Title page for ETD etd-04202012-091113


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 safe

and 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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