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This paper reports time-dependent C(t)-integral calculations for generalised creep laws using the user subroutine CREEP within the general-purpose FE code, abaqus [ abaqus Version 5.8. User's Manual (1999)]. The evaluation of the strain energy density rate function is emphasised. As examples, the external circumferential cracked cylinder subject to mechanical loading and combined mechanical and thermal loading was considered for two different generalised creep laws, the θ-projection creep law and a secondary–tertiary creep law. The resulting abaqus C(t)-integral results were then compared with the results from another FE code, bersafe [ bersafe User's Guides (1990)], to check reliability of the abaqus calculations. Excellent agreement between these results provides confidence in the abaqus C(t)-integral calculation for generalised creep laws.

In two previous papers, mis-match yield load solutions for middle crack tension and single edge cracked bars in pure bending were derived. These specimens contained cracks which were located in the centre of the weld metal as well as in the interface between weld metal and base plate, and in positions in between. The present paper investigates additional three specimen types, namely double edge crack tension, single edge cracked bend and compact specimens, with cracks in the centre of the weld metal and in the interface between weld metal and base plate. As in the previous investigations, the conditions of plane strain and plane stress are considered. The results are presented as closed form solutions and diagrams.

The effect of the T-stress and plastic mismatch on interfacial crack-tip stress under small scale yielding condition is investigated in this paper via detailed finite element analyses. The mismatch in plastic strength/hardening is focused, and plane strain elastic–plastic crack-tip fields have been modeled with modified boundary layer formulation. Plastic mismatches as well as compressive T-stresses in bi-material are shown to affect the interfacial crack-tip constraint substantially. Simple patching of slip-line fields is presented to characterize the interfacial crack-tip stress fields. Effects of T-stress and plastic hardening mismatch on asymmetry of the J-integral for bi-materials, and its implication on interfacial toughness are also discussed.

The accuracy of the defect assessment methods for strength mismatched structures is directly related to the accurate estimate of the (mismatch) yield load of the defective component of interest. This paper provides accurate closed form solutions of mismatch yield loads for two representative cracked plates, a middle crack tensile plate and a single edge cracked plate in pure bending. The weld configurations are idealised as a simple strip model, and the crack is assumed to be located in the centre of the weld metal. Solutions are given for two limiting out-of-plane constraint conditions, plane strain and plane stress. Comparisons with the results from detailed finite element limit analyses show excellent agreement, for almost all values of strength mismatch levels, ligament-to-weld width ratios, and crack lengths. Another important outcome is that, based on the proposed solutions, useful guidelines are given for assessing cracked structures with weldments, in the form of windows where the plastic yield load solutions of mismatched components can be obtained assuming the component can be wholly characterised by either base material or weld material properties. Such guidelines could be very useful when complex components with weldments are to be assessed, for which the plastic yield load solutions are not available or difficult to find.

This paper presents simplified J-estimation equations for defective homogeneous and strength mismatched structures, based on the Engineering Treatment Model (ETM). For homogeneous structures, two modifications are made to the existing ETM J-estimation equations; firstly a modification of the contained yielding solutions, and secondly modification of J-estimation equations for materials exhibiting Luders strain. Based on the proposed J-estimation equations for homogeneous structures, J-estimation equations for welded structures with strength mismatch are proposed. The proposed J-estimation equations for both homogeneous and mismatched structures are then compared with selected elastic–plastic finite element results. The comparisons show excellent agreement and so provide confidence in the use of the proposed J-estimation equations for defect assessment. Finally, comparison with another simplified method, the R6 method, is discussed.

Based on the reference stress approach, two sets of the crack opening displacement (COD) estimation equations are proposed for a complex cracked pipe. One set of equations can be used for the case when full stress-strain data are known, and the other for the case when only yield and tensile strengths are available. To define the reference stress, a simple plastic limit analysis for the complex cracked pipe subject to combined bending and tension is performed, considering the crack closure effect in the compressive-stressed region. Comparison with ten published test data and the results from the existing method shows that the present method not only reduces non-conservatism associated with the existing method, but also provides consistent and overall satisfactory results. These results provide sufficient confidence in the use of the present method to estimate the COD (and thus the leak rate) for the Leak-before-Break (LBB) analysis of complex cracked pipes. Finally, the J-estimation equations are also provided for complex cracked pipes, for the LBB analysis of complex cracked pipes.

This review article summarizes recent activities within the SAFE Research Center, which aim to open a new horizon in the field of structural integrity. These activities include (i) enhancement of fracture assessment methodologies, (ii) development of sensing technologies and (iii) development of IT (Information Technology)-based intelligent plant management system. The first issue is to describe the more reliable fracture assessment methodology, recently proposed by authors, and its application to non-linear fracture mechanics problems. The second issue is to describe how to implement the current advances in fiber-optic technology to condition monitoring systems. Two fiber-optic sensors for condition monitoring systems are introduced. Finally, an integrated intelligent system for the plant management is introduced by incorporating advances in fracture assessment methodologies and sensing technologies into a currently available IT-based plant management system. The proposed intelligent plant management system is not only flexible to adopt advances in fracture assessment methodologies and sensing technologies, but also easily accessible to field engineers and experts. This system is expected to play a key role in combining advances in structural integrity assessment methodologies and fast-developing information technology in the future, and thus will become a key element in safe and informative plant management.

