Yuji Sano

Institute for Molecular Science · Division of Research Innovation and Collaboration

In order to investigate the effect of laser peening treatment on high cycle fatigue properties, rotating bending fatigue tests were carried out for laser peened gas-carburized SCM420H steel. In this study, two types of pulse laser oscillators such as conventional high power laser equipment and hand-held compact laser equipment were prepared to gene...

Over the past century, understanding the nature of shock compression of condensed matter has been a major topic. About 20 years ago, a femtosecond laser emerged as a new shock-driver. Unlike conventional shock waves, a femtosecond laser-driven shock wave creates unique microstructures in materials. Therefore, the properties of this shock wave may b...

Laser peening (LP) is a well-established technique for introducing compressive residual stress (RS) near the surface of metal components to improve their high-cycle fatigue properties. In this study, butt-welded joint specimens of SBHS500 steel with angular distortion were prepared and treated with LP. X-ray diffraction showed that the maximum comp...

Laser peening can introduce compressive residual stresses on the surface of various materials, thereby effectively prolonging their fatigue lives. In this study, the effects of laser peening with pulse energies of 20 and 70 mJ on residual stress and fatigue life were investigated on two types of HT780 box-welded specimens of different sizes, consid...

Laser peening can introduce compressive residual stresses on the surface of various materials, thereby effectively prolonging their fatigue lives. In this study, the effects of laser peening with pulse energies of 20mJ and 70mJ on residual stress and fatigue life were investigated on two types of HT780 box-welded specimens with different sizes, con...

Laser peening can introduce compressive residual stress on the surface of various materials and, therefore, is effective in enhancing the fatigue strength. This study clarifies whether the laser peening with lower pulse energy comparing to the preceding studies generates compressive residual stress, and whether such stress would account for prolong...

Laser peening (LP) is a well-established technique for introducing compressive residual stress (RS) near the surface of metal components, to improve their high-cycle fatigue properties. The authors have developed a compact LP device with a thumb-sized Nd:YAG microchip laser mounted on a collaborative robot arm. The device was applied to 9-mm-thick...

The advantage of laser peening is the possibility of fine execution management and the capability to introduce deep compressive residual stresses on the material surfaces. It is well known to be highly effective in inhibiting stress corrosion cracking and fatigue cracking on material surfaces. In addition, laser peening has an excellent effect on i...

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 diffrac...

A high-power pulsed microchip laser, which has a pulse duration of sub-nanosecond order, had been developed. A focused microchip laser pulse can induce an effective shock wave for deforming the irradiated metal surface plastically. When a sheet metal surface is scanned by the laser, dieless sheet forming, called laser peen forming, is achieved thro...

Synchrotron radiation (SR) and X-ray free electron laser (XFEL) are indispensable tools not only for the exploration of science but also for the evolution of industry. We used SR and XFEL to elucidate the mechanism and the effects of laser peening without coating (LPwC) which enhances the durability of metallic materials. X-ray diffraction (XRD) em...

Grain boundary engineering (GBE) has a high potential to suppress intergranular degradation and improve weld properties. Thermomechanical processing is typically used to optimize grain boundary character distributions (GBCDs) for the GBE of face-centered cubic materials with low stacking fault energy. Pre-straining plus annealing has achieved the o...

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...

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...

We found some damage at the forks of low-pressure turbine blades caused by random vibration and steam-flashback vibration at nuclear power plant. In this study, to improve fatigue property, we developed and examined laser peening technology for 12Cr stainless steel and material properties. Laser peening induces compressive residual stress on materi...

Laser peening was applied to A7075-T73 aluminum alloy and HT780 high-strength steel with low energy pulses of 2.5 mJ to 20 mJ which is attainable by ultra-compact handheld lasers. Then, we measured surface residual stresses of both materials by x-ray diffraction using a cos α method and confirmed that compressive residual stresses were built on the...

Laser peening can generate compressive residual stress on the object surface. In this study, effects of the laser peening for fatigue crack propagation of friction stir welded butt joint were investigated. As a result of fatigue crack propagation investigating with laser peening treated specimen with a thickness of 3mm which have a surface fatigue...

