報告書番号

H09003

タイトル（和文）

レーザ超音波による回転体の非接触探傷技術 ―表面探傷法の開発―

タイトル（英文）

Flaw detection technology for rotating bodies by laser ultrasound -development of surface flaw detection method-

概要 （図表や脚注は「報告書全文」に掲載しております）

超音波探触子などの従来技術の適用が困難な回転体の表面探傷にレーザ超音波を適用した。超音波発生用レーザを試験体に照射して表面波を発生させ，一定の離隔距離をおいた位置にてレーザ干渉計で表面波波形を測定した。円盤状の試験体に模擬欠陥として径方向および円周方向に深さ1mmのスリットを施し，1200rpmに近い回転数で回転させた。レーザの繰り返し周波数（20Hz）と試験体の回転数が僅かに異なる場合，スリット位置はレーザ照射位置，すなわち探傷領域に対してゆっくりと移動した。よって，この状態で表面波波形を連続測定することにより探傷領域を円周方向に走査することが出来た。波形処理法について検討を行った結果，高周波数成分と低周波数成分の強度比，および測定波形と参照波形のコントラスト関数がスリットの有無を判定する指標として有効であることが分かった。また，500℃においても実験を行い，本手法が高温部品にも適用可能であることを示した。

概要 （英文）

Laser ultrasound is an effective method for noncontact flaw detection. In this research, laser ultrasound was applied to surface flaw detection of rotating specimens, for which conventional techniques such as ultrasonic transducers are difficult to apply. Surface waves propagating along the surface of a disk-shaped specimen were generated using a Nd:YAG laser and detected using a laser interferometer, both operating at a repetition rate of 20 Hz. The specimen was made of SUS316, with artificial slits of depth 1 mm in the radial and tangential directions. The specimen was rotated at frequencies close to 1200 rpm. When the repetition rate of the lasers and the rotation frequency of the specimen were slightly out of synchronization, the slit position moved slowly with respect to the laser irradiation position. This allowed the flaw detection region to be scanned in the tangential direction without mechanical movement of the laser beams. The waveforms obtained when the slit was present within the flaw detection region showed a distinct difference compared to the waveforms obtained when the slit was not present. Various waveform processing methods were investigated in order to judge the presence of the slit. The parameters which showed the best correlation with the presence of the slit (the best indicators for surface flaw detection) were (1) the ratio of the high frequency component (f >1 MHz) relative to the low frequency component (f < 1 MHz), and (2) the contrast function between the measured and reference waveforms. The experiment was also performed at 5000C, and showed that the method is applicable at high temperature.

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