scholarly journals Quarter Century Development of Laser Peening without Coating

Metals ◽  
2020 ◽  
Vol 10 (1) ◽  
pp. 152 ◽  
Author(s):  
Yuji Sano
Keyword(s):  
Pulse Energy ◽  
Nuclear Power ◽  
Surface Preparation ◽  
Laser Pulses ◽  
Intense Laser ◽  
Fatigue Properties ◽  
Laser Peening ◽  
Quarter Century ◽  
Pulse Density ◽  
Laser Peening Without Coating

This article summarizes the development of laser peening without coating (LPwC) during the recent quarter century. In the mid-1990s, the study of LPwC was initiated in Japan. The objective at that time was to mitigate stress corrosion cracking (SCC) of structural components in operating nuclear power reactors (NPRs) by inducing compressive residual stresses (RSs) on the surface of susceptible components. Since the components in NPRs are radioactive and cooled underwater, full-remote operation must be attained by using lasers of water-penetrable wavelength without any surface preparation. Compressive RS was obtained on the top-surface by reducing pulse energy less than 300 mJ and pulse duration less than 10 ns, and increasing pulse density (number of pulses irradiated on unit area). Since 1999, LPwC has been applied in NPRs as preventive maintenance against SCC using frequency-doubled Q-switched Nd:YAG lasers (λ = 532 nm). To extend the applicability, fiber-delivery of intense laser pulses was developed in parallel and has been used in NPRs since 2002. Early first decade of the 2000s, the effect extending fatigue life was demonstrated even if LPwC increased surface roughness of the components. Several years ago, it was confirmed that 10 to 20 mJ pulse energy is enough to enhance fatigue properties of weld joints of a structural steel. Considering such advances, the development of 20 mJ-class palmtop-sized handheld lasers was initiated in 2014 in a five-year national program, ImPACT under the cabinet office of the Japanese government. Such efforts would pave further applications of LPwC, for example maintenance of infrastructure in the field, beyond the horizons of the present laser systems.

scholarly journals Effects of Laser Peening with a Pulse Energy of 1.7 mJ on the Residual Stress and Fatigue Properties of A7075 Aluminum Alloy

Metals ◽  
2021 ◽  
Vol 11 (11) ◽  
pp. 1716
Author(s):  
Yuji Sano ◽  
Kiyotaka Masaki ◽  
Yoshio Mizuta ◽  
Satoshi Tamaki ◽  
Tomonao Hosokai ◽  
...  
Keyword(s):  
Aluminum Alloy ◽  
Pulse Energy ◽  
Laser Pulses ◽  
Microchip Laser ◽  
Fatigue Properties ◽  
Laser Peening ◽  
Robot Arm ◽  
X Ray Diffraction ◽  
Bending Fatigue ◽  
Laser Peening Without Coating

Laser peening without coating (LPwC) using a palmtop-sized microchip laser has improved the residual stresses (RSs) and fatigue properties of A7075 aluminum alloy. Laser pulses with a wavelength of 1.06 μm and duration of 1.3 ns from a Q-switched Nd:YAG microchip laser were focused onto A7075 aluminum alloy samples covered with water. X-ray diffraction revealed compressive RSs on the surface after irradiation using laser pulses with an energy of 1.7 mJ, spot diameter of 0.3 mm, and density of 100–1600 pulse/mm2. The effects were evident to depths of a few hundred micrometers and the maximum compressive RS was close to the yield strength. Rotation-bending fatigue experiments revealed that LPwC with a pulse energy of 1.7 mJ significantly prolonged the fatigue life and increased the fatigue strength by about 100 MPa with 107 fatigue cycles. The microchip laser used in this study is small enough to fit in the hand or be mounted on a robot arm. The results may lead to the development of tools that extend the service life of various metal parts and structures, especially outdoors where conventional lasers are difficult to apply.

scholarly journals A Mechanism for Inducing Compressive Residual Stresses on a Surface by Laser Peening without Coating

Metals ◽  
2020 ◽  
Vol 10 (6) ◽  
pp. 816 ◽  
Author(s):  
Yuji Sano ◽  
Koichi Akita ◽  
Tomokazu Sano
Keyword(s):  
Single Pulse ◽  
Laser Pulses ◽  
Mechanical Effect ◽  
Intense Laser ◽  
Laser Peening ◽  
X Ray Diffraction ◽  
X Ray ◽  
Intense Laser Pulses ◽  
Laser Peening Without Coating ◽  
Compressive Residual Stresses

