bluuebunny/crossref_metadata_2025 huggingface dataset:
Residual Stress Analysis of a Bimetallic Weld Subjected to Stress Improvement and Weld Overlay Repair
Authors: Cofie Nathaniel G. , Dijamco David G. , Limpus Carl R. , Cirilli James J. , Malikowski Heather M. , Roberts Allen T.
Published: July 2008

Bimetallic welds associated with nozzle-to-safe end welds typically involve the use of Alloy 82/182 weldments. These weld materials are susceptible to intergranular stress corrosion cracking (IGSCC) in boiling water reactor (BWR) environment in the presence of tensile stresses. To mitigate IGSCC in these welds, stress improvement using either mechanical stress improvement process (MSIP) or induction heating stress improvement (IHSI) has been applied to convert the tensile stresses on the inside surface of the components to favorable compressive stresses on several of these welds at many BWR plants. The stress improvement applications to most of these welds were performed at the time when UT inspection technology for detecting and sizing flaws was at its infancy. As such, with improved modern day UT technology, it is not uncommon to detect flaws in these previously stress improved welds. Typically, weld overlay repairs using IGSCC resistant Alloy 52 weld metal are implemented on these welds when flaws are detected. Even though IGSCC resistant material is used for the design of the overlay, it is desirable to have adequate compressive residual stresses on the inside surface of the configuration after the overlay repair to provide further resistance against IGSCC. This paper describes a weld residual stress evaluation performed for a nozzle-to-safe end bimetallic weld that was previously stress improved with MSIP, and in which a flaw was identified during inspections. Four operating cycles were performed after application of MSIP. To repair the flaw, a weld overlay repair was implemented on this weld. The analytical process closely simulated the history of operation of this weld including the assumption of a weld repair during the original weld fabrication process. A thermal analysis was performed using a two-dimensional finite element model to simulate the welding process of the repair followed by one heatup and cooldown cycle, the weld overlay, and final operating heatup and cooldown. A non-linear, elastic-plastic stress analysis was then performed to calculate the residual stress state at various stages. The MSIP loading was simulated by pressure applied to the outside surface of the safe end, and iterated in order to produce the measured residual reduction in pipe circumference as measured in the field following the application of MSIP. The post stress improvement and the post weld overlay residual stresses at normal operating conditions resulted in beneficial compressive stresses on the inside of the configuration, assuring that crack growth into the weld overlay is highly unlikely.
DOE-ASME Generation IV Materials Tasks
Authors: McGreevy Timothy E. , Jetter Robert I.
Published: July 2008

The Department of Energy (DOE) and the American Society of Mechanical Engineers (ASME) wish to update and expand appropriate materials, construction and design codes for application in future Generation IV nuclear reactor systems that operate at elevated temperatures. The scope of interest addresses specific materials and design tasks, all of which are tied to the Generation IV Reactors Integrated Materials Technology Program Plan. Many of the tasks are directly applicable to ASME Section III Subsection NH. The tasks are summarized and discussed with respect to Generation IV needs.
Multiaxial Fatigue of 16MnR Steel
Authors: Jiang Yanyao , Zhao Tianwen , Wang Xiaogui , Gao Zengliang
Published: July 2008

Uniaxial, torsion, and axial-torsion fatigue experiments were conducted on a pressure vessel steel, 16MnR, at room temperature. The uniaxial experiments were conducted using solid cylindrical specimens. Axial-torsion experiments employed thin-walled tubular specimens subjected to proportional and nonproportional loading. A critical plane multiaxial fatigue criterion recently developed was found to correlate well with all the experiments conducted for the material. In addition, the fatigue criterion correctly predicted the cracking behavior of the material subjected to different loading paths.
New Technique of Developing a Composite by the Penetration of Hard Powders Into Metal Pipe
Authors: Tanaka Shigeru , Hokamoto Kazuyuki , Itoh Shigeru
Published: July 2008

A new attempt in developing a composite material using explosive processing was attempted. Shock wave derived from explosion energy is a viable technique and can be used to penetrate diamond powders into the metal pipe without permitting the reaction with the base metal. In this method, the overall heat conductivity property of the composite is expected to be improved by the diamond powders, which possess high heat conductivity property. The purpose of this research is to clarify the experimental conditions for obtaining a new composite material with unique properties. Some sizes powders were used for the experiments and the difference in the experimental results are reported.
Evaluation of Creep Strength Reduction Factors for Welded Joints of HCM12A (P122)
Authors: Takahashi Yukio , Tabuchi Masaaki
Published: July 2008

