2026-09-19T11:38:14Zhttps://dspace.mit.edu/server/oai/requestoai:dspace.mit.edu:1721.1/505102021-07-05T14:03:20Zcom_1721.1_7582com_1721.1_7581col_1721.1_131022
Christopher Leung.
Elvin, Niell Glen
Massachusetts Institute of Technology. Department of Civil and Environmental Engineering
2010-01-07T20:47:26Z
2010-01-07T20:47:26Z
1998
1998
http://hdl.handle.net/1721.1/50510
42363862
Thesis (Ph.D.)--Massachusetts Institute of Technology, Dept. of Civil and Environmental Engineering, 1998.
Includes bibliographical references (p. 107-110).
The detection of subsurface damage is important in ensuring the safety and timely repair
of structures. Existing methods for non-destructive evaluation of structural elements tend
to be either expensive or unreliable for monitoring large scale systems. The novel fiber
optic based technique developed in this research overcomes many of the limitations of traditional
non-destructive evaluation methods by providing an interferometric sensing technique
coupled with a simple mechanical test. The method is based on monitoring the
phase change in an integral interferometric fiber optic sensor caused by moving a mechanical
load over the damaged structure. The method has been shown to unambiguously
detect both the position and size of damage. The theoretical and experimental validation of
the proposed method is presented for the case of open cracks in which the faces are not
allowed to come into contact. The effect of damage position and damage size on sensor
performance for two typical structural elements is also presented. A closed loop fiberoptic
interferometer with modulated load is shown to overcome the traditional problems of
environmental drift such as material creep, temperature and ambient noise. This interferometric
technique is also shown to be one of the few fiber-optic based techniques that have
adequate sensitivity for integral damage detection.
Many traditional non-destructive evaluation methods tend to be insensitive in detecting
closed cracks. Thus the closed crack problem represents a special challenge for structural
damage monitoring. A fast iterative based boundary element method has been developed
to solve this problem. This method is used to show the theoretical feasibility of detecting
closed cracks with the developed novel sensing method.
by Niell Elvin.
Ph.D.
110 p.
eng
Massachusetts Institute of Technology
M.I.T. theses are protected by
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http://dspace.mit.edu/handle/1721.1/7582
Civil and Environmental Engineering
Subsurface damage detection using a novel fiber optic sensing technique
Thesis
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of structures. Existing methods for non-destructive evaluation of structural elements tend
to be either expensive or unreliable for monitoring large scale systems. The novel fiber
optic based technique developed in this research overcomes many of the limitations of traditional
non-destructive evaluation methods by providing an interferometric sensing technique
coupled with a simple mechanical test. The method is based on monitoring the
phase change in an integral interferometric fiber optic sensor caused by moving a mechanical
load over the damaged structure. The method has been shown to unambiguously
detect both the position and size of damage. The theoretical and experimental validation of
the proposed method is presented for the case of open cracks in which the faces are not
allowed to come into contact. The effect of damage position and damage size on sensor
performance for two typical structural elements is also presented. A closed loop fiberoptic
interferometer with modulated load is shown to overcome the traditional problems of
environmental drift such as material creep, temperature and ambient noise. This interferometric
technique is also shown to be one of the few fiber-optic based techniques that have
adequate sensitivity for integral damage detection.
Many traditional non-destructive evaluation methods tend to be insensitive in detecting
closed cracks. Thus the closed crack problem represents a special challenge for structural
damage monitoring. A fast iterative based boundary element method has been developed
to solve this problem. This method is used to show the theoretical feasibility of detecting
closed cracks with the developed novel sensing method.</Abstract>
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