2001 Fiscal Year Final Research Report Summary
Low frequency laser ultrasonics for nondestructive testing of large structures
| Project/Area Number |
12555192
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| Research Category |
Grant-in-Aid for Scientific Research (B)
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| Allocation Type | Single-year Grants |
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| Section | 展開研究 |
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| Research Field |
Material processing/treatments
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| Research Institution | Tohoku University |
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Principal Investigator |
YAMANAKA Kazushi Tohoku Univ., Graduate School of Enginieering, Professor, 大学院・工学研究科, 教授 (00292227)
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| Co-Investigator(Kenkyū-buntansha) |
CHO Hideo Tohoku Univ., Graduate School of Enginieering, AssociateProfessor, 大学院・工学研究科, 助手 (60296382)
MIHARA Tsuyoshi Tohoku Univ., Graduate School of Enginieering, Associate Professor, 大学院・工学研究科, 助教授 (20174112)
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| Project Period (FY) |
2000 – 2001
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| Keywords | Resonance Frequency / Tile / Concrete / Large Structures / Plate Paves / In-plane Directivity / Vibration / Photorefractive Crystal / Realtime Imaging |
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| Research Abstract |
(1 ) Analysis of laser properties
We compared two types of lasers, a long pulse YAG laser (pulse width 50μ s , energy 2.5J, peak power50 kW) and a Q-switched YAG laser (pulse width 10ns, energy 0.1J, peak power 10MW). We found that the Q-switched laser can damage the object surface but excite low intensity vibration, whereas the long pulse laser does not damage the object surface but excite large amplitude vibration.
(2) Evaluation of large structures by fast scanning of laser beam
We developed a testing method of large metal plate structures. When the long pulse laser is scanned at the phase velocity of Lamb waves, directive Lamb waves are generated. We found that the propagation angle of each frequency component with respect to the scanning direction is not constant but dependent on the frequency. This frequency-dependent directivity is useful for identifying direction of unknown scatterer. We developed an effective method for detecting and locating defects within a area of 250 X 250 mm
… More
in one excitation by using the frequency dependent directivity.
(3) Evaluation of large structures by low frequency resbnance method
We developed a method by scanning the excitation YAG laser beam to realize a robust imaging of odd-shaped and/or rough objects. We succeeded to obtain clear images of resonance vibration modes in 600 x 300 x 60 mm concrete plate specimen covered by ceramic tiles on the surface, with a slit of 3 mm width and 10 - 40 mm depth. The vibration amplitude is significantly enhanced when the excitation YAG laser beam irradiates the position just above the subsurface slit, and we precisely evaluated the depth of the slits, from a decrease in the resonance frequency.
(4) Visualization of rough surfaces
To shorten the time required for testing wide area, we developed a vibration imaging method by using a photorefractive crystal BSO. When we introduce the optical lock-in method using phase modulated reference beam, vibration modes of rough metal surface in the frequency range from 1 to 500 KHz were visualized. Structural ceramic tile was also studied. Less
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