The University of Osaka · Engineering
Professor Yuji Sano's research lab specializes in advanced surface engineering and materials processing, with a primary focus on laser peening without coating (LPwC) for enhancing the mechanical integrity and durability of structural materials. The lab investigates the fundamental mechanisms of compressive residual stress formation under ultra-short laser pulses, particularly in aqueous environments relevant to nuclear and aerospace applications. Key research directions include the non-destructive evaluation of residual stresses using synchrotron radiation, the mitigation of stress corrosion cracking, and the improvement of high-cycle fatigue performance in critical alloys such as titanium, aluminum, and stainless steels. The lab also explores fluid dynamics and mass transfer in agitated vessels and bubble columns, contributing to process intensification in chemical and biochemical engineering.
Figures are computed from collected data and may differ slightly.
Mass transfer coefficients of suspended particles were measured in agitated vessels and in bubble columns. Four sizes of agitated vessels (diameter: 9.5, 17.5, 20, 40 cmØ) including both fully baffled and non-bafHed conditions and two sizes of bubble columns (diameter: 10, 20cmØ) were used. Particle sizes ranged from 60 to 1100 μØ including both spherical beads (ion exchange resin) and granules (benzole acid, KMnO4, and β-naphthol). We correlated the mass transfer coefficients using the surface
Laser peening without coating (LPwC) is an innovative surface enhancement technology, which imparts compressive residual stress without any surface preparations. Materials were peened in aqueous environment with laser pulses of about 100 mJ from a Q-switched and frequency-doubled Nd:YAG laser. Surface roughness of the materials somewhat increased due to ablative interaction. Compressive residual stress nearly equal to the yield strength of the materials appeared at the surface after LPwC in spit
Interrelations among the non-dimensional mixing time, the power number and the discharge flow rate number for baffled mixing vessels are experimentally investigated for paddles and turbines of various dimensions. The correlation equations with the geometrical dimensions of the impellers are presented for the mixing time, the power number and the discharge flow rate number, respectively. The power number can be directly correlated to the discharge flow rate number to the 1.34 power. The mixing ti
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 mu
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
Laser peening without protective coating (LPwC) has been applied to metallic materials using low energy pulses of a Q-switched and frequency-doubled Nd:YAG laser. Compressive residual stresses of several hundred megapascals were imparted on the surface of the materials. Redistribution of the residual stress in the top surface due to thermal loading was evaluated non-destructively by synchrotron radiation of SPring-8. Accelerating stress corrosion cracking (SCC) tests showed that LPwC prohibited
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 HT780 high-strength steel plate samples with irradiated pulse energies of 7.5−8.0 mJ, spot sizes of 0.42−0.58 mm and pulse densities of 100−1,600 puls
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
The authors have applied laser peening without coating (LPwC) to metallic materials. Compressive residual stress nearly equal to the yield strength of the materials was imparted on the surface. Accelerating stress corrosion cracking (SCC) tests showed that LPwC had a significant effect to prevent the SCC initiation of sensitized materials of SUS304, Alloy 600 and the weld metal, Alloy 182. Push-pull type fatigue testing demonstrated that LPwC drastically enhanced the fatigue strength of fillet-w
This paper describes recent advances in the observation and modeling of laser peening phenomenon. Laser peening changes the stress field in metallic materials from tensile to compressive by the impulsive effect of laser-induced plasma. The plasma, generated by the irradiation of the second harmonic of a Nd: YAG laser on an SUS304 test piece, was directly observed by imaging the plasma luminescence. Comparing the observed image to the plasma expansion velocity calculated using an analytical model
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 10
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