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To predict fracture behavior for ductile materials, some ductile fracture simulation methods different from classical approaches have been investigated based on appropriate models of ductile fracture. For the future use of the methods to overcome restrictions of classical approaches, the applicability to the actual components is of concern. In this study, two benchmark problems on the fracture tests supposing actual components were provided to investigate the prediction ability of simulation methods containing parameter decisions. One was the circumferentially through-wall and surface cracked pipes subjected to monotonic bending, and the other was the circumferentially through-wall cracked pipes subjected to cyclic bending. Participants predicted the ductile crack propagation behavior by their own approaches, including finite element method (FEM) employed Gurson–Tvergaard–Needleman (GTN) yielding function with void ratio criterion, are FEM employed GTN yielding function, FEM with fracture strain or energy criterion modified by stress triaxiality, extended FEM with J or ΔJ criterion, FEM with stress triaxiality and plastic strain based ductile crack propagation using FEM, and elastic-plastic peridynamics. Both the deformation and the crack propagation behaviors for monotonic bending were well reproduced, while few participants reproduced those for cyclic bending. To reproduce pipe deformation and fracture behaviors, most of the groups needed parameters that were determined to reproduce pipe deformation and fracture behaviors in benchmark problems themselves and it is still difficult to reproduce them by using parameters only from basic materials tests.

This paper examines the effect of complex crack geometry on the J-resistance curves obtained by strain-based ductile tearing simulation of complex cracked tension (CC(T)) specimens. The damage model is determined by analyzing the results of a smooth bar tensile test and a compact tension (C(T)) specimen toughness test on an SA508 Gr.1a low-alloy steel at 316 °C. The validity of the damage model and simulation method is checked by comparing the fracture test data for two CC(T) specimen tests. To investigate the effect of the complex crack geometry on the crack growth profiles and J-resistance curves, two geometric parameters (namely, the through-wall crack length and the surface crack depth) are systematically varied. It is found that the J-resistance curves for the CC(T) specimens with various through-wall crack lengths and surface crack depths are consistently lower than the corresponding 1 T C(T) J-resistance curves. The effect of the through-wall crack length upon the J-resistance curve is found to be less significant than that of the surface crack depth. Moreover, the J-resistance curve decreases continuously with increasing surface crack depth.

Spent nuclear fuels are stored in dry storage canisters made of austenitic stainless steels. Canisters have a sensitivity to chloride-induced stress corrosion cracking since some storage facilities are located in coastal regions, and this environment could have a higher risk for pits and cracks to form on the surface of canisters. Hence, this paper suggests an experimental method of evaluating crack initiation for austenitic stainless steels. Notched bar specimens fabricated using AISI 304 and 304L stainless steels are designed to simulate loads corresponding to welding residual stresses on the surface of canisters. For testing to be conducted in chloride environments, the developed tester for evaluating CISCC is designed such that the notched bar specimens are immersed into the brine of 5% salinity and are loaded by tightening a spring to provide a constant load condition at 50 °C temperature. Also, initial load applied to each notched specimen is verified using finite element analysis as in the same experimental condition. As a result, the areas by pitting corrosion on notches are 1measured using the Image Analyzer program and the stress parameters obtained from the finite element analysis are used to correlate the effect of the pit formation.

