Non-damage-related influences on Lamb wave–based structural health monitoring of carbon fiber–reinforced plastic structures

Abstract

Structural health monitoring with actively excited Lamb waves is a promising technology for health monitoring of aerospace carbon fiber–reinforced plastic structures with reasonable effort, as it has the potential to cover large areas with few sensors and a high sensitivity to damage. The high signal complexity inherent to wave propagation in complex, finite, and anisotropic structures, especially in combination with the sensitivity toward environmental and operational loads, presents the main challenge on the road toward the utilization of this potential. In this study, the effects that real structural features and damage, in combination with environmental conditioning, have on Lamb wave propagation and measurement are investigated. For this, the composite-specific behavior is discussed. Based on the local temporal coherence method, changes of sensor responses containing reflections and interaction with stiffness discontinuities, both unrelated and related to damage, are identified in anisotropic composite materials. The amount of signal changes unrelated to damage, as well as their high dependency on the specific conditions of the measurements, is an indicator for the complex issues faced by compensation. While damage of a sufficient size will be detectable even in the most complex, finite, and anisotropic structures, the establishment of a sufficiently reliable damage detection with an acceptable low detection threshold will require even more careful consideration of the monitored structure and its environmental and operational loads than for metallic structures.