Laser peening without coating (LPwC) involves irradiating materials covered with water with intense laser pulses to induce compressive residual stress (RS) on a surface. This results in favorable effects, such as fatigue enhancement; however, the mechanism underlying formation of the compressive RS is not fully understood. In general, tensile RS is imparted on the surface of the material due to shrinkage after heating by laser irradiation. In this study, we assessed the thermo-mechanical effect of single laser pulse irradiation and introduce a phenomenological model to predict the outcome of LPwC. To validate this model, RS distribution across the laser-irradiated spot was analyzed using X-ray diffraction with synchrotron radiation. In addition, the RS was evaluated across a line and over an area, following irradiation by multiple laser pulses with partial overlapping. Large tensile RSs were found in the spot irradiated by the single pulse; however, compressive RSs appeared around the spot. In addition, the surface RS state shifted to the compressive side due to an increase in overlap between neighboring laser pulses on the line and over the area of irradiation. The compressive RSs around a subsequent laser spot effectively compensated the tensile component on the previous spot by controlling the overlap, which may result in compressive RSs on the surface after LPwC.

scholarly journals The Effect of Laser Peening without Coating on the Fatigue of a 6082-T6 Aluminum Alloy with a Curved Notch

Metals ◽  
2019 ◽  
Vol 9 (7) ◽  
pp. 728 ◽  
Author(s):  
Enrico Troiani ◽  
Nicola Zavatta
Keyword(s):  
Aluminum Alloy ◽  
Fatigue Life ◽  
Residual Stresses ◽  
Fatigue Behavior ◽  
Surface Hardness ◽  
Element Model ◽  
Fatigue Tests ◽  
Fatigue Properties ◽  
Laser Peening ◽  
Laser Peening Without Coating

Laser shock peening has established itself as an effective surface treatment to enhance the fatigue properties of metallic materials. Although a number of works have dealt with the formation of residual stresses, and their consequent effects on the fatigue behavior, the influence of material geometry on the peening process has not been widely addressed. In this paper, Laser Peening without Coating (LPwC) is applied at the surface of a notch in specimens made of a 6082-T6 aluminum alloy. The treated specimens are tested by three-point bending fatigue tests, and their fatigue life is compared to that of untreated samples with an identical geometry. The fatigue life of the treated specimens is found to be 1.7 to 3.3 times longer. Brinell hardness measurements evidence an increase in the surface hardness of about 50%, following the treatment. The material response to peening is modelled by a finite element model, and the compressive residual stresses are computed accordingly. Stresses as high as −210 MPa are present at the notch. The ratio between the notch curvature and the laser spot radius is proposed as a parameter to evaluate the influence of the notch.

Compressive Residual Stress Evolution Process by Laser Peening

2005 ◽  
Vol 490-491 ◽  
pp. 370-375 ◽  
Author(s):  
Koichi Akita ◽  
Hirotomo Tanaka ◽  
Yuji Sano ◽  
Shin Ichi Ohya
Keyword(s):  
Residual Stress ◽  
Plastic Deformation ◽  
Laser Pulse ◽  
Tensile Stress ◽  
Thermal Effect ◽  
Stress Component ◽  
Laser Pulses ◽  
Intense Laser ◽  
Evolution Process ◽  
Pulse Density

Microscopic residual stress distribution on laser-irradiated materials was measured using a synchrotron radiation source. Intense laser pulses were irradiated in water to high tensile strength steel and austenitic stainless steel without any surface coating. Residual stress was measured in a laser-irradiated spot (0D), line (1D) and area (2D) on the materials in order to clarify the evolution process of residual stress. Tensile residual stresses were observed in the laser single pulse irradiated spot (0D). In the line (1D) and area (2D) irradiation, however, the tensile residual stress gradually changed into compressive side as the density of irradiated laser pulses increased. In case of laser irradiation in water, resulting residual stress is considered to be the sum of a tensile stress component by thermal effect and a compressive one by plastic deformation due to shock wave. The tensile stress component remains constant even if the laser pulse density increases, because the thermal effect may be reset every pulse, whereas the compressive stress component increases with laser pulse density, until the saturation of plastic deformation. As a result, the surface residual stress changes into compression with increasing the laser pulse density.

