Evaluation of the effect of microstructure on the propagation speed of LCR waves using ultrasonic arrays

Abstract

The inspection of stress state at which a component is subjected in service is very important to ensure its safe operation. Nondestructive techniques for stresses evaluation are most suitable for components that cannot be replaced or removed from the operating site. Among the non-destructive techniques, it is worth highlight the ultrasonic techniques based on acoustoelasticity, particularly the technique that uses Longitudinal Critically Refracted waves (LCR). The principle of acoustoelasticity is related to the variation of the speed of elastic waves as a function of stress variation of the material. However, not only stress influences the wave velocity, but also the microstructure of the material inspected. The influence of the microstructure can lead to errors in stress measurement. The objective of this research project is to evaluate the effect of microstructure on the propagation velocity of the LCR wave through the analysis of speckle images obtained by the Total Focusing Method (TFM) with an ultrasonic array. By TFM, images or speckle patterns are generated from the waveforms obtained by the array. They result from the multiple reflections caused by grain boundaries of the material. With the relationship between the speckle pattern and LCR wave velocity, we believe that is possible to separate the effect of the microstructure and the stress in the wave speed. As a result of this project, it is expected to develop a new method for nondestructive stress measurements that will provide safer inspections with more reliable and economically viable results. Also, we intend to train undergraduate and graduate students, to submit scientific papers in journals and conferences in the area, and generate a patent about the technique developed. (AU)