This paper describes the defect assessment method for strength mismatched welded structures, resulting from the Brite Euram structural integrity assessment procedures for European industry (SINTAP) project. Finite element and experimental validation of the proposed method is provided. This shows that the proposed method is conservative, and that the degree of conservatism is similar to that embedded in the methods for homogeneous structures. It provides confidence in the use of the proposed SINTAP method for assessing defective weld strength mismatched structures.

This paper presents a framework how to estimate crack driving forces in terms of crack-tip opening displacement andJ-integral for mismatched dissimilar joints with interface cracks. The mismatch in elastic, thermal, and plastic hardening properties is not considered, but the mismatch in plastic yield strengths is emphasized here. The main outcome of the present work is that the existing methods to estimate crack driving forces for homogeneous materials can be used with slight modification. Such modification includes (i) mismatch- corrected limit load solutions, and (ii) evaluating the contribution of each material in dissimilar joints to the total crack driving force, which depends on the strength mismatch of the dissimilar joints.

Via detailed finite clement limit analyses, plastic limit loads, rotation factors, and crack-tip stress field are investigated for a combined tension and bending of a plance strain single-edge-cracked bimaterial specimen. Limiting bimaterial specimens are considered, consisting of an clastic/perfectly plastic material bonded to an elastic material having the same elastic properties. The limit loads of bimaterial specimens are shown to be very close to those of homogeneous specimens, so that limit load information for homogeneous specimens can be used even for bimaterial specimens. A tractable, approximate elliptical yield locus is proposed, which first the FE. results within 1% for all ranges of tension-to-bending ratios. The plastic rotation factor of bimaterial specimens can be higher than that of homogeneous specimens as much as 25%, when the specimen is subject to small tensile forces. Results from the present analysis is applied to the analysis of typical fracture testing specimens such as compact tension specimens. For both homogeneous and bimaterial specimens, larger tensile forces are associated with substantial loss of crack-tip constrait. Bimaterial specimens have as much as 2 times higher constraint than homogenous specimens, due to plastic strength mismatch. Tractable closed form approximations for crack-tip stresses are proposed in terms of tension-to-bending ratio.

Ductile failure of an interleaf tension specimen consisting of a metal interleaf bonded between two elastic substrates, with a crack located in the centre of the metal, is studied by means of detailed finite element (FE) analyses. The rate-independent version of the Gurson model is used. This accounts for ductile failure mechanisms of micro-void nucleation, growth and coalescence within the framework of a finite deformation plasticity theory. Also, the rapid evolution of void density due to coalescence, which leads to ultimate failure, is considered. The effect of the interleaf thickness on failure (crack initiation and limited amount of crack growth) is investigated. The results show that the interleaf thickness affects crack initiation only slightly. For all specimens considered, crack initiation takes place at the crack tip. However, after crack initiation, the interleaf thickness affects stress and strain distributions significantly. Reducing the interleaf thickness significantly increases the load-carrying capacity. Moreover, reducing the interleaf thickness increases the maximum hydrostatic stress in the interleaf, which is no longer developed at the crack tip but at a distance far away from the crack tip. The resulting fracture toughness thus decreases as the interleaf thickness decreases. The shielding of the crack tip due to constrained plasticity is observed at higher load levels for interleaf specimens.

Crack growth in a metal layer constrained by two elastic substrates, with a crack lying in the center of the metal layer, was simulated via a 2D plane strain, finite element (FE) analysis. The fracture process was modeled using a cohesive zone model (CZM) where the fracture process zone is represented by a microscale strip (cohesive zone) and is described by a continuum traction-separation law with a constant traction T 0 and the work of separation per unit area, Γ 0 . The interfaces between the ductile layer and the elastic substrates were assumed to be perfectly bonded. The crack growth resistance curves were computed by applying mode I loading under small scale yielding conditions. Attention was focused on the effect of the CZM parameter, T 0 , and the layer thickness on fracture resistance. Two fracture mechanisms were found: (1) near-tip void growth and coalescence with the main crack and (2) cavitation at highly stressed sites far ahead of the crack tip. The steady-state toughness and the toughness at which first cavitation occurs were quantitatively given in terms of the CZM parameter, T 0 , and the layer thickness for both fracture mechanisms.

