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[en] The method is not new in the sense that the stress-modified fracture strain model is based on the well-known concept that the fracture strain for ductile fracture strongly depends on the stress state. Virtual testing using FE damage analysis should ultimately be used to simulate failure of large-scale components such as full-scale pipe tests (possibly with long, stable crack growth). To simulate long, stable ductile crack growth in full-scale cracked pipes, existing methods need to be modified to incorporate larger element sizes. In this paper, an element-size-dependent damage model based on the stress-modified fracture strain model is proposed to simulate failure of full-scale cracked plates including the influence of residual stresses. The proposed method is then compared with published experimental full-scaled cracked plates with and without electron-beam welds. This paper has presented the results from an element size dependent model to predict the influence of residual stress effects on ductile tearing behavior of AL2024 and AL5083 alloys. The proposed method is based on the stress-modified fracture strain model, proposed previously by the authors. Incremental damage is defined by the ratio of the plastic strain increment to the fracture strain. In our work, progressive cracking was assumed to occur when the accumulated damage becomes unity and provided a proper finite element size. It has been shown that this method worked very well to simulate the ductile crack growth in laboratory specimens, simulating long, stable crack growth in large-scale cracked plates containing residual stresses
[en] As most part of pressurized plant components are subject to various stresses. Stresses applied to plant components can be classified into primary (mechanical loading) and secondary stress (such as thermal and residual stress). When a crack is found in a pressurized plant component under combined primary and secondary stress, it is important to estimate relevant fracture mechanics parameters. J-integral is one of the fracture mechanics parameters used for elastic plastic analysis. Detail procedure for J-integral estimation under combined stresses are tabulated in R6 and A16. This paper compares the estimated J-integral between R6 and A16 for combined stresses through FE analysis results. J value for the fully circumferential surface crack are conservative in contained yielding regime in A16 method. But in R6 method, less conservative result in contained yielding regime. Under large scale yielding (LSY) regime, R6 simplified method and A16 method produced similar result to J estimation. But detailed method are close to the FE results even for large Lr values. And this paper revealed that occurs when thermal loading is applied after mechanical loading the most severe loading sequence
[en] This paper presents approximate J estimates for circumferential through-wall cracked pipe bends under in-plane bending. These load and estimates are based on small strain finite element limit analysis using elastic-plastic materials. Geomatric variables are considered possible locations. In this paper, approximate J are considered for each crack position.
[en] This paper provides a comparison of the J-integral estimation method under combined primary and secondary stress in the R, RBC-MR A code. The comparisons of each code are based on finite element analysis using Abacus with regard to the crack shape, crack depth, and magnitude of secondary load. The estimate of the R code is conservative near Lr = 1, and that of the RBC-MR A code is conservative near Lr = 0. As a result, this paper proposes a modified method of J-integral estimation in the R, RCCMR A code. The J-integral using the modified method corresponds to the finite element analysis result
[en] In pressurized water nuclear reactors (PWRs), the reactor pressure vessel (RSV) upper head contains penetration nozzles that use a control rod drive mechanism (CD-ROM). The penetration nozzle uses J-groove weld geometry. Recently, the occurrence of cracking in alloy 600 CD-ROM penetration nozzle has increased. This is attributable to primary water stress corrosion cracking (PWSCC). PWSCC is known to be susceptible to the welding residual stress and operational stress. Generally, the tensile residual stress is the main factor contributing to crack growth. Therefore, this study investigates the effect on weld residual stress through different analysis methods for normal operating conditions using finite element analysis. In addition, this study also considers the effect of repeated normal operating condition cycles on the weld residual stress. Based on the analysis result, this paper presents a normal operating condition analysis method
[en] This paper reports C(t)-integral for cracked pipe under different types of combined mechanical load and thermal load. C(t)-integral, describes stress and strain rate field near a crack tip, is a parameter for crack assessment. Estimation formula C(t)-integral for the high-temperature under combined mechanical and thermal loads has not been provided for the cracked assessment. In this paper, C(t)-integral for cracked pipe under combined mechanical and thermal load is proposed via 2-dimensional and 3-dimensional finite element analysis.
[en] Primary water stress corrosion cracking (PWSCC) instances have been reported in the Alloy 600 reactor pressure vessel head penetration nozzle and the Alloy 82/182 dissimilar metal butt weld nozzle in several PWRs. Therefore, in service inspection programs have been adopted worldwide to prevent failure at the weld region. If a PWSCC is observed at the dissimilar metal weld region during inspection, its structural integrity should be evaluated; however, this requires considerable time and effort, and this might lead to a decrease in the plant utilization coefficient. To prevent this, KHNP CRI have established integrity assessment criteria and developed a computer program for the fast evaluation and judgment of PWSCC. In this paper, the results and current status of the same are presented. Through this study, criteria for the structural integrity evaluation of PWSCC have been established, and a computer program has been developed to realize technical means for the evaluation of PWSCC structural integrity
[en] There is a trend towards the progressive use of higher operating temperatures and stresses to achieve improved efficiencies in power-generation equipment. It is important to perform the crack assessment under high temperature and high-pressure conditions. The C(t)-integral is a key parameter in crack assessment for transient creep states. The estimation of the C(t)-integral is complex when considering the mechanical and thermal loads simultaneously. In this paper, we study estimation of C(t)-integral under combined mechanical and thermal load depending on loading conditions
[en] Recently, several circumferential cracks were found in the control rod drive mechanism nozzles of U. S. nuclear power plants. According to the accident analyses, coolant leaks were caused by primary water stress corrosion cracking. The tensile residual stresses caused by welding, corrosion sensitive materials, and boric acid solution cause PWSCC. Therefore, an exact estimation of the residual stress is important for reliable operation. In this study, finite element simulations were conducted to investigate the effects of the tube geometry on the residual stresses in a J-groove weld for different CD-ROM tube locations. Two different tube locations were considered, and the tube radius and thickness variables included two different reference values
[en] This paper presents the procedure for the dynamic finite element elastoplastic seismic analysis for the structural integrity of a nuclear piping system under a beyond-design basis earthquake. The effects of finite element modeling parameters on a maximum equivalent plastic strain are investigated. Based on the analysis results, it was effective to use the first order incompatible continuum element for the elbow region and the first order beam element for the straight region. Furthermore, it was confirmed that the transition region of a continuum element modeling length should be set as one times the bend radius with a consideration of the fluid effect. Finally, the minimum number of elements in the direction of thickness, longitude, and circumference should be examined to obtain reliable results.