Optical Fiber Loop-Sensors for Structural Health Monitoring of Composites
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1129-V07-11
Optical Fiber Loop-Sensors for Structural Health Monitoring of Composites
Nguyen Q Nguyen and Nikhil Gupta Composite Materials and Mechanics Laboratory Mechanical and Aerospace Engineering Department Polytechnic Institute of New York University Brooklyn, NY 11201 U.S.A. Phone: 718-260 3080, Fax: 718-260 3532, Email: [email protected]
ABSTRACT In the present work a fiber-optic loop-sensor is designed and tested for possible applications in structural health monitoring of composite materials. It is known that bending an optical fiber beyond a critical curvature leads to loss of optical power through the curved region. The optical power loss depends on the radius of curvature of the loop. The optical power can be measured by a photodetector and a change in the power due a change to the curvature can be measured. In the present research optical fiber-optic loop-sensors are developed that can exploit this concept. Single-mode optical fiber sensors having different loop radii, from 6-10 mm, are fabricated and calibrated for applied strain on the loop. The calibration is carried out using a 0.098 N load cell and a computer controlled translation stage having 50 nm step resolution. Results show that the sensors provide highly repeatable curves for loading and unloading cycles. Smaller loop radii lead to higher optical power losses, resulting in higher sensitivity. Calibration results show that such sensors can be used in structural health monitoring applications. In this approach the coating and cladding of optical fibers are maintained intact; therefore, the sensors are robust and can withstand several composites fabrication processes.
INTRODUCTION High performance fiber- and particle-reinforced composite materials are widely used in aerospace, automobile, and marine structures. In addition, in these applications early detection of damage is desirable to enhance the safety and reliability of the structure. The detection of damage is carried out by a variety of sensors, which can either continuously monitor the structural health and the ambient conditions, or are triggered by any of the parameters that crosses the threshold. Sensors of small size and light weight are usually preferred because of the possible adverse effects of large sensors on the structural integrity of the component. Fiber-optic sensors have become an important class of sensors for structural health monitoring applications in aerospace structures and automobiles. These sensors are commonly used in monitoring stress, strain, acceleration, temperature and humidity. Several studies can be found in the published literature elaborating various fiber-optic sensing schemes, some of which are briefly discussed below. Use of fiber-optic sensors in composite materials is advantageous because they can become an integral part of the structure and provide strengthening in addition to the sensing function. A variety of intrinsic and extrinsic fiber-optic sensors are used in structural health monitoring of
composite materials. Examples of fiber-optic sen
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