Use of Microelectromechanical Systems Technologies To Sensitively Measure and Monitor Stress Corrosion Crack Propagation, 18-9342

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Principal Investigators
C. Sean Brossia
Heather S. Hanson
Andrew L. Veit

Inclusive Dates:  08/01/02 - 08/01/04

Background - Many engineering structures are subjected to the simultaneous conditions of an applied stress (or load) and a corrosive environment. During these conditions, numerous cases of structural failures from stress corrosion cracking (SCC) have been reported in boilers, pressure vessels, oil and gas production and transmission piping, components associated with nuclear power generation, bridges, sea craft, and aircraft. There are a number of experimental methods to determine SCC susceptibility and measure crack propagation rates. One main limitation of these methods is that the crack propagation rate detection limit of 10-11 m/s is often too high to gage if SCC may lead to component failure during the long term. Extending the test time to overcome this limitation can become prohibitively expensive. The second limitation with the existing methods is that they cannot easily be converted and implemented as sensors or monitoring methods.

Approach - The goal of this project is to develop MEMS (Microelectromechanical Systems) devices using structural engineering materials for sensitive crack growth rate measurements and to do so in such a way as to facilitate SCC sensing and monitoring. The operating principle of this project is to construct MEMS devices that utilize structural materials or analogues for the study of SCC. High sensitivity to low crack propagation rates is achieved using small SCC members in combination with traditional crack monitoring methods and microscopic examination.

Accomplishments - During the course of the project, the following tasks were accomplished:

  • A finite element model was developed to aid in the design of MEMS SCC devices to enable in-situ monitoring of crack propagation
  • Small SCC devices in the form of single and double cantilever beams (Figure 1) were fabricated from engineering materials instead of polysilicon, using standard MEMS fabrication methods
  • Initiation of SCC was achieved in brass MEMS devices and propagation rates on the order of 10-10 m/s were measured in-situ (Figure 2).
Figure 1. Metallic MEMS Double cantilever beam specimen. Figure 2. Crack growth rate measurements for metallic MEMS SCC device.

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