Using Electrochemical Fatigue Sensor Systems to Identify Active Fatigue Crack Growth

For nearly a decade, the highway and railroad bridge industries have been utilizing a powerful asset management sensor technology called the Electrochemical Fatigue Sensor (EFS). The two primary systems that utilize this technology are FatigueWatch (a long-term monitoring system) and CrackChek (a short-term system with increased sensitivity.) Developed in the early 90’s in conjunction with the US Air Force and the University of Pennsylvania, the EFS method determines: 1. The presence of a growing fatigue crack; 2. The presence of microplasticity, the precursors to crack initiation and propagation; and 3. Qualitatively, the crack growth rate. By applying a small voltage (0.4 for steel) to an electrode/electrolyte system, the sensor detects new surface area within the inspection region, which oxidizes and changes the resistance of the cell and indicates crack growth. A two-sensor system is used to easily cancel out the elastic deformation, leaving an indication of only permanent deformation, that is, active crack growth. The technology is applicable to any metallic structure that undergoes cyclic or repetitive loading. Testing and monitoring the critical locations with the EFS provides owners with vital information used to avoid failure and in making cost effective asset management decisions.

References
  1. Miceli, M., Moshier, M., Hadad, C. “Fatigue Crack Growth Activity Determination During Inspection on Highway Bridge in Three States.” ASNT-Structural Materials Technology VIII Proceedings 2008, Oakland, CA.
  2. Reliability of Visual Inspection for Highway Bridges, Volume I: Final Report, FHWA-RD-01-105, June 2001.
  3. “Structural Features of Fatigue”, Key to Metals; http://steel.keytometals.com/Articles/Art162.htm, 2009.
  4. Miceli, M., S. Schwartz, B. Phares, M. Moshier. “Active Fatigue Crack Inspection, Detection and Analysis on Three Steel Pennsylvania Bridges Using the Electrochemical Fatigue Sensor.” [IBC 07-49] Proceedings and Papers of the 2007 International Bridge Conference. Pittsburgh, Pennsylvania: Engineer’s Society of Western Pennsylvania, 2007.
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