Kevin J. Lin

Date of Award


Document Type


Degree Name

Master of Science in Applied Mathematics


Department of Mathematics and Statistics

First Advisor

Richard P. Uber, PhD


In 2008, the Department of Defense published a guidebook for a methodology named Condition-Based Maintenance Plus (CBM+) which capabilities include improving productivity, shortening maintenance cycles, lowering costs, and increasing availability and reliability. This push replaces existing inspection criteria, often conducted as non-destructive testing (NDT), with structural health monitoring (SHM) systems. The SHM system addressed utilizes guided Lamb waves generated by piezoelectric wafer active sensors (PWAS) to detect the existence, size, and location of damage from through-thickness cracks around a rivet hole. The SHM field lacks an experiment testing how small changes in receiver sensor distances affect damage detection. In addition, prior research has shown that transmitter and receiver PWAS angles significantly affected the received signal. Experiments here used existing damage detection metrics to establish thresholds for detection. Tests with two transmitter angles θ = 9°; 27° and three receiver distances, linearly incremented by 5mm, illustrated that damage detection capabilities significantly changed as the receiver distances were incremented at both 50mm and 1000mm transmitter distances. For 1000mm, the PWAS was able to detect the damage at certain geometries. This work validates of the PWAS detection capabilities for small changes and motivates further pursuits for varying PWAS geometries for long distances.

AFIT Designator


DTIC Accession Number