Development of Distributed,
Serially Controlled, Active Sensor for Structural
Inclusive Dates: 12/12/01- Current
Background - To increase safety and reliability and at the same time reduce operating and maintenance costs of large structures such as airplanes, ships, plants, and bridges, industry is shifting 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 likely 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 research and development of technologies for structural health monitoring (SHM), including sensors for assessing structural health conditions, is ongoing worldwide.
Approach - The team's approach for efficient and low-cost SHM is based on the thin-nickel-strip magnetostrictive sensor (MsS®) guided-wave probe patented recently by the Institute (U.S. Patent No. 6,396,262 issued May 28, 2002). The probe, illustrated below, 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 thin-nickel-strip MsS guided-wave probe is low-profiled, lightweight, surface-attachable, and durable. Because a single probe can inspect and monitor a large area of a structure, SHM of large structures can be achieved efficiently and economically. Thus, the SwRI approach has high potential for providing an efficient, low-cost SHM technology that can enable implementation of the CBM.
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 the 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. Evaluation of electroplated nickel substrate for MsS guided-wave probe use is ongoing. Using the prototype printed-circuit-board MsS coils and milled thin-nickel strips adhesively bonded to the structure surface, the team members demonstrated the potential of the approach for SHM 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. In this demonstration, a single simulated corrosion pit, approximately 0.25 inch in diameter and 50-percent thickness in depth, was successfully detected using a probe approximately 33 feet from the defect location.
For more information, please contact Glenn M. Light, Ph.D.