Stress relaxation and precursor decay in laser shock-loaded iron

Abstract

Iron samples of different thicknesses have been submitted to laser shocks of short duration. Transmitted wave measurements have been performed by means of polymeric piezoelectric transducers. The records indicate a decrease of the elastic precursor amplitude with increasing propagation distance, as well as a stress relaxation behind the elastic wave front. These features were already observed in shock-loaded iron, but this paper extends the experimental data to a previously unexplored range of thin targets and high strain rates. Postshock examinations of the recovered specimens reveal significant twin formation. Computer simulations of the experiments have been made using a constitutive model from the literature, including a theoretical description of rate-dependent twinning. The ability of that model to predict the experimental results has been tested. A correct overall agreement has been obtained, except for some discrepancies which have been discussed.

Laser shock experiments to investigate and to model various aspects of the response of metals to shock loading

“…2, showing both elastic precursor decay and stress relaxation. Similar profiles have been recorded with piezoelectric transducers and reported in the past, together with micrographs of the recovered targets showing considerable twin formation [6]. The measured values of elastic particle velocities are much higher than those reported in thicker specimens under conventional shock loading [4,5], which confirms the rate-dependency of the response.…”

“…Dislocation slip, assumed to be much faster than twinning, is treated as rate-independent through instantaneous accommodation of the plastic strain above a threshold stress τ 1 . The values of the model parameters θ, τ 0 and τ 1 in laser shock-loaded iron have been determined as 18 ns, 0.4 GPa and 1 GPa, respectively [6], significantly different from the original values fitted at lower strain rates. A fair agreement is obtained between measured and computed acceleration fronts (Fig.…”

“…The measured values of elastic particle velocities are much higher than those reported in thicker specimens under conventional shock loading [4,5], which confirms the rate-dependency of the response. A constitutive model [5] has been adapted to simulate this behaviour, as fully detailed elsewhere [6]. It involves a volume fraction of twinned material ξ:…”

Laser-Driven Ramp Compression to Investigate and Model Dynamic Response of Iron at High Strain Rates

“…We use an elastic-plastic model fully described in [21]. It includes a macroscopic description of both dislocation slip and deformation twinning.…”

Wave Propagation and Dynamic Fracture in Laser Shock-Loaded Solid Materials

“…Thereafter, wave reverberation within the spalled layers generates damping oscillations in the velocity profiles. These profiles are compared to the results of 1D simulations with the SHYLAC code, involving a two-phase equation of state with a description of the kinetics of the phase change (De Rességuier & Hallouin, 2001), a constitutive law accounting for time-dependent twinning (De Rességuier & Hallouin, 1998), and a simple spall criterion assuming instantaneous rupture and subsequent relaxation as soon as the tensile stress reaches a threshold value. This comparison, which has been discussed in details elsewhere (De Rességuier & Hallouin, 2008), shows a good overall consistency.…”