Elastic precursor wave decay in shock-compressed aluminum over a wide range of temperature

Abstract

The effect of temperature on the dynamic flow behavior of aluminum is considered in the context of precursor wave decay measurements and simulations. In this regard, a dislocation-based model of high-rate metal plasticity is brought into agreement with previous measurements of evolving wave profiles at 300 to 933 K, wherein the amplification of the precursor structure with temperature arises naturally from the dislocation mechanics treatment. The model suggests that the kinetics of inelastic flow and stress relaxation are governed primarily by phonon scattering and radiative damping (sound wave emission from dislocation cores), both of which intensify with temperature. The manifestation of these drag effects is linked to low dislocation density ahead of the precursor wave and the high mobility of dislocations in the face-centered cubic lattice. Simulations performed using other typical models of shock wave plasticity do not reproduce the observed temperature-dependence of elastic/plastic wave structure.

Dislocation drag from phonon wind in an isotropic crystal at large velocities

“…However, in focusing on the analytic behavior of dislocation drag up to c T , we presently require the simplifications of the isotropic limit. In fact, many dislocation-based material strength models for polycrystals [1,4,5,7] make use of the isotropic approximation and as such would benefit from a first-principles derivation of dislocation drag as a function of velocity in the isotropic limit.…”

“…We note that drag is initially dominated by thermal effects at very low dislocation velocities, and that phonon wind becomes important only at velocities of the order of 1% transverse sound speed and higher.2 Many authors estimate the velocity dependence of the drag coefficient by means of "relativistic" factors ∝ 1/(1 − v 2 /c 2 ) m with different exponents m and a limiting (sound) speed c based on purely empirical arguments which lack a first-principles theoretical framework, see[3][4][5][6][7] and references therein.…”

Analytic model of the remobilization of pinned glide dislocations: Including dislocation drag from phonon wind

“…[22] which relied on experimental shock data for their model parameters in order to make predictions in the high stress regime. More recent approaches [4,[34][35][36][37][38][39][40] aim at providing a more accurate description of the high stress regime based on the microscopic physics of dislocation mobility. However, one of the main obstacles encountered by these "microscopic" strength models has been the uncertainty as to how B behaves at high velocities, temperatures, and pressures.…”

“…(see e.g. [40][41][42][43]) to B ∼ √ v above some threshold velocity [4,38,39], to "relativistic factors" B ∼ 1/(1 − v 2 /v 2 crit ) m with a limiting (critical) velocity v crit and a range of powers 1/2 ≤ m ≤ 4 [34][35][36][37]. In these references, the pressure and density dependence of B is largely ignored (except for the "relativistic factors" whose limiting velocity depends on the shear modulus).…”

“…[48,49] in order to introduce a limiting velocity using a simple analytic form to account for the divergence in self energy of dislocations in the isotropic limit [50]. Numerous recent authors have copied this form [32,34,36,37] and some have changed the power m to better match their simulations; see e.g. [35] and references therein.…”