Fiber optic acoustic emission distributed crack sensor for large structures

Abstract

Preliminary experiments leading to the development of an optical fiber acoustic emission sensor is described. The objective was to develop a single sensor for simultaneous detection of acoustic emission events, from many locations within a large structure. The optical fiber sensor can be adhered to the surface of structural materials, i.e. steel or concrete. There are no individual sensor arrays or components built into the fiber. This characteristic provides simplicity and renders the system practical for applications in bridge structures. Alternatively, the optical fiber could be embedded in new concrete construction. Acoustic emissions from micro-cracks or defects from various locations in the stmcture create stress wave perturbations in the optical fiber that are detected by a portable interferometer. Time-domain measurements are instantaneous, in real-time, and the entire structure is interrogated through a one-time operation. The time domain signal acquired from the optical fiber discerns the number and locations of damage zones i.e., weld cracks, bolt-hole cracks, corrosion activity, or brittle fracture of fibers in composite materials.

A novel technique for acoustic emission monitoring in civil structures with global fiber optic sensors

“…Examples are fiber Bragg gratings (FBG), which can be located at different points along an optical fiber to obtain data in several locations through multiplexing [20] or coiled sensors in which the optical fiber is winded to increase sensitivity [21]. Global sensors might operate as a fully distributed sensor network which can be interrogated at any point along the fiber length or integrate the response along the length of the fiber optic sensor and can thus cover a larger area [22,23]. The disadvantage of global damage detection systems is the difficulty in accurately locating the damage once it has been detected.…”

“…A number of techniques have been suggested for detection of acoustic emissions with fiber optic sensors. Good results have been obtained with interferometric setups which rely on detection of highfrequency phase modulations [23,26] or with FBGs [22]. AE detection in concrete by means of fiber optic sensors has been investigated by Kageyama et al [27] who applied coiled fiber sensors for detection of acoustic emissions in a concrete railway girder, based on the frequency shift of a light wave transmitted through a curved waveguide upon interaction with an ultrasonic wave.…”

Non-destructive evaluation (NDE) of composites: using fiber optic sensors

“…Interferometric techniques have provided means for high-resolution detection of damage within different types of materials. For instance, Chen and Ansari (2000) developed a white-light AE sensor for detection of micro-cracks in concrete beams. In applications to composites, Pierce et al (1996) used a fi ber-optic Michelson interferometer for detection of lamb waves generated from the splitting of carbon fi bers in carbon fi ber-reinforced polymer (CFRP) composites.…”

Acoustic emission monitoring of structural perturbations with serially multiplexed optical fiber sensors

“…The coiled AE sensor segments, S 1 and S 2 , were designed to operate within a signal frequency range of 100-300 kHz. Details pertaining to the selection of coil diameter and optical fiber lengths to achieve the frequency range of interest are given in reference [5]. Each coil consisted of an optical fiber segment wrapped around 35 mm annular aluminum disks.…”

“…Their work demonstrated the superior sensitivity of optical fibers in detection of Lamb waves during splitting of the fibers. Chen et al (2000) developed a novel optical fiber sensor with capability for making distributed measurements. Design of the sensor involved development of AE sensing regions along the length of an optical fiber.…”