Fiber Optic Strain Measurement Research Articles

Distributed Strain Behavior of a Reinforced Concrete Bridge: Case Study

To effectively assess and manage aging infrastructure, sensing technologies that produce accurate and useful quantitative data are required. Distributed fiber optic strain measurement systems are one potential technology that could fulfill this requirement. This case study investigates the performance of a distributed fiber optic strain measurement technology with high accuracy and spatial resolution during a load test on a RC bridge. The measurements from the fiber optic system are compared with conventional strain gauges and linear transducers, and good agreement between the sensors was found. The fiber optic measurements are also used to examine the bridge support conditions as well as the load distribution between beams. The results show that assumptions made about the support conditions during design do not match the actual bridge behavior, although the load distribution between beams is as expected.

Dynamic fiber optic strain measurements and aliasing suppression with a PDA-based spectrometer

Dynamic fiber optic strain measurements at 3.3 kHz were performed employing a photodiode array spectrometer. The occurrence of aliasing components in the spectral data is investigated, and their dependence on the spectrometer integration time is analyzed. A theoretical model describing the aliasing components is discussed and could be confirmed by the experimental data. It is shown that the aliasing components can be partly suppressed by maximizing the duty cycle of the spectrometer.

Fatigue testing of a composite propeller blade using fiber-optic strain sensors

The performance of surface-mounted extrinsic Fabry-Perot interferometric (EFPI) sensors during a seventeen-million-cycle, high-strain fatigue test is reported. Fiber-optic strain measurements did not degrade during the test. The sensors were applied to a composite propeller blade subject to a constant axial load and a cyclic bending load. Strain measurements were taken at four blade locations using two types of EFPI sensors and co-located electrical resistance strain gages. Static and dynamic strain measurements were taken daily during the 65 days of this standard propeller-blade test. All fiber-optic sensors survived the fatigue test while most of the resistive gages failed. The suitability of fiber-optic monitoring for fatigue testing and other high-cycle monitoring is demonstrated.

A fiber-optic strain measurement and quench localization system for use in superconducting accelerator dipole magnets

A novel fiber-optic measurement system for superconducting accelerator magnets is described. The principal component is an extrinsic Fabry-Perot interferometer to determine localized strain and stress in coil windings. The system can be used either as a sensitive relative strain measurement system or as an absolute strain detector. Combined, one can monitor the mechanical behaviour of the magnet system over time during construction, long time storage and operation. The sensing mechanism is described, together with various tests in laboratory environments. The test results of a multichannel test matrix to be incorporated first in the dummy coils and then in the final version of a 13 T Nb/sub 3/Sn accelerator dipole magnet are presented. Finally, the possible use of this system as a quench localization system is proposed. >

Fiber optic strain measurements using an optically-active polymer

A study encompassing the use of an optically-active polymer as the strain-sensing medium in an organic matrix composite was performed. Several compounds were synthesized for use as the inner cladding material for silica fiber-optic cores. These materials include a diacetylene containing polyamide. It is possible to dynamically modify the optical properties of these materials through changes in applied strain or temperature. By doing so the characteristic absorption in the visible is reversibly shifted to a higher energy state. The polymer coated fiber-optic cores were initially studied in epoxy resin. Additionally, one of the polyamide/diacetylene polymers was studied in a spin-fiber form consisting of 15 micron filaments assembled in multifilament tows. The most promising configuration and materials were then investigated further by embedding in graphite/epoxy composite laminates. In each case the shift in the visible absorption peak was monitored as a function of applied mechanical strain.

Fiber optic sound and strain measurements employing newly developed digital demodulators

Fiber optic interferometric sensor systems for “smart” materials and structures applications offer a number of advantages including minimal electrical interference, geometric flexibility, and multisensor capability. Demodulation of these interferometric sensor signals typically is carried out by analog hardware. However, accuracy, bandwidth, and linearity are hampered by limitations in available electronic components and low-performance analog filters. A high-precision off-line digital demodulator has been developed and the techniques with fiber optic strain gauges and hydrophones are demonstrated. The measurement system is unique and represents an advancement in the state-of-the-art. A real-time implementation for control applications based on the Texas Instruments Inc. TMS 320C25 signal processing chip set is also proposed.