Modern lightweight structures are characterized by their maximized exploitation of material properties. However, this optimization makes them prone to unexpected damage that can result in structural failure. Particularly composite materials show complex damage behaviors that are difficult to predict, especially if they are caused by impact events or manufacturing defects. SHM techniques such as the electro-mechanical (E/M) impedance method help to identify structural damages by systems of sensors.
In this contribution we consider an aircraft spoiler of a large commercial aircraft. A crucial damage mode of this composite sandwich construction is the debonding of the face layer from the core. The investigations focus on the evaluation of the E/M impedance method as SHM technique for such sandwich panels. In the study the structure is simplified as a circular sandwich panel of constant thickness, consisting of isotropic face layers and a honeycomb core. The debonding is assumed to be circular and situated at the center of the panel, only variable in its radius. The Piezoelectric Wafer Active Sensor (PWAS) used to excite the structure and to measure its response is placed on the face layer at the center of the considered debonding. This setting is of course an idealization of reality but allows to analyze the driving parameters of the E/M impedance method by both analytical and numerical models. The study is performed in five steps. First, experiments are conducted. Second, an analytical model is developed to thoroughly understand the problems physical behavior. Third, a numerical model is developed and validated by the analytical results.
Fourth, the level of details in the numerical model is increased to converge to the experimental results. And fifth, different debonding sizes are analyzed to identify the key parameters for debonding identification in sandwich structures with the E/M impedance method.