A Novel Experimental Approach to Structure Health Monitoring

Fatigue Corrosion (FC) phenomenon is a mechanical degradation due to occurrence of both a mechanical cyclic stress and a corrosive environment. FC can be an occasional problem in commercial and military aircrafts, thanks to the presence of an effective protective surface layer (anodic oxidation, primer, enamel and so on). Although each single effect of both fatigue and corrosion have been extensively documented for aluminium alloys, their synergic action is not thoroughly understood and it continues to be an area of considerable scientific and industrial interest. In this paper, a novel and effective approach is outlined and applied for monitoring, contemporary, the electrochemical behaviour and the true strain of an aluminium alloy coupon, while it is subjected to a fatigue test. Fatigue experiments were conducted on bare AA 2024 T3 specimens in presence of an aggressive environment consisting of a water aerated solution with 3.5 % of NaCl in weight. The mechanical stress was imposed on simple cantilever beam way in high-cycle fatigue. The open circuit potential (OCP) has been monitored by using microcell technique. The actual true strain at the root of the specimen has been monitored by means of a Fibre Optic Bragg Grating (FOBG) sensor. The strain and OCP variations have been monitored as a functions of number of cycles, and an interpretation has been proposed taking into account the numerous and complex phenomena occurring on the material as time goes on. The pits birth and their subsequent growth seem to play a significant role as crack initiation and subsequent propagation up to final catastrophic failure of the coupon