This study designed a specimen that simulates the deformation and failure behaviors of the piping components in nuclear power plants (NPPs) under excessive seismic loads beyond the design basis, and conducted ultimate-strength tests using this specimen at room temperature (RT) and 316 °C. SA312 TP316 stainless steel (SS) and SA508 Gr.3 Cl.1 low-alloy steel (LAS) were used in the experiments. Displacement-controlled cyclic loads with constant and random amplitudes of load-line displacement (LLD) were applied as input loads. A set of input cyclic loads consisted of 20 cycles, and the LLD amplitudes of the cyclic load were determined to induce the maximum membrane plus bending stress intensity of 6–42Sm on the specimen, where Sm is the allowable design stress intensity. Multiple sets of input cyclic loads, with increasing amplitude of LLD, were applied to the specimen until cracking initiated. The results demonstrate that the simulated specimen adequately showed the ratcheting deformation and fatigue-induced cracking of piping components under displacement-controlled excessive seismic loads. In addition, samples of both materials failed under displacement-controlled cyclic load levels that were several times higher than those of the design basis earthquake (DBE). The SA316 TP316 SS had greater resistance to failure under large-amplitude cyclic loads than did SA508 Gr.3 Cl.1 LAS. For both materials, resistance to failure was lower at 316 °C than at RT. This study confirmed that the evaluation procedure of the ASME design code predicted the fatigue failure of specimens very conservatively under large-amplitude cyclic loads simulating displacement-controlled excessive seismic loads.

When discrete multiple flaws are in the same plane, and they are close to each other, it can be determined whether they are combined or standalone in accordance with combination rules provided by fitness-for-service (FFS) codes. However, specific criteria of the rules are different among these FFS codes. On the other hand, plastic collapse bending stresses for stainless steel pipes with two circumferential similar flaws were obtained by experiments, and the prediction procedure for collapse stresses for pipes with two similar flaws was developed analytically. Using the experimental data and the analytical procedure, plastic collapse stresses for pipes with two similar flaws are compared with the stresses in compliance with the flaw combination criteria. It is shown that the calculated plastic collapse stresses based on the flaw combination criteria are significantly different from the experimental and analytical stresses.

In this paper, applicability of net-section collapse load approach to circumferential multiple-cracked pipe assessment is investigated using finite element (FE) damage analysis. The FE damage analysis based on the stress-modified fracture strain model is validated against limited fracture test data of two circumferential surface-cracked pipes. Then, the systematic parametric study is performed using the FE damage analysis for symmetrical and asymmetrical surface-cracked pipes. It is found that predictions using the net-section collapse load approach tend to be more accurate with increasing the distance between two symmetrical cracks. For asymmetrical cracks, it is found that the deeper crack plays a more important role and that the existing net-section collapse load expression can be potentially nonconservative. Idealization to symmetrical cracks based on the deeper crack is proposed.

This paper investigates the effect of initial residual stress and prestrain on residual stresses due to laser shock peening for Alloy 600 using numerical simulation. For simulation, the strain rate dependent Johnson–Cook hardening model with a Mie–Grüneisen equation of state is used. Simulation results are compared with published experimental data, showing good agreement. It is found that the laser shock peening (LSP) process is more effective for higher initial tensile residual stress and for larger initial prestrain in terms of compressive stress at the near surface. However, the effective depth decreases with increasing initial tensile residual stress and initial prestrain.

In this study, an engineering approach for estimations of fracture mechanics parameters, i.e., J-integral and crack opening displacement (COD), for complex-cracked pipes was suggested based on reference stress concept, where stress-strain data of the material was used to assess structural integrity of complex-cracked pipes. In the present study, new reference loads that can reduce the dependency on strain hardening of the material have been suggested for complex-cracked pipes under each loading mode. By using the proposed optimized reference load for complex-cracked pipes, J-integral and COD estimation procedures have been proposed based on the reference stress concept together with the elastic solutions for complex-cracked pipes. The predicted J-integrals and CODs based on the proposed method have been validated against published experimental data and FE results using actual stress–strain data. Moreover, the predictions using the proposed methods are also compared with those using the existing solutions for simple through-wall cracks (TWCs) based on reduced thickness analogy concept.

This paper presents numerical ductile tearing simulation results of four complex cracked pipes made of two materials, performed at Battelle, Columbus, OH. In ductile tearing simulation, stress-modified fracture strain model is used, which is determined from tensile test results and fracture toughness test data. Overall good agreement is found in comparing simulation results with experimental load, crack length, and crack mouth opening displacements versus load-line displacement (LLD) data. The effect of the complex crack on J–resistance curves is discussed.

