A modified sideband peak count based nonlinear ultrasonic technique for material characterization.

The ultrasonic Non-Destructive Testing and Evaluation (NDT&E) has been widely used for Structural Health Monitoring (SHM). The conventional linear ultrasonic technique which is suitable for detecting macro-scale defects is routinely used in industry; however, it often fails to detect the micro-scale defects. Generally, micro-defects in a material appear first due to dislocations at grain boundaries. These micro-defects then grow and coalesce to form macro-defects. The crack growth rate is much faster for macro-defects than micro-defects. Therefore, monitoring micro-defects is important to avoid catastrophic failures of structures. Nonlinear ultrasonic techniques help to detect micro-defects. A recently developed nonlinear ultrasonic technique called Sideband Peak Count - Index (SPC-I) technique has some inherent advantages over other nonlinear techniques for monitoring progression of micro-defects. In this research, the SPC-I technique is further modified. This modified technique, Sideband Peak Intensity (SPI) technique, is shown to be more robust and easier to implement. Both SPC-I and SPI techniques are used to monitor the damage progression in impact induced damages in metals. Similarities and dissimilarities between these two techniques are investigated. Then it is concluded that the SPI technique is good as a general-purpose robust damage monitoring tool that can be used by less skilled users while the SPC-I technique although requires more skills has more sensitivity and has the flexibility for an in-depth damage analysis in materials.