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In this study, fatigue assessment was performed to evaluate fatigue lifetime of the buried natural gas pipe repaired using a composite material sleeve. Lap shear tensile and shear fatigue tests were firstly carried out in order to determine mechanical properties and to establish a damage model. Then from the test results, the damage model of the composite material sleeve was determined, based on stiffness reduction phenomenon due to adhesive damage. Via finite element damage analysis using the damage model and a structural stress/fracture mechanics approach presented in ASME B&PV Code Sec. VIII Div. 2, delamination behavior, burst pressure of the damaged pipe and fatigue lifetime of the damaged pipe after occurrence of the delamination are investigated. As results, it is confirmed that damage of the adhesive did not significantly affect the fatigue lifetime of the buried natural gas pipe even when delamination between composite layers due to adhesive damage occurred around corroded damage of the pipe.

// In Ja Park 1 , Soyeon An 5 , Sang-Yeob Kim 3, 4 , Hye Min Lim 4 , Seung-Mo Hong 2 , Mi-Ju Kim 4 , Yun Jae Kim 4 and Chang Sik Yu 1 1 Department of Colon and Rectal Surgery, University of Ulsan College of Medicine and Asan Medical Center, Seoul, Korea 2 Department of Pathology, University of Ulsan College of Medicine and Asan Medical Center, Seoul, Korea 3 Department of Convergence Medicine, University of Ulsan College of Medicine and Asan Medical Center, Seoul, Korea 4 Asan Institute for life sciences, Asan Medical Center, Seoul, Korea 5 Department of Pathology, Incheon St. Mary's Hospital, College of Medicine, The Catholic University of Korea, Incheon, Korea Correspondence to: Chang Sik Yu, email: csyu@amc.seoul.kr Sang-Yeob Kim, email: sykim3yk@amc.seoul.kr Keywords: rectal cancer, preoperative chemoradiotherapy, responsiveness, immune infiltrates Received: April 04, 2017 Accepted: July 14, 2017 Published: July 25, 2017 ABSTRACT We evaluate whether the tumor immune infiltrate (TIL) could be used for prediction of responsiveness to preoperative chemoradiotherapy (PCRT) in rectal cancers. Using formalin-fixed paraffin-embedded slides of pretreatment biopsies, co-stain for CD4, CD8, CD274 (PD-L1), FOXP3, cytokeratin, and DAPI was performed with Opal multi staining kit (Perkin-Elmer, Waltham, MA). Multispectral imaging and digital analysis to visualize and quantify specific immune infiltrates were performed using the Vectra imaging system (Perkin-Elmer). The density (number of cells per mm 2 ) and proportion of total TILs and specific cell types in the stroma were calculated by inForm ™ 2.2.1 software (Perkin-Elmer). The density and proportion of total TILs and specific cell types in the stroma were calculated by inForm ™ 2.2.1 software (Perkin-Elmer, Waltham, MA). Patients were classified as group with total regression (TR, n = 25) and group with residual disease (near total, moderate, and minimal regression, RD, n = 50). The mean density of T cell infiltration and CD274 (PD-L1)+ lymphocyte were significantly higher in TR ( p = 0.005, p = 0.001). The proportion of CD4+ lymphocyte (p=0.042) and CD274 (PD-L1)+ lymphocyte ( p = 0.002) were different between 2 groups. The TR group has lower CD4+ and higher CD274 (PD-L1)+ proportions than RD group. The ratio among CD4+, CD8+, CD274 (PD-L1)+, FOXP3+ T cell was different between groups. TR group showed lower CD4/ CD274 (PD-L1) ( p = 0.007), CD8/ CD274 (PD-L1) ( p = 0.02), and FOXP3/ CD274 (PD-L1) ( p = 0.003) ratio than RD group. The determination of the immune infiltrate in biopsies before treatment could be a valuable information for the prediction of responsiveness to PCRT.

The F420-reducing hydrogenase of methanogens functions in methanogenesis by providing reduced coenzyme F420 (F420H2) as an electron donor. In non-methanogens, however, their physiological function has not been identified yet. In this study, we constructed an ΔfrhA mutant, whose frhA gene encoding the hydrogenase α subunit was deleted, in the non-methanogenic Thermococcus onnurineus NA1 as a model organism. There was no significant difference in the formate-dependent growth between the mutant and the wild-type strains. Interestingly, the mutation in the frhA gene affected the expression of genes involved in various cellular functions such as H2 oxidation, chemotactic signal transduction, and carbon monoxide (CO) metabolism. Among these genes, the CO oxidation gene cluster, enabling CO-dependent growth and H2 production, showed a 2.8- to 7.0-fold upregulation by microarray-based whole transcriptome expression profiling. The levels of proteins produced by this gene cluster were also significantly increased not only under the formate condition but also under the CO condition. In a controlled bioreactor, where 100% CO was continuously fed, the ΔfrhA mutant exhibited significant increases in cell growth (2.8-fold) and H2 production (3.4-fold). These findings strongly imply that this hydrogenase is functional in non-methanogens and is related to various cellular metabolic processes through an unidentified mechanism. An understanding of the mechanism by which the frhA gene deletion affected the expression of other genes will provide insights that can be applied to the development of strategies for the enhancement of H2 production using CO as a substrate.

