A Study of the Applications of SMART Layer System and Structural Health Monitoring (SHM) of Single Shear Lap Joint Structure

Abstract

The purpose of the structural health monitoring (SHM) aims at the early warning when monitoring damages in structures Once the damages found in the structures the maintenance or repair can be conducted to avoid structural failure which may causes catastrophe in human lives and properties In this study the experiments on single shear lap joint metallic structures based on the SMART? Layer system were presented This system can excite a Lamb wave propagating on the structure The signal is then detected by the system to identify the existence of the damage as the wave propagation altered by the damage In the experiments to validate the group velocity of Lamb wave in single shear lap joint metallic structure theoretical time of flight (TOF) of S0 mode Lamb wave was calculated and compared with experiment results The performance of the system on monitoring the damage in metallic single lap joint was evaluated by comparing the fatigue crack observations The transducers used in the SMART? Layer system are made of piezoelectric materials (Lead Zirconate Titanate PZT) Based on the piezoelectric effect which is the coupling between electrical energy and mechanical energy the Lamb wave is excited by inputting Hanning window signal The Lamb wave propagates in the plate-like structure and then is detected by a sensor The mechanical energy is converted to voltage signal for analyzing Based on the damage index (DI) the damages in structures is evaluated by calculating the baseline signal and scatter signal of first arrival window (FAW) In the experiments the finite element analysis was conducted to obtain the stress distribution The areas with maximum stresses are potential crack initiation cites The transducers are mounted near such areas to increase the detectability In this study the concept of Damage Ratio (DR) was presented Based on the experimental data a DR reference value of 70% was proposed For a damaged structure if DR is higher than this reference value a necessary action to the structure such as maintenance or repair should be taken The observations of the fatigue cracks were also compared with the DR criterion The comparisons showed that DR is a reliable parameter for monitoring damages in metallic single shear lap joints

Date of Award	2020
Original language	English
Supervisor	Chung-De Chen (Supervisor)