Theory and simulation of 1D TO 3D plastic relaxation in tantalum

Abstract

(2003)Abstract. In plane shockwaves the uniaxial strain rate can greatly exceed the rate at which dislocation flow can relax the concomitant shear stress. The result is an overdriven plastic state in which the compression is 1D uniaxial initially and only after a period of time does the lattice relax to a more 3D compressed state due to plastic flow. Here we use an analytic calculation based on a generalization of the Gilman model of flow involving dislocation evolution to predict the phases of plastic relaxation and to derive an analytic estimate of the relaxation time, including a decomposition into incubation and flow times, suitable for comparison with in-situ x-ray diffraction. We use molecular dynamics (MD) to study the threshold for homogeneous nucleation both in shock compression of single crystal Ta 100 . We find that shock heating on the Hugoniot substantially lowers the threshold pressure for homogeneous nucleation.

Analysis of deformation twinning in tantalum single crystals under shock loading conditions

“…Utilizing molecular dynamics (MD) simulations, Rudd et al showed that in Ta, homogenous nucleation is expected to occur at normal stresses above 62 GPa under laser driven conditions, which is a higher normal stress and strain rate than observed in these experiments 28 .…”

Femtosecond X-Ray Diffraction Studies of the Reversal of the Microstructural Effects of Plastic Deformation during Shock Release of Tantalum

“…Shock-induced plasticity in tantalum, a body-centered cubic metal, has been studied extensively, with post facto analyses [6,[16][17][18][19] being complemented by a number of MD studies [9,[20][21][22][23]. Here we use XRD to directly monitor lattice orientations during shock release.…”

X-ray diffraction measurements of plasticity in shock-compressed vanadium in the region of 10–70 GPa

“…Coordinate system for analysis of the diffraction images from a polycrystalline vanadium sample situated as shown in the x, y plane at the base of the pyramidal BBXRD x-ray diffraction camera. The ray path from the collimated x-ray source lies in the x, z plane and is incident at 45 at the surface of the sample. Debye-Scherrer diffraction from (002) planes of vanadium is shown schematically on the bottom (negative-y side) image platecompare Fig.…”

“…In this way, Debye-Scherrer diffraction images from both the undisturbed material ahead of the shock and the shock-compressed vanadium are recorded simultaneously. The 45 angle of incidence of the x-ray probe beam relative to the direction of propagation of the shock was chosen to provide sensitivity in the diffraction images to anisotropic strain of the shock-compressed vanadium.…”