This study investigates the interaction effect of multiple-axial part-through-wall (PTW) flaws on the failure behavior of Alloy 690TT steam generator (SG) tubes. Burst tests of tubes with single and multiple flaws were conducted at room temperature (RT). The flaws were made by the electrodischarge machining (EDM) method on the outer surface of the specimens. Six different configurations of multiple flaws were considered to see the interaction effect; two and three collinear, two and three parallel, and two and three nonaligned flaws. In all cases, an axial flaw with a constant depth of 50% wall-thickness was considered, and the following variables were systematically varied; the axial and/or circumferential separating ligament lengths between flaws, the flaw length, and the number of flaws. Effects of these variables on the failure pressure and failure mode were investigated based on experimental data. The effects of separating ligament lengths and flaw lengths on the failure pressure were dependent on the type of flaw configuration. For collinear and nonaligned flaws, the decrease in failure pressure by the interaction of multiple flaws became significant as the number of flaws increased. The failure mode of multiple flaws was strongly dependent on the length of the flaws.

In the present paper, the closed-form expressions for the stress intensity factors (SIFs) and the elastic crack opening displacements (CODs) of complex-cracked pipes are derived based on the systematic three-dimensional (3D) elastic finite-element (FE) analyses. The loading conditions that are evaluated include global bending moment, axial tension, and internal pressure. In terms of geometries, the geometric variables affecting the SIFs and the elastic CODs of complex-cracked pipes, i.e., the crack angle of through-wall cracks (TWCs), the crack depth of fully circumferential, internal surface cracks in the inner surface of pipe, and the ratio of pipe mean radius to thickness, are systematically considered in the present FE analyses. The FE analysis procedure employed in the present study has been validated against the existing solutions for the circumferential TWC pipes. Using the present FE results, the shape factors of SIF and elastic COD for complex-cracked pipes are tabulated as a function of geometric variables. The results are applied for closed-form expressions of SIF and elastic COD when the pipe is subjected to simple loading conditions of bending, axial tension, or internal pressure. The proposed closed-form expressions can estimate SIF and elastic COD of complex-cracked pipes within maximum differences of 2.4% and 5.9% with FE results, respectively.

The present paper provides plastic limit load solutions for axial and circumferential through-wall cracked pipes based on detailed three-dimensional (3D) finite element (FE) limit analysis using elastic-perfectly plastic behavior. As a loading condition, axial tension, global bending moment, internal pressure, combined tension and bending, and combined internal pressure and bending are considered for circumferential through-wall cracked pipes, while only internal pressure is considered for axial through-wall cracked pipes. In particular, more emphasis is given for through-wall cracked pipes subject to combined loading. Comparisons with existing solutions show a large discrepancy in short through-wall crack (both axial and circumferential) for internal pressure. In the case of combined loading, the FE limit analyses results show the thickness effect on limit load solutions. Furthermore, the plastic limit load solution for circumferential through-wall cracked pipes under bending is applied to derive plastic η and γ factor of testing circumferential through-wall cracked pipes to estimate fracture toughness. Being based on detailed 3D FE limit analysis, the present solutions are believed to be meaningful for structural integrity assessment of through-wall cracked pipes.

In the previous work carried out by the authors, a new method to estimate failure strength of a pipe with local wall thinning subject to either internal pressure or global bending has been proposed. The proposed method was based on the equivalent stress averaged over the minimum ligament in the locally wall thinned region, and the simple scheme to estimate the equivalent stress in the minimum ligament was proposed, based on the reference stress concept for creep stress analysis. This paper extends the new method to combined internal pressure and global bending. The proposed method is validated against FE results for various geometries of local wall thinning under combined loading. The effect of internal pressure is also investigated in the present study. Comparison of maximum moments, predicted according to the proposed method, with published full-scale pipe test data for locally wall thinned pipes under combined internal pressure and global bending, shows good agreement.

