LAUSR

Abstract The nonlinear ultrasonic technique has been used to assess the plastic damage in High strength Q690 steel. The Q690 steel was stretched to different levels of plastic strain so as to obtain the specimen with different degrees of plastic damage. When strain was increased from 1% to 9%, the nonlinear parameter shows a general upward trend, and in the subsequent strain process, the nonlinear response drop off instead of going up. Meanwhile, metallographic examination indicates that, within the strain 9%, the growth of the void as well as the variation of dislocation structure and density are the main damage characteristic in Q690 steel. Many dislocation structures such as the dislocation cell and dislocation wall have formed in the tensile specimen, which is contribute to raise of the nonlinear effect. The results indicate that the nonlinear ultrasonic technique can be utilized to characterize the plastic damage in Q690 structural steel at the early stage.