This paper compares FE ductile fracture simulation results with compact tension (C(T)), small punch (SP) and notched small punch (NSP) test data for SA508 Gr. 3 material. Ductile fracture simulation method in this paper is based on the stress-modified fracture strain model, recently proposed by the authors. Tensile properties and stress-modified fracture strains are extracted from smooth and notched bar tensile tests, and SP test. To extract tensile property from SP test, tensile property constitutive equations are assumed. Using the extracted tensile properties and stress-modified fracture strains, C(T), SP and NSP tests are simulated and the results are compared with experimental data. The results using the properties from smooth and notched bar tensile tests agree well with experimental data. And the SP and NSP simulations using the properties from SP test well predict the maximum loads and fracture behaviors, However, C(T) test simulations have conservative results relatively. C(T) and NSP simulation results are sensitive to element size. However, SP simulation results are not sensitive to element size.Copyright © 2013 by ASME

J contour integral still has great importance to predict fracture of both small specimen and full-scaled pipes. However, it is difficult to obtain experimental J resistance curve of full-scaled pipes due to the differences of defect shape and complexity of loads. Due to the recent development of the FE damage analysis to predict fracture of full-scaled pipes, it is also possible to predict J resistance of full-scaled pipes. To use this FE damage model for fracture estimation, it is necessary to verify the validity of this model by compared with toughness testing specimens. In this paper, J resistance curves of full-scaled pipes using FE damage analysis were compared with various toughness testing specimens from Pipe Fracture Encyclopedia performed by Battelle. And the J contour integral were calculated from FE analysis using the element-size-dependent damage model recently proposed by the authors. Compared results showed that J calculation using FE damage analysis could be used for J-estimation of full-scaled pipes by compared with fracture toughness testing specimens.

This paper provides simulations of ductile crack growth in test specimens using an element-size dependent damage model. The present method used in this paper is based on a stress modified fracture strain damage model with a stress reduction technique. The calibrated damage model is used to predict the load versus ductile crack growth response of test specimens. These tests included some samples that contained self-balancing residual stress distributions. The influence of a residual stress on the load versus crack growth relationship is accurately simulated using the element-size dependent damage model.Copyright © 2013 by ASME

This paper describes steady-state stresses on welded straight pipes with the heat-affected zone (HAZ) using detailed two dimensional elastic creep finite element analyses. In our previous studies [9,10], it was found that the mis-match effect in creep on steady-state stresses within the weld metal for a various branch junction could be uniquely quantified by the mis-match factor, defined as a function of creep exponent and constants. The present study expands the findings to be applicable for welded straight pipes, not only the most widely used but also relatively simple compared to branch junctions. To see the effects of mis-match in creep properties and weld configuration, the parametric studies have been performed for various mismatched creep properties and three different groove angles, respectively. Internal pressure, tension and its combined cases are applied to investigate the effect of the loading mode. It is found that steady-state creep stresses can be quantified as mis-match factor and creep exponent. In conclusion, validation of the findings is presented and discussed through an application to the CMV pipe.Copyright © 2013 by ASME

Discontinuous cracks ahead of the leading crack tip may be present in observedcertain creep crack growth tests as well as in components. In this work, a single crack of different dimensions and distance from the leading crack has been numerically modeled in a compact tension specimen using elastic, elastic-plastic and elastic-plastic-creep loading. In order to examine their effects on fracture mechanics parameters a sensitivity analysis was performed to determine the effects of size and distance of the secondary crack with respect to the main crack. t The elastic analysis shows that the compliance is insensitive small cracks ahead of the main crack. Limit load analyses, assuming an elastic-perfectly plastic material, show that the limit load decreases due to the presence of discontinuous cracks ahead of the main crack. Theload versus plastic load-line displacement response of the specimen was significantly influenced by discontinuous cracking. The J contour parameter and C*-integral have been evaluated at the three crack tips and the average of all of them derived for the appropriate contours were compared with the valuesobtained from on ASTM E1820(1) and E1457(2). Whilst the average values of the contour integral are similar to the ASTM J and C* values there is significant differences in J and C* for the individual crack tip values. This need to be further evaluated in future work.Copyright © 2013 by ASME

This paper a new simple numerical method to predict burst pressures of Alloy 600 steam generator tubes with multiple through-wall cracks, based on the stress-modified fracture strain damage model with stress reduction technique. To validate the new method, simulated results using the proposed method are compared with thirty-on published test data of Alloy 600 thin plates and tubes with single or multiple through-wall cracks. Simulated results showing that predicted loads are within 10% of experimentally-measured ones for all cases considered. Moreover, a parametric study is performed to investigate the interaction effect of two axial surface cracks in Alloy 600 steam generator tubes under internal pressure.

