Presented is a novel technique for damage detection in a monolithic plate platform containing a small through-the-thickness slightly elliptic hole in addition to precision drilled holes to support an aircraft engine. Partially cantilevered, the plate is interrogated by a hammer-generated impulsive force applied sequentially over points on spanning interrogation lines. The impulse-induced transverse acceleration is sampled simultaneously by three sensors placed at the apexes of a local triangle in a selected sensing area. Dynamics effects of the presence of the hole (damage) are extracted by decomposing the three local collocated acceleration databases into their intrinsic proper orthogonal decomposition (POD) modes. The POD spatial modulations of the three collocated databases are smooth and reflect in a clear manner symmetries of the interrogation lines. We find that the dynamic effect of the presence of the hole is reflected as robust destruction of symmetry in all POD spatial modulations. This result holds for a large number of local sensing areas covered by the triangular formation of the three sensors. The technique has promising potential to extract robust and highly indicative spatial patterns of damage in coupled machinery-structural systems of complex geometry.

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