2 - A novel approach for implementing structural health monitoring systems for aerospace structures

Abstract

Operations and support (O&S) expenses of the Department of Defense (DoD) weapon systems account for 65–80% of the total life cycle cost. One of the principal contributors to O&S cost is the airframe maintenance process. The US Air Force airframes are maintained using the Aircraft Structural Integrity Program (ASIP). ASIP's goal is to ensure the desired level of structural safety, durability, and supportability with the least possible economic burden throughout the aircraft design service life. ASIP uses a schedule-based maintenance approach by establishing predefined maintenance intervals for performing manual inspections. This approach requires vehicles to be removed from service at predetermined times regardless of their actual condition. In most cases, inspections performed during this process do not find any damage, and the airframe is returned to service until the next inspection interval. In December 2007, the DoD implemented the “Condition-Based Maintenance Plus” policy. As the name indicates, the DoD plans to move toward a process that services weapon systems based on their actual condition instead of the presumptive schedule-based approach. As a result of this policy, an increased emphasis has been placed on the development of advanced health management technologies, such as structural health monitoring (SHM). An essential element of condition based maintenance is improved decision making.