This paper addresses load order effects on elastic-plastic J estimation under combined mechanical and thermal loads for circumferentially cracked pipes. The load order effects, for various thermal gradient types and mechanical loading, are evaluated for a range of magnitudes of the loadings, crack sizes and material hardening. Variations of elastic-plastic J obtained by finite element analysis are compared with existing and proposed methods for use with the R6 defect assessment procedure. The load order effects are presented on the R6 failure assessment diagram (FAD) by calculating the two parameters Kr and Lr from the finite element results. It is shown that there are significant load order effects at large secondary stress cases but these are successfully treated by simplified methods proposed for use with R6.Copyright © 2013 by ASME

The present work reports mis-match limit loads for V-groove welded pipe for a circumferential crack using finite element (FE) analyses. In our previous paper [14], closed-form solutions of mis-match limit loads were proposed for idealized butt weld configuration as a function of the strength mis-match ratio with only one geometry-related slenderness parameter. To integrate the effect of groove angles on mis-match limit loads, the geometry-related slenderness parameter has to be modified by relevant geometric parameters including groove angle, crack depth and root opening based on plastic deformation patterns in theory of plasticity. Circumferential through-wall cracks are located at the centre of the weld considering two different groove angles (45°, 90°). With regards to loading conditions, axial (longitudinal) tension is applied for all cases. For the parent and weld metal, elastic-perfectly plastic materials are used to simulate under-matching and over-matching conditions in plasticity. The overall results from the proposed solutions agree well with FE results.Copyright © 2013 by ASME

In power plants, piping installations with a circumferential crack can be operated under combined bending and torsion. ASME Boiler and Pressure Vessel code Section XI non-mandatory Appendix C provides the flaw evaluations for fully-plastic fracture using limit load criteria for the structural integrity of the cracked pipes. According to the recent version of Code, combined loading is provided only for membrane and bending. Even though actual operating conditions have torsion loading, the methodology for evaluating torsion load is not established, and assumed torsion is relatively small compared to membrane and bending and can be ignored in the evaluation. This paper provides the results of limit load analyses by using finite element models for circumferentially cracked pipes under pure bending, pure torsion and combined bending and torsion with tension. Theoretical limit load solutions based on net-section fully-plastic criteria are compared with the results of finite element analyses. The validation of theoretical limit loads for combined bending and torsion with tension is discussed.

Detailed finite element (PE) analyses are performed to study the effect of crack depth on crack-tip constraint at full yielding for pure bending of plane strain single-edge-cracked specimens. Analyses are based on small-strain formulations and perfect plasticity. The crack depth a/W ranges from 0.1 to 0.7, and the deformation is applied up to the limiting state of full plasticity where crack-tip stresses reach steady-state limiting values.

Plane strain fracture by hole growth in ordinary-sized parts of low-to-medium strength steels is essentially rigid-plastic, and may be approximated as non-hardening. Quasi-steady crack growth for such materials is predicted for crack-tip fields approximated by a pair of slip lines, such as unequally grooved specimens in tension and deep singly-face-cracked specimens under combined bending and tension. The crack growth increment Δa is given in terms of material parameters, far-field geometry, and loadings and their increments. For the rigid-plastic, non-hardening approximation, stress and strain increment fields for growing cracks are identical to those for stationary cracks. For fields with a pair of symmetric slip-lines, the flanks of the decohering zone turn out to be rigid, and the decohering zone does not affect the crack-tip opening angle (CTOA), which then depends only on the micromechanisms of hole nucleation, growth and linkage by flow localization or fine cracking. These mechanisms are in turn approximately controlled by the near-field plasticity parameters: the angle of the slip plane θs, and the normal stress and displacement increment across the slip plane σs and Δus. Note the three-parameter characterization of the near-tip fields, in contrast to the one- or two-parameter characterization in elastic or nonlinear elastic fracture mechanics. A sliding off and shear-cracking model for a growing crack, based on a hole growth equation, gives an approximate CTOA in terms of σs, θs, and material parameters. When hole nucleation strain is negligible, the estimated CTOA exhibits an inverse exponential dependence on σs and a higher order parabolic dependence on θs. For a given material, a series of fully plastic crack growth experiments is suggested to determine the approximate material parameters needed to characterize the dependence of CTOA on σs and θs, or from kinematics, of the shear strain behind the slip plane, γf, on σs.

In nuclear power plants, RPV (Reactor Pressure Vessel) upper head CRDM (Control Rod Drive Mechanism) penetration tubes has been fabricated J-groove weld geometry. Recently, the incidences of cracking in Alloy 600 CRDM tubes and their associated welds have increased significantly. The cracking mechanism has been attributed to PWSCC (Pressurized Water Stress Corrosion Cracking) and has been shown to be driven by welding residual stresses and operational stresses in the weld region. Weld induced residual stress is main factor for crack growth. Therefore exact estimation of residual stress is important for reliable operating. In this point, we have been conducting detailed welding simulation analyses for Korea Nuclear Reactor Pressure Vessel to predict the magnitude of weld residual stresses in penetration tubes. In the present work, the FE (Finite Element) simulations were conducted to investigate the effects of tube geometry (location and ro/t) and material properties on the residual stresses in the J-groove weld for a different location of CRDM tubes. The variables of tube location included three (center-hole, intermediate and steepest side hill tube) inclination angles (Ψ). And this comparison was performed for different tube geometry (ro/t = 2, 3, 4), different yield strength (σo) of tube. In CRDM tube, when increases in tube inclination angle (Ψ), axial residual stress are gradually increased, but hoop residual stresses are decreased at the nearby weld root. In effect of tube radius and thickness, when the thickness of CRDM tubes increases the residual stresses are gradually decreased at the inner surface of tube. And there is no effect of CRDM tube radius (ro). In effect of plastic properties of Alloy 600 material in CRDM, when yield strength of the tube increases the axial residual stresses decreases but hoop residual stress increases.Copyright © 2012 by ASME

