報告書番号

H09004

タイトル（和文）

レーザ超音波を用いた開口亀裂深さ監視手法の開発

タイトル（英文）

Development of open crack depth monitoring method using laser ultrasound

概要 （図表や脚注は「報告書全文」に掲載しております）

高温部品の欠陥や損傷のオンライン監視を目的とした，レーザ超音波を用いた表面開口亀裂深さ測定手法を開発した。深さが0～5mmの範囲で連続的に変化する傾斜スリットを施したSUS316試験体を対象に表面波を測定した結果，スリットを通過（迂回）した表面波の時間遅れから亀裂深さ測定が可能であることを示した。深さ2mm，3mm，5mmのスリットを施したケーシング部材試験体を対象に表面波を測定した結果，深さに対応する時間遅れが観測された。温度変化による表面波の時間遅れ変化を補正するために2台のレーザを用いてスリットを通過しない参照波とスリットを通過する迂回波を発生させ，参照波の到達時間をもとに迂回波の到達時間を補正する手法を考案し，室温～500℃に昇温した試験体に適用した結果，本手法によって温度変化の影響を除去できることを示した。

概要 （英文）

Monitoring of surface crack depth is important for on-line monitoring of damage or flaws. For example, cracks whose depths were measured to be below tolerance values at servicing and maintenance while the plant was shut down may grow during plant start-up or operation due to thermal and mechanical stress. Although crack depth measurement using ultrasonic transducers is a well-established technique, it cannot be applied to high temperature components, which require non-contact measurement. Laser ultrasound is a non-contact measurement technique which may can potentially provide on-line monitoring of crack depth in high temperature components. In this research, the surface wave waveforms were measured by laser ultrasound, using a specimen with a slant slit whose depth varied continuously from 0 to 5 mm. The results showed that the time delay of the transmitted surface wave can be used to monitor the crack depth. Experiments were also carried out using a casing material specimen, with artiricial slits of depths 2mm, 3 mm, and 5 mm. The time delay showed the expected dependence on the slit depth. Since the propagation speed of the Rayleigh wave depends on the temperature, the observed time delay includes both the effect of the slit depth and the temperature. In order to separate these effects, a reference wave and a transmitted wave were generated using two lasers. The time delay of the reference wave was used to correct for the temperature effect on the time delay of the transmitted wave. Experiments with the specimen was heated from room temperature to 500C showed that this method is effective in removing the effect of temperature change.

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