Experimental and Numerical Modeling Study of Ductile Tearing Fracture in The Welded Joints

摘要

The gas tanks (LPG) and pipes of vapor in the secondary circuit of the pressurized water reactors (PWR) are consisting of Carbon - Manganese steel tubes (A48AP), assembled by welding. These welded joints are always privileged zones for appearance of defects. For safety requirement for this type of installations, the study of the rupture in these components became essential. The fracture mechanic concepts and particularly the global approaches such as the Rice's J integral are used to analyze the defect nocivity in the welded joints. In this work, we have study the different parameters intervening at the same time, to explain the ductile tearing phenomena in a welded joint in order to develop a method of analysis adapted to this type of junction. In the experimental part, the tearing fracture test results showed the influence of the voluminal fraction on the values of tenacity to characterize by the energetic parameter J_(0,2) and on the resistance to the crack propagation J-Δa. The fatigue tests showed that the fatigue resistance of the welded joints does not depend only on the properties of the base metal and the filler metal used but also on the presence of internal or surface geometrical defects. The numerical simulation of the ductile tearing realized using the model of Rice and Tracey based on the cavity growth, allowed to highlight the importance of the parameters related to the model. In the case of an important overmatching, the mechanical characteristics of the base metal have a dominating effect on the global behavior of this type of structures and the cavities growth rate R/R_0 is sensitive to any change in the fields of the constraints and deformations at the bottom of the crack.