Laser shock peening (LSP) is an innovative surface treatment technique, which is successfully applied to improve fatigue performance of metallic components. After the treatment, the fatigue strength and fatigue life of a metallic material can be increased remarkably owing to the presence of compressive residual stresses in the material. Recently, the incidences of cracking in Alloy 600 small-caliber penetration nozzles (CRDM (control rod drive mechanism) and BMI (bottom mounted instrument)) have increased significantly. The cracking mechanism has been attributed to primary water stress corrosion cracking (PWSCC) and has been shown to be driven by welding residual stresses and operational stresses in the weld region. For this reason, to mitigating weld residual stress, preventive maintenance of BMI nozzles was considered application of laser shock peening process. The present study is to predict the residual stresses distribution along the peening surface and the interior of the target (Inconel alloy 600 steel) induced by single and multiple LSP processes using the finite element method. The simulations were accomplished using a commercial finite element package ABAQUS, employing both explicit and implicit methodologies. Effects of parameters related to finite element simulation of laser shock peening process to determine compressive residual stresses of Inconel alloy 600 steel are discussed, in particular parameters associated with the LSP process, such as the maximum pressure, pressure pulse duration, laser spot size and number of shots. It is found that about 2HEL maximum pressure and a certain range of the pulse duration can produce maximum compressive residual stresses near the surface, and thus proper choices of these parameters are important. But plastically affected depth increase with increasing maximum pressure and pulse duration. For the laser spot size, residual stresses are not affected, provided it is larger than a certain size. Magnitudes of the compressive residual stresses and plastically affected depth are found to increase with increasing number of shots, but the effect is less pronounced for more shots. Thus, the amplitude of the initial tensile residual stresses was remarkably changed by LSP. Additionally, In order to evaluate the influence of initial residual stresses in Inconel alloy 600 steel, the initial condition option was employed in the finite element code.

In this work a method to simulate failure due to creep is proposed using finite element damage analysis. The creep damage model is based on the creep ductility exhaustion concept. Incremental damage is defined by the ratio of incremental inelastic (plastic & creep) strain and multi-axial ductility. A simple linear damage summation rule is applied. When accumulated damage becomes unity, element stresses are reduced to almost zero to simulate progressive crack growth. The model is validated through comparison with experimental data on various sized compact tension, C(T), specimens of 316H stainless steel at 550 °C. The influence of the inelastic strain rate on the uniaxial ductility is considered. Good agreement is found between the simulated results and the experimental data.Copyright © 2012 by ASME

This paper introduce theoretical creep crack growth prediction model and provides experimental validation of the approach for simulating creep crack growth using finite element analysis method, recently proposed by the authors. The FE creep damage model is based on the creep ductility exhaustion concept, and incremental damage is defined by the ratio of incremental creep strain and multi-axial creep ductility. A simple linear damage summation rule is applied. When accumulated damage becomes unity, element stresses are reduced to zero to simulate progressive crack growth. For validation, simulated results are compared with experimental data for a compact tension specimen of modified 9Cr-1Mo at 600°C under various loading levels. The simulated results agree well with experimental C*-da/dt data. The test data are also compared with theoretical CCG prediction model.

The purpose of this study is to simulate ductile failure of bending pipes with multiple circumferential surface cracks using an element-size dependent damage model. This method is based on the stress-modified fracture strain damage model with stress reduction technique proposed previously by the authors [9,10]. For validation, simulated results using the proposed method are compared with experimental data of Type 304SS pipes performed by Japanese researchers [19]. To calibrate the proposed method, pipe test data with a single surface crack were compared with simulated results using the damage model. Based on the calibrated damage model, the pipe tests with multiple circumferential surface cracks were simulated. The bending moment at both crack penetration and coalescence were calculated from the FE damage analysis. These results were compared with the experimental results. In spite of its simplicity, the results show that proposed method can simulate ductile failure behavior of bending pipes with multiple circumferential surface cracks.

This paper proposes an element-size-dependent damage model to simulate ductile crack growth in full-scale cracked pipes. The proposed method is based on the stress-modified fracture strain damage model modified from stress reduction technique proposed previously by the authors. A modification is made that the critical accumulated damage for progressive cracking is assumed to be dependent on the element size. The proposed method is then compared with a circumferential through-wall cracked pipe test that was conducted during Degrade Piping Program[18]. The bending moment at crack initiation, maximum bending moment, crack extension, and J-integral values were calculated from the FE damage analysis. These results were compared with the experimental results. In addition, results obtained from an existing J-estimation scheme were provided for comparison. All results showed reasonable agreement. The results of the present study demonstrate that the element-size-dependent damage modeling can be applied to simulate the ductile crack growth behavior of a through-wall cracked pipe.

