Evaluation of Bolt Axial Stress Based on Nonlinear Ultrasonic Technique

The stress in the material will affect the quality of its service, so the evaluation of stress is of great significance for safe production. Since the variation of the stress in the material has influence on the nonlinear characteristics, the nonlinear response of the ultrasonic wave will also change. In this paper, the bolts are taken as the research objects, and the ultrasonic nonlinear detection platform is built to explore the effect of the axial stress of bolts on the ultrasonic nonlinear response. First, the relationship model of bolt length and nonlinear response is established by controlling variables, and the optimal length of bolts is determined. Then, the electronic tensile testing machine is used to load axial stress of the bolt within the elastic deformation range. The nonlinear responses under different stresses are observed through calculating the corresponding relative nonlinear coefficient. The experimental results show that within the elastic deformation range, the nonlinear coefficient of the bolt increases monotonously with the variation of the axial stress, which proves the feasibility of nonlinear ultrasonic technique to characterize the stress in the material.