This article presents an energy-based method to simulate ductile tearing under dynamic loading conditions. The strain rate–dependent material properties are characterized by the Johnson–Cook-type model. The damage model is defined based on the multi-axial fracture strain energy concept. The proposed damage model is applied to simulate the fracture toughness test of SA508 Gr. 1a under four different test speeds. Simulated results show a good overall agreement with the experimental results.

Little is known about the characteristics and clinical implications of specific subsets of intragraft natural killer (NK) cells in kidney transplant recipients. We analyzed 39 for-cause renal transplant biopsies performed at our center from May 2015 to July 2017. According to histopathologic reports, 8 patients (20.5%) had no rejection (NR), 11 (28.2%) had T cell-mediated rejections (TCMR) only, and 20 (51.3%) had antibody-mediated rejection (ABMR). NK cells were defined as CD3–CD56+ lymphocytes that are positive for CD57, CD49b, NKG2A, or KIR. The density of NK cells was significantly higher in the ABMR group (2.57 ± 2.58/mm2) than in the NR (0.12 ± 0.22/mm2) or the TCMR (0.25 ± 0.34/mm2) group (P = 0.002). Notably, CD56+CD57+ infiltrates (2.16 ± 1.89) were the most frequently observed compared with CD56+CD49b+ (0.05 ± 0.13), CD56+NKG2A+ (0.21 ± 0.69), and CD56+KIR+ (0.15 ± 0.42) cells in the ABMR group (P P = 0.025). In conclusion, CD56+CD57+ infiltrates are a major subset of NK cells in kidney transplant recipients with ABMR and NK cell infiltration is significantly associated with graft failure post-transplant.

BackgroundGas-fermenting acetogens have received a great deal of attention for their ability to grow on various syngas and waste gas containing carbon monoxide (CO), producing acetate as the primary metabolite. Among them, someClostridiumspecies, such asC. ljungdahliiandC. autoethanogenum, are of particular interest as they produce fuel alcohols as well. Despite recent efforts, alcohol production by these species is still unsatisfactory due to their low productivity and acetate accumulation, necessitating the isolation of strains with better phenotypes.ResultsIn this study, a novel alcohol-producing acetogen (Clostridiumsp. AWRP) was isolated, and its complete genome was sequenced. This bacterium belongs the same phylogenetic group asC. ljungdahlii,C. autoethanogenum,C. ragsdalei, andC. coskatiibased on 16S rRNA homology; however, the levels of genome-wide average nucleotide identity (gANI) for strain AWRP compared with these strains range between 95 and 96%, suggesting that this strain can be classified as a novel species. In addition, strain AWRP produced a substantial amount of ethanol (70–90 mM) from syngas in batch serum bottle cultures, which was comparable to or even exceeded the typical values obtained using its close relatives cultivated under similar conditions. In a batch bioreactor, strain AWRP produced 119 and 12 mM of ethanol and 2,3-butanediol, respectively, while yielding only 1.4 mM of residual acetate. Interestingly, the alcohologenesis of this strain was strongly affected by oxidoreduction potential (ORP), which has not been reported with other gas-fermenting clostridia.ConclusionConsidering its ethanol production under low oxidoreduction potential (ORP) conditions,Clostridiumsp. AWRP will be an interesting host for biochemical studies to understand the physiology of alcohol-producing acetogens, which will contribute to metabolic engineering of those strains for the production of alcohols and other value-added compounds from syngas.

A strictly anaerobic, dissimilatory Fe(III)-reducing hyperthermophilic archaeon, designated as strain IOH1T, was isolated from a new deep-sea hydrothermal vent (Onnuri Vent Field) area in the Central Indian Ocean ridge. Strain IOH1T showed > 99% 16S rRNA gene sequence similarity with Thermococcus celericrescens TS2T (99.4%) and T. siculi DSM 12349T (99.2%). Additional three species T. barossii SHCK-94T (99.0%), T. celer Vu13T (98.8%), and T. piezophilus (98.6%) showed > 98.6% of 16S rRNA gene sequence similarity, however, the maximum OrthoANI value is 89.8% for the genome of T. celericrescens TS2T. Strain IOH1T cells are coccoid, 1.2-1.8 μm in diameter, and motile by flagella. Growth was at 70-82°C (optimum 80°C), pH 5.4-8.0 (optimum pH 6.0) with 2-4% (optimum 3%) NaCl. Growth of strain IOH1T was enhanced by starch, pyruvate, D(+)-maltose and maltodextrin as a carbon sources, and elemental sulfur as an electron acceptor; clearly different from those of related species T. celecrescens DSM 17994T and T. siculi DSM 12349T. Strain IOH1T, T. celercrescence DSM 17994T, and T. siculi DSM 12349T reduced soluble Fe(III)-citrate present in the medium, whereas the amount of total cellular proteins increased with the concomitant accumulation of Fe(II). We determined a circular chromosome of 2,234 kb with an extra-chromosomal archaeal plasmid, pTI1, of 7.7 kb and predicted 2,425 genes. The DNA G + C content was 54.9 mol%. Based on physiological properties, phylogenetic, and genome analysis, we proposed that strain IOH1T (= KCTC 15844T = JCM 39077T) is assigned to a new species in the genus Thermococcus and named Thermococcus indicus sp. nov.

