Transferability of specimen J–R curve to straight pipe with circumferential surface flaw

Abstract

A B S T R A C T Specimen J-R curve is extensively used for structural integrity of large components. It is well known that J-R curve heavily depends on constraint level ahead of crack tip in remaining ligament. In earlier work, it was demonstrated that J-R curve from Three Point Bending (TPB) specimen is transferable to straight pipe with circumferential through wall crack. In this paper, the transferability of J-R curve is investigated from TPB specimen to pipe with circumferential surface crack. A 16 in. diameter pipe with circumferential surface crack and TPB specimen machined from same piping material (SA333Gr6 Steel) are tested. Consequently, 3D finite element analysis (FEA) has been performed on surface cracked pipe and TPB specimen. Crack-initiation load is also predicted for surface cracked pipe by FEA and compared with experimental result. J-R curve is calculated for the pipe using experimental data, that is, load, load line displacement and crack growth. J-R curve of pipe is compared with TPB specimen and it is found that the pipe is predicting much higher J-R curve than TPB. This difference of J-R curve is investigated by evaluating stress triaxiality in remaining ligament for both cases. Stress triaxiality is quantified using triaxiality factor (h) ahead of crack tip for pipe and TPB specimen. It is found that the TPB specimen has considerably higher constraint level than pipe with surface crack, which is well supported by trend of J-R curves for specimen and pipe. A study has also been carried out to investigate the effect of internal pressure on the stress triaxiality. It is found that there is negligible difference in stress triaxiality because of internal pressure. The stress triaxiality is re-established as a qualitative parameter to assess the transferability of J-R curve from specimen to component. a = initial crack size A 2 = A 2 -stress (valid for large strain region) c = half crack length D 0 = outer diameter of pipe E = Young's modulus h = stress triaxiality factor J e = J-elastic J i = crack initiation toughness J p = J-plastic k = stiffness K = stress intensity factor p = internal pressure Correspondence: M. K. Sahu.

In‐plane and out‐of‐plane constraint parameters along a three‐dimensional crack‐front stress field under creep loading

“…As a secondary fracture parameter was proposed by authors 17,18 a local parameter of crack‐tip constraint because the validity of some above‐mentioned concepts depends on the chosen reference field. This stress triaxiality parameter is the following: where σ kk and s ij are hydrostatic and deviatoric stresses, respectively.…”

Fracture studies of straight pipes subjected to internal pressure and bending moment

“…16(a) is also showing the prevalence of machine compliance which has been corrected and shown in this figure. The detailed procedure of compliance correction for these cases has been discussed in detail by Sahu et al [16]. Load vs. CMOD results are compared in Fig.…”

“…Similar procedure is adopted for computation of J-R curve for PRSPTWC8-3. The details of computation of J-R curve for surface cracked pipe, PRSPPTC16-1 are explained by Sahu et al [16]. J-R curve for TPB specimen of the piping material is already computed by Chattopadhyay et al [24].…”

“…Three dimensional FEA were already carried out for pipes, as explained in section-4. Similarly, the 3D elasticeplastic analysis was carried out for the TPB specimen as well [16]. The stress triaxiality parameter, Q, is dependent on applied loading and consequent crack driving force, J.…”

Corrected stress intensity factor solution for a British standard single edge notched tension (SENT) specimen

“…It has been recognized that the standard SENB specimen has high constraint and its J‐R curve cannot be directly transferred to surface‐cracked pipes . However, it was also found that SENT specimens in a clamped condition, as shown in Fig.…”