M.S. Thesis Presentation by Charles Michael Rosen
Monday, June 18, 2001

(Dr. David McDowell, advisor)

"Demonstration:  Integrated Diagnostics/Prognostics for Condition-Based Maintenance"

Abstract

The purpose of this investigation is to experimentally demonstrate a mockup in which acoustic data are taken for crack length and then used as estimates for inputs to remaining life algorithms. They are subsequently displayed on a graphical user interface. The system alerts the user when the component is approaching fatigue failure. The types of acoustic measurement methods that are utilized are surface acoustical waves (SAW) and acoustic emission (AE). While the crack is small, the remaining life algorithms used are Navarro-de los Rios, linear elastic fracture mechanics (LEFM), and the Robust Small Crack Growth Model. For the Robust Small Crack Growth Model, there is one version that incorporates mean stress and another that neglects it. The long crack growth rate is used once the crack is sufficiently long that these small crack models no longer predict propagation accurately.

In this project, cracks were initiated at the root of a single notch specimen.  Then, both the AE and SAW acoustical transducers are used to provide an estimate of crack length.  These estimates are used to develop probability distribution functions for predicted crack lengths.  The results of these functions are entered into the various crack growth models, and a remaining life estimate is generated for each model.  The projected cycles to failure are then displayed on the graphical user interface, along with the probability function curves.  Additionally, the GUI displays the notched specimen with a hot spot that changes color from green to red, depending on how near the specimen is to failure.  Key findings include that a real time component failure monitoring device can be developed once sensor technology is advanced enough.