Damage evolution and damage model validation in spalled tantalum

The dynamic damage resistance of two grades of very clean tantalum is compa red. The materials were loaded to incipient failure using an 80 mm gas gun equipped with soft recovery using a parallel flyer plate experimental confi guration. Both loading time and applied shock pressure was varied from 1.1- 2 mu s and 5.6-9.8 GPa, respectively. A VISAR recorded the back surface vel ocity. The recovered samples were metallographically sectioned, polished, a nd etched. Image analysis and optical profilometry quantified the resulting damage. Longitudinal porosity distributions of the tests are compared. A c alibrated hydrocode based damage model was used to simulate the tests. We c ompare predicted and experimental measurements of free surface velocity and porosity. The model also produced free surface pullback signals suggesting high spall strength with little evolved porosity. This is further confirma tion that in clean, high Peierls energy materials the VISAR pullback signal is associated with the creation of a region of enormous hydrostatic tensil e stresses in the material, but is relatively distinct from the void coales cence process. A transition in coalescence mechanism, from primarily void g rowth impingement to long-range plastic instabilities, occurs with increasi ng hydrostatic tension and increasing stress pulse duration.