• Hutchison, Alistair
• Mehnen, Jorn
• Wathavana Vithanage, Randika Kosala
• Mohseni, Ehsan
• Lotfian, Saeid
• Zimermann, Rastislav
• Gachagan, Anthony
• Javadi, Yashar
• Macleod, Charles N.
• Pierce, Stephen

Abstract

Background, Motivation and Objective ‎<br/>In this paper, a new ultrasonic system is developed to measure the mechanical stresses. The ‎study is part of a larger research project to use the Phased Array Ultrasonic Testing (PAUT) ‎system for the residual stress measurement of high-value manufacturing and safety-critical ‎components, like aerospace, wind turbines and nuclear structures. The stress measurement ‎using the ultrasonic method is explained by the acoustoelastic effect which is based on the ‎sound velocity change in an elastic material subjected to the static stress field. ‎<br/><br/>Statement of Contribution/Methods ‎<br/>Single element transducers are conventionally used for stress measurement using the ultrasonic ‎method while the PAUT system is innovatively used in this paper. The mechanical stresses, ‎tensile and compressive, are applied using a customized tensile test machine and vice clamp ‎system. The ultrasonic arrays are 5 MHz transducers manufactured by IMASONIC (France) and ‎configured in Longitudinal Critically Refracted (LCR) setup (see Fig. 1). The transmitter array ‎generates 8 ultrasonic waves ‎which are ‎received by 8 elements of the receiver array. ‎Therefore, ‎a matrix of 8 × 8 ‎acoustic paths can be generated. This has resulted in higher stress ‎measurement ‎accuracy, compared to the traditional setup ‎in which only one acoustic path can ‎be generated using two single element transducers, through minimization of the Time of Flight ‎‎(ToF) measurement error, created by transmitter triggering uncertainty, wave speed changes in ‎the transducers/wedge, positioning uncertainty, transducer alignment and material texture ‎effects. Additionally, a higher measurement resolution was achieved because of the lower ‎distance between the elements, array pitch was 0.5 mm compared to the &gt;10 mm transducers ‎distance in the single element setup.‎<br/><br/>Results/Discussion ‎<br/>The PAUT-LCR system was able to detect variations in ToFs of the sample subjected to the stress ‎changes. Therefore, the mechanical stress was successfully measured using this newly ‎developed PAUT-LCR system. Using the acoustoelasticity law, the novel setup was also used to ‎measure the acoustoelastic coefficient required for future residual stress measurement.‎<br/>

Topics

• impedance spectroscopy
• texture
• ultrasonic