| In the welded structures, the weld defects may be the hidden danger to the safety of the entire structure. In this paper, according to Friction Stir Welding and variable polarity TIG welding process, the effects of the UIP(Ultrasonic Impact Peening) on the fatigue performance of the weld joints which has the weld defects were studied. the fatigue performance of the welded joints of the 7075-T651aluminum by the friction stir welding, improve by the UIP, in the case of the stress ratio R=0.1, the fatigue strength increase by about 57.7% by the UIP treatment; and in the case of the stress ratio R=0.5,the fatigue strength increase by about 37.9% by the UIP treatment.The strengthened layer caused by the plastic variation, surface hardening and uniformity of tissue, and transversal residual stress of base metal after UIP becomeing compressive residual stress in the surface, which are the main reasons that lead to the improvement of fatigue performance.In order to reveal the effect of the UIP on the welded joints further, by adjusting the variable polarity TIG welding process, the welded joints which contain weld defects were prefabricated for the purpose of the fatigue performance testing, in the case of the stress ratio R=0.1 and the△σ= 50MPa. The result shows that: the fatigue performance of the welded joints were better after the UIP.The crack growth rate tests were carried out under different stress ratio, the result of the tests show that: in the case of the stress ratio R=0.1, in the Paris fatigue crack growth rate expression, the material parameters m = 3.50, C=4.8E-8(50% survival rate); in the case of the stress ratio R=0.1, in the Paris fatigue crack growth rate expression, the material parameters m = 4.03。The tests of the stress distribution of the specimens after the UIP show that the UIP treatment adjust the stress distribution of the tip of the defect, which is the main reason cause the improvement of the fatigue performance. |
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