Interaction of two laser shocks inside iron samples

Hallouin

2008

Phys. Rev. B

Despite extensive research work on the ␣-phase transition occurring in shock-loaded iron, the kinetics of this transformation remain largely unknown. Here, we present time-resolved free surface velocity measurements in iron foils of thicknesses ranging from 150 to 520 m subjected to laser shocks of peak pressure of about 130 GPa and duration of about 3 ns. The records show an elastic precursor followed by a plastic front, but the double wave structure that is usually associated with the phase change does not appear over such short propagation distances. The measured profiles are compared to the predictions of one-dimensional simulations involving rate-dependent descriptions of both twinning and phase transitions. Such comparisons provide an estimate of a time constant governing the transformation kinetics, which is found to strongly condition the evolution and attenuation of the pressure pulse during its propagation. The spall stress evaluated from the records is shown to be significantly higher after the ␣--␣ cycle. Metallurgical observations of the recovered samples confirm both the phase transition and the spall damage inferred from the velocity profiles. Finally, they show the very clear change in fracture surface morphology to the so-called smooth spall expected above the phase transformation.

Section: Introductionmentioning

confidence: 99%

Effects of theα−εphase transition on wave propagation and spallation in laser shock-loaded iron

Hallouin

2008

Phys. Rev. B

“…with the details of the equation of state for each pure phase described in the References [16,17]. The time evolution of the epsilon mass fraction X is governed by a kinetics law derived from the classical concept of nucleation and growth of phase [23][24][25] …”

Section: α − ε Kinetics Modelmentioning

confidence: 99%

“…Then, this calculated ramp profile is used as boundary condition in the 1 D finite difference, Lagrangian hydro code SHYLAC [16,17] to simulate the dynamic response of iron, including the kinetics of the phase transition. The iron sample is discretized into cells of same mass, as recommended in Reference [18], of initial thickness about 0.01 µm.…”

Section: Numerical Simulationsmentioning

confidence: 99%

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

Amadou

Brambrink

et al. 2016

Metals

Efficient laser shock processing of materials requires a good characterization of their dynamic response to pulsed compression, and predictive numerical models to simulate the thermomechanical processes governing this response. Due to the extremely high strain rates involved, the kinetics of these processes should be accounted for. In this paper, we present an experimental investigation of the dynamic behavior of iron under laser driven ramp loading, then we compare the results to the predictions of a constitutive model including viscoplasticity and a thermodynamically consistent description of the bcc to hcp phase transformation expected near 13 GPa. Both processes are shown to affect wave propagation and pressure decay, and the influence of the kinetics of the phase transformation on the velocity records is discussed in details.

“…Figure 3 shows free surface velocity records in iron samples subjected to laser shocks of about 130 GPa. They are compared to the predictions of a model detailed elsewhere [7], involving a two-phase equation of state and a phenomenological expression of the transformation rate…”

Section: Twinning and Polymorphic Transformationsmentioning

confidence: 99%

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

Lescoute

Signor

et al. 2010

EPJ Web of Conferences

Self Cite

Abstract. Laser driven shocks allow studying the dynamic behaviour of condensed matter over small spatial (∼ μm to mm-order) and temporal (∼ps to ns-order) scales, at extremely high strain rates (∼10 7 s −1 ). They can be used to test the predictive capability of constitutive models over wide ranges of loading pressures and pulse durations. We present experimental results in laser shock-loaded metals (iron, gold, tin), based on various, complementary techniques including time-resolved velocity measurements, transverse shadowgraphy and post-shock analyses of recovered samples. The data are used to investigate several shock wave processes such as yielding and polymorphic transformations, melting, spall fracture and dynamic fragmentation in both solid and melted states. On the basis of comparisons with numerical simulations, the abilities and limitations of several models are briefly discussed.