Durability testing of an aircraft structural health monitoring system

Abstract

Structural health monitoring (SHM) is an emerging technology leading to systems capable of continuously monitoring structures for damage. Aerospace structures have one of the highest payoffs for SHM systems because damage can lead to catastrophic and expensive failures. Prior work in SHM has focused on damage detection methods and sensor optimization, however, the topics of durability, reliability, and longevity of these systems has not been addressed. A framework for developing SHM durability test standards for aerospace vehicles is offered. Existing standards for the durability of commercial and military aircraft avionics are identified, and the relation to SHM systems is described. Using these existing standards, a test matrix and testing specifics are developed to assess the durability of SHM systems. Careful consideration is necessary in defining the 'system' under testing. Criteria are defined to establish whether a sensor/structural system has been affected by the various environments. Extensive experimental results from durability testing of a surface-mounted piezoelectric Lamb-wave SHM system are presented. Environments tested include temperature extremes, humidity, fluid susceptibility, altitude, and mechanical strain.

(cont.) A voltage change criteria, which measures pre- vs. post-test sensed wave amplitude, proved useful in assessing the SHM system's performance. All sensors survived the tested environments, with an average voltage degradation of -16%. The high-temperature, humidity, and water-based fluids susceptibility tests had the greatest influence on the sensors, with an average voltage degradation of -38%. In several of the tests, the sensors had significant voltage degradation during environmental exposure, which recovered somewhat in most cases after ambient conditions were reestablished. A clear need exists for a supplemental standard geared specifically towards smart structure technologies that would address SHM and other embedded or surface mounted smart structure components and systems. Additional testing of the Lamb-wave sensors, including consideration of ultrasonic fatigue, is recommended.