A Modified Method for Measuring Nonuniform Absolute Stress Field of Steel Members Using Ultrasonic Array Sensor

The stress field of steel members in service is unevenly distributed under complicated loads. The existing single-path ultrasonic (SPU) sensors can only measure stress in a single measurement point and direction. Multiple operations of the SPU sensors are required to measure stress at different measuring points and directions. The approach has low measurement efficiency and increases the measurement deviations caused by multiple operations. In this study, a modified method using an ultrasonic array sensor to measure the nonuniform absolute stress field of steel members was proposed. The relationship between the acoustic time differences of the longitudinal critically refracted (LCR) waves and the plane stress field was revealed in this method. The acoustoelastic equations of the three directional acoustic time differences and the plane principal stresses were derived. An innovative ultrasonic array nonuniform absolute stress field measurement scheme was designed, which integrated an ultrasonic array sensor capable of transmitting and receiving five LCR waves. Nineteen sets of acoustic time differences were measured by arranging the array sensor in the 0°, 45°, and 90° directions. Finally, the acoustic time differences were decoupled simultaneously to solve the acoustoelastic equation, thus achieving a nonuniform absolute stress field measurement of the steel member in service. The verification experiment indicates that the relative deviations of measurement stresses between the array sensor and strain gauges are less than 10%. Furthermore, the measurement accuracy and efficiency of the array sensor are higher than those of the SPU-LCR wave method and SPU-shear wave method, validating that the array sensor can rapidly and accurately measure the nonuniform absolute stress field of steel members.