This paper presents a new test method for assessing chloride induced stress corrosion cracking occurred in metal canisters used for storing spent nuclear fuels. The material applied to experiment is austenitic stainless steel, SS304 similarly used on manufacturing canisters and the experiment is carried out with immersing a compact tension specimen to chloride solution made up with artificial sea salt. Constant displacement condition using bolt tightening is applied to the test and a load is measured as a function of time using a load cell. Five specimens are used for the experiment at temperature of 50 °C for several months and stress intensity factor is calculated through the measured relaxed load and crack length on fractured surface of the specimen. Crack growth rate is presented in terms of test periods and consequently this apparatus suggests a method for evaluating structural integrity of chloride stress corrosion cracking.

Stress corrosion cracking may occur when chloride-bearing salts deposit and deliquesce on the external surface of stainless steel spent nuclear fuel storage canisters at weld regions with high residual stresses. Although it has not yet been observed, this phenomenon leads to a confinement concern for these canisters due to its potential for radioactive materials breaching through the containment system boundary provided by the canister wall during extended storage. The tests for crack growth rate have been conducted on bolt-load compact tension specimens in a setup designed to allow initially dried salt deposits to deliquesce and infuse to the crack front under conditions relevant to the canister storage environments (e.g., temperature and humidity). The test and characterization protocols are performed to provide bounding conditions in which cracking will occur. The results after 2- and 6-month exposure are examined in relation to previous studies in condensed brine and compared with other experimental data in the open literature. The knowledge gained from bolt-load compact tension testing is being applied to a large plate cut from a mockup commercial spent nuclear fuel canister to demonstrate the crack growth behavior induced from starter cracks machined in regions where the welding residual stress is expected. All these tests are conducted to support the technical basis for ASME Boiler and Pressure Vessel Section XI Code Case N-860.

This study conducts failure tests using a simulated specimen to investigate the effect of thermal aging on the deformation and failure behaviors of system, structure, and components (SSCs) of nuclear power plants (NPPs) made of cast austenitic stainless steels (CASSs) under excessive seismic loads. Both unaged and thermally aged CF8A CASSs were used for the experiment, and the large cyclic loads in the form of displacement-control and load-control were applied at a quasi-static displacement rate. Displacement-controlled tests were performed at room temperature (RT) and 316°C and load-controlled tests were performed at RT. The results show that the deformation behaviors of aged CF8A CASS under both types of cyclic load are almost the same as those of unaged CF8A CASS. The thermal aging slightly promotes the failure of CF8A CASS under displacement-controlled cyclic loads, but the failure of specimen still occurs under the cyclic load levels several times higher than the load of the design basis earthquake. Under load-controlled cyclic loads, thermal aging retards the failure of CF8A CASS. Consequently, the thermal aging has no apparent negative effect on the deformation and failure behaviors of CASSs under large cyclic loads, even if it considerably changes the strength, ductility, and fracture toughness of CASSs.

In this paper, allowable bending moments for circumferential inner surface cracked pipes are evaluated. ASME Boiler and Pressure Vessel code Section XI, “Rules for Inspection of Nuclear Power Plant Components” provides analytical evaluation procedures. Analytical evaluation methods based on the failure mechanism are provided in nonmandatory Appendix C and those based on failure assessment diagram are given in nonmandatory Appendix H. Allowable bending moments are evaluated using both appendices and compared with experiments. Conservativeness is compared quantitatively between both methods by normalizing allowable bending moments with experimental maximum moments.

This paper compares engineering J estimates for Spent Fuel Canisters (SFCs) under combined mechanical and welding residual stress (WRS) with finite element (FE) results. Engineering J estimates are based on reference stress method provided in the R6 procedure considering interaction between primary and secondary stresses using the V-factor. It is found that residual stress should be considered in fracture assessment and the R6 estimates are reasonably conservative compared to FE analysis results.