This paper proposes a method to determine the elastic follow-up factors for C(t)-integral under secondary stress. The rate of creep crack growth for transient creep is correlated with C(t)-integral. The elastic follow-up behaviour, which occurs in structures under secondary loading, prevents a relaxation of stress during transient creep. Thus, both the value of C(t) and creep crack growth increase with an increasing elastic follow-up. An estimation solution for C(t) has been proposed by Ainsworth and Dean based on the reference stress method. In order to predict the value of C(t) using this solution, an independent method to determine the elastic follow-up factors for cracked bodies is required. This paper proposes that the elastic follow-up factors for C(t) can be determined by elastic-plastic analyses by using the plastic-creep analogy. Finite element analyses have been performed to verify this method.Copyright © 2012 by ASME

This paper proposes a simple method to estimate stress intensity factors due to welding residual stresses. In this study, finite element analyses for circumferentially cracked pipe are performed to calculate stress intensity factors. Four cracked geometries and two types of weld geometry are considered. KI-solutions for the nonlinear stress distribution on the crack face were determined in accordance with codes and standards. The results are compared with KI-solutions from finite element results. It is found that proposed simple method agrees well with FE results.Copyright © 2012 by ASME

The hyperthermophilic archaeon, Thermococcus onnurineus, was grown in media supplemented with either CO, formate, or starch. H(2) was produced with each substrate with respective maximum rates of 1.55, 3.83 and 2.66 mmol H(2)/l h. The yields (mol H(2)/mol substrate) were 0.98, 1 and 3.13, respectively. This microbe is the first example where a single microorganism can grow and produce H(2) using CO, formate or starch as substrate.

This paper presents finite element solutions for elastic-plastic J for circumferentially cracked pipes under combined mechanical and thermal loads in terms of the V/Vo factor used within a strain-based failure assessment diagram. In this study, 3-dimensional finite element analyses are conducted to calculate the V-factor under combined mechanical and thermal load. It is found that estimation of V/Vo is sensitive to the method used for its evaluation. For larger thermal stresses, currently proposed estimation methods are overly conservative.Copyright © 2011 by ASME

This paper describes steady-state stress on welded branch components using detailed three dimensional elastic creep finite element analyses. In our previous paper [1], it was found that the mismatch effect in creep on steady-state stresses within the weld metal for a various branch junction could be uniquely quantified by the mis-match factor, defined as a function of creep exponent and constant. In actual branch components, the branch junction contains the heat-affected zone (HAZ) when the branch pipe is welded. Thus, additional mismatch factor for HAZ should be presented. This paper deals with not only the mismatch effect for weld metal but also that for HAZ. The creep exponent and constant for the base and weld metal as well as HAZ were systematically varied to analyze under-matching, even-matching and over-matching conditions in creep. In order to investigate the effect of the loading mode, FEA was carried out under internal pressure and in-plane bending to the branch pipe. Two geometries such as large bore branch and medium bore branch were considered. It was found that steady-state creep stresses within HAZ can be quantified as mismatch factor with specific characteristics.

This paper derives analytical solutions of the elastic follow-up factor for power-law creeping cruciform plates under bi-axial displacements to investigate the effect of multi-axial stress states on elastic follow-up behaviors. Validity of the proposed solutions is checked against the results from finite element analyses using power-law creep material. Based on proposed solutions, effects of the biaxiality, geometry, Poisson’s ratio and creep exponent on elastic follow-up factors are discussed. Present results show that the elastic follow-up factor for structure with structural discontinuity can be significantly affected by the multi-axial stress states.Copyright © 2011 by ASME

Finding plastic (limit) loads for elbows under various loading conditions such as in-plane bending and out-of-plane bending is not an easy task due to complexities involved in plastic analyses. Considering complexities involved in plastic limit analysis of elbow, deriving analytical solutions of plastic loads for elbows would be extremely difficult. So, recently the limit analysis using finite element program has been widely adopted. Based on extensive and systematic FE limit analyses using elastic-perfectly plastic materials, closed-form solutions of plastic loads for defect-free elbows under in-plane closing, in-plane opening and out-of-plane bending were presented. This paper summarizes the well-known criteria for finding plastic (limit) loads proposed by ASME BPVC Sec.III [1], Zahoor [4], Chattopadhyay et al. [17] and Kim et al. [19] The purpose of this paper is to integrate and improve the proposed solutions by Kim et al. Also, comparison results with published experimental data are presented. From these results, the pros and cons of each criterion for finding plastic (limit) loads for elbows are discussed.Copyright © 2011 by ASME

