Analysis On Crack Growing Behaviour In Dissimilar Welded Joint Of Nuclear Power Plant

During the welding process of dissimilar metal welded joints in nuclear power plants,the mechanical properties of the welding region will change dramatically due to thermal flow and element migration,resulting in high strength and low toughness regions.In order to accurately characterize the distribution of mechanical properties in welding area.In this paper,combined with hardness test,function fitting and USDFLD subroutine,the continuous uneven change of mechanical properties model in welding area(continuous heterogeneous model)is established.Combined with XFEM technology and continuous heterogeneous material characterization model,the crack propagation behavior at different positions in the welding area was explored.Taking A508 heat affected zone as the research object,the influence of material mechanical properties and distribution state of heat affected zone on crack propagation was analyzed.The main research contents of this paper are as follows:The linear relationship between hardness and strength of 316L material was obtained based on hardness test and tensile test.The hardness values of base metal,welding material and heat affected zone of A508/Inconel-600/316L dissimilar metal welded joint were obtained by hardness experiment.According to the linear relationship between yield strength,strength limit and hardness value,the main mechanical properties of the material in the welding zone of welded joint were obtained.According to the mechanical property parameters of the welding region,the nonlinear fitting of the mechanical property of the material in the welding region was carried out,and the functional relationship between the mechanical property of the material in the welding region and the position parameters was obtained.Based on the USDFLD subroutine,a simplified material model for the uneven change of the mechanical property about the welded joint was established.The "sandwich" material model and continuous heterogeneous model were used to characterize the mechanical properties of the material in the welding area.The correctness and rationality of the continuous heterogeneous material model are compared and verified,and the mechanical state of the welding area of dissimilar metal welded joints in nuclear power under internal pressure load is obtained,which provides a basis for exploring the crack propagation behavior at different positions in the welding area.The crack propagation behavior at different positions in the welding region of dissimilar metal welded joints in nuclear power was investigated by using the extended finite element technology and the sub-model technology.Taking A508 homogeneous material and its heat affected zone as the research object,the effects of yield strength,fracture parameters and yield strength of heat affected zone on crack propagation behavior in heat affected zone are studied,which provides theoretical basis for material selection and welding process of dissimilar metals in nuclear power.