This paper is aimed to characterize ductile and cleavage fracture behavior of API X70 pipeline steel and investigate applicability of a micro-damage mechanics model to simulate static and dynamic crack propagation of single-edge notched tension (SENT) and drop-weight tear test (DWTT) specimens, as well as a local approach to describe cleavage fracture behavior. Gurson-Tvergaard-Needleman (GTN) model was applied to simulate ductile fracture behavior of SENT and DWTT specimens, where GTN model has been widely known for well-established model to characterize micro-damage process of void nucleation, growth and coalescence. As for a local approach, Beremin model was considered to estimate probability of cleavage fracture. In this regard, this study was especially focused on abnormal fracture appearance of DWTT specimen. In the present study, firstly, experiment data from tensile specimen test was used to obtain plastic flow curve (i.e. stress and strain curve). And load-CMOD and J-integral/CTOD resistance curves obtained from SENT test were used to characterize static ductile fracture and calibrate GTN model parameters for X70 pipeline steel. And the calibrated GTN model parameters were verified by comparing experiment data from DWTT test such as load-displacement and crack length-time curves with those from FE analysis. To accommodate dynamic effect on material properties, rate-dependent stress-strain curves were considered in FE analyses. To describe cleavage fracture, the Weibull stress was calculated from FE analyses of DWTT and Weibull parameters were calibrated by comparing with probability distribution of cleavage fracture from experiment data of DWTT specimen. Using Weibull parameters, the whole of cleavage fracture probability can be estimated as ductile shear area of DWTT specimen increases.

In this study, we developed a rapid and sensitive enzymatic assay for 2,3-butanediol (2,3-BDO) detection. The concentration of 2,3-BDO was determined by measuring the reduction of NADP(+) using Clostridium ljungdahlii 2,3-butanediol dehydrogenase (CL-Bdh). The enzymatic assay could detect as low as 0.01 mM of 2,3-BDO, while the high-performance liquid chromatography (HPLC) method required a much higher concentration than 0.15 mM. Gratifyingly, the developed method was 15 times more sensitive than the HPLC method. When the enzymatic assay was applied to high-throughput screening, the enzymatic assay detected 14 positive samples out of 23 tested, as compared to 8 by the HPLC method. These results suggest that the enzymatic assay is an effective screening method for the detection of 2,3-BDO-producing microbes in a microtiter plate-based format. ELECTRONIC SUPPLEMENTARY MATERIAL: The online version of this article (10.1007/s13205-019-1705-9) contains supplementary material, which is available to authorized users.

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.

This paper presents investigation results on effect of neutron irradiation embrittlement on cyclic hardening behavior of core shroud assembly in pressurized water reactor under beyond-design basis earthquake (BDBE). In order to simulate the cyclic hardening behavior considering the neutron irradiation embrittlement, the previous user subroutines developed for monotonic hardening behavior were updated based on some cyclic hardening test results of irradiation-simulated specimens. Finite element (FE) elastic-plastic seismic analysis was performed by using Chaboche combined hardening models considering cyclic hardening or cyclic softening and a bi-linear kinematic hardening model. As a result, it is found that the bi-linear kinematic hardening model derived the most conservative results, and the Chaboche combined hardening model considering cyclic softening derived the analysis results close to those of the bi-linear kinematic hardening model. In addition, variation of the FE elastic-plastic seismic analysis results vs. neutron irradiation dose was investigated using the bi-linear kinematic hardening model. Finally, it is identified that von-Mises effective stress and plastic strain energy increase and equivalent plastic strain decreases with increasing the neutron irradiation dose.This paper presents investigation results on effect of neutron irradiation embrittlement on cyclic hardening behavior of core shroud assembly in pressurized water reactor under beyond-design basis earthquake (BDBE). In order to simulate the cyclic hardening behavior considering the neutron irradiation embrittlement, the previous user subroutines developed for monotonic hardening behavior were updated based on some cyclic hardening test results of irradiation-simulated specimens. Finite element (FE) elastic-plastic seismic analysis was performed by using Chaboche combined hardening models considering cyclic hardening or cyclic softening and a bi-linear kinematic hardening model. As a result, it is found that the bi-linear kinematic hardening model derived the most conservative results, and the Chaboche combined hardening model considering cyclic softening derived the analysis results close to those of the bi-linear kinematic hardening model. In addition, variation of the FE elastic-plastic seismic analysis...

Ductile failure under ultra-low cycle fatigue (ULCF) loading is often the limit service state of a nuclear structure. In the paper, ULCF tests for a C-Mn-Si steel are carried out. It is observed that the fracture displacement decreases as the number of fatigue cycles increases. An energy-based model, which considers the effects of both stress triaxiality and cyclic loading on the critical fracture strain energy, is proposed. Coupled with the new model, finite element analyses of the round notched specimens can predict the equivalent plastic strain and the number of fatigue cycles to fracture within a scatter band of 1.5.