Thermococcus onnurineus NA1 is a hyperthermophilic archaeon that can be used for the screening of thermophilic enzymes. Previously, we characterized the metabolic enzymes of the cytosolic proteome by two-dimensional electrophoresis/tandem mass spectrometry (2-DE/MS–MS). In this study, we identified a subset of hyperthermostable proteins in the cytosolic proteome using enrichment by in vitro heat treatment and protein identification. After heat treatment at 100°C for 2 h, 13 and 149 proteins were identified from the soluble proteome subset by 2-DE/MS–MS and 1-DE/MS–MS analysis, respectively. Representative proteins included intracellular protease I, thioredoxin reductase, triosephosphate isomerase, putative hydroperoxide reductase, proteasome, and translation initiation factors. Intracellular protease, deblocking aminopeptidases, and fructose-1,6-bisphosphatase were overexpressed in Escherichia coli and biological activity above 85°C was confirmed. The folding transition temperature (Tm) of identified proteins was analyzed using the in silico prediction program TargetStar. The proteins enriched with the heat treatment have higher Tm than the homologous proteins from mesophilic strains. These results suggested that the heat-stable protein set of hyperthermophilic T. onnurineus NA1 can be effectively fractionated and enriched by in vitro heat treatment.

In this paper, a prediction of C(t), a crack tip parameter for the transient creep condition, for the circumferential cracked pipe under combined mechanical and thermal stresses are presented. The estimation formulae for C(t)-integral of the cracked component operating under mechanical load alone have been provided for decades [1–6]. However, high temperature structures usually work under combined mechanical and thermal load. And the interactions between mechanical and thermal loads make the relaxation rate different from those produced under mechanical load alone. In this study, 3-dimensional finite element analyses are conducted to calculate the C(t)-integral under combined mechanical and thermal load. As a result, redistribution time for the crack under combined mechanical and thermal load is re-defined to quantify the C(t)-integral. The estimation of C(t)-integral using this proposed redistribution time agrees well with FE results.

This paper provides the through-thickness welding residual stress profile in dissimilar metal nozzle butt welds of pressurized water reactors. For systematic investigations of the effects of geometric variables, i.e. the thickness and the radius of the nozzle and the length of the safe end, on welding residual stresses, idealized shape of nozzle is proposed and elastic-plastic thermo-mechanical finite element analyses are conducted. Through-wall welding residual stress profiles for dissimilar metal nozzle butt welds are proposed, which take a modified form of existing welding residual stress profiles developed for austenitic pipe butt weld in R6 code.Copyright © 2010 by ASME

In this paper, a prediction of V-factor, the correction factor for the plasticity interaction between the primary stress and secondary stress, for the cracked pipe under combined mechanical and thermal stresses with significant elastic follow-up is presented. Recently, present authors suggested enhanced V-factor solution using failure assessment curve, which is less conservative than R6 code. However, this solution is limited to weak elastic follow-up condition. The degree of elastic follow-up is related to the variations of Vo with β according to this study. Based on this observation, a prediction solution for the V-factor which can be applied to the crack assessment ranging from weak elastic follow-up condition to strong elastic follow-up condition is proposed.Copyright © 2010 by ASME

This paper describe steady state stress distribution into the weld metal of welded branch components using detailed three dimensional elastic creep finite element analyses. In order to show the effect of the loading mode, this research is carried out under various loading conditions such as internal pressure, in-plane bending to the branch pipe and out-of-plane bending to branch pipe. Also, to generalize the unique aspect, three geometries of branch components including welded large bore branch, medium bore branch, and trunnion are considered. It is a well-known fact that the creep strain rate of welds material is faster than that of parent material. Therefore, the creep exponent and constants for the parent and weld metal are systematically varied to analyze under-matching, even-matching and over-matching conditions in creep. It can be shown that mismatch effect can be quantified as mismatch factor with specific characteristics.Copyright © 2010 by ASME

This paper provides the virtual simulation method for creep crack growth test, based on finite element (FE) analyses with damage mechanics. Creep tests of smooth bars are used to quantify the constants of creep constitutive equation. The reduction of area resulting from creep tests of smooth and notched bar is adopted as a measure of creep ductility under multiaxial stress conditions. The creep ductility exhaustion concept is adopted for calculating creep damage, which is defined as the ratio of creep strain to the multiaxial creep ductility. To simulate crack propagation, fully damaged elements are forced to have nearly zero stresses using user-defined subroutine UHARD in the general-purpose FE code, ABAQUS. The results from 2D or 3D FE analyses are compared with experimental data of creep crack growth. It is shown that the predictions obtained from this new method are in good agreement with experimental data.Copyright © 2010 by ASME

