Science and Technology of Energetic Materials

Vol.65, No.5 (2004)ガス爆発特集号(2)

Research paper -ガス爆発特集号(2)-

Influence of metal plate thickness on underwater pressure waves induced by laser peening (*in Japanese)
Keiko Watanabe, Yuji Sano, Naruhiko Mukai, Hiroyuki Torikai, and Akihiro Sasoh


Behavior of pressure waves generated due to a laser ablation of a metal plate in water has been investigated with shadowgraph technique and measurement of their pressure histories. A second harmonic radiation of a Q-switched Nd:YAG laser (wavelength; 532 nm, pulse duration (FWHM); 7 ns) was focused onto a water-immersed plate made of type 304 stainless steel (SUS304). The plate thickness was 0.1 mm, 1 mm and 10 mm, and the laser energy was varied from 49 to 470 mJ. High-pressure ablation plasma was generated on the plate surface by the laser irradiation, and three types of pressure waves, i.e., blast wave, transmitted wave and leaky wave, were visualized. The blast wave, which was directly driven in water by expansion of the high-pressure plasma, propagated as an-almost-hemispherical wave without being influenced by the plate thickness. Behavior of other waves was influenced by the thickness. In case of 1-mm and 10-mm-thick plates, the transmitted waves were emitted as a result of transmission of pressure waves repeatedly propagating between the plate surfaces. Their frequency was consistent with a round travel period through the plate thickness. For the thick plate, the leaky waves, which were caused by longitudinal and Rayleigh or transversal waves propagating along the plate surface, were observed. Especially, leaky wave produced by Rayleigh or transversal wave had a width approximately the same as a spot diameter of the laser irradiation. For the sufficiently thin plate, the leaky waves produced by lamb waves propagating along the plate surface were observed.

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