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.