In this paper, 316H creep crack growth data at 550 °C are analysed to investigate the effect of in-plane constraint on creep crack initiation times. A constraint parameter is proposed to quantify the difference between an actual opening stress and the Riedel-Rice opening stress field in plane strain, using experimentally measured C*. Test data analysis shows that creep crack initiation times can be well characterized by the C* integral with the proposed parameter. A modified form of a model due to Nikbin, Smith and Webster is suggested, and scatter in predictions is shown to be reduced from ~40 to ~5.

This paper presents cyclic fracture test results using small-scale through-wall cracked pipe specimens to investigate the effects of large-amplitude cyclic loads on failure behaviour for different pipe materials. SA508 Gr.1a low-alloy steel (LAS) and SA312 TP316 stainless steel (SS) pipes were used in the experiment. The tests were conducted under quasi-static monotonic, displacement-controlled, and load-controlled cyclic loadings at room temperature (RT). Regardless of the pipe material, displacement-controlled reversed cyclic loading significantly reduced deformation-ability and fracture resistance, promoting crack growth. These effects were more pronounced in the SA312 TP316 SS than in the SA508 Gr.1a LAS specimen. The material-dependence on fracture behaviour was considerable under monotonic load, but was near-negligible under displacement-controlled reversed cyclic loading. Under load-controlled cyclic loading, the number of cycles to failure, the maximum allowable crack extension, and deformation-ability of pipe specimens decreased as the amplitude and compressive level increased. For all load-controlled cyclic loads, the SA312 TP316 SS specimen was less resistant to failure than the SA508 Gr.1a LAS specimen. Regardless of the loading type, a circumferential through-wall crack grew out of the initial crack plane for the SA508 Gr.1a LAS specimen, but propagated in a straight line from the initial crack plane for the SA312 TP316 SS specimen.

In this work, the effect of material ductility on the notch fracture resistance is quantified using FE damage analysis based on a multi-axial fracture strain model. Material properties of SUS316 stainless steel with three different levels of cold work (5%, 20% and 40%) are used to represent materials with different strength and ductility. Using validated FE damage analysis, notch fracture resistance data for these three materials with three different notch radii (0.2 mm, 0.4 mm and 0.8 mm) are generated numerically. Examination of notch fracture resistance data suggests that fracture initiation resistance (corresponding to 0.2 mm crack growth) depends almost linearly on notch radius. A linear dependence of the normalized fracture resistance of a notched specimen (with respect to that of a cracked one) on the material ductility is also found. The results are useful to estimate notch fracture resistance from the material ductility and the J-resistance curve obtained from a cracked specimen.

This paper proposes a method to simultaneously simulate interacting ductile and cleavage fracture in a DWTT (drop-weight tear test). The stress-modified fracture strain (SMFS) damage model is used to simulate ductile fracture and the maximum principal stress criterion is applied to simulate cleavage fracture. By incorporating the element size effect in the ductile and cleavage damage models, the numerical method to simulate the interacting ductile and cleavage fracture behavior in a DWTT is constructed. To validate the proposed method, the simulation results are compared with six API X80 data measurements at temperatures ranging between -97 °C to -20 °C. The comparison of the experimental load-displacement curve and fracture surface with the FE simulation results shows good agreement.

Fabrication of Al2O3 doped ZnO (AZO) thin films on transparent polyimide substrates using ex-situ oxygen plasma-assisted atomic layer deposition (ALD) is studied. The alumina composition is controlled by adjusting the ALD cycle ratio in the reaction sequence from 9:1 to 49:1 (diethylzinc/H2O:trimethylaluminum/H2O). Nanoscratch and electromechanical tensile tests are performed to evaluate the mechanical reliability of the AZO thin films fabricated under various processing conditions. Conventionally deposited AZO shows the lowest sheet resistance of 294 Ω/sq at a doping ratio of 19:1 at 150 ℃. However, the resistance of AZO grown on a polymer surface modified by plasma is higher at 429 Ω/sq. Nanoscratch results reveal that the first critical load could be increased by surface hardening and strong adherence as a function of the process temperature and plasma treatment. Under a tensile strain, doping of alumina delayed the strain (%) at crack initiation from 0.58 to 0.82%. The initial elastic modulus of the AZO/transparent polyimide composites showed a transient decrease with an increase in the alumina content from 2.7 to 3.8 at.%. These results demonstrating the mechanical characteristics of thin films as a function of the processing conditions are significant for flexible display manufacturing.

This paper presents a numerical method to simulate ductile tearing in cracked components under high strain rates using finite element damage analysis. The strain rate dependence on tensile properties and multiaxial fracture strain is characterized by the model developed by Johnson and Cook. The damage model is then defined based on the ductility exhaustion concept using the strain rate dependent multiaxial fracture strain concept. The proposed model is applied to simulate previously published three cracked pipe bending test results under two different test speed conditions. Simulated results show overall good agreement with experimental results.

