Probability of detection and false alarms for metallic aerospace panel health monitoring

The continuing shift toward the damage tolerant design approach is powering the research on Structural Health Monitoring Systems (SHMS). A key aspect is the research in the field of sensor equipment configurations in order to produce the most reliable and easily affordable system to realize the on-board structural health diagnosis, thus setting the basis for the Condition Based Maintenance (CBM). The evaluation of the sensor network competence in detecting a crack growing over the monitored structure is one of the most challenging issues. The proposed document, developed contextually to a wider project (HECTOR) financed and promoted by EDA, is aimed to provide a methodology to evaluate the economical affordability of SHM on helicopter fuselage panels, through the combined use of the Probability of False Negatives (PFN) and False Alarms (PFA), thus estimating the Probability of Detection (PoD). A statistical FEM-based method is proposed to model the sensibility of one sensor to a growing crack, in function of the crack size and location, as well as depending on the sensor position over the panel. A comparison is also carried out with experimental data relative to strain measurements over different panel locations and in function of the growing semi-crack lengths. A good detection capability is found for some strain sensors, even when located far from the occurring damage. 1. Introduction