This work reports for the first time the effect of femtosecond laser shock peening (fLSP) without a sacrificial overlay under atmospheric conditions (no confinement) on the corrosion behaviour of AA2024-T3. After fLSP and additional exposure to air a superhydrophobic state (θ=160 ± 4°) is achieved. Moreover, fLSPed corrosion-resistant surface contr...

Laser peening can introduce compressive residual stress on the surface of various materials and, therefore, is effective in enhancing the fatigue strength. This study clarifies whether the laser peening with lower pulse energy comparing to the preceding studies generates compressive residual stress, and whether such stress would account for prolong...

We measured the refractive index of germanium and gold prisms at 1.7 MeV to explore if there are refractive index enhancements to 6th power of atomic number due to high order nonlinear process of Delbrück scattering in quantum electrodynamics. We measured the deflection by prisms using imaging plates and laser Compton scattering γ-rays with linear...

The authors have successfully performed femtosecond laser peening on a 2024 aluminum alloy without any sacrificial overlays. Laser pulses were directly irradiated to the surface of specimens in the air without water film as a plasma confinement medium during the peening treatment. The fatigue life was improved as much as 38 times in comparison with...

In order to improve the fatigue properties of a similar butt friction stir welded joint of A2024 Aluminum alloy, two types of laser peening with femtosecond or nanosecond pulse laser equipment were applied. Fatigue tests were conducted at stress ratio R= -1, road frequency 23Hz with plane bending fatigue condition. Fatigue property was improved by...

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 oper...

Laser peening can introduce compressive residual stress to the surface and, therefore, is effective in enhancing the fatigue strength. This study targets 780 MPa grade high-strength steel (HT780) in order to clarify whether laser peening generates compressive residual stress on the surface of HT780, and whether such stress would account for prolong...

In order to improve the fatigue properties of similar butt friction stir welded joint of A2024 Aluminum alloys, laser peening which was laser peening treatment with femtosecond pulse laser equipment was applied. This femtosecond laser peening does not need water in the peeing processing. And fatigue tests were conducted at stress ratio R= -1, road...

Cosmic-ray-muon imaging is proposed to assess the damages to the Fukushima Daiichi reactors. Simulation studies showed capability of muon imaging to reveal the core conditions.The muon-imaging technique was demonstrated at Toshiba Nuclear Critical Assembly, where the uranium-dioxide fuel assembly was imaged with 3-cm spatial resolution after 1 mont...

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 enviro...

Laser Shock Peening is a fatigue enhancement treatment using laser energy to induce compressive Residual Stresses (RS) in the outer layers of metallic components. This work describes the variations of introduced RS-field with peen size and coverage for thin metal samples treated with under-water-LSP. The specimens under investigation were of alumin...

Disclosed is a coating method using a plasma shock wave, the method including the steps of: irradiating a pulse laser to a first surface of a mixed layer obtained by mixing powders and resin to generate a plasma, the mixed layer being formed on a second surface of a substance to be coated; striking the powders on the second surface by using a shock...

Compressive residual stresses induced by peening techniques improve the strength properties of steels, such as fatigue and stress corrosion cracking. However, the compressive residual stress might be reduced owing to thermal and mechanical loading in-service. In this study, the behavior of surface and internal residual stresses of a laser-peened fe...

Reactor imaging using scattering of cosmic-ray muon is proposed to assess the damages to the reactors at Fukushima Daiichi. Simulation studies showed feasibility of the reactor imaging with muons, and the technique has been demonstrated at a research reactor, Toshiba Nuclear Critical Assembly, where the reactor core was imaged with spatial resoluti...

A technical demonstration of cosmic-ray muon radiography of a UO2 fuel assembly was performed at Toshiba Nuclear Critical Assembly (NCA). The fuel assembly in the NCA was imaged through obstacles such as steel and concrete. The result suggested that the method can be applicable to assess the damage to the reactors at the Fukushima Daiichi nuclear p...

Plane bending fatigue testing was performed to study the fatigue properties of friction stir welded (FSW) 3 mm thick AA6061-T6 aluminum alloy plates. Fatigue cracks propagated with bends and curves on the specimens, showing large deviation from a linear line. This might be reflecting the material flow and microstructure in the weld zone. The fatigu...

