Experimental and numerical activities on damage detection using magnetostrictive actuators and statistical analysis

The purpose of this work is to present the formulation of a new experimenta l procedure to employ in problems of damage analysis of structural elements . The proposed method is based on the acquisition and comparison of Frequen cy Response Functions (FRFs) of the monitored structure before and after da mage occurred. Structural damages modify the dynamic behaviour of the struc ture and consequently its FRFs making possible calculation of a representat ive "Damage Index." The experimental activity was carried on using two prot otypes of magnetostrictive actuators developed within the European Commissi on funded project named MADAVIC (Magnetostrictive Actuators for Damage Anal ysis and VIbration Control). Three kinds of damages have been simulated on two beam-like structures: little mass disturbances, partial cuts of the bea m sections and constraint yielding. Two expressions of damage indices were calculated and analysed. The main target of the work was to assess the reli ability of the damage identification by using a "repetitiveness index." Thi s index is related to the lowest measurable damage extension and the statis tical t-test, in order to verify if each calculated index was really repres entative of a structural damage, rather than of unforeseen differences betw een the FRFs. A simple Finite Element Model (F.E.M.) of the second test-art icle has also been developed for numerically simulating the experimental te sts and comparing the corresponding results.