The Application Stuty Of The Unified In-plane And Out-of-plane Constraint Parameter A_p In Prediction Of Specemen And Pipe Fracture

In order to improve the accuracy of fracture assessment in cracked structure,the in-plane and out-of-plane geometry constraint and material constraint in welded joint need to be incorporated.In this paper,the applications of the unified in-plane and out-of-plane constraint parameter A_p in prediction of the specimen and pipe fracture have been investigated by numerical simulations,experiments and theorical analyses.The main work and results obtained are as followings:(1)Applicability of the unified constraint parameter A_p in a wide range of in-plane and out-of-plane constraints has been investigated.The results show that for a wide range of constraint,the parameter A_p still can characterize both in-plane and out-of-plane constraints.The unified correlation of parameter A_p with fracture toughness of materials can be established,and the correlation line is independent of the selection of standard reference specimen.(2)The method to establish the unified correlation of parameter A_p with ductile fracture toughness of materials has been investigated.The suitable range of the equivalent plastic strain?p isolines around the crack-tip in the specimens with different constraints for establishing the correlation lines has been given.Through experiments and finite element simulations,the correlation lines can be obtained by using a small number of specimens(at least three specimens)with different in-plane constraints or different in-plane and out-of plane constraints.(3)The effects of in-plane and out-of-plane geometry constraint and material constraint on ductile fracture resistance of welded joint have been investigated.The results show that the higher geometry constraint leads to the decrease of fracture resistance in welded zone.For the same geometry constraint,the fracture resistance of heat-affected-zone(HAZ)is lower than that of weld metal due to the higher material constraint in HAZ.(4)The method to predict the ductile fracture of specimens and pipes with different constraints by using the two-parameter J-AP has been investigated.It has been found that based on the inserction of the crack driving force line(J-A_p1/2)line)and the resistance line(JC/Jref—A_p1/2 correlation line),the ductile fracture toughness and fracture load of specimens and pipes with different constraints can be predicted accurately.For smaller size cracks in pipes,the prediction results will be excessively conservative if the constraint is not incorporated.For semiellipse cracks in pipes,the calculations of the two-parameter J-A_p at the deepest point along the crack front can be used to predict and assess fracture of pipes.