Absolute stress field measurement in structural steel members using the Lcr wave method

The absolute stress in structural steel members is an important indicator of the performance of steel structures. Among the existing non-destructive testing (NDT) methods, ultrasonic methods have received the most research attention. The existing ultrasonic methods can evaluate the average stress in a fixed acoustic path but cannot easily measure the stress field within the tested objects. We present a non-destructive method to evaluate the absolute stress field in a structural steel member using longitudinal critically refracted (Lcr) waves. Specifically, a theoretical expression is derived for absolute stress measurement. A measurement system is developed to demonstrate the performance of the proposed method. A sensor group, which contains one transmitter and two receiver transducers connected by a Vernier calliper, is designed to transmit and receive Lcr waves. The proposed method is applied to two steel members with variable cross-sections. The traditional strain gauge method is used for verification. The results show that the proposed method can efficiently evaluate the stress distribution and stress extremum in structural steel members.