Mechanical surface treatments such as laser-shock peening or deep rolling are known to induce highly strain-hardened nanoscale microstructures as well as deep compressive residual stress layers into surface regions of fan blade titanium alloys such as Ti-6Al-4V. The benefit of such treatments is well documented for cyclic loading at room temperatur...

The precipitation hardened ordered copper-based alloy CuMn20Ni20 is used as a non-magnetic high strength alloy in offshore- and onshore oil drilling exploration. In spite of already excellent mechanical properties, mechanical enhancement methods such as swaging, deep rolling (ball burnishing), shot peening or laser peening remain attractive for enh...

A technical demonstration to image a research reactor, Toshiba Nuclear Critical Assembly, with cosmic-ray muons is presented. The demonstration was performed as a precursor to Fukushima Daiichi muon imaging. We have obtained resolution of 3 cm during 1 month of exposure time. This result is in agreement with previous simulation results conducted on...

Many fatigue cracks from welded joints have been detected in steel bridges. Among various methods to improve the fatigue strength of welded zones, this paper focuses on laser peening, which introduces compressive residual stresses on surfaces because they effectively enhance the fatigue lives of welded components. Tensile residual stress due to wel...

A 1.2 x 1.2 m(2) muon tracker was moved from Los Alamos to the Toshiba facility at Kawasaki, Japan, where it was used to take similar to 4 weeks of data radiographing the Toshiba Critical Assembly Reactor with cosmic ray muons. In this paper, we describe the analysis procedure, show results of this experiment, and compare the results to Monte Carlo...

In recent years, friction stir welding (FSW) joints are used for structural components of cars, ships, aircrafts et al. It is important to investigate the fatigue properties of the FSW joints because the structural components are usually subjected to repeated stresses. In this study, laser peening without coating (LPwC) treatment was applied to imp...

Laser peening can introduce compressive residual stress to the surface and therefore is effective in enhancing fatigue strength. In this study, we conducted laser peening in air with a water film formed by a nozzle and examined whether the distribution of residual stress along the thickness was different from that achieved by laser peening in water...

Microstructure and a fatigue crack propagation path inside a dissimilar friction stir welded plate between A2024 and A6061 aluminum alloys were visualized with synchrotron radiation computed laminography at SPring-8. A fatigue crack propagated in a different direction from the perpendicular to fatigue loading under the influence of the plastic flow...

A technical demonstration to image a research reactor, Toshiba Nuclear Critical Assembly, with cosmic-ray muons is presented. The demonstration was performed as a precursor to Fukushima Daiichi muon imaging. We have obtained resolution of 3 cm during 1 month of exposure time. This result is in agreement with previous simulation results conducted on...

Synchrotron radiation computed laminography (SRCL) was carried out at SPring-8 to visualize a fatigue crack inside a friction stir welded plate and to investigate the propagation behavior. The surface fatigue crack shape and its size reproduced by SRCL agree well with the observation by an optical microscope. A fatigue crack propagation curve obtai...

In order to investigate the effects of laser peening on high cycle fatigue properties of (α + β) type T1-6A1-4V alloy, rotating bending fatigue tests were carried out. The laser peening conditions were a spot size of 0.8mm in diameter, a pulse energy of 200mJ and an irradiation pulse density of 38 pulse/mm2. The fatigue properties were not improved...

The axial fatigue tests with constant load and stress rations of -1.0 and 0.1 were conducted in order to investigate the effects of the laser peening (LP) treatment on the fatigue strength and the fatigue crack behaviors in the rolled aluminum alloy A7050 for aircraft structures. The LP treatment was effective for fatigue strength improvement in th...

In order to improve the high cycle rotating bending fatigue property of Ti-6Al-4V Titanium alloy, laser peening without coating and shot peening with zirconia shot were applied. As the result of investigating the relation between fatigue property, surface roughness and residual stress, it proposed that fatigue life property was improved by giving t...

In order to visualize a fatigue crack inside a friction stir welded plate, synchrotron radiation computed laminography (SRCL) was carried out at SPring-8. As the results of SRCL, the surface fatigue crack shape and its size were well in agreement with the observation by an optical microscope. Furthermore, it was clear that the crack inside the spec...

In order to visualize a fatigue crack inside a friction stir welded plate, micro computed tomography was carried out using Industrial X-ray CT. The contrast of reconstructed slice image has been improved as a result of using the specimen holder for making a tabular specimen into pillar specimen. And the surface fatigue crack shape and its size were...