This technical note presents the effect of elastic-plastic properties on calculated time-dependent C ( t ) and J ( t ) values. This is investigated via systematic elastic-plastic-creep finite element (FE) analysis. Three different stress-strain curves are used, having essentially the same plastic properties at large strains but different tensile data near the 0.2% proof (yield) strength. It is found that the plastic property in stress-strain curve affects the FE C ( t ) values only at short times (within approximately 20% of the redistribution time). The plastic property affects the initial J values at time t = 0 but not the rate of change of J ( t ) with time.

In this study, the plastic influence functions, h 1 , for estimates of J -integral of a pipe with a complex crack were newly proposed based on the systematic 3-dimensional (3-D) elastic-plastic finite element (FE) analyses by using Ramberg-Osgood (R-O) relation, in which global bending moment, axial tension and internal pressure were considered as loading conditions. Based on the present plastic influence functions, the GE/EPRI-type J -estimation scheme for complex-cracked pipes was suggested, and the results from the proposed J -estimation were compared with the FE results using both R-O fit parameters and actual tensile data of SA376 TP304 stainless steel. The comparison results demonstrate that although the proposed scheme provided sensitive J estimations according to fitting ranges of R-O parameters, it showed overall good agreements with the FE results using R-O relation. Thus, the proposed engineering J prediction method can be utilized to assess instability of a complex crack in pipes for R-O material.

This paper presents a numerical method using FE damage analysis to simulate ductile tearing in CT specimen under low cycle fatigue loading conditions. To define a cyclic material properties, the nonlinear kinematic hardening model is adopted. The damage model is defined based on the ductility exhaustion concept using the multi-axial fracture strain energy concept. The proposed model is then applied to simulate two cyclic fracture toughness tests with different R-ratios. Simulated results show overall good agreement with experimental results.

We propose a primary water stress corrosion cracking (PWSCC) initiation model of Alloy 600 that considers the stress triaxiality factor to apply to finite element analysis. We investigated the correlation between stress triaxiality effects and PWSCC growth behavior in cold-worked Alloy 600 stream generator tubes, and identified an additional stress triaxiality factor that can be added to Garud's PWSCC initiation model. By applying the proposed PWSCC initiation model considering the stress triaxiality factor, PWSCC growth simulations based on the macroscopic phenomenological damage mechanics approach were carried out on the PWSCC growth tests of various cold-worked Alloy 600 steam generator tubes and compact tension specimens. As a result, PWSCC growth behavior results from the finite element prediction are in good agreement with the experimental results.

In this article, a semi-analytical method to estimate elastic follow-up factor as input to estimate the transient creep C( t) parameter under secondary loading is presented and validated against finite element results for a cracked two-bar structure under constant displacement loading. Predicted values of C( t) agree well with the finite element results for both elastic-creep cases and for elastic-plastic cases with the same creep and plastic hardening exponents. For elastic-plastic-creep cases with different creep and plastic hardening exponents, the proposed method gives good predictions at long time but can under- or over-predict C( t) at short time.

In this paper, numerical ductile tearing simulation results are compared with six circumferential through-wall and surface cracked pipes made of two materials (SA-333 Gr. 6 and A106 Gr. B carbon steels), performed at Battelle. For simulation, a model using a simplified fracture strain model is employed, by analysing tensile data of the material. By comparing experimental J-R data with FE simulation results, the damage model dependent on the element size is determined based on the ductility exhaustion concept. The model is used to simulate ductile tearing behaviour of six circumferential through-wall and surface cracked pipes. In all cases, simulated results agree well with experimental load, crack length and crack mouth opening displacement versus load line displacement data.

The plastic influence functions for calculating fully plastic Crack opening displacement (COD) of complex-cracked pipes were newly proposed based on systematic 3-dimentional (3-D) elastic-plastic Finite element (FE) analyses using Ramberg-Osgood (R-O) relation, where global bending moment, axial tension and internal pressure are considered separately as a loading condition. Then, crack opening analyses were performed based on GE/EPRI concept by using the new plastic influence functions for complex-cracked pipes made of SA376 TP304 stainless steel, and the predicted CODs were compared with FE results based on deformation plasticity theory of tensile material behavior. From the comparison, the confidence of the proposed fully plastic crack opening solutions for complex-cracked pipes was gained. Therefore, the proposed engineering scheme for COD estimation using the new plastic influence functions can be utilized to estimate leak rate of a complex-cracked pipe for R-O material.

A method to simulate ductile tearing in large-scale pipes using finite element analysis is proposed, based on the stress-modified fracture strain model. An element-size-dependent critical damage model is also introduced in damage simulations. The damage model and associate parameters are determined from tensile and fracture toughness test data. The method is applied to simulate five bending tests of circumferential cracked carbon steel pipes. Simulated results agree overall well with two through-wall cracked pipe test data, but consistently over-predict the maximum loads for three surface cracked pipe tests. Advantages of the proposed method in practical application is briefly discussed.

