Locating Structural Defects Using Operational Deflection Shapes

Abstract

This paper presents a Boundary Effect Detection (BED) method for pinpointing defects in plates using Operational Deflection Shapes (ODSs) measured by a scanning laser vibrometer. An ODS consists of central and boundary solutions. Central solutions are periodic functions, and boundary solutions are exponentially decaying functions due to boundary constraints. Because defects introduce new boundaries to a structure, boundary solutions exist around structural boundaries and defects. The BED method uses a sliding-window surface-fitting technique to extract boundary solutions from a measured ODS to reveal locations of defects. The proposed defect detection method is non-destructive because structures only need to be excited to have very small vibrations, and it works without using any structural model or historical data for reference. An in-house finite element code GESA1 is used to analyze a 579 × 762 × 3.10 mm aluminum plate using 108 higher-order rectangular plate elements. Numerical results show that high-order spatial derivatives of ODSs are sensitive defect indicators for locating small defects. Experimental studies on the 579 × 762 × 3.10 mm aluminum plate with four different defects show that this defect detection method is capable of pin-pointing small defects.