Laser peening without coating (LPwC) can introduce compressive residual stress to the surface and, therefore, is effective in enhancing the fatigue strength. This study used butt welded structural steel joints to investigate changes in the residual stress and the hardness near the toe of the welded zone and to examine the major factor causing the i...

Laser shock peening can potentially enhance fatigue life of titanium components by inducing compressive residual stresses in surface layers much deeper than caused by traditional shot peening (SP). In the present study, the high cycle fatigue (HCF) performance of α Ti-alloy Ti–2.5Cu, (α + β) Ti-alloy TIMETAL 54M and the metastable β Ti-alloy TIMETA...

Rotating beam fatigue specimens of Ti-6A1-4V were mechanically surface treated by various methods. Conventional shot peening (SP), ultrasound shot peening (USD.laser shock peening (LSP) and ball-burnishing (BB) were applied varying the main process parameters to a wide extent. The resulting changes in surface topography,micro-hardness-depth and res...

Investigation of fatigue crack propagation behavior is important for understanding the fatigue fracture of metal materials. The authors have applied computed tomography (CT) with synchrotron radiation (SR) of SPring-8 to the nondestructive observation of fatigue cracks in aluminum alloys. The results are summarized in this paper, which includes: (1...

In order to visualize fatigue cracks inside a specimen, computed tomography (CT) was carried out using synchrotron radiation at SPring-8 and industrial X-ray CT scanner. The images of the crack were reconstructed by both CTs under conditions as similar as possible. Refraction contrast effect is the major difference between reconstructed slice image...

Purpose Laser peening without coating (LPwC) is an innovative surface enhancement technology for introducing compressive residual stress in metallic materials. The purpose of this study is to examine the characteristic at the laser‐peened welded zone and the fatigue lives of the welding joints. Design/methodology/approach LPwC conditions for 490 M...

Laser peening which introduces compressive residual stress on surface is effective in extending fatigue lives of welded components, because tensile residual stress after welding is one of the most important factors reducing the fatigue lives. Steels for structures are widely used for bridges, buildings, etc., however the effects of laser peening on...

Some damages were found at the forks of low pressure turbine blades due to high-cycle fatigue caused by random vibration and steam-flashback vibration. In this study, laser peening technology was developed to improve high-cycle fatigue properties of 12Cr stainless steel of blades material, and the effect on the material properties was examined. Las...

Tensile stress is necessary for observing fatigue cracks by X-ray computed tomography (CT) because the fatigue crack tip is normally closing without fatigue loading. In this study, the influence of the tensile stress on the observing results of a fatigue crack by micro CT with synchrotron radiation was investigated. The area of the fatigue crack pr...

The relaxation behavior of residual stress induced by laser peening during mechanical loading was investigated on an aluminum alloy A2024. The residual stress relaxation process was measured by x-ray diffraction method and analyzed by a finite element method (FEM). The plastic deformation behavior was evaluated from the x-ray diffraction peak width...

Purpose The purpose of this paper is to investigate the influence of mechanical surface treatments on the surface layer properties and the fatigue performance of the aircraft alloys Al 7075‐T73 and Ti‐6Al‐4V Design/methodology/approach Laser peening without coating (LPwC), shot peening (SP), ultrasonic shot peening (USP) and ball burnishing (BB) w...

As a result of the variety of mechanical surface treatments, studies of surface and near-surface characteristics are becoming increasingly important in a variety of industrial fields. This is to achieve more gains by balancing between optimum conditions and costs. In the present study, shot peening (SP), ball-burnishing (BB), laser shock peening (L...

Purpose – The purpose of this paper is to investigate the behavior of compressive residual stress induced by laser peening under external loading on an age‐hardened high‐strength aluminum alloy A2024‐T3, a low‐carbon austenitic stainless steel SUS316L (Type 316L) and a nickel‐based alloy NCF600 (Alloy 600). Design/methodology/approach – The surfac...

The authors have applied laser peening without coating (LPwC) to fatigue specimens cut out from friction stir welded (FSWed) A6061-T6 aluminum alloy plates with a thickness of 3 mm. Both crown and root sides of the specimens were peened by laser pulses with an energy of 60 mJ and a peak power density of 2 GW/cm2 from a frequency-doubled Nd:YAG lase...

