The inertial confinement fusion has not been achieved yet. The reasons for this phenomenon are not fully understood. In our opinion, the main factor influencing the decrease in the yield is the ...evolution of hydrodynamic instabilities due to geometric inhomogeneities (surface roughness, the presence of asymmetric elements etc.). The perturbed density field can result from these inhomogeneities. The results of a theoretical study of the influence of density perturbations on the stability of the boundary under accelerated motion are presented in this paper. The performed numerical simulations are compared with theoretical results.
The material model of iron and steel is developed for fluid dynamics simulations of samples under extreme loading induced by an impact or explosion. The model is validated on a set of plate impact ...tests using the contact smoothed particles hydrodynamics method. The model takes into account the polymorphic α-ε phase transition in iron which is shown to be correctly reproduced, including the hysteresis effect at unloading. The equation of state for steel is shown to be very close to that of iron on a set of tests with spherical shells under explosive compression; however the yield strength of steel is greater.
Laser shock peening Inogamov, N A; Zhakhovsky, V V; Ilnitsky, D K ...
Journal of physics. Conference series,
02/2021, Volume:
1787, Issue:
1
Journal Article
Peer reviewed
Open access
Elastic-plastic transformations together with or separately of polymorphic phase transitions are important for the theory of shock waves. Here we discuss changing a classification consisting from ...elastic, split elastic-plastic, and pure plastic shocks. The split shocks means that there are two jumps: the elastic precursor and plastic shock, and that the elastic jump is independent relative to plastic one. In the split regime the precursor moves with elastic speed of sound overrunning the plastic jump and going further and further ahead relative to plastic jump as time proceeds and becoming weaker and weaker. We oppose the split shock to the one-wave (1W) two zones (elastic and plastic-2Z) shock (1W2Z shock). The 1W2Z wave propagates as whole (therefore one-wave), the plastic shock dynamically supports the elastic one, and the average distance between the jumps does not change in time. The powerful elastic shocks (their amplitudes are much higher than are usually suggested for elastic shocks) were found in experiments with femtosecond laser pulses and confirmed in large scale molecular dynamics (MD) simulations. The observation of the 1W2Z shocks is another important finding coming from MD. The report is devoted to lasers, shocks, and applications. In the second part of the report the generation and propagation of the shocks created for laser shock peening by lasers with ultrashort or nanosecond pulses are considered.
The dislocation model is used to estimate the plastic strain in high explosive (HE) crystals at relatively low impact velocities. Due to anisotropic distribution in orientation of HE grains the ...localization of heat production is observed. At certain impact velocities this heating is sufficient to induce chemical reactions with energy release.
We report on the ablation phenomena in gold sample irradiated by femtosecond laser pulses of moderate intensity. Dynamics of optical constants and expansion of a heated surface layer was investigated ...in a range from picosecond up to subnanosecond using ultrafast interferometry. Also morphology of the ablation craters and value of an ablation threshold (for absorbed fluence) were measured. The experimental data are compared with simulations of mass flows obtained by two-temperature hydrodynamics and molecular dynamics methods. Simulation shows evolution of a thin surface layer pressurized by a laser pulse. Unloading of the pressurized layer proceeds together with electron-ion thermalization, melting, cavitation and spallation of a part of surface liquid layer. The experimental and simulation results on two-temperature physics and on a fracture, surface morphology and strength of liquid gold at a strain rate ∼ 109 s-1 are discussed.
Study of material flow in two-temperature states is needed for a fundamental understanding the physics of femtosecond laser ablation. To explore phenomena at a very early stage of laser action on a ...metallic target our in-house two-temperature hydrodynamics code is used here. The early stage covers duration of laser pulse with next first few picoseconds. We draw attention to the difference in behavior at this stage between the cases: (i) of an ultrathin film (thickness of order of skin depth dskin or less), (ii) thin films (thickness of a film is 4-7 of dskin for gold), and (iii) bulk targets (more than 10dskin for gold). We demonstrate that these differences follow from a competition among conductive cooling of laser excited electrons in a skin layer, electron-ion coupling, and hydrodynamics of unloading caused by excess of pressure of excited free electrons. Conductive cooling of the skin needs a heat sink, which is performed by the cold material outside the skin. Such sink is unavailable in the ultrathin films.
We investigate behavior of the ruthenium targets under x-ray. In this paper, the two-temperature equation of state for Ru is developed. Electronic spectrum of ruthenium is calculated using density ...functional theory. We have defined an electron-ion coupling parameter of ruthenium and its two-temperature thermal conductivity. With this input we run our two-temperature hydrodynamic code.
Electron–ion relaxation lasts few tens of picoseconds in a submicrometer surface layer of metal after irradiation by femtosecond laser pulse of moderate intensity. During this stage, the electron ...temperature is many times higher than ion (lattice) temperature. The rate of this relaxation is slower for noble metals due to their small electron–ion coupling. Thus, effects caused by high electron temperature reveal more obviously for those metals. To study electron transport in noble metal nanofilms, we combine the first-principle calculations and our analytical models. The newly calculated electron–phonon coupling and heat conductivity are used in two-temperature hydrodynamics modeling. Results of such modeling are in good agreement with the experimental data and molecular dynamics simulation.
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