CC BY
17HiLASE-I-17
Quarter century development of laser shock peening and expansion of applications with novel palmtop lasers
Y. Sano1
institute for Molecular Science, Division of Research Innovation and Collaboration, Okazaki, Japan
Compressive residual stress (RS) in the near surface layer of metallic materials has favourable effects to prolong fatigue life and reduce stress corrosion cracking (SCC) susceptibility [1,2]. Laser shock peening (LSP) is known as an effective tool to introduce compressive RS by irradiating intense laser pulses to the surface of materials covered with water for confining laser-induced plasma [3]. LSP has been applied to jet engine fan blades to prolong their service lives since 1990's
[4]. However, the application of LSP is limited mainly to production in factories because the laser system was huge and sensitive to surrounding conditions, consequently it is not convenient for field operation.
To cope with this situation, we reduced the pulse energy down to 10 mJ, one to three orders of magnitude smaller than that of the usual LSP conditions, and applied to HT780 (780 MPa grade structural steel) base material and the welded joints [5]. Compressive RS was built on surface by LSP with 10 mJ pulse energy. Fatigue test results showed that LSP with 10 mJ significantly prolonged fatigue life and has the almost same effect as LSP with 200 mJ pulse energy (Fig. 1). Then, we started developing ultra-compact palmtop laser oscillators with pulse energy of 20 mJ
[5] and completed a prototype together with a battery-driven power supply. The laser oscillators can be easily handled by a multi-axes robotic arm (Fig. 2), which could realize actual applications of LSP to the maintenance of aged infrastructure such as bridges in the field. The effects of LSP with low energy laser pulses on RS and fatigue properties, the status of the palmtop laser development and concept to apply LSP to infrastructure will be presented.
Fig.1. Fatigue test results of as-welded and LSPed HT780 joints.
Fig. 2. A palmtop laser oscillator driven by a robotic arm.
References
[1] Y. Sano, M. Obata, T. Kubo, N. Mukai, M. Yoda, K. Masaki and Y. Ochi: Retardation of Crack Initiation and Growth in Austenitic Stainless Steels by Laser Peening without Protective Coating, Mater. Sci. Eng. A, vol. 417 (2006) 334-340.
[2] Y. Sano, M. Kimura, K. Sato, M. Obata, A. Sudo, Y. Hamamoto, S. Shima, Y. Ichikawa, H. Yamazaki, M. Naruse, S. Hida, T. Watanabe and Y. Oono: Proceedings of the Eighth International Conference on Nuclear Engineering (ICONE-8), Baltimore, 2000 (paper no.: ICONE-8441).
[3] Y. Sano, N. Mukai, K. Okazaki and M. Obata: Nucl. Instrum. Meth. Phys. Res. B, vol. 121 (1997) 432-436.
[4] D.W. See, J.L. Dulaney, A.H. Clauer and R.D. Tenaglia: The Air Force Manufacturing Technology Laser Peening Initiative, Surface Eng., vol. 18 (2002) 32-36.
[5] https://www.youtube.com/watch?v=nMsOkkEPK5I.
