Structural Health Monitoring During Assembly of Aerospace Structures

With the objective of verifying and validating the novel methodology for Structural Health Monitoring before, during and after an assembly of aerospace structures, by use of multiple PAMELA SHM™ system wirelessly controlled [1][2], a SHM test campaign on a simplified six component aluminum wingbox was performed. The methodology was implemented and a full assessment of its advantages together with identification of potential unforeseen problems was made. During the tests was found out that each one of the different assembly phases, by mechanical fastening of all interface screws, induces complex changes into ultrasonic responses of each one of the joining components, in a form of new and different ultrasonic wave trains than the initial ones with the components separated. The direct consequence of these effects, which emerged and is of utmost importance for efficient and reliable SHM in the near future, is the need to first completely understand all changes and different boundary condition effects on ultrasonic wave structural responses, not just during the assembly but also for any other structure life cycle phase. The ultrasonic tests in this first test campaign phase were performed by monitoring only one structural component, the upper skin, in the pulse-echo inspection mode, for several test configurations of interest and in sixteen different boundary conditions of the subassembly, starting with the skin alone until the bay wingbox was completely closed. Tests were performed by use of one integrated Phased Array transducer (PhA III) [3][4], surface bonded onto the interior face of the upper skin, by one integrated on-board PAMELA III electronic device [1] electromechanically installed above the transducer and controlled wirelessly by PAMELA SHM™ System Controller software on a external host computer. A brief overview of typical changes in ultrasonic time signals for several assembly steps is presented in the paper, with the recommendations for future actions, aimed to make easier interpretation and identification of these structural changes.