Loose Joint Detection, Localization, and Quantification Through a Pattern Correlation Method of Dynamical Properties on the Modular Test Structure

This article presents a novel procedure for detecting, locating, and quantifying damage caused by a loose bolted joint in a modular plate structure. The primary aims of this work are to locate the loose joint with a minimum number of measurement points and to quantify the damage based on acquired modal data. The proposed method is based on the direct correlation of patterns of modal property changes using simulated and measured data. These patterns combine the relative shifts in natural frequencies and the norms of relative changes in mode shapes, derived from a pre-computed database of finite element method (FEM) simulations for various potential damage scenarios. The experimental validation demonstrates that the procedure can effectively and accurately locate the position of a loose joint using only five accelerometers. A foundational study on damage quantification is presented through a sensitivity analysis using FEM model data on a single connection plate of the test structure. The results demonstrate the nonlinear relationship between the damage state and natural frequency change, based on the mode shape, mode number, and the location of the damage.