Enhancement of Surface Properties by Laser Peening Without Coating

2006 ◽  
Author(s):  
Yuji Sano ◽  
Igor Altenberger ◽  
Berthold Scholtes ◽  
Kiyotaka Masaki ◽  
Yasuo Ochi ◽  
...  
Keyword(s):  
Residual Stress ◽  
Compressive Residual Stress ◽  
High Cycle Fatigue ◽  
Laser Pulses ◽  
Cast Aluminum Alloy ◽  
Laser Peening ◽  
Cycle Fatigue ◽  
Cast Aluminum ◽  
Rotating Bending ◽  
Laser Peening Without Coating

Laser peening without coating (LPwC) has been applied to water-immersed materials using a water-penetrable light of a Q-switched and frequency-doubled Nd:YAG laser. Compressive residual stress of several hundred MPa was introduced at the surface of the materials. High-cycle fatigue (HCF) properties were evaluated through rotating-bending or push-pull type testing for an austenitic stainless steel (SUS316L), a titanium alloy (Ti-6Al-4V) and a cast aluminum alloy (AC4CH). LPwC prolonged the fatigue lives significantly, in spite of the increase in surface roughness ascribed to the ablative interaction of laser pulses with the materials.

Laser Peening Systems for Preventive Maintenance Against Stress Corrosion Cracking in Nuclear Power Reactors

2008 ◽  
Author(s):  
Takuya Uehara ◽  
Masaki Yoda ◽  
Yuji Sano ◽  
Naruhiko Mukai ◽  
Itaru Chida ◽  
...  
Keyword(s):  
Stress Corrosion ◽  
Stress Corrosion Cracking ◽  
Preventive Maintenance ◽  
Nuclear Power ◽  
Laser Pulses ◽  
Corrosion Cracking ◽  
Prototype System ◽  
Impulsive Effect ◽  
Laser Peening ◽  
Beam Delivery

Laser peening introduces compressive residual stress on metal surface by irradiating laser pulses underwater without any surface preparations. The process utilizes the impulsive effect of high-pressure plasma generated through ablative interaction of each laser pulse with material. Laser peening systems, which deliver laser pulses with mirrors or through an optical fiber, were developed and have been applied to preventive maintenance against stress corrosion cracking (SCC) in nuclear power reactors since 1999. Each system was composed of laser oscillators, a beam delivery system, a laser irradiation head, remote handling equipment and a monitor/control system. Beam delivery with mirrors was accomplished through alignment/tracking functions with sufficient accuracy. Reliable fiber-delivery was attained by the development of a novel input coupling optics and an irradiation head with auto-focusing. At present, we are developing a newer concept and the prototype system has been just completed, which is extremely small, reliable and easy-handled.

scholarly journals High laser induced damage threshold photoresists for nano-imprint and 3D multi-photon lithography

Nanophotonics ◽  
2021 ◽  
Vol 0 (0) ◽  
Author(s):  
Elmina Kabouraki ◽  
Vasileia Melissinaki ◽  
Amit Yadav ◽  
Andrius Melninkaitis ◽  
Konstantina Tourlouki ◽  
...  
Keyword(s):  
Nanoimprint Lithography ◽  
Three Dimensional ◽  
Damage Threshold ◽  
Laser Pulses ◽  
Intense Laser ◽  
Optical Elements ◽  
Photonic Circuits ◽  
Future Production ◽  
Intense Laser Pulses ◽  
Laser Induced Damage

Abstract Optics manufacturing technology is predicted to play a major role in the future production of integrated photonic circuits. One of the major drawbacks in the realization of photonic circuits is the damage of optical materials by intense laser pulses. Here, we report on the preparation of a series of organic–inorganic hybrid photoresists that exhibit enhanced laser-induced damage threshold. These photoresists showed to be candidates for the fabrication of micro-optical elements (MOEs) using three-dimensional multiphoton lithography. Moreover, they demonstrate pattern ability by nanoimprint lithography, making them suitable for future mass production of MOEs.

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