Date of Award


Document Type


Degree Name

Master of Science in Aeronautical Engineering


Department of Aeronautics and Astronautics

First Advisor

Som R. Soni, PhD


Today many USAF aircraft are approaching the end of their projected service life. However, those aircraft, such as the F-15 Eagle, are still being operated to accomplish the mission of the USAF. As the F-15 ages the required maintenance increases, as does the risk of structural failure. A goal of structural health monitoring (SHM) programs is to increase aircraft safety by monitoring areas known to have structural failures. Currently, time intensive manual inspections are used to monitor failure “hotspots” decreasing the readiness of the F-15 fleet. The lead ziconate titanate (PZT) is a commonly used piezoelectric transducer that has shown the potential to detect damage in aircraft structures without time consuming manual inspections. However, many locations where damage has occurred that have been identified by the USAF for SHM systems have restricted geometries consisting of thickness changes and boundary surfaces located near the damage. The restricted geometry presents challenges when using PZT sensors because of the interference of reflected waves coming off of boundary surfaces, and the behavior of the signals going through thickness changes. For this research, a location has failed on multiple F-15 aircraft and has been selected as a basis to evaluate some of the challenges of using PZT sensors for SHM. The goal of this research is to detect fatigue cracks in plates that represent the restricted geometry of the aircraft bulkhead so as to determine if a real damage detection system could be built for F-15 bulkheads. This research shows that detecting closed fatigue cracks can be more challenging than detecting cracks opened by a static load, but applying static loads present new challenges.

AFIT Designator


DTIC Accession Number