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Academic Articles
Regular Paper (Invited) Vol.2 (2010/2011) p.191 - p.199
 

Strain Monitoring and Defect Detection in Welded Joints by Using Fiber-Optic Distributed Sensors with High Spatial Resolution

 
Hideaki MURAYAMA1,*, Kohei OHARA1, Nozomi KANATA1, Kazuro KAGEYAMA1 and Hirotaka IGAWA2
 
1 School of Engineering, The University of Tokyo, 7-3-1 Hongo, Bunkyo-ku, Tokyo 113-8656, Japan
2 Japan Aerospace Exploration Agency, 6-3-1 Osawa, Mitaka-shi, Tokyo 181-0015, Japan
 
Abstract
We have developed a fiber-optic distributed sensor that can measure strain or temperature distributions at an arbitrary position along long-length fiber Bragg gratings (FBGs) with the high spatial resolution of less than 1 mm. In order to determine the position of a grating in FBGs, at which the light of the particular wavelength is reflected, optical frequency domain reflectometry (OFDR) and a signal processing technique are used. Although the length of an FBG is usually about 10 mm, that of the long-length FBG is more than 100 mm. We applied this sensing technique to strain measurements and defect detection in a welded joint. We monitored the strain distributions along the weld lines of the tubular joints of steel pipes subjected to tensile loads. We could successfully measure the development of the strain distributions along the weld lines, where the sharply fluctuating strain distributions resulting from some defects were observed. In this paper, we describe the sensing principle and then show the results of strain monitoring in the welded joints.
 
Keywords
Welded joint, Strain distribution, Fiber-optic distributed sensor, FBG, OFDR, Spatial resolution, Structural health monitoring
 
Full Paper: PDF EJAM Vol.2 pp.191-199 "Strain Monitoring and Defect Detection in Welded Joints by Using Fiber-Optic Distributed Sensors with High Spatial Resolution"
Article Information
Article history:
Received 1 February 2011
Accepted 17 February 2011