Detection, characterization and prognosis of fatigue-induced damage using electromechanical-impedance technique

• Main Author: Chan, Fei Ling.
• Other Authors: Soh Chee Kiong
• Format: Final Year Project
• Language: English
• Published: 2010
• Subjects: DRNTU::Engineering::Civil engineering::Structures and design
• Online Access: http://hdl.handle.net/10356/40047
• Institution: Nanyang Technological University

Continuous fatigue loads often cause buildings and structures to experience progressive damage, which gradually decreases their workability. This may cause them to fail unexpectedly, way before their predicted failure. Under such loads, these structures incur different degrees of damage as they go through the different damage phases, starting from the initiation phase, through the propagation phase, to the critical phase where the structures ultimately fail. Such damages are often not only destructive, but also come with a heavy price tag. Therefore, it is crucial that effective, reliable and inexpensive Structural Health Monitoring (SHM) techniques are available for the continuous monitoring of structural health. This can help structure owners to reduce unnecessary maintenance costs and maximize their structures’ usage without jeopardizing the occupants’ safety. Currently, there are many conventional local non-destructive techniques that are being used for SHM. However, these techniques posed many problems and that spurred researchers to venture into other damage detection techniques which employ smart materials. One such common technique is the Electro-Mechanical Impedance (EMI) technique, which uses piezoelectric materials as actuators and sensors to detect and characterize structural damage. In this study, the main focus is to investigate the feasibility of using the EMI technique to detect and characterize damage through experimental means. During the experiment, uniaxial cyclic tensile load is applied on four lab-sized aluminium notched specimens that are each bonded with a lead zirconate titanate (PZT) patch till failure. The conductance signatures that are being obtained from all four of these specimens are being monitored and recorded regularly at predetermined number of load cycles. Progressive reduction in the resonant frequency as the number of load cycles increases shows the EMI technique’s effectiveness in detecting damage while the different rates of reduction in resonant frequency at the different crack growth phases displays the technique’s ability to characterize damage. The proportional reduction of the resonant frequency with the increasing crack length during the crack propagation phase also shows the technique’s ability to aid the damage prognosis of its host structure. These highly repeatable behaviours of the resonant conductance signatures sparked the possibility of relying on these signatures obtained from the EMI technique to estimate and monitor the health status of the host structure and predict its failure. Recommendations for possible future works to achieve that are also being discussed in the last chapter.