Dynamic Deformation Twinning in Shock-Loaded Iron

Abstract

Deformation twinning has been observed in shock-loaded samples of heat-treated Ferrovac E iron at peak stresses from 3 to 16 kbar. In this range, the volume fraction of twins increases monotonically from zero to approximately 4%. In instrumented transmitted-wave measurements stress relaxation was observed behind the elastic precursor for propagation distances of 12 mm or greater, but not at smaller distances. An analytical description of dynamic deformation twinning which adequately describes experimental observations on shock-wave propagation in Ferrovac E iron is proposed. This analysis is based on models for the growth of twin platelets combined with the equation γ=kα relating the plastic strain γ to the twinning shear k and the volume fraction of twins α. Dynamic deformation twinning in impact-loaded solids appears to be fairly well established both from experimental and analytical points of view and certainly must be considered as a possible physical mechanism in the description of plastic flow at high strain rates.

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

“…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. A constitutive model [5] has been adapted to simulate this behaviour, as fully detailed elsewhere [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. 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:…”

“…The amplitude of the elastic precursor is reported to decrease with increasing propagation path length, and stress relaxation is observed before the plastic wave [4]. This highly rate-dependent behaviour has been attributed to the nucleation and motion of dislocations and deformation twinning [5]. Free surface velocity profiles measured in laser shock-loaded iron samples are plotted in Fig.…”

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

“…Time-dependent description of twin growth [22] accounts for viscoplastic behaviour while a perfectly plastic formulation is used for slip.…”

Laser shock processing as a method of decreasing fatigue of a die-casting die made of maraging steel

“…The plástic deformation will occur to the depth where the shock wave can still cross the so-called Hugoniot's Elastic Limit (HEL), also dealt with by Johnson and Rhode (1971). The magnitude of the stress owing to the compressive shock-wave is conditioned exclusively by the material properties, Le., the dynamic yield strength and Poisson's ratio.…”