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Mathematical modeling of dynamic metal fragmentation with ultrashort laser pulses
V. Mazhukin1, A. Shapranov1, M. Demin1, A. Aleksashkina1
1Keldysh Institute of Applied Mathematics of Russian Academy of Sciences KIAM RAS, Mathematical Modelling, Moscow, Russian Federation
In the fs-ps-second range of laser irradiation of a metal target (Al), 2 high-speed PLA mechanisms [1] were investigated: separation and spallation. Both mechanisms are realized with the direct action of ultrashort (fs, ps) laser pulses on the surface, which provide large negative pressure values in the spallation zone. The expansion of the cavity and the departure of the surface layer of the material occurs due to inertial forces. The simulation results showed:
a) The separation is a stage of dynamic fragmentation of the liquid phase closely related to the process of homogeneous melting, which takes place under conditions of strong overheating (Tmax ~ 1.4 Tm) of the near-surface region of the solid phase [2]. Removal of material occurs in the form of periodically repeating bursts of liquid metal, forming a cloud of small droplets on the side of the irradiated surface.
b) In the spallation, the solid-state metal fragments are removed from the back side of the target (Al). The mechanism of destruction in this case is determined by compression pulses, which, when reflected from the free surface, create tensile stresses that can lead to breaks (spalling) from the back surface. Solid fragmentation is promoted by the nucleation of a liquid phase (melting) near the back surface, the conditions for the occurrence of which are greatly facilitated by tensile stresses.
Acknowledgements:
The work was funded by the Russian Foundation for Basic Research grant No. 19-07-01001. References
[1] V.I. Mazhukin, M.M. Demin, A.V. Shapranov. High-speed laser ablation of metal with pico-and subpicosecond pulses. Appl. Sur. Sci., 2014, 302, 6-102.
[2] V.I. Mazhukin, A.V. Shapranov, A.V. Mazhukin, O.N. Koroleva. Mathematical formulation of a kinetic version of Stefan problem for heterogeneous melting/crystallization of metals. Mathematica Montisnigri, 2016, vol. 36, pp. 58-77.
