The Effect Of UIT On Mechanical Properties And Its Finite Element Modelling

The beneficial effect of Ultrasonic Impact Treatment(UIT) on residual stress, fatigue strength, et al. had been demonstrated by a mass of research achievement. However, the effect of UIT on mechanical properties of materials had been involved rarely. In this paper, the microzone mechanical properties of EQ56, which is used in ocean platform, was tested by using shear punch method. The effect of UIT on mechanical properties was studied in this way. The test results showed that the material was softened to some degree because of the acoustic softening effect. But different degrees of softening took place in different zones. Giving tensile strength, the maximum decrease of base metal was 11%, while HAZ was 9%, and welding was 19%. The reason of most significant softening of welding was the longest treatment time of it. Besides, a hardened layer, with finer grain, would appear in the surface of workpiece after UIT. Compared with that without UIT, more excellent strength and plasticity, took place in this layer. What’s more, mechanical heterogeneous was improved in this layer, and the difference of yield strength decreased from 30 MPa to 15 MPa.Otherwise, for the reason of complicated process of UIT, a finite element modeling(FEM) of UIT was established by developing Abaqus secondly using Python. The process of UIT could be reflected really by this FEM, and its accuracy was verified. Based on this FEM, 304 L stainless steel, without initial residual stress, was simulated with different process parameters. The simulation results showed that the effect of initial velocity of pin on residual stress was significant. The maximum value of residual stress verified from-412 MPa to-460 MPa, When the initial velocity of pin verified from 1m/s to 3m/s, at the same time, the location of maximum residual stress verified from 1.74 mm from surface to 2.46 mm. Besides, with treatment time increasing, the maximum value of residual stress verified from-433 MPa to-449 MPa, but the trend of this increasing became slowly. This showed that there existed an optimal value of treatment time. Nevertheless, the effect of friction coefficient on residual stress could be ignored.