報告書番号

Q05024

タイトル（和文）

マルチビームレーザ超音波探傷システムの開発と傷深さ測定への応用

タイトル（英文）

Development of a Multi-Beam Laser Ultrasonic Inspection System and Its Application on Flaw Sizing

概要 （図表や脚注は「報告書全文」に掲載しております）

レーザ超音波法は非接触測定法であることから，従来の超音波法では測定が困難な高温環境下の測定対象物や複雑形状を有する測定対象物への適用が期待されている。本研究ではレーザ超音波法の課題である，送信超音波の伝搬方向制御，超音波の検出感度向上を実現するために，マルチビームレーザ装置を開発した。性能評価を行った結果，表面波・バルク波双方において指向性制御，感度向上が確認できた。また，これまで困難であったレーザ超音波法による測定対象物の裏面に存在する欠陥の検出および深さ測定を行う手法を開発した。

概要 （英文）

Laser ultrasonic technique is a powerful tool for non-contact, nondestructive testing of materials. It is expected to apply to where the conventional ultrasonic technique is not applicable. However, this technique suffers from low sensitivity. In order to overcome this shortcoming, a multi-beam laser ultrasonic system was developed to increase signal-to-noise ratio (SNR) and steer beam direction. The system consisted of eight pulsed Nd:YAG lasers used for ultrasonic generation, and a two-wave mixing interferometer with a long-pulsed Nd:YAG used for ultrasonic detection. Spatial and temporal control of the firing of the individual lasers permitted the generation of both phased array single pulse and narrow-band ultrasonic signals. The performance of developed system was verified using aluminum specimens with the wave generation in a slight ablation mode. A significant increase in sensitivity was obtained, with an increase in signal amplitude with no change in noise level. In the narrow band case, tone bursts were successfully generated in both surface and bulk waves. Beam steering of bulk waves was also performed, and the directivity was confirmed by visualization using a conventional transducer. The developed system was applied to flaw sizing using two techniques: shadow and short-path of diffraction (SPOD), using aluminum specimens with 2-mm, 5-mm, 8-mm slit depths. The shadow technique accurately measured the 5-and 8-mm slits, but not the 2-mm slit. The SPOD technique, carried out using a 5-MHz normal longitudinal transducer as a detector instead of TWM interferometer, accurately measured slits in all specimens with an error less than 0.5mm.

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