Research on Nonlinear Ultrasonic Testing Technology for Preload Force of Top Cover Bolts of Hydraulic Turbine
The top cover bolts of hydraulic turbine are subjected to complex loads in service and are prone to safety ac-cidents,so the preload detection of top cover bolts has become a necessary means to guarantee the safe operation of hy-draulic turbine.Aiming at the lack of simulation research on ultrasonic stress detection of top cover bolts and the influ-ence of axial stress distribution on detection,this paper introduces the effective stress coefficient and proposes a nonlinear ultrasonic detection method for bolt preload.First of all,the finite element model for ultrasonic stress detection of top cover bolts is established.The axial stress distribution characteristics of bolts and the influence of preload force and clam-ping distance on the distribution characteristics are obtained through static analysis,so as to get the expression of effective stress coefficient.Then the effective stress coefficient is calibrated through the simulation of ultrasonic wave propagation under different preload forces.Finally,the bolt preload test is carried out using the calibration formula,and the error of the measurement results is within±4%,which proves the reliability of the ultrasonic detection method of the preload force for the top cover bolt.
top cover bolteffective stress coefficientnonlinearityultrasonic
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