HCM12A (ASME Grade 122) is used for boiler components in thermal power plants because of its high creep strength. However, type IV creep damage formed in heat affected zone brings about considerable decrease in creep strength of the weldment and a failure of large diameter piping in a thermal power plant due to this damage took place recently. In order to update the design method and develop life estimation method for this kind of piping system with axial weld, creep rupture data of base metal and welded joints has been collected and analyzed in the SHC (Strength of High-Chromium Steel) committee in Japan since 2004. In the present paper, the creep rupture data of over 400 points for welded joint specimens of HCM12A offered from six Japanese organizations were analyzed. These data clearly indicated that the long-term creep strength of welded joints becomes weaker than that of base metal at above 600C due to Type IV fracture in fine grain heat-affected zone. After discussing the effects of product form, welding procedure and specimen sampling etc. on the creep strength, the master creep life equation for the welded joints was developed. So-called region decomposition technique was adopted to fit the data both in high and low stress regimes with a reasonable accuracy. The creep strength reduction factor obtained from 100,000 hours creep strength of welded joints and base metal was given as a function of temperature.
Residual Stress and Hardness Distributions by Surface-Machining Near the Circumferential Welding Zone
Authors: Katsuyama Jinya , Mochizuki Masahito , Toyoda Masao
Published: July 2008

The stress corrosion cracking (SCC) of core internals and/or recirculation pipes of SUS316L stainless steel are, in many cases, developed at inner surface due to the tensile residual stress by the circumferential welding and at the hardening layer by the cutting work. In present work, the residual stress and hardness distributions by cutting work were calculated by the FEM method by taking strain hardening into account which was measured experimentally. We discussed the effect of residual stress introduced by both of circumferential welding and cutting work on SCC progress.
Numerical Analysis of Thermomechanical Behavior of a Multimaterial Under Thermal Cycling Conditions
Authors: Taher Bilal , Youne`s Rafic , Abboudi Said
Published: July 2008

The increasing need of structures having multiple functions orientates designers to combine materials in order to obtain, according to coupling scales, multi-materials structures. The lifetime of these structures represents the essential decisive element for study offices and manufacturers. The results of this work should add to the set of functional charges and constraints of resistance, the improvement of the lifetime as an objective to optimize a multi-material. In this study, we propose a numerical analysis by the finite elements method of the thermo mechanical behavior of these materials and their damage under thermal cyclic solicitations. The sample is a two-dimensional plate constituted of two different isotropic layers (steel, aluminum) submitted to variable thermal conditions (heat flux condition on one side and convection exchange condition on the opposite side). The sample is supposed to be fixed in one direction and free in the other. The damage model is based on the works of Lemaiˆtre and Chaboche [8]. Numerical results are presented for different forms of heat flux cycling (triangular, square and sinusoidal excitations) with a comparison of the multi-material damage for each excitation. The study is concluded by an empirical optimizing of the thickness of materials according to the total lifetime caused by thermo-mechanical effect.
Investigation of Tube Hydroforming Process Envelope for Macro/Meso Scalability
Authors: Cochran Joey L. , Gibson M. Christopher
Published: July 2008

The process of tube hydroforming (THF) requires tube stock to be internally pressurized and possibly axially fed inside a die cavity in which the tube plastically deforms to fill the cavity. The purpose (of this investigation) is to explore the impact of the tube geometry, diameter and wall thickness, on the formability of a part. Knowing how the scale of the tube influences formability should allow projections on the performance at the meso forming scale. The most common type of failure is tube wall nominal thickness reduction in excess of 20%. Reductions greater than 20% are deemed more likely for rupture and buckling due to axial forces. Tribological properties are also investigated to determine the impact of friction coefficients on the thinning of the tube wall. The friction impact on the forming dictates the lubrication requirements of the THF process. Process modeling simulations using the finite element method (FEM) are conducted analyze the effect of the various parameters that limit THF processes. Scaling the simulation for meso forming indicates promising results. The macro analysis indicates the tube is capable of being formed at smaller scale.
Dynamic Elastic Responses of Orthotropic Double-Layered Cylinders Under Dynamic Loading
Authors: Zheng Jinyang , Chen Yongjun , Deng Guide , Wu Xiaodan
Published: July 2008

