Low frequency laser ultrasonics for nondestructive testing of large structures

用于大型结构无损检测的低频激光超声波

基本信息

批准号：
12555192
负责人：
YAMANAKA Kazushi
金额：
$ 7.94万
依托单位：
Tohoku University
依托单位国家：
日本
项目类别：
Grant-in-Aid for Scientific Research (B)
财政年份：
2000
资助国家：
日本
起止时间：
2000 至 2001
项目状态：
已结题

项目摘要

(1 ) Analysis of laser propertiesWe 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 beamWe 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 methodWe 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 surfacesTo 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

（1）对激光属性的分析比较了两种类型的激光器，一个长的脉冲YAG激光器（脉冲宽度50μs，能量2.5J，峰值50 kW）和Q开关的YAG激光器（脉冲宽度10NS，能量10NS，Energy 0.1J，峰值功率10MW）。我们发现，Q开关的激光器会损坏物体表面，但激发了低强度振动，而长脉冲激光器不会损坏对象表面，而是激发了大型放大器振动。（2）通过快速扫描激光束对大型结构进行评估，开发了大型金属板结构的测试方法。当长脉冲激光器在羔羊波的相速度处扫描时，会产生指令波。我们发现，相对于扫描方向，每个频率分量的传播角度不是恒定的，而是取决于频率。该频率依赖性方向性可用于识别未知散射器的方向。我们开发了一种有效的方法，用于在250 x 250毫米内检测和定位缺陷。通过使用频率依赖性方向性，在一次兴奋中进行了更多的方法。（3）通过低频resbnance方法评估大型结构，通过扫描兴奋性yag激光束以实现奇数形状和//或粗或/或粗或粗体的对象，从而开发了一种方法。我们成功地获得了600 x 300 x 60 mm混凝土板样品中的共振振动模式的清晰图像，该样品在表面上被陶瓷瓷砖覆盖，宽度为3 mm，深度为10-40 mm。当兴奋的YAG激光束在地下狭缝上方的位置照射位置时，振动放大器显着增强，我们通过降低共振频率的降低来仔细评估裂隙的深度。（4）可视化粗糙的表面速度缩短了测试范围的粗糙面积所需的时间，我们通过使用振动的方法来实现振动的光孔。当我们使用相位调制的参考梁引入光学锁定方法时，可视化频率范围内的粗糙金属表面的振动模式从1到500 kHz。结构陶瓷瓷砖也进行了研究。较少的