Type of Document Dissertation Author Dodson, Jacob Christopher Author's Email Address dodsonjc@vt.edu URN etd-04202012-091113 Title Guided Wave Structural Health Monitoring with Environmental Considerations Degree PhD Department Mechanical Engineering Advisory Committee
Advisor Name Title Inman, Daniel J. Committee Chair Borggaard, Jeffrey T. Committee Member Foley, Jason R. Committee Member Pierson, Mark A. Committee Member Wicks, Alfred L. Committee Member Keywords
- thermal sensitivity
- Lamb waves
- guided waves
- environmental factors
- structural health monitoring
Date of Defense 2012-04-09 Availability unrestricted Abstract Damage detection in mechanical and aerospace structures is critical to maintaining safeand optimal performance. The early detection of damage increases safety and reduces cost
of maintenance and repair. Structural Health Monitoring (SHM) integrates sensor networks
and structures to autonomously interrogate the structure and detect damage. The
development of robust SHM systems is becoming more vital as aerospace structures are
becoming more complex. New SHM methods that can determine the health of the structure
without using traditional non-destructive evaluation techniques will decrease the cost
and time associated with these investigations. The primary SHM method uses the signals
recorded on a pristine structure as a reference and compares operational signals to the
baseline measurement. One of the current limitations of baseline SHM is that environmental
factors, such as temperature and stress, can change the system response so the
algorithm indicates damage when there is none. Many structures which can benefit from
SHM have multiple components and often have connections and interfaces that also can
change under environmental conditions, thus changing the dynamics of the system.
This dissertation addresses some of the current limitations of SHM. First the changes
that temperature variations and applied stress create on Lamb wave propagation velocity
in plates is analytically modeled and validated. Two methods are developed for the
analytical derivative of the Lamb wave velocity; the first uses assumes a thermoelastic material
while the second expands thermoelastic theory to include thermal expansion and
the associated stresses. A model is developed so the baseline measurement can be compensated
to eliminate the false positives due to environmental conditions without storage
of dispersion curves or baseline signals at each environmental state. Next, a wave based
instantaneous baseline method is presented which uses the comparison of simultaneously
captured real time signals and can be used to eliminate the influence of environmental effects
on damage detection. Finally, wave transmission and conversion across interfaces in
prestressed bars is modeled to provide a better understanding of how the coupled axial
and flexural dynamics of a non-ideal preloaded interface change with applied load.
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