MODIFIED DAMAGE POTENTIAL TO PREDICT CRACK INITIATION IN WELDED PIPES-THEORETICAL AND EXPERIMENTAL VERIFICATION

Abstract

Failure of Primary Heat Transport (P.H.T) piping of nuclear reactors can lead to disastrous consequences. Thus, it is desirable to be able to predict the crack initiation load accurately. For this purpose a new criteria for crack initiation has been developed at - - Reactor Safety Division, B.A.R.C, which has been found to be mesh independent, unlike its other counterparts. As a part of this work this new criteria was applied to 8" pipes and elbows having different measure of throughwall and circumferential cracks and subjected to bending moment and compare this with the experimental data available, which showed a good agreement. For this purpose. an in-house finite element code MADAM Material Damage Modeling) has been used. In the present analysis, the work is further extended on 8" and 12 straight welded pipes (piping material SA518) having through wall crack with different initial crack angles. The tests have been performed on these pipes at S.E.R.C, Chennai and on fracture specimens at N.M.L, Jamshedpur. 3-D elastic-plastic finite element analyses have been carried out on the specimens and welded pipes for various initial crack angles to predict the onset of crack initiation load. Present work emphasizes the importance of modified damage potential. The applicability of the proposed numerical methodology is shown by comparing with the experimental results. Key Words: Local approach, ductile fracture, void nucleation, void growth and coalescence, Rice and Tracey's model, J-integral, xy-integral