Normalization method for evaluating J-resistance curves of small-sized CIET specimen and crack front constraints

Abstract

Available online xxxKeywords: J -resistance curves Normalization method CIET specimen Crack front constraints J -Q -M theory J -A 2 -M theory a b s t r a c t Based on dimensionless load separation principle, the normalization method for estimating J -resistance curves of CIET specimen for ductile materials has been developed. Experiments of ductile crack growth resistance on a typical pressure vessel steel SA-508 are conducted by using CT, SEB and CIET specimens. The resulted J -resistance curves show outstanding influence by load configuration and specimen dimensions. J -Q -M and J -A 2 -M approaches are introduced to quantify the crack front constraint of the three types of specimens. According to finite element analyses (FEA) under plane strain and 3D conditions, the distance-independent constraint parameters are calibrated by matching the FEA results with the J -Q -M and J -A 2 -M solutions using weight average method. The analyses show that the parameters of Q and A 2 are load-independent under plane strain condition, but under 3D condition, the J -A 2 -M approach is incapable of characterizing the stress and deformation fields ahead of crack front of CIET specimen for SA-508 steel, and the parameter Q is no longer load-independent. Because of different crack front constraint, the CIET specimen with B = 10 mm, a 0 = 5 . 8 mm gets the lowest fracture resistance while the SEB specimen with B = 20 mm, a 0 = 11 mm and the CT specimen with B = 15 mm, a 0 = 29 mm obtain the highest fracture resistance for SA-508 steel. The size requirements of J -Q -M dominance for each used CIET, CT and SEB specimens are got. Finally, the constraint-modified J -resistance curves of SA-508 steel based on J -Q -M approach are constructed to predict the crack growth resistance for any fracture specimens or actual flawed structures.

A modified normalization method for determining fracture toughness of steel

“…With further improvement, the three-parameter LMN function was finally incorporated in the ASTM E1820-18 Annex 15 2 as the calibration function of the NM. The NM was also verified by Scibetta et al 15 in 2006 using numerical simulations, and with different materials, including steels, [16][17][18] alloys 19 and polymers. [20][21][22][23][24] Furthermore, Dubey et al 25 successfully used the NM to determine the fracture toughness of un-irradiated Zircaloy-2 pressure tubes under different temperatures.…”

A new method for determining the accurate J‐R curves of steels

“…6,7,10,12 The calibration function adopted in the current standard ASTM E1820-18 Annex 15 1 is the four-parameter LMNO (or a b c d) function. 1,12 NM has since been applied to different materials, including steels, [12][13][14] alloys 15 and polymers, [16][17][18][19][20] and structures. 21 However, J-R curves determined using the UC method and the NM are usually different as demonstrated in the literature.…”

“…The calibration function adopted in the current standard ASTM E1820‐18 Annex 15 1 is the four‐parameter LMNO (or a b c d ) function 1,12 . NM has since been applied to different materials, including steels, 12–14 alloys 15 and polymers, 16–20 and structures 21 …”

A method to evaluate ductile fracture toughness based on load separation principle

“…Bao et al pointed out the disadvantages of multiple specimen method, unloading compliance method, and electric potential drop method, then developed an improved normalization method for compact tension (CT) and single edge‐notched bending (SEB) specimens on the basis of dimensionless load separation principle. Further, this modified normalization method was successfully applied to measure growing crack size of a type of small‐sized C‐shaped inside edge‐notched tension specimen in the J ‐resistance curves estimation of SA‐508 steel . The normalization method and S p b method dated back to load separation principle, they required apparent load drop and relative larger crack extension.…”

“…Further, this modified normalization method was successfully applied to measure growing crack size of a type of small-sized C-shaped inside edge-notched tension specimen in the J-resistance curves estimation of SA-508 steel. 12 The nor-malization method and S pb method dated back to load separation principle, they required apparent load drop and relative larger crack extension. For normalization method, the relationship between normalized load and displacement was supposed to conform with an empirical function, especially the determination of crack size after crack tip blunting had limited accuracy.…”