Fatigue damage detection and monitoring using lamb wave technique

• Main Author: Chin, Alvin Han Liang.
• Other Authors: Soh Chee Kiong
• Format: Final Year Project
• Language: English
• Published: 2013
• Subjects: DRNTU::Engineering
• Online Access: http://hdl.handle.net/10356/53377
• Institution: Nanyang Technological University

Structural Health Monitoring (SHM) refers to the development of a system for pinpointing damage in a structure for the purpose of providing information about the state of a structure so that evaluation of the integrity of the structure can be made instantaneously. This study focuses on fatigue damage. Fatigue is caused by repeated and long term loading of an element. The data acquired through the SHM systems will allow for damage prognosis to be carried out. Damage prognosis is defined as the forecast of the structure’s remaining lifespan. This project aims to obtain a damage index that best predicts the fatigue crack length. The scope of this report is the give a brief introduction of the project, explain the methodology behind the experiment, present and analyse the results, compare the damage indices, provide a conclusion and possible future works. A damage index utilizes several features which have been extracted from the results in order to quantify the fatigue damage and subsequently used to predict the crack lengths. The four damage indices explored include: Transient Wave Energy (TWE), Time of Flight (TOF), Amplitude Reduction (AR) and Scattered Energy (SE). A systematic approach of comparison and elimination was adopted. Linear regression was used for comparison of the damage indices. The results of comparisons have shown that the Transient Wave Energy damage index was best able to predict the crack lengths for all the samples in this experiment. However, due to limitations of the experimental equipment, the time of flight damage index was not fully explored. Further research is needed to further examine the use of time of flight as an effective parameter in quantifying crack propagation damage. Fatigue damage detection is vital to an effective damage prognosis model. Lamb wave technology is still in its early stages of research and integration into existing structural health monitoring systems. The author hopes that this research will contribute to the collective research and effort in making lamb waves a mainstay in structural health monitoring systems, allowing it to be used in most structures in the future.