Recent Developments in Non-destructive Testing and Structural Health Monitoring Technology

Assessment of the health of a structure before and after an earthquake is of immense importance to engineers. It is important because only after monitoring the structural health engineers can conclude if a structure should be demolished, repaired or no action is needed. There are two approaches to structural health monitoring - global approach and local approach. Both approaches have their advantages and shortcomings as discussed later in the paper. In global approach such as operational modal analysis (OMA) the vibration characteristics of an entire structure are monitored while in the local approach critical structural components are monitored by non-destructive testing (NDT) techniques. Structural Health Monitoring (SHM) is a common terminology that is used for automatic monitoring of the entire structure as well as structural components. This paper presents the research and developmental work over the last three decades on NDT and SHM techniques for critical structural components. It focuses on numerical modelling and experimental investigations related to acoustic source localization techniques and ultrasonic NDT technology. Both linear and nonlinear ultrasonic NDT techniques are needed for inspecting materials and structures at different scales - from microscopic fatigue cracks and dislocation to large scale cracks in civil structures made of concrete, metal and polymer composites. The nonlinear ultrasonic technique developed by the author, called Sideband Peak Count - Index (SPC-I) technique will be discussed in detail, and advantages of this technique over conventional linear and nonlinear ultrasonic techniques such as ultrasonic pulse velocity and attenuation measurement and higher harmonic generation techniques will be demonstrated. The acoustic source localization technique that does not require the knowledge of material properties is also discussed. For ultrasonic wave propagation modelling the mesh-free semi-analytical modelling technique called distributed point source method (DPSM) developed by the author and his colleagues is also presented. Advantages of all these newly developed techniques - DPSM, SPC-I and the new acoustic source localization technique for nondestructive evaluation and structural health monitoring purposes are highlighted in this paper.