Experimental analysis of structural damage in tensile membranes

Different numerical and experimental methods have recently been introduced in the literature for the diagnosis of structural damage by using location-dependent changes in the modal parameters (natural frequencies, damping factors and mode shapes). The main task is to determine the presence, location and extent of the damage. This work is concerned with the possibility of introducing, along with a manufacturing process, an on-line quality control for structural components before assembly using modal parameters. The assembly process is usually realized by welding joints or bolts. The structural reliability of the entire system results, therefore, is dependent on the reliability of the single elementary components as well as on the local quality of the welding processes. As a result, a non-destructive control provided together with the relevant assembly or manufacturing process can be important for the integrity of the whole system. The modal analysis techniques [Giannoccaro NI, Messina A, Trentadue B, Masciocco G, Montuori G. Detection of Changes in Mechanical Components for Automobile Chassis Using Modal Data. ATA International Edition, 2001; Messina A, Williams EJ, Contursi T. J. Sound Vib. 1998, 216 (5), 791-808] lend themselves well to the case because they are based on the measurement of parameters (natural frequencies and mode shapes). They are sensitive to the structural modifications but have a different sensitivity for the variations in the generic investigated zones of the system. To enact the real possibility of using such a technique, the defects that are troublesome for integrating the assembled or elementary component must be established. These defects have to induce some variations in the checked parameters (modal parameters) in order to be out of experimental repeatability of the same parameters connected with healthy structural systems. In this work, natural frequencies are shown and compared to a non-contact optical technique subsequently experimentally reliable when used in diagnostic routines connected with geometrically similar components from a molding process