Simulation, Realization and Validation of Guided Wave SHM System Solutions for Aircraft Metallic Structural Repairs

Abstract

Repairs in aircraft structures are an essential affair when the structural components may be subjected to either critical or non-critical damages during their service. Many of those repairs follow standardized designs while others turn out to be only solved as unique designs. To meet lightweight design criteria damage tolerance principles have to be applied. This is where SHM gains a specific interest and where optimised solutions have to be found. This describes the process of a SHM based approach for a metallic repair on a metallic aircraft fuselage where the approach is based on guided waves. The minimum requirement of any such SHM system to be developed is to reliably detect the given tolerable damage based on optimized actuator-sensor configurations. Unlike conventional ultrasonic transducers, which are free to move on the surface of the structure to be inspected and where data samples can be taken for a virtually unlimited combination of transducer positions, the piezo actuators/sensors an SHM-system consists of, are fixed regarding their position. Those positions have therefore to be clearly identified in advance with regard to an optimized location to capture the signals resulting from the damage. Finding that optimum location can reasonably only be achieved through simulation. In this paper a patched metallic repair solution is numerically modelled with regard to guided waves travelling through it for an undamaged condition and a condition with a tolerable damage respectively. The results for the two conditions are subtracted from each other and the resulting differential image is considered to indicate the locations where most of the damage resulting information can be ‘harvested’. This approach has been performed in simulation and validated experimentally