Evaluation of structures for cracks due to dynamic loads

• Main Author: Zaw, Hein Lin
• Other Authors: Soh Chee Kiong
• Format: Final Year Project
• Language: English
• Published: 2016
• Subjects: DRNTU::Engineering
• Online Access: http://hdl.handle.net/10356/68125
• Institution: Nanyang Technological University

Early detection of structural damages before reaching a critical state is a very important aspect of public safety. Visual inspection used to be the most common way to detect structural damages. Unfortunately, this kind of approach is expensive, labour extensive and only reliable to a certain extent. Structural health monitoring (SHM) becomes an essential tool to monitor structures and evaluate their state of health. Electromechanical impedance (EMI) technique for SHM which uses piezoelectric materials as sensors stands out as a powerful technique. A Piezo-ceramic transducer (PZT) is widely used in EMI technique due to its unique properties and active ability. Additionally, SHM method using wireless technology also becomes popular in the recent years. Most of the research has been focused on static load and little emphasis being reported on dynamic load. Additionally, the frequency domain is commonly performed in EMI technology, but time domain is barely practiced. This report presents experimental studies on dynamic load based on the artificial time domain method in EMI using PZT. The experiments were performed on laboratory sized aluminium specimens, including 1-D, 2-D, and 3-D as well as on the real-life structure (a steel frame). The effects of various dynamic parameters such as changing the drop-weight, drop-height, angle of free swing, walking and jumping were investigated. This report also discusses the usage of a wireless communication system that monitors the structure by integrating a strain gauge sensor. It was shown through the experiments that by using the time domain approach, impact load was detected using EMI and was quantified as well. Additionally, the vibration of the structure was detected live. The observation was further reinforced by the statistical analysis. It was also shown that the PZT transducer was able to detect impacts along x, y and z coordinates. Moreover, live jumping and walking action can be identified using the EMI approach. This report is expected to be very useful in monitoring of the structures, especially in airplanes, bridges, elevators and so forth.