Locating structural defects using operational deflection shapes

This paper presents a Boundary Effect Detection (BED) method for pinpointin g defects in plates using Operational Deflection Shapes (ODSs) measured by a scanning laser vibrometer. An ODS consists of central and boundary soluti ons. Central solutions are periodic functions, and boundary solutions are e xponentially decaying functions due to boundary constraints. Because defect s introduce new boundaries to a structure, boundary solutions exist around structural boundaries and defects. The BED method uses a sliding-window sur face-fitting technique to extract boundary solutions from a measured ODS to reveal locations of defects. The proposed defect detection method is non-d estructive because structures only need to be excited to have very small vi brations, and it works without using any structural model or historical dat a for reference. An in-house finite element code GESA1 is used to analyze a 579 x 762 x 3.10 mm aluminum plate using 108 higher-order rectangular plat e elements. Numerical results show that high-order spatial derivatives of O DSs are sensitive defect indicators for locating small defects. Experimenta l studies on the 579 762 3.10 mm aluminum plate with four different defects show that this defect detection method is capable of pinpointing small def ects.