Simulation of gel effects on the ultrasonic LCR wave for residual stress error quantification

Residual Stress (RS) is present after many manufacturing processes, and is essential to detect and reduce in order to avoid potential early and unexpected failure of parts. A methodology that is gaining popularity is Phased Array Ultrasonics for Residual Stress Measurement (PAURS) which utilises Phased Array probes to provide a robust RS value using a portable and easy to use setup, ideal for in-situ inspections. However, this method is very sensitive to sources of error such as couplant thickness and sample temperature variations. The aim of this study is to utilise Finite Element Analysis software to quantify the errors that these sources cause, such that one can reliably state the RS with uncertainties following an inspection, which will allow for both calibration protocols to be developed and key sources of error to be identified and mitigated for in-situ inspections. It was found that gel thickness and temperature did contribute uncertainty towards the final Time of Flight and Residual Stress values, and methods are proposed for compensating for this.