CC BY
7ALT'22
LM-I-6
LASER-MATTER INTERACTION
3D inflection and 1D-3D attenuation of initially planar shock wave generated
by femtosecond laser pulse
1- Institute for Computer-Aided Design of the Russian Academy of Sciences, 19/18, 2nd Brestskaya st., Moscow 123056, Russia 2- Landau Institute for Theoretical Physics of the Russian Academy of Sciences, 1a, Akademika Semyonova st.,
Chernogolovka, Moscow region 142432, Russia 3- Moscow Institute of Physics and Technology, 9, Institutskiy per., Dolgoprudny, Moscow Region 141701, Russia 4- Dukhov All-Russian Research Institute of Automation, 22, Sushchevskaya st., Moscow 127055, Russia 5- Joint Institute for High Temperatures of the Russian Academy of Sciences, 13 Bldg.2, Izhorskaya st., Moscow 125412, Russia nailinogamov@gmail.com
Evolution of wavefront geometry during propagation and attenuation of initially planar shock waves generated by femtosecond laser pulses in aluminum is studied. We demonstrate that three stages of shock front inflection take place in consistent hydrodynamics and molecular dynamics simulations [1].
During the first stage, the distance (D) traveled by a near-planar shock wave (SW) DSW ^ RL is smaller than the radius of heated laser spot RL. Wave attenuation is associated with one-dimensional plane (1D) rarefaction wave coming from the free surface. Such rarefaction wave shapes the shock wave to a 1D triangular pressure profile along direction normal to target surface with a shock front followed by an unloading tail. The second transitional stage starts after propagation of DSW ~ RL, at which the unloading lateral waves begin to arrive to a symmetry axis of flow and initiate inflection of the initially planar shock front. Next at the third stage, the wavefront geometry is finally rounded and rapid attenuation of shock pressure begins at DSW ^ RL.
It is shown that such divergent shock wave cannot generate plastic deformations in aluminum shortly after propagation of DSW ~ RL. Thus, we may estimate the maximal laser shock peening (LSP) depth as a radius of focal spot, which sets an upper limit for the laser shock peening.
The cessation of plastic deformation is caused by the fall of the shockwave amplitude below the Hugoniot elastic limit (HEL). Value of the HEL is much larger for ultrashort SWs than is usually supposed [2,3]. When SW amplitude becomes less than HEL, then the laser elastic-plastic wave transits to a purely elastic mode of propagation [1,4,5]. For large-sized light spots, this transition ends in the 1D mode of propagation.
[1] V. Shepelev et al., Attenuation and inflection of initially planar shock wave generated by femtosecond laser pulse, Optics & Laser Technology, vol. 152, 108100, (2022). https://doi.org/10.1016/j.optlastec.2022.108100
[2] V. Zhakhovsky and N. Inogamov, Elastic-plastic phenomena in ultrashort shock waves, JETP Lett., vol. 92(8), pp. 521-526, (2010). DOI: 10.1134/S0021364010200063
[3] S. Ashitkov et al., Behavior of Aluminum near an Ultimate Theoretical Strength in Experiments with Femtosecond Laser Pulses, JETP Lett., vol. 92(8), pp. 516-520, (2010). https://doi.org/10.1134/S0021364010200051
[4] N. Inogamov et al., Laser Shock Wave: The Plasticity and Thickness of the Residual Deformation Layer and the Transition from the Elastoplastic to Elastic Propagation Mode, JETP Lett., vol. 115, pp. 71-78, (2022). Doi 10.1134/S0021364022020047
[5] В. Хохлов и др., Плавление титана ударной волной, вызванной мощным фемтосекундным лазерным импульсом, Письма ЖЭТФ, том 115(9), сс. 576-584, (2022). DOI: 10.31857/S1234567822090051
V. Shepelev1, Y. Petrov2"3, N. Inogamov2'4, V. Zhakhovsky45, E. Perov5, S. Fortova1
