Effect Of A Single Overload On Mechanical State At Crack Tip In Welded Joints

It is known as a single overload that the load increases suddenly and returned to normal level in a very short period, which is occasionally occurred in mechanical structures during service. Corresponding researches and experiments indicate that a single overload would induce the crack closed phenomenon at the crack tip, and which would affect the crack growing course. To understand the effect of a single overload on the mechanical state at the crack tip in the structure with flaws, the stress-strain fields at crack tip were simulated and analyzed under a single overload by using the finite element simulation method, in which the dissimilar metal joint in safety end of the primary loop in nuclear power plant was as a research object. Main works were performed as follows:(1) The finite element model of a single material compact tensile specimen was established, and the mechanical field at the crack tip in nickel-based alloy 600 was simulated and analyzed. The effects of different crack length and a single overload ratio on the stress-strain field at the crack tip in nickel-based alloy were obtained.(2) The local stress and strain field at the crack tip nearby the interface of the two material specimen in the 182 alloy-A508 low alloy dissimilar metal welded joint were analyzed and simulated in detail, and the effects of the different location of the crack on the stress and strain field and the plastic zone at the crack tip under a single overload condition were obtained.(3) The stress and strain field in the inner surface radial crack fronts of the dissimilar metal joint in safety end under the normal load service and a single overload condition were simulated respectively, in which the mechanical heterogeneous properties of welded joint was considered and three dimensional model was constructed, and the effects of the crack location, crack depth and a single overload ratio on the mechanical state around crack fronts were obtained.