Feasibility study of residual stress measurement using phased ‎array ultrasonic method

Residual stress measurement using the ultrasonic method is based on the acoustoelasticity law, which ‎states that the Time-of-Flight (ToF) of an ultrasonic wave is affected by the stress field. Traditionally, single-element ultrasonic transducers are used for residual stress measurement. In ‎this paper, a Phased Array Ultrasonic Testing (PAUT) system is used and the single ‎element transducers are replaced by 5 MHz and 10 MHz arrays with 8 and 16 elements, respectively. The 10 MHz transmitter array can generate 16 ultrasonic waves ‎and each of them can be received by any of the 16 elements of the 10 MHz receiver array. ‎Therefore, a matrix of 16 × 16 acoustic paths can potentially be generated. Each of these 256 LCR paths ‎is different from the others (i.e., different distance or different position of the travel path in the ‎material) whereby 256 ToFs can be generated. This is anticipated to increase the measurement ‎accuracy in comparison with the traditional setup in which only two acoustic paths can be generated by using three single element transducers. In this paper, a feasibility study is ‎conducted to investigate the requirements of a residual stress measurement system using the PAUT method. An advanced processing algorithm is also developed to analyse Full Matrix ‎Capture (FMC). Based on the preliminary results, some variations between different acoustic paths are ‎measured which prove that the effect of the residual stress on the ultrasonic wave is detectable using ‎the PAUT system.‎ Furthermore, the potential of this system for robotic residual stress measurement is discussed