Research team of Professor Naoki Hosoya, Department of Mechanical and Functional Engineering, Faculty of Engineering, Shibaura Institute of Technology, Sho Wakata, Department of Mechanical Engineering, Senior Researcher Noboru Hasegawa, Kansai Optical Science Research Institute, Quantum Beam Science Division, Quantum Science and Technology Research and Development Organization, Masaru Kinno Has developed the world's first completely non-destructive remote tapping inspection method that detects defects in concrete structures with shock waves generated from laser-induced plasma.

 The soundness of a concrete building is diagnosed by visual inspection and tapping sound inspection by a professional engineer, but the larger the structure, the longer it takes to inspect, and the effect of the inspection depends on the skill of the inspector. Therefore, in order to cope with the ever-increasing aging of infrastructure, the efficiency and reliability of inspections have become issues.

 To solve this problem, a research team at Shibaura Institute of Technology and others has developed a new method for identifying defects using shock waves generated from laser-induced plasma.In this method, a Rayleigh wave is generated by laser-induced plasma near the surface of a concrete structure, and a defective portion can be identified.It does not directly impact the building and has fewer measurement points than the tapping sound inspection, so it can detect concrete defects quickly and non-destructively.

 To evaluate the new method, the research team generated shock waves with a high-power laser near the surface of an artificially formed concrete block and analyzed vibrations at multiple points on the concrete surface inside and outside the defect.As a result of the analysis, it was found that a Rayleigh wave with a large amplitude was generated in the defective part.This is a surface wave that moves at a faster speed than other shock waves, and by detecting the location where this Rayleigh wave was observed, we succeeded in identifying the defective location, including those buried inside.

 By visualizing the Rayleigh wave, defects in the structure can be detected faster than other remote measurement methods that analyze vibration, and the number of measurement points can be reduced compared to the measurement in the natural vibration mode. Evaluating cracks in concrete structures using LIP shock waves is a safe and rapid method that can be used to maintain infrastructure and prevent structure destruction.In the future, we will proceed with improvements and development aimed at social implementation of this method.

* Rayleigh waves are a type of surface acoustic waves that propagate on the surface of a solid and vibrate in a direction parallel to the propagation direction.If there is a cavity or boundary near the surface, a part of it will be reflected, and it will spread evenly around the impact point like ripples on the water surface, so it is possible to inspect a wide range by using this. ..

Paper information: [International Journal of Mechanical Sciences] Defect detection of concrete in infrastructure based on Rayleigh wave propagation generated by laser-induced plasma shock waves

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