Fracture Prediction And Assessment Of Welded Joints Incorporating Unified Geometry And Material Constraints

The welded joints are the weakest link for failure in engineering structures,and their fracture behavior influence the life and safe operation for structures.Due to the effects of geometry and material compound constraints which have significant effect on crack-tip stress field and fracture toughness,it is necessary to consider this effect in the fracture prediction and assessment of joints,so as to improve the accuracy of safety assessment.In this paper,the narrow gap welded joint and the dissimilar metal welded joint of safe-end in nuclear power plant are taken as the research object,combining with the method based on finite element numerical simulation and test data.The The studies of this paper mainly focus on the correlation of unified geometry and material constraints with ductile fracture toughness of welded joints with different crack positions;the correlation of a wide range of material constraint caused by strength mismatch and fracture toughness;and the fracture prediction and assessment of the dissimilar metal welded joint specimens and structures in nuclear power plant based on the J-A.two parameter approach.The main conclusions are as follows:(1)The in-plane and out-of-plane constraint caused by specimen size,the material constraint caused by high strength mismatch and their interaction have significant influence on J-R resistance curve and fracture toughness Jc of narrow gap welded joints.The J-R resistance curve and the fracture toughness Jc of the crack at different positions decreases with the enhancement of the geometry and material constraint effects.Therefore,it is necessary to quantify the effects of these factors in the fracture prediction and assessment of the welded joints.(2)For the cracks in narrow gap welded joints with different positions,the constraint parameter Ap can characterize in-plane constraint,out-of-plane constraint and material constraint,and a unified linear correlation with fracture toughness can be establish.This correlation line is material constraint fracture resistance line,which can be used in the prediction and assessment of structural fracture.(3)For narrow gap welded joints,a linear correlation between a wide range of material constraint caused by weld strength mismatch and fracture toughness can also be established.It is shown that for a given geometry constraint,the parameter Ap can also characterize a wide range of material constraints.(4)Based on the J-Ap two parameter,the fracture of welded joints with different geometry constraints and loading modes can be predicted through the combination of material constraint fracture resistance line and crack driving force line,and the prediction results are consistent with the test results.Both the prediction and the test data show that the fracture toughness decreases with the increase of the thickness of the welded joint specimen(out-of-plane constraint)and the crack depth a/W(in-plane constraint).(5)The combined parameter J/(Jref*(?))based on J-Ap can predict initiation positions of semi-elliptical surface cracks in nuclear power welded joint structure.The fracture initiation of cracks in safe-end welded structure with different positions can be predicted,based on J-Ap two parameters,through combining material constraint fracture resistance line with crack driving force line.Compared with the traditional single parameter prediction,the conservatism degree can be reduced.It can getmore accurate results by the calculation of the J-Ap two parameter at the initiation position along the crack front.