27. Applying Concepts of Complexity to Structural Health Monitoring

The process of implementing a damage detection strategy for aerospace, civil, and mechanical engineering infrastructure is referred to as structural health monitoring (SHM). The SHM method complements traditional nondestructive evaluation by extending these concepts to online, in situ, system monitoring on a more global scale. For long term SHM, the output is periodically updated information that provides details on the continual deterioration of a system. After severe events, SHM is used for short term rapid condition screening and aims to provide reliable, near real-time information on structural integrity. The hypothesis of this paper is that structural degradation increases the complexity of a system, and that SHM can be used to detect this change over both long and short-term periods. Various measures of complexity were investigated, including Shannon and spectral entropies of accelerometer readings for real time damage detection and gradient measures for image-based corrosion detection. It was concluded that different measures of complexity were more appropriate for varying types of damage, i.e. spectral entropy was more appropriate for identifying cracks in a structure, while Shannon entropy was more appropriate for identifying corrosion on a plate.