Issue34

K.L. Yuan et alii, Frattura ed Integrità Strutturale, 34 (2015) 476-486; DOI: 10.3221/IGF-ESIS.34.53 479 26% in ultimate tensile strength under ultrasonic impact was observed, which is just a little less than the 27-30% reduction in the case of direct ultrasonic action. Nevertheless, the results suggested that the UIT could effectively transfer ultrasound into the treated objects through the area of plastic deformation by means of ultrasonic impact. To the best knowledge of the authors, there is no model to directly quantify the acoustic softening effect related to UIT. Hence, in this work a yield stress reduction parameter η accounting for acoustic softening in Eq.3 is employed. The value of η is iteratively adjusted by comparing the predicted indentation depth with experiment. as o (1 )      (3) where σ as is the flow stress considering acoustic softening, σ o is the flow stress without vibration and η ranges from 0 to 1 depending on the amount of acoustic softening. F INITE ELEMENT MODELING n the present study, a three dimensional simulation procedure is set up including the uncoupled thermo-mechanical welding simulation by SYSWELD [23], transfer of the results to the initial-stress state of a dynamic model of UIT by explicit method in LS-DYNA [24], as shown in Fig.4. Figure 4 : Flowchart of welding-UIT process simulation. Figure 5 : Geometry and dimensions of UIT specimen. Analysis model and process parameters A non-load-carrying cruciform joint used in the recent experimental work by Suzuki et al [20] is selected as analysis object. Fig.5 shows the dimensions of test specimen, which was welded using CO 2 fillet welding with JIS-SM490A base metal plate. The welding parameters are given in Tab. 1. I