Date of Award

Spring 1996

Document Type

Thesis

Degree Name

Master of Science in Civil Engineering - (M.S.)

Department

Civil and Environmental Engineering

First Advisor

Farhad Ansari

Second Advisor

Edward G. Dauenheimer

Third Advisor

George Pincus

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.

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