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Proceedings Paper

Process and application of shock compression by nanosecond pulses of frequency-doubled Nd:YAG laser
Author(s): Yuji Sano; Motohiko Kimura; Naruhiko Mukai; Masaki Yoda; Minoru Obata; Tatsuki Ogisu
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Paper Abstract

The authors have developed a new process of laser-induced shock compression to introduce a residual compressive stress on material surface, which is effective for prevention of stress corrosion cracking (SCC) and enhancement of fatigue strength of metal materials. The process developed is unique and beneficial. It requires no pre-conditioning for the surface, whereas the conventional process requires that the so-called sacrificial layer is made to protect the surface from damage. The new process can be freely applied to water- immersed components, since it uses water-penetrable green light of a frequency-doubled Nd:YAG laser. The process developed has the potential to open up new high-power laser applications in manufacturing and maintenance technologies. The laser-induced shock compression process (LSP) can be used to improve a residual stress field from tensile to compressive. In order to understand the physics and optimize the process, the propagation of a shock wave generated by the impulse of laser irradiation and the dynamic response of the material were analyzed by time-dependent elasto-plastic calculations with a finite element program using laser-induced plasma pressure as an external load. The analysis shows that a permanent strain and a residual compressive stress remain after the passage of the shock wave with amplitude exceeding the yield strength of the material. A practical system materializing the LSP was designed, manufactured, and tested to confirm the applicability to core components of light water reactors (LWRs). The system accesses the target component and remotely irradiates laser pulses to the heat affected zone (HAZ) along weld lines. Various functional tests were conducted using a full-scale mockup facility, in which remote maintenance work in a reactor vessel could be simulated. The results showed that the system remotely accessed the target weld lines and successfully introduced a residual compressive stress. After sufficient training for operational personnel, the system was applied to the core shroud of an existing nuclear power plant.

Paper Details

Date Published: 7 February 2000
PDF: 13 pages
Proc. SPIE 3888, High-Power Lasers in Manufacturing, (7 February 2000); doi: 10.1117/12.377033
Show Author Affiliations
Yuji Sano, Toshiba Corp. (Japan)
Motohiko Kimura, Toshiba Corp. (Japan)
Naruhiko Mukai, Toshiba Corp. (Japan)
Masaki Yoda, Toshiba Corp. (Japan)
Minoru Obata, Toshiba Corp. (Japan)
Tatsuki Ogisu, Toshiba Corp. (Japan)

Published in SPIE Proceedings Vol. 3888:
High-Power Lasers in Manufacturing
Xiangli Chen; Tomoo Fujioka; Akira Matsunawa, Editor(s)

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