ADS-79D-HDBK Downloaded from https://www.everyspec.com K.5.4.2 Structural Health Monitoring Credit Validation Process Upon successfully verifying the credit methodology, the production unit is generated. The production unit is essential for validating the methodology. This section explains the process by which the Structural Health Monitoring - based Credit methodology should be validated. A flowchart illustrating the process is presented in Figure K-15. The entry criterion for the Structural Health Monitoring - based Credit Validation Process is that the verification process must have been completed.
The basic assumption here is that upon successful completion of verification, the system elements, including both software and hardware, will be fully integrated into suitable production unit. The validation process of SHM highlighted in Figure K-15 resembles the one in Figure K-9 for Validation of the Mechanical Health Monitoring. The most significant difference is that the SHM process begins with performing quantitative risk assessment. One of the key characteristics associated with structural health application is related to its severity of the application.
In general, structural health monitoring application is associated with the structural components possessing significant hazard to structural safety. Therefore, a more rigorous approach in determining the risk associated with potential failure of credit methodology and mitigation plan to manage the risk needs to be defined and followed. In this step, the risk associated with failing to perform required damage detection will be quantified first. The obtained information will be used in subsequent reliability allocations to establish target structural reliability.
In addition, uncertainty quantification of damage detection system should be performed to establish confidence bounds of potential detection variation. Based on aforementioned assessment, validation requirements and associated sample size for the pertinent credit application are established. The remaining steps follow a similar path as used for Validation of Mechanical Health Monitoring. The final validation can be achieved via the Fielded Data Validation, Seeded Fault Testing, or In-Service Validation. Caution should be taken in the Seeded Fault Validation option.
If the subject application has significant impact on flight safety and the anticipated damage growth rate is not slow enough in vicinity of the detection threshold, seeded fault validation with flight test may not be a viable choice. For specifics and examples on seeded fault testing, reference Appendix J. K.5.5. Structural Prognostics. For structural elements and components which are critical safety items, prognostics involves setting appropriate component retirement intervals and inspection intervals to maintain component reliability, as discussed in Appendix A.
Similarly, prognostics for damage tolerant structure (including slow crack growth structure, fail-safe multiple load path structure, and fail-safe crack arresting structure) is based on setting service lives and inspection intervals, as discussed in Appendix A. In either case, these intervals depend on usage monitoring and integrated-NDI based structural health processes discussed in Appendices B and C. Verification and validation of these usage monitoring and structural health processes discussed earlier in this appendix are necessary to enable structural prognostics. 217