Distributed, Serially Controlled, Active Sensor for Structural Health Monitoring, 14-9285

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Principal Investigators
Hegeon Kwun
Sang Y. Kim
Ronald H. Peterson

Inclusive Dates: 12/12/01 - 12/12/02

Background - To increase safety and reliability and at the same time to reduce operating and maintenance costs of large structures such as airplanes, ships, plants, and bridges, there is an industrywide shift from the traditional time-based maintenance (TBM) to condition-based maintenance (CBM). CBM employs periodic, intermediate, time-scheduled assessment of the health condition of structures, determines if a failure will occur before the next scheduled assessment, and schedules maintenance tasks accordingly. To implement the CBM in practice, efficient and low-cost techniques for assessing the structural health conditions are necessary. To meet this need, extensive R&D of technologies for structural health monitoring (SHM), including sensors for assessing structural health conditions, is ongoing worldwide.

Approach - Our approach for efficient and low-cost SHM is based on the thin-nickel-strip magnetostrictive sensor (MsS®) guided-wave probe patented recently by Southwest Research Institute (U.S. Patent No. 6,396,262). The probe consists of a thin nickel substrate (or strip) and a thin MsS coil in a printed-circuit board that is placed on the nickel strip. The nickel strip is permanently mounted on the surface of the structure being monitored by using either adhesive or other joining methods such as plating. The probe generates and launches a pulse of guided waves that interrogates and inspects a large area of the structure. The same probe also detects signals reflected from defects or other geometric irregularities in the structure that, in turn, are analyzed for defects and structural changes. Periodic examination of the structure with the permanently installed MsS guided-wave probe and comparison of these periodically acquired data allow quick, comprehensive, and cost-effective assessment of structural condition changes occurring over time.

The objectives of this project were to (1) design and fabricate working prototype thin printed-circuit-board MsS coils, (2) evaluate different nickel substrates (such as milled nickel sheet and deposited via electroplating) for their suitability for use in the probe, and (3) demonstrate the potential of our approach for SHM.

Accomplishments - Prototype thin (no more than 0.01-inch thick) printed-circuit-board MsS coils were designed and fabricated. The performance of these prototype coils was tested on plate samples and found to be as excellent as the ferrite-core-plate MsS probe developed and patented previously for long-range guided-wave plate inspection. Milled nickel strips with thicknesses ranging from 0.002 to 0.010 inch were found to be suitable for use in the MsS guided-wave probe. An electroplated nickel strip was also found to be suitable for MsS use. Using the prototype printed-circuit-board MsS coils and the milled thin-nickel strips that were adhesively bonded to the structure surface, the potential of our approach for SHM was demonstrated on a 0.25-inch x 4-foot x 40-foot carbon steel plate sample. The ability to control and operate multiple MsS guided-wave probes with a multiplex system was also confirmed.

For more information, please contact Glenn M. Light, Ph.D.

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