One important element of the Leak-Before-Break analysis of nuclear piping is how to determine relevant fracture toughness (or the J-resistance curve) for nonlinear fracture mechanics analysis. The practice to use fracture toughness from a standard C(T) specimen is known to often give conservative estimates of toughness. To improve the accuracy of predicting piping failure, this paper proposes a new method to determine fracture toughness using a nonstandard testing specimen, curved wide-plate in tension. To show validity of the proposed curved wide-plate test, the J-resistance curve from the full-scale pipe test is compared with that from the curved wide-plate test and that from C(T) specimen. It is shown that the J-resistance curve from the curved wide-plate tension test is similar to, but that from the C(T) specimen is lower than, the J-resistance curve from the full-scale pipe test. Further validation is performed by investigating crack-tip constraint conditions via detailed three-dimensional finite element analyses, which shows that the crack-tip constraint condition in the curved wide-plate tension specimen is indeed similar to that in the full-scale pipe under bending.

The present paper proposes a robust method for the Ramberg-Osgood (R-O) fit to accurately estimate elastic-plastic J from the engineering fracture mechanics analysis based on deformation plasticity. The proposal is based on engineering stress-strain data to determine the R-O parameters, instead of true stress-strain data. Moreover, for practical applications, the method is given not only for the case when full stress-strain data are available but also for the case when only yield and tensile strengths are available. The reliability of the proposed method for the R-O fit is validated against detailed three-dimensional FE analyses for through-wall cracked pipes under global bending using five different materials, three stainless steels and two ferritic steels. Taking the FE J results based on incremental plasticity using actual stress-strain data as the reference, the FE J results based on deformation plasticity using various R-O fits are compared with reference J values. Comparisons show that the proposed R-O fit provides more accurate J values for all cases, compared to existing methods for the R-O fit. Advantages of the proposed R-O fit in practical applications are discussed, together with its accuracy.

This paper proposes a new method to estimate failure strength of a pipe with local wall thinning. The method is based on the equivalent stress averaged over the minimum ligament in the locally wall thinned region. The highlight of the proposed method is to propose a simple scheme to estimate the equivalent stress in the minimum ligament. Inspired by the reference stress method for approximate creep stress analysis, approximate estimation equations are proposed for the equivalent stress in the minimum ligament, which are then calibrated using detailed elastic-plastic three-dimensional FE analysis. Remarkably the resulting estimation equations are found to be insensitive not only to pipe and defect geometries but also to material. Comparison of failure loads, predicted according to the proposed method, with published test data for corroded pipes shows excellent agreement, which provides confidence in the use of the proposed method to assess local wall thinning in pipes. Furthermore, the proposed method is conceptually simple and thus easy to be extended to more complex situations.

This paper investigates elastic and elastic–plastic responses of a plane strain compact tension specimen containing a discontinuous crack using two-dimensional (2D) finite element analyses. Discontinuous cracking is represented by modeling two (main and sub) cracks with the distance between them systematically varied. The finite element predictions show that the presence of subcracks has minimal effect on the elastic compliance and potential difference but significantly influences the plastic limit loads and load line displacements (LLDs). The evaluation of the elastic and elastic–plastic behavior of the J-integrals evaluated using different contours for discontinuous cracks are also examined and explained.

The present paper provides experimental J estimation equation based on the load-crack opening displacement (COD) record for testing the circumferential through-wall cracked pipe under combined tension and bending. Based on the limit analysis and the kinematically admissible rigid-body rotation field, the plastic η-factor for the load-COD record is derived and is compared with that for the load-load line displacement record. Comparison with the J results from detailed elastic-plastic finite element analysis shows that the proposed method based on the load-COD record provides reliable J estimates even for shallow cracks (small crack angle), whereas the conventional approach based on the load-load line displacement record gives erroneous results for shallow cracks. Thus, the proposed J estimation method could be recommended for testing the circumferential through-wall cracked pipe, particularly with shallow cracks.

After a brief review of existing slip line and upper bound fields, we provide a completely analytical formulation for Rice's least upper bound. Then, we propose an improved approximate elliptical yield locus and compare it with finite element limit analyses of Lee and Parks