• Title/Summary/Keyword: Laser Peening

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Laser Peening Process and Its Application Technique (레이저 피닝 처리 및 적용 기술)

  • Kim, Jong-Do;KUTSUNA, Muneharu;SANO, Yuji
    • Journal of Welding and Joining
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    • v.33 no.4
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    • pp.1-6
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    • 2015
  • Advances in laser technology have yielded a multitude of innovative processes and applications in various industries. Laser peening is a typical example invented in the mid-1990s as a surface technology, which converted residual stress from tension to compression by just irradiating successive laser pulses to metallic materials under aqueous environment without any surface preparation. The effects of laser peening have been experimentally studied on residual stress, stress corrosion cracking(SCC) susceptibility and fatigue properties with water-penetrable frequency-doubled Nd:YAG laser. In addition, laser peening has been widely used in aviation and aerospace industries, automobile manufacturing and nuclear plant. One of the most important causes to improve the above-mentioned properties is the deeper compressive residual stress induced by laser peening. Taking advantage of the process without reacting force against laser irradiation, a remote operating system was developed to apply laser peening to nuclear power reactors as a preventive maintenance measure against SCC.

The Laser Peening Effect for Improving the Surface Properties of Metals (금속표면 특성향상을 위한 laser peening 효과)

  • Chung, Chin-Man;Baik, Sung-Hoon;Kim, Joung-Soo;Lee, Sang-Bae
    • Laser Solutions
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    • v.11 no.3
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    • pp.5-9
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    • 2008
  • The effect of a laser peening on the surface residual stress of SUS 304 was investigated using a second harmonic Nd:YAG laser beam. The energy density and the diameter of the laser beam were $400mJ/mm^2$ and about 1mm, respectively. According to the test results, the effect of a laser peening for improving the surface residual stress was not big enough to induce a high compressive stress on the SUS 304 surface. This is thought to be attributed to the small radius of the laser beam used in this study, even though its energy density is big enough. From this study, it can be concluded that to induce a recognizably high compressive stress on a metal surface, the energy density as well as the size (diameter) of the laser beam should be large enough to generate surface plasma with a high energy to have a big impact to a metal surface.

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Laser Peening: A Novel Tool to Reduce SCC Susceptibility and Prolong Fatigue Life of Metallic Components

  • Sano, Yuji;Kim, Jong-Do
    • Journal of Advanced Marine Engineering and Technology
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    • v.34 no.5
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    • pp.661-669
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    • 2010
  • The effects of laser peening on metallic materials have been investigated with water-penetrable frequency-doubled Nd:YAG laser. Laser pulses of 200 mJ energy and 8 ns duration focused on samples underwater with 0.8 mm spot diameter. X-ray study showed that compressive residual stress was imparted on SKD61 from the surface to nearly 2 mm depth. Stress corrosion cracking (SCC) was prohibited for sensitized SUS304 even in a severely corrosive environment fatigue lives of SUS316L and SM490A welded samples were prolonged significantly in the high-cycle regime. Since 1999, laser peening has been applied to prevent SCC in operating nuclear power plants in Japan.

Laser Peening Application for PWR Power Plants (비등수형 원자로 발전소에의 레이저 피닝 적용기술)

  • Kim, Jong-Do;SANO, Yuji
    • Journal of Welding and Joining
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    • v.34 no.5
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    • pp.13-18
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    • 2016
  • Toshiba has developed a laser peening system for PWRs(pressurized water reactors) as well after the one for BWRs(boiling water reactors), and applied it for BMI(bottom-mounted instrumentation) nozzles, core deluge line nozzles and primary water inlet nozzles of Ikata Unit 1 and 2 of Shikoku Electric Power Company since 2004, which are Japanese operating PWR power plants. Laser pulses were delivered through twin optical fibers and irradiated on two portions in parallel to reduce operation time. For BMI nozzles, we developed a tiny irradiation head for small tubes and we peened the inner surface around J-groove welds after laser ultrasonic testing (LUT) as the remote inspection, and we peened the outer surface and the weld for Ikata Unit 2 supplementary. For core deluge line nozzles and primary water inlet nozzles, we peened the inner surface of the dissimilar metal welding, which is of nickel base alloy, joining a safe end and a low alloy metal nozzle. In this paper, the development and the actual application of the laser peening system for PWR power plants will be described.

Fatigue Life Prediction of a Laser Peened Structure Considering Model Uncertainty (모델 불확실성을 고려한 레이저 피닝 구조물의 피로 수명 예측)

  • Im, Jong-Bin;Park, Jung-Sun
    • Journal of the Korean Society for Aeronautical & Space Sciences
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    • v.39 no.12
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    • pp.1107-1114
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    • 2011
  • In this paper, the fatigue life of a laser peened structure was predicted. In order to calculate residual stress induced by laser peening finite element simulation was carried out. Modified Goodman equation was used to consider the effect of compressive residual stress induced by laser peening in fatigue analysis. In addition, additive adjustment factor approach was applied to consider S-N curve model uncertainty. Consequently, the reliable bounds of the predicted fatigue life of the laser peened structure was determined.

Prediction of the Constitutive Properties of Metal from Laser Peening Simulation (레이저 피닝 시뮬레이션을 통한 금속재료의 물성치 예측)

  • Yeo, In Kyu;Lim, Hyun Taek;Lim, Jong Bin;Jeong, Sung Ho
    • Laser Solutions
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    • v.16 no.1
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    • pp.15-19
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    • 2013
  • For numerical simulation of the deformation and residual stress development in metals during laser peening, the constitutive equations describing material behavior at various strain rates and plastic properties at high strain rate impact conditions are prerequisite. However, these parameters are often unknown for various engineering materials. In this study, the parameters of Johnson-Cook constitutive equation of duplex stainless steel were determined by comparing the residual stress profile predicted by numerical simulation using trial values and the measured residual stress profile with x-ray diffraction.

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A Numerical Analysis on Application of Laser Peening to Dissimilar Metal Welds in a Safety Injection Nozzle of Integral Reactor (일체형 원자로 안전주입 노즐 이종금속 용접부에 대한 레이저 피닝 적용의 수치 해석적 연구)

  • Seo, Joong-Hyun;Kim, Jong-Sung;Jhung, Myung-Jo;Ryu, Yong-Ho
    • Transactions of the Korean Society of Mechanical Engineers A
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    • v.36 no.6
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    • pp.599-608
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    • 2012
  • A numerical analysis has been performed through implicit dynamic finite element analysis using the commercial package, ABAQUS in order to investigate effect of laser peening on welding residual stress mitigation of dissimilar metal welds in a safety injection nozzle of integral reactor. The implicit dynamic finite element analysis are compared with the previous experimental results. By comparison, it is identified that the implicit dynamic finite element analysis is valid for residual stress mitigation via laser peening. Implicit static finite element residual stress analysis has been performed for the dissimilar metal welds subject to inner repair welding. The analysis results represent that both axial and hoop residual stresses are tensile on inner surface of safety injection nozzle due to inner repair welding. Also Parametric study has performed to investigate effect of laser peening variables such as maximum impact pressure, duration time of pressure, spot diameter and peening direction on the welding residual stress mitigation. As a result, it is found that laser peening has the preventive maintenance effect to mitigate mainly residual stresses of region near inner surface.