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Sensor Technology & Acoustic Emission

There are hundreds of various sensor technologies that MISTRAS can utilize, with most being well-known by bridge engineers. One of MISTRAS’ most powerful sensor technologies for bridge monitoring is Acoustic Emission (AE). There are a variety of different sources that can be detected by AE in various materials. For metals, typical sources include crack initiation, crack propagation, fretting (between crack faces, bolts), movement of dislocations, slipping (e.g. bearings) and fractures. For concrete and composites, sources include corrosion spalling, cracking, tendon or fiber breakage, debonding, and delamination. For bridge structures, AE detection may be a result of crack initiation and/or growth, crack opening and closing (i.e. fretting/rubbing of crack faces and bolts), and/or dislocation movement in steel components. AE has also been successfully used for monitoring bearings in swing and lift bridges, deteriorating reinforcing steel, concrete decks, concrete cracking and corrosion of substructure components.

In previous work with the FHWA, Acoustic Emission was used to determine whether or not identified cracks were propagating in areas without retrofits or whether those areas with retrofits had completely arrested the cracks. While stresses in the areas of the crack may be below the elastic design limit, the regional area around the crack tip may have large local stresses due to excessive deformation or movement. The rise in local stresses may cause the crack tip to propagate and act as the source for acoustic emission waves. This transient elastic stress wave radiates from the discontinuity (or other damage area) and is detected as a waveform at the surface of the material using high frequency AE sensors that are mounted directly to the structure.

    Benefits of Monitoring:
  • If active damage is occurring
  • Where active damage is occurring
  • When active damage is occurring
  • What type of damage is occurring
  • The rate and/or frequency of damage
    Additional Benefits:
  • Predictive maintenance tool in RBI (risk based inspection)
  • Optimization of maintenance budget for repairs
  • Reduction in failures (active defects are detected early)
  • Increased confidence in structural integrity
  • Increase in safety through reduction in confined space entries and other access
  • Remote monitoring - reduces need for site visits
    AE Monitoring Applications for
    Structural Health Monitoring (SHM):
  • Condition Ranking
  • Continuous Remote Monitoring
  • Real Time Damage Location (e.g. crack, wire rupture)
  • Assist in Locating Hidden/Buried Defects
  • Inspection of Inaccessible Areas
  • Can be Combined with External Parametric Sensors (e.g. strain, displacement, temperature, pressure, etc.)
  • Reduce Unnecessary Maintenance Repairs
  • Prolong Remaining Useful Life, SHM can help to keep structures in service longer
  • Prioritize Future Repair, Rehabilitation or Replacement Decisions
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