Probability of detection, localization, and sizing: The evolution of reliability metrics in Structural Health Monitoring

Abstract

The successful implementation of Structural Health Monitoring (SHM) systems is confined to the capability of evaluating their performance, reliability, and durability. Although there are many SHM techniques capable of detecting, locating and quantifying damage in several types of structures, their certification process is still limited. Despite the effort of academia and industry in defining methodologies for the performance assessment of such systems in recent years, many challenges remain to be solved. Methodologies used in Non-Destructive Evaluation (NDE) have been taken as a starting point to develop the required metrics for SHM, such as Probability of Detection (POD) curves. However, the transposition of such methodologies to SHM is anything but straightforward because additional factors should be considered. The time dependency of the data, the larger amount of variability sources and the complexity of the structures to be monitored exacerbate/aggravate the existing challenges, suggesting that much work has still to be done in SHM. The article focuses on the current challenges and barriers preventing the development of proper reliability metrics for SHM, analyzing the main differences with respect to POD methodologies for NDE. It was found that the development of POD curves for SHM systems requires a higher level of statistical expertise and their use in the literature is still limited to few studies. Finally, the discussion extends beyond POD curves towards new metrics such as Probability of Localization (POL) and Probability of Sizing (POS) curves, reflecting the diagnosis paradigm of SHM.

Qualification of distributed optical fiber sensors using probability of detection curves for delamination in composite laminates

“…In this case, the hypothesis of statistical independence of the observations does not hold anymore, making it impossible to apply the standard linear regression model used for POD in NDE studies. 21 The LaD method avoids the issue of dealing with repeated measurements by considering only one observation among the time series of data. Similar to the standard method proposed in the MIL-HKBK-1823A, 12 detection is positive if a certain measurement is above a certain threshold.…”

Multi-level damage diagnosis on stiffened composite panels based on a damage-uninformative digital twin

“…Actions related to the first category aim to provide insight about the presence, location, type as well as extent of the damage. 14 Prognostics in turn perform predictions regarding the remaining useful life of the monitored structure. 15 The DT concept is a promising approach for SHM that combines sensor data with a numerical model, for example, FE model, in order to interpret the underlying phenomena of damage evolution in the structure.…”

Performance Assessment for a Guided Wave-Based SHM System Applied to a Stiffened Composite Structure

“…Generally, a detailed bibliography on the topic was presented by Falcetelli et al [ 21 ], who focused on the main challenges and barriers that currently prevent the development of proper reliability metrics for SHM. Starting from the analysis of the main differences with respect to POD methodologies for NDE, the authors found that a higher level of statistical expertise is required to achieve POD curves for SHM systems.…”

“…On the other hand, some simplified experiments have been carried out on extending the reliability concept to complex structures, such as aeronautical composite coupons and subsystems [ 22 ]. Falcetelli et al [ 21 ] also oriented the discussion beyond classical POD curves, approaching new metrics such as probability of localization (POL) and probability of sizing (POS) curves. Actually, this aspect reflects the diagnosis paradigm of SHM, which aims to detect, localize and assess the size of a damage.…”