This paper presents a numerical method to extract ductile fracture toughness from notched small punch test data using FE ductile damage analysis based on the stress-modified fracture strain model. To validate the proposed method, analysis results are compared with series of mechanical (notched tensile, fracture toughness and small punch) test data for three different materials; low alloy steel SA508 Gr.3, TP316L austenitic stainless steel and CF8M cast austenitic stainless steel. Comparison with experimental fracture toughness data shows that the proposed method can predict fracture initiation values relatively well and tearing resistance conservatively.

This paper presents equations for estimating the crack tip characterizing parameters C(t) and J(t), for general elastic-plastic-creep conditions where the power-law creep and plasticity stress exponents differ, by modifying the plasticity correction term in published equations. The plasticity correction term in the newly proposed equations is given in terms of the initial elastic-plastic and steady-state creep stress fields. The predicted C(t) and J(t) results are validated by comparison with systematic elastic-plastic-creep FE results. Good agreement with the FE results is found.

The paper presents verification results for the validity of a numerical method considering the effect of cold work on Primary water stress corrosion cracking (PWSCC) growth rate in the Alloy 600TT steam generator tubes with a part-through single axial PWSCC. PWSCC growth simulations using Finite element (FE) analysis were performed with considering various cold work levels of the material. From the FE analysis results, the cold work effect was investigated from the variations of the PWSCC growth rate vs. Stress intensity factor (SIF) for the various cold work degrees and initial SIF values. Investigated results were compared with experimental test data available. It was identified that the numerical method could adequately assess the cold work effect on PWSCC growth in the Alloy 600TT tubes. In the simulation, it was found that the cold work could strongly influence the PWSCC growth rate even in a low degree of cold work, less than 2%.

This paper proposes ductile failure simulation under high strain rate conditions using finite element (FE) analyses. In order to simulate a cracked component under a high strain rate condition, this paper applies the stressmodified fracture strain model combined with the Johnson/Cook model. The stress-modified fracture strain model determines the incremental damage in terms of stress triaxiality (σm/σe) and fracture strain (ef) for a dimple fracture using the tensile test results. To validate the stress-modified fracture strain model under dynamic loading conditions, the parameters are calibrated using the tensile test results under various strain rates and the fracture toughness test results under quasi-static conditions. The calibrated damage model predicts the CT test results under a high strain rate. The simulated results were then compared with the experimental data. † Corresponding Author, kimy0308@korea.ac.kr C 2016 The Korean Society of Mechanical Engineers 남현석 · 김지수 · 김진원 · 김윤재 168 하중도 실험속도에 따라 다른 경향을 보인다고 보고되었다. 하지만 현재 적용되고 있는 지진하중 조건의 배관 건전성 평가 절차를 보면, 선형탄성해석을 통해 배관에 작용되는 지진하중의 크기를 계산하고 정적 하중 조건에서 실험된 재료 물성치를 이용하여 결함 안정성을 평가한다. 그러나 지진하중 조건에서 실제 배관에 작용하는 하중은 동적이고 반복적인 특징을 가지고 있다. 따라서 지진 하중 조건에서 배관 계통에 대한 건전성 평가를 수행하기 위해서 다양한 실험속도에 따른 재료 물성치 및 파손 거동 모사에 대한 연구가 요구되고 있다. 그러나 다양한 실험속도에 따른 재료에 대한 물성 실험을 수행하기 위해서는 많은 비용 및 시간과 노력이 요구 된다. 이러한 실기실험의 대안으로서 유한요소 손상해석을 이용한 가상 실험법은 하중과 시편 형상에 변경이 용이하고 경제적으로도 효율적이다. 이러한 이유로 본 논문에서는 다양한 실험 속도의 인장 물성 및 정적 하중조건에서의 파괴인성 실험결과를 이용하여 동적 하중조건이 작용하는 구조물의 파괴거동을 예측할 수 있는 파손 모델에 대한 연구를 수행 하였으며 이와 같은 기법을 토대로 미국 바텔 연구소(Battelle Memorial Institute)에서 수행한 동적 하중이 작용하는 파괴인성 시편(CT 시편) 실험결과를 모사하고 해석을 통한 예측 결과와 실험결과를 비교하여 변형률 속도에 따른 연성파손 해석기법의 신뢰성을 검증하였다.

This paper characterizes the elastic-plastic-creep crack-tip stress fields under load and displacement control. The stress field has been calculated from finite element (FE) transient creep analysis under each load control condition and displacement control condition. Varying the magnitude of initial step load is considered to investigate the influence of plasticity to creep. Both same stress exponent and different stress exponent in power-law creep and plasticity were considered. In the displacement control condition, elastic-follow-up factor is estimated by comparing FE results with existing formula. This paper proposes an equation to predict crack-tip stress fields under transient creep using a modification of the existing formula and verifies the proposed equation by comparing with FE results.