Laser Maintenance Technologies for Nuclear Power Reactors

The axial fatigue tests with stress rations of -1.0 and 0.1 were conducted in order to investigate the effects of the laser peening (LP) treatment on the fatigue strength and the fatigue crack behaviors in the rolled aluminum alloy A7050 for aircraft structures. The LP treatment was effective for fatigue strength improvement in the fatigue lives be...

Stress intensity factor of fatigue crack tip after two fatigue cracks had connected it was estimated by conventional method using replication technique under rotating bending load. The stress intensity factor was calculated with the surface crack length which was obtained by replica film observation and aspect ratio which was obtained by some way....

In order to investigate the effect of laser peening (LP) treatment for the fatigue property improvement of friction stir welded A6061-T6 aluminum alloy joints (FSW), plane bending fatigue tests were carried out. Although the surface roughness was increased by LP treatment, the fatigue limit of the laser peened FSW specimen was higher than the fatig...

In order to investigate the effects of surface polishing for high cycle fatigue property on the laser peened Ti-6Al-4V specimen, the rotating bending fatigue test were carried out with three kinds of the electrical polished(EP) specimen, mechanical polished(MP) specimen and MEP specimen was polished with both polishing. As the results, the fatigue...

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. Stre...

Some fatigue damages were found at the forks of low pressure turbine blades caused by random vibration and steam-flashback vibration. In this study, laser peening technology for 12Cr stainless steel was developed and the improvement of fatigue property was examined. As the results, the fatigue strength of laser peened specimens was improved about 4...

Axial fatigue tests with stress ratio of −1 and 0.1 were conducted in order to investigate effects of laser peening treatment without protective coating (LPwC) on fatigue property such as the fatigue strength and the surface crack behaviors of rolled aluminum alloy A7050-T7451 for aircraft structures. As results, The LPwC treatment was effective fo...

Laser peening is an emerging surface technology to enhance fatigue properties of metallic materials through imparting compressive residual stress on the surface. Samples of AC4CH cast aluminum alloy were peened with a Q-switched and frequency-doubled Nd:YAG laser. Compressive residual stress was introduced from the surface to the depth of 1mm or de...

Laser peening without protective coating (LPwC) treatment is one of surface enhancement techniques using an impact wave of high pressure plasma induced by laser pulse irradiation. High compressive residual stress was induced by the LPwC treatment on the surface of low-carbon type austenitic stainless steel SUS316L. The affected depth reached about...

Fatigue crack propagation behavior is essential to investigate the mechanism of fatigue fracture. The replication technique has been used to observe the behavior on the surface of various materials; however, the technique does not provide the information on the shape of cracks inside materials. In the present study, the authors have attempted micro...

Fine ceramics have high strength, excellent wear resistance, chemical stability and high strength at high temperature and are receiving attention in various fields such as construction, engineering, aerospace and marine science. Finish machining process is required to obtain precise ceramics components because sintering process necessary for obtain...

The interference behavior of two surface fatigue cracks on A7050-T7451 aluminum alloy was investigated by replication technique and micro computed tomography (μCT) with synchrotron radiation of SPring-8. From the results, fatigue crack propagation behavior inside the specimen was obtained. And furthermore, values of stress intensity factor of the c...

Rotating bending fatigue tests were conducted in order to investigate effects of laser peening (LP) treatment on fatigue property of rolled aluminum alloys A7050-T7451 for aircraft structures. As the results, the LP treatment was effective for the fatigue property improvement of A7050-T7451 alloys. The fatigue strength of the alloys at 107 cycles w...

High cycle fatigue tests with an axial loading were carried out on the extended aluminum alloy A7050-T7451 in order to investigate the Laser peening (LP) effects on the surface crack behaviors of smooth and notched specimens. The propagation rates of the surface cracks on the smooth specimens were reduced and the cracks from notched specimens were...

Some damages were found at the forks of low pressure turbine blades caused by random vibration and steam-flashback vibration. In this study, for the aim of fatigue property improvement, laser peening technology for 12Cr stainless steel was developed and material properties were examined. Laser peening is a process to induce compressive residual str...