SAE ARP6821

This document contains information and guidance necessary for the development of a representative, repeatable validation program that may be utilized to assess the capability of SHM systems. The nature of SHM data differs from that seen in traditional nondestructive evaluation (NDE) applications in that the position of SHM sensors is fixed and SHM data can be available much more frequently (if not continuously) over time. This document presents methodologies that can be used to arrive at SHM capability while considering the unique nature of SHM deployment. Each SHM system must be considered independently to determine the applicability and limitations of the guidance contained here for each SHM system being assessed. The goal of this document is to provide guidance for establishing the damage detection capability of Structural Health Monitoring (SHM) systems to assist in the safe adoption of SHM systems for assessing aircraft integrity. The maturity of SHM systems has evolved to the point where some SHM systems have demonstrated sensitivities that meet or exceed current damage detection requirements and are being considered for on-aircraft use. As a result, there is a growing need for well-defined methods to statistically quantify the capabilities of SHM systems. However, while there are many agreed-upon procedures for quantifying the performance of nondestructive inspection (NDI) techniques, there are limited guidelines for assessing SHM systems. While the intended function of the SHM and NDI systems may be very similar, there are distinct differences in the parameters that affect their capability and differences in their implementation that require special consideration. For example, some factors that affect SHM sensitivity include the flaw size, shape, orientation, and location relative to the sensors, equipment hardware and software, structural configuration, variability in the damage, residual strains, stress fields, operational and environmental variables, and issues related to the presence of multiple flaws within a sensor network. The objective is to apply statistical methods to laboratory and flight test data to derive Probability of Detection (POD) values for SHM sensors in a fashion that agrees with current NDI validation requirements. It is anticipated that all people in the aviation industry that are working in the SHM arena will benefit from standardized methods to establish the performance and reliability of SHM systems. They should be able to use the SHM reliability document to clearly define the different types of SHM damage detection approaches and to assess the damage detection capability of each SHM application.