The mα-tangent method is a simple way to estimate limit load for mechanical components. The method is based on a linear elastic finite element analysis to estimate the limit loads. Present work reports limit loads for branch pipe junctions under internal pressure and in-plane bending which is determined by ma-tangent method. All results are compared with published closed-form solutions and also FE results. The FE results can be found by small-strain three-dimensional finite element (FE) limit load analyses using elastic–perfectly plastic materials. Various branch pipe geometries are considered to verify the accuracy of the ma-tangent method.

This paper propose estimation equations of transient C(t)-integrals for general material properties where plastic and creep stress exponent are different under load and displacement control. The new equations are made by modifying the plasticity correction term in the existing equations. The modified plasticity corrections term is expressed in terms of initial elastic-plastic and steady state creep stress fields. For validation, elastic-plastic-creep finite element analysis are performed. FE results are compared with predicted C(t) results using proposed equations. Good agreement with FE results is found even when plastic and creep stress exponents are different.

Due to the loss of constraint, shallow cracked specimens can ‘absorb’ more energy than deeply cracked specimens commonly used to define the critical value to fracture and therefore exhibit a higher fracture toughness. The increase in energy absorption allows a reduction in the inherent conservatism when assessing components in low constraint conditions. This study addresses the benefit of using shallow cracked SE(T) fracture toughness specimens in fitness for service (FFS) assessment of defects under low constraint conditions, e.g. blunt defects or shallow cracks. Tearing resistance curves (J-R curves) have been constructed by means of a virtual test framework to determine crack initiation and propagation for shallow cracked SE(T) specimens and parametric notched C(T) specimens. The effect of constraint level on J-R curves is compared. It is observed that most of the blunted C(T) specimens analysed exhibit the same or a lower toughness value than that of a shallow cracked SE(T) specimen. The results are used to show how reduced conservatism can be made in defect assessment of blunt defects or in cases in which reduced constraint conditions can be demonstrated.

In this paper, the effect of plastic models on initial C(t) and J(t) values was investigated. Plastic material properties used in this research are based on three different plastic models. One model consists of one-term equation, which is similar to Ramberg-Osgood equation and was used as a reference model in this research. Another model is composed of two-term equations and the other model is consist of three-term equations. FE results of these two models were used for comparison. Elastic-plastic-creep finite element analysis were performed for SE(B) specimen. FE results were analyzed through normalizing C(t) and J(t) values of two-term and three-term models by those of the reference model. It is confirmed that different plastic models contribute to the difference only in early stage of C(t) and J(t).

This paper compares a combined plastic and creep damage model with only creep damage model by simulating creep crack growth of P91. The previous model considered only creep damage is extended to consider effect of plastic damage to creep crack growth. The damage model is based on the stress-modified fracture strain model using the ductility exhaustion concept. Also, creep fracture strain depending on the strain rate is considered. Total damage is defined simply through linear addition of plastic and creep damage. When the accumulated damage becomes unity, all stress components at the finite element gauss point are reduced to a small value to simulate failure. Finite element damage analysis results using previous and proposed model are compared with experimental data for P91. The proposed model gives a better agreement with the experimental data compared with the previous model.

As a companion paper of Part I, this paper presents ductile tearing simulation results of STS410 through-wall cracked pipe test data with different amplitudes of load-controlled fully-reversed cyclic loading. The multiaxial fracture strain energy damage model is used with the Chaboche model. The simulated crack growths are not dependent on the ratcheting term in the Chaboche model, but deformations are slightly sensitive. Simulation results suggest that acceleration and retardation behavior in crack growth rates due to the load sequence may not occur under large-amplitude cyclic loading.

In this study, fracture mechanics analysis was performed to calculate crack growth under very low cycle fatigue loading conditions. The calculation results are compared with 11 experimental datasets concerning through-wall cracked pipes made from three different materials under fully reversed large-amplitude cyclic loading. In the analysis, it was assumed that the crack growth rate under large-amplitude cyclic loading is the linear summation of the fatigue crack growth rate and ductile tearing rate. Relevant fracture mechanics parameters were determined using the reference stress approach. It was found that the calculated failure cycles are around half of those using the experimental data regardless of the material and load amplitude. The most important factors affecting the calculation results were the accuracy of estimating J and ΔJ, and the crack closure coefficient when calculating ΔJ. Their effects on the analysis results are discussed herein.

In this paper, experiment and FE analyses are performed to investigate crack tip deformation and stress fields under monotonic and large amplitude cyclic loading. Fracture tests using C(T) specimens made of SA508 Gr.1a and TP316 are performed under monotonic and cyclic loading. Using the debonding analysis, it is found that the isotropic hardening model is relevant for monotonic loading, the kinematic hardening for SA508 Gr.1a under cyclic loading, and the Chaboche combined hardening for TP316 under cyclic loading. Using the relevant hardening model, crack tip deformation and stress fields at crack initiation and growth are presented.