Under monotonic loading, structures should ideally be ductile enough to provide continued resistance during crack growth. Such fully plastic behavior is of interest in design against collisions, tank car accidents, earthquakes, and ship groundings. For fully plastic crack growth in low strength alloys, existing asymptotic solutions for elastic-plastic growing cracks are not applicable because they reach the fracture strain only in regions small compared to the inhomogeneities of the actual fracture process. For the limiting case of non-hardening fully-plastic plane strain crack growth, in a number of geometries and loadings the near-tip fields are characterized in terms of three parameters: an effective angle 2θ s between a pair of slip planes, and the normal stress σ s and the increment of displacement δμ s across the planes. This three-parameter characterization is in contrast to the one- or two-parameter (K or J and T or Q) characterization in linear or non-linear elastic fracture mechanics. These θ s , σ s , and δu s parameters are found from the far-field geometries and loadings through slip line fields or least upper bound analyses based on circular arcs. The resulting crack growth, in terms of the crack tip opening angle (CTOA), is a function of θ s , σ s , and the material. The geometry of the crack growing between two moving slip planes emanating from its tip reduces this function to the critical fracture shear strain left behind the slip planes, γ f , as a function of σ s . γf(σ s ) is found theoretically from a hole initiation and growth model. It is also found from preliminary fully plastic crack growth experiments on unequally grooved specimens with fixed-grip extension or 4-point bending of a 1018 CF steel. At high triaxialities and also after strain aging, cleavage intervened abruptly, even during stable, slow deformation.

This paper represents the results of tensile test for NiCo thin films, to investigate the size effect on tensile properties. An axial loading tensile tester developed by authors was used to measure the mechanical characteristics of thin film materials. The tester has a load cell with maximum capacity of 0.5N and a non-contact position measuring system based on the principle of capacitance micrometry. The “dog-bone” type specimen was designed and fabricated by electroplating process. The 50 and 150μm width of reduced section respectively were designed on 6 in. wafer. The length of reduced section is 1,000μm and the radius of the blending fillet is 1,000μm to minimize a stress concentration of the specimen. The thickness is 10μm. The elastic moduli of NiCo thin film were about 18 ± 4.1GPa for 50μm width and about 148 ± 8.4GPa for 150μm width. The ultimate tensile strength for the width of 50 and 150μm were 2,431±87.8 and 2,348±93.3MPa, respectively. However, the difference between tensile strengths is a little, as 3.3%.

This paper provides V-factor estimation under combined mechanical and thermal load for circumferential cracked pipes. In this study, the effects of types and magnitudes of the thermal stress, mechanical loading mode, crack geometry, and plastic strain hardening on variations of V-factor are estimated. The results of finite element analyses are compared with R6 values. As a result, it is shown that R6 gives generally conservative results. The conservatism is especially increased for the combination of large mechanical and thermal load. As a result, new estimation equation which uses failure assessment curve in R6 is proposed for V-factor and gives less conservative results.

This paper proposes a simple numerical method to simulate plastic behaviours of tensile plates with twin through-wall cracks. The method is based on finite element analysis with a simple damage theory. To validate the proposed method, simulated results are compared with experimental data performed by Japanese researchers. Despite its simplicity, the proposed method well predicts plastic behaviours of tensile plates with twin cracks, including crack coalescence. Predicted maximum loads are overall lower than experimentally-measured ones.Copyright © 2009 by ASME

Members of the genus Thermococcus , sulfur-reducing hyperthermophilic archaea, are ubiquitously present in various deep-sea hydrothermal vent systems and are considered to play a significant role in the microbial consortia. We present the complete genome sequence and feature analysis of Thermococcus onnurineus NA1 isolated from a deep-sea hydrothermal vent area, which reveal clues to its physiology. Based on results of genomic analysis, T. onnurineus NA1 possesses the metabolic pathways for organotrophic growth on peptides, amino acids, or sugars. More interesting was the discovery that the genome encoded unique proteins that are involved in carboxydotrophy to generate energy by oxidation of CO to CO 2 , thereby providing a mechanistic basis for growth with CO as a substrate. This lithotrophic feature in combination with carbon fixation via RuBisCO (ribulose 1,5-bisphosphate carboxylase/oxygenase) introduces a new strategy with a complementing energy supply for T. onnurineus NA1 potentially allowing it to cope with nutrient stress in the surrounding of hydrothermal vents, providing the first genomic evidence for the carboxydotrophy in Thermococcus .

The uracil-sensing domain in archaeal family B-type DNA polymerases recognizes pro-mutagenic uracils in the DNA template, leading to stalling of DNA polymerases. Here, we describe our new findings regarding the molecular mechanism underpinning the stalling of polymerases. We observed that two successive deaminated bases were required to stall TNA1 and KOD1 DNA polymerases, whereas a single deaminated base was enough for stalling Pfu DNA polymerase, in spite of the virtually identical uracil-sensing domains. TNA1 and KOD1 DNA polymerases have a much higher extension rate than Pfu DNA polymerase; decreasing the extension rate resulted in stalling by TNA1 and KOD1 DNA polymerases at a single deaminated base. These results strongly suggest that these polymerases require two factors to stop DNA polymerization at a single deaminated base: the presence of the uracil-sensing domain and a relatively slow extension rate.