining void growth, are included in the modelling. During the initial stage of void growth, effects of material properties are essentially appearing through the magnitude of the nucleation pressure. In the later stage, the weakening of the matrix due to the increase of porosity has been taken into account. The constitutive relationship proposed in the present work has been formulated in order to be applied in the context of plate impact experiments, where the stress state is highly hydrostatic. The model has been applied to determine spall stresses on tantalum. A good agreement is observed when spall stresses on tantalum are calculated and compared to experimental data from Roy (2003, Ph.D. Thesis, Ecole Nationale Supérieure de Mécanique et d'Aéronautique, Université de Poitiers, France).