| It is of great significance to enhance the fatigue strength during and after welding by effective methods. Ultrasonic impact treatment (UIT) is an effective and convenient method to enhance the fatigue strength of welded joints and suchlike structures. After investigation on the details of UIT, a new power supply, called ultrasonic power,based on secondary inversion technology has been invented successfully. In order to ensure the resonance during all the treatment process, the device can fulfill its function normally, frequency-trace system based on the phase-lock principle in the power was designed; In order to control the quality of treatment, it was applied to control constant current output, then to control the terminal vibrate rate, by combination employing of PWM and network match to change the excitation voltage. The output variation of the power shows it really does work for some following advantages: wide modulation range, quick response, almost no wave distortion, constant output with non-linear load. The whole UIT device comprises the power and the execution unit. Fatigue tests were conducted on the specimens respectively made of X65, Q235B, 16Mn. The test specimens were investigated on the fatigue strength and the fatigue life at same stress range level by comparing the ones peened by UIT with the others without the treatment. The test results show: as for specimens of X65, butt joints, the fatigue life of the former is 1.85-11 multiples of the latter and the fatigue strength was increased by 37.9%; as for Q235B, cruciform joints, the fatigue life of the former is 40 multiples of the latter and the fatigue strength was increased by 67%; as for 16Mn, joints like Q235B, 34 and 67%. So UIT is an effective and convenient method to enhance the fatigue strength of welded joints and suchlike structures.
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