Evaluation of J/CTOD for Clamped SE(T) Specimens With Welds

Abstract

In BS 7448, Part 2, the stress intensity factor, J-integral and crack tip opening displacement (CTOD) equations developed for evaluation of fracture toughness of a homogeneous material using experimentally measured quantities, such as load-load line displacement, are applied to SE(B) specimens with yield-strength-mismatched welds. The accuracy of this procedure was studied by Gordon and Wang using finite element analysis (FEA). Recently, the so-called “η factor” method for J-integral evaluation of SE(T) specimens with weld-center-line-cracked and yield-strength-mismatched welds was studied by Ruggieri using detailed FEA calculations and the load separation method proposed by Paris et al. For application to strain-based design of pipelines, CANMET has developed equations to evaluate J-integral and CTOD resistance curves for clamped SE(T) specimens of homogeneous materials using experimentally measured load and crack-mouth-opening displacement (CMOD) in a single-specimen procedure similar to that in ASTM E1820. In the present study, the accuracy of using these equations for J-integral evaluation of clamped SE(T) specimens with weld-center-line-cracked and strength-mismatched welds was studied. It was found that the errors in J and CTOD using the equations developed for SE(T) specimens of homogenous materials for these strength-mismatched welds are similar to those for SE(B) specimens with the same weld geometry and mismatch level as reported by Gordon and Wang. It was also found that using the higher of the strength of base and weld metals σY (= (σYS+σTS)/2), (i.e. (σY)w for overmatching and (σY)B for undermatching) in converting J to CTOD gives reasonable and conservative CTOD evaluations for specimens with weld-center-line-cracked and yield-strength-mismatched welds.

Numerical verification of stress intensity factor solution for clamped single edge notched tension (SENT) specimens

“…Note that in 2D analysis, B N = B. The FE results as well as those predicted from the 2 polynomials 4,6 are tabulated in Table 3 and displayed graphically in Figure 3. The results are reported over a range of 0.05 ≤ a/W ≤ 0.9 in 0.05 intervals.…”

“…Note that the SIF solution from the ASTM standard E1820 for bending specimens is also normalized in the same form. The function of K developed by CANMET has the following form: The parameters for the 11 th ‐order polynomial used for G are given in Table …”

“…In 2008, CANMET (now CanmetMATERIALS) developed a single-specimen method for both the determination of J-R and crack-tip opening displacement-resistance (CTOD-R) curves. 3,4 BSI essentially adopted the procedure developed at Det Norske Veritas, with alterations. These alterations included the use of a single specimen (from the CANMET procedure) with a daylight-to-width ratio of 10 and a separate solution for thinner specimens with a thickness-to-width ratio of (1/2 ≤B/W≤ 1).…”

“…6 It is important to note that for SENT specimens there is no exact solution available for the stress intensity factor K, and numerical methods are required to obtain their values. The CANMET solution is based on curve fitting of FE data, 4 and Zhu's solution is based on curve-fitting data from the compliance analyses. 5,6 The input for the compliance analyses are the reference K solutions for edge-cracked plate under remote tension and bending loads obtained from the literature.…”

“…Note also that the accuracy of K is critical to the further evaluation of J , CTOD as well as other fracture toughness related factors, eg, η‐factor . It is the aim of the present work to compare the functions proposed by Zhu and by CANMET utilizing new numerical results generated by the authors using state‐of‐the‐art FE software as a quantitative basis.…”