The New Jersey Institute of Technology's
Electronic Theses & Dissertations Project

Title:	Development of a fiber optic polarimetric sensor for concrete
Author:	Lee, Insang
View Online:	njit-etd1996-060 (ix, 55 pages ~ 1.4 MB pdf)
Department:	Department of Civil and Environmental Engineering
Degree:	Master of Science
Program:	Civil Engineering
Document Type:	Thesis
Advisory Committee:	Ansari, Farhad (Committee chair) Dauenheimer, Edward G. (Committee member) Pincus, George (Committee member)
Date:	1996-05
Keywords:	Strains and stresses--Measurement. Strains and stresses--Data processing. Optical detectors. Concrete--Testing.
Availability:	Unrestricted
Abstract:	Development of a fiber optic sensor for embedment in cementitious composites and measurement of displacements associated with the opening of microcracks is described. The sensor can be employed as a transducer for measurement of crack tip opening displacements during fracture tests. A polarization maintaining fiber is used as the sensing element, and transduction mechanism is similar to those of other polarimetric type based sensors. However, the deformation resolving power of the sensor is increased by way of increasing the effective length of the optical fiber. This is done by winding the optical fiber into a coil. A direct relationship between the number of loops in the coil and sensitivity of measurements is obtained. A calibration procedure is developed by which the optical signal is converted to displacements. The sensor was employed in a series of fracture tests. Experiments involved embedment of the optical fiber in concrete beams. Specimens were center edge notched, and the fiber coil sensors were embedded at the tip of the notch. This arrangement allowed for direct measurement of displacements associated with the opening of microcracks at the crack tip. Experimental results are presented, and crack tip opening displacement(CTOD) results are compared with crack opening displacements(COD) measured by conventional transducers at the crack mouth.