2014 Fiscal Year Research-status Report
Two-beam probing laser-based system for remote inspection of unstable structures
| Project/Area Number |
25420495
|
|---|
| Research Institution | Institute for Laser Technology |
|---|
Principal Investigator |
コチャエフ オレグ 公益財団法人レーザー技術総合研究所, その他部局等, 研究員 (80399352)
|
|---|
| Project Period (FY) |
2013-04-01 – 2016-03-31
|
| Keywords | laser-based system / remote inspection / two-beam probing / highway bridge |
|---|
| Outline of Annual Research Achievements |
During the second year of the project, optimization of laser impact was completed. CO2 and Nd:YAG laser units have been examined as possible sources of laser impact. Both lasers can initiate detectable vibration in the inspected area of highway bridge. However, CO2 laser has been found to be more appropriate source of impact. Its main advantage over Nd:YAG laser is possibility of real non-destructive inspection. Impact laser generated by Nd:YAG laser leaves noticeable spot on the inspected object, even in the thermal mode of impact (ablation mode leaves a small hole). This is not acceptable. In contrast, CO2 laser provides enough impact efficiency without surface damage if impact energy density does not exceed 1 J/cm2. Another advantage of CO2 laser is silent character of impact, there is no strong acoustic noise affecting the system performance. Finally, CO2 laser units are cheaper than Nd:YAG lasers. The main disadvantage of available CO2 laser is necessity of setting the image relay between laser output aperture and surface of inspected object. Otherwise, impact energy delivery is not effective. To avoid this problem, the impact laser cavity should be modified. As well, overall dimensions of the system using CO2 lasers are bigger. So, one of the future tasks is development of proper CO2 laser unit. Within this project, we will continue using the available CO2 laser as source of impact.
|
| Current Status of Research Progress |
Current Status of Research Progress
2: Research has progressed on the whole more than it was originally planned.
Reason
Speckled character of the signals makes defect detection difficult: spectrum of speckled signal instability has wide irregular maximum just around frequency of laser-initiated vibration which is supposed to be detected by the system (1-10 kHz). That is why the system was supposed to wait for time windows with comparatively stable signals. However, these time windows appear not so frequently, especially if the inspected bridge is under heavy traffic. Fortunately, it was discovered that unstable two-beam probing signal has noticeable change in its waveform just after laser impact. Conventional one-beam probing signal does not have this change. Probably, this effect can be used as another criterion of defect recognition with the use of two-beam probing. So, we plan to inspect this effect in more detail and correspondingly modify the algorithm of real-time data processing.
|
| Strategy for Future Research Activity |
In the end of the second year of the project, we received two sets of new photodetectors. Within the third year, the system with two detection channels will be assembled and tested in laboratory. Possible usage of unstable signals will be examined in more detail. If the effect is proved, the algorithm of real-time data processing will be modified.
The image relay for effective impact energy delivery for distance up to 15 m will be optimized. Possible modification of laser cavity will be considered.
If permission to do experiments under real highway bridge is granted, the tests of current design of the system will be taken in real field conditions.
|
| Causes of Carryover |
430407 yen was not used. This money was supposed to be spent for electronic filter and additional optical components for two-channel detection scheme. However, the use of two-channel detection scheme was shifted to the next year.
|
| Expenditure Plan for Carryover Budget |
The electronic filter and additional optical components for the two-channel detection scheme will be purchased in June-August 2015.
|
