Fiber optic stress-corrosion sensor and system

• US 5,367,583 A
• Filed: 02/09/1994
• Issued: 11/22/1994
• Est. Priority Date: 02/09/1994
• Status: Expired due to Fees

• Current Assignee: University of Maryland
• Original Assignee: University of Maryland
• Inventors: Sirkis, James S.
• Primary Examiner(s): Lee, John D.
• Application Number:
  US08/194,294
• Time in Patent Office: 286 Days
• Field of Search: 385/12, 385/13, 356/345, 356/352, 250/227.14, 250/227.19, 250/227.23, 250/227.24, 250/227.25, 250/227.27, 250/231.1, 250/231.19, 250/230
• US Class Current: 385/12
• CPC Class Codes: G01D 5/35303 using a reference fibre, e.g. interferometric devices
• CPC Class Codes: G01L 1/24 by measuring variations of optical properties of material when it is stressed, e.g. by photoelastic stress analysis using infrared, visible light, ultraviolet
• CPC Class Codes: G01M 11/083 by using an optical fiber in contact with the device under test [DUT]

Abstract

This invention pertains to an integral Fabry-Perot stress corrosion, strain and material corrosion sensor and associated system that allows for in-situ monitoring of stress-corrosion, strain and corrosion at a given location of a specimen in real-time. The sensor uses an intrinsic Fabry-Perot cavity with one mirror integrally mounted on the specimen that provides a means for: i) transducing information of stress-corrosion of the specimen; ii) measuring strain of the specimen; and iii) measuring the corrosive environment.

Claims

1. A fiber optical based stress-corrosion, strain and corrosion sensor and associated system for monitoring stress-corrosion, strain and corrosion of a structural specimen comprising:

a modulated laser light source;

light transmitting means for communicating the laser light source with an intrinsic Fabry-Perot interferometer that is attached to the structural specimen;

a dual photodetection and signal processing means for determining phase angle shift and reflected intensity of the modulated laser light source, the dual photodetection means provides a signal for;

i) phase angle shift which corresponds to strain induced in the structural specimen and ii) a normalized reflectance which corresponds to corrosion of the structural specimen; and

an outputting means for outputting a signal that corresponds with stress-corrosion, strain and corrosion of the structural specimen.

2. The fiber optical based stress-corrosion, strain and corrosion sensor and associated system of claim 1 wherein the intrinsic Fabry-Perot interferometer includes two semi-reflective mirrors that are spaced by a given distance so as to define a Fabry-Perot cavity having transmittance and reflectance properties which are affected by the stress and corrosion of the specimen which cause optical properties of the modulated laser light source to vary in response to the stress and corrosion which the specimen is subjected to, one of the semi-reflective mirrors is made of the same material as the structural specimen.

3. The fiber optical based stress-corrosion, strain and corrosion sensor and associated system of claim 1 wherein the dual photodetection and signal processing means for determining phase angle shift and reflected intensity of the modulated laser light source includes:

a means for phase demodulation that electronically resolves time dependent phase angle shift; and

an envelope detection means for electronically determining the normalized reflectance which is a signal that corresponds with a predetermined corrosion state of the structural specimen.

4. The fiber optical based stress-corrosion, strain and corrosion sensor and associated system of claim 3 wherein the means for phase demodulation is a means for heterodyne demodulation.

5. The fiber optical based stress-corrosion, strain and corrosion sensor and associated system of claim 3 wherein the means for phase demodulation is a means for homodyne demodulation.

6. A fiber optical based strain and corrosion sensor for monitoring a structural condition of a structural specimen comprising:

a lead-in optical fiber means for introducing light into the sensor; and

an intrinsic Fabry-Perot interferometer which includes two semi-reflective mirrors that are spaced by a given distance and made of a solid fiber optical material so as to define a Fabry-Perot cavity having transmittance and reflectance properties which are affected by the stress and corrosion of the specimen which cause optical properties of a modulated light source to vary in response to the stress and corrosion which the specimen is subjected to, one of the semi-reflective mirrors is part of the surface of the structural specimen and made of the same material for corrosion measurements of the structural specimen in real-time.

7. The sensor of claim 6 the lead-in optical fiber means for introducing light into the sensor and the intrinsic Fabry-Perot interferometer are made from high-birefringent optical fiber material.

8. The sensor of claim 6 wherein the semi-reflective mirror that is part of the surface of the structural specimen and made of the same material is selected from the group consisting of aluminum and aluminum alloys.