Double-layered cylinders are widely used in engineering. In order to predict its elastic dynamic responses which are crucial to establish design method, its radial displacement considering the effect of axial strain is divided into two parts: a quasi-static part meeting inhomogeneous stress boundary conditions and a dynamic part complying with homogeneous stress boundary conditions. The quasi-static part is determined by homogeneous linearity method, and the dynamic part is worked out by the separation of variables method and orthogonal expansion technique. In the expression of displacement there still exists two unknown variables, i.e., the axial strain and the radial stress at the interface between the inner shell and outer shell of the double-layered cylinder. By using axial force balance and radial displacement continuity, a set of Volterra integral equations of the second kind are derived, which can be solved successfully by an interpolation method. Numerical results are presented and discussed for comparison dynamic responses between a monobloc cylinder and a comparable double-layered cylinder.
Analysis of Plain and Gouged Dents in Steel Pipes Subjected to Pressure and Moment Loading
Authors: Blachut J. , Iflefel I. B.
Published: July 2008

Six laboratory scale, mild steel pipes with the outside diameter-to-wall-thickness ratio, Do/t ≅ 40, were dented to about 15%–20% of outside diameter Do, by a hemispherical indenter with its diameter to pipe’s outside diameter ratio, d/Do ≅ 0.41. Three pipes had surface gouges running axially in them, and the remaining three were gouge-free. Five of them were then collapsed by a bending moment followed by pressure burst tests. Experimental test data has been used to benchmark the FE results, details of which are given in the paper. Good agreement between experimental and numerical results was obtained.
Failure of Locally Buckled Pipelines
Authors: Dama E. , Karamanos S. A. , Gresnigt A. M.
Published: July 2008

Mechanical damage in steel pipelines in the form of local buckles due to excessive bending deformation, may severely threaten their structural integrity. The present paper describes experimental and numerical research conducted to assess the structural condition of buckled pipes, subjected to both bending and internal pressure. Fatigue failure under repeated loading is mainly investigated, whereas pipe burst due to internal pressure is also examined. Three full-scale buckled pipe specimens are tested under pressure and bending loads to determine their structural capacity. In addition, using nonlinear finite element tools, an extensive parametric study is conducted, to determine the critical locations at the buckled area, at which maximum strain variation occurs, as well as to investigate the influence of several geometrical and mechanical parameters. Using the maximum strain range from the finite element computations, and a simple S-N approach, reasonable predictions are obtained for the number of cycles to failure observed in the tests. The results of the present study demonstrate that under repeated loading, fatigue failure occurs in the buckled area at the location of maximum strain range. It is also found that the burst pressure may not be affected by the presence of buckles.
Combining Methods of Fluid Transients and Acoustics in Analysis of Pressure Pulsation in Tapered Channels
Authors: Karvinen Timo
Published: July 2008

Pressure wave propagation problems in liquids have traditionally been solved using the methods of fluid transients, i.e. methods of characteristics and impedance. For gases the equations of acoustics are employed. In short pipe lines, in which friction can be ignored, the equations of fluid transients reduce into the form of the wave equation used in acoustics in a channel of constant cross-section. If the wave motion is harmonic, the one-dimensional Webster’s equation and the impedance method yield exactly the same results in tapered channels. The boundary conditions are the known pressure amplitude upstream and zero pressure at the channel outlet. These two methods have been compared for solving wave propagation problems in tapered channels used in many different industrial applications. It was found that these two methods yield exactly the same results, which are also the same as those obtained numerically with the method of characteristics. A desired quality of the tapered channel in many different industrial processes is to minimize the volume flow rate oscillation at the channel outlet. This can be achieved by changing the channel shape from the traditional linear taper, the parabolic shape giving the lowest amplitude. The effect of different quantities such as oscillation frequency and channel dimensions on volume flow rate oscillation was shown. Also, the effect of free air which affects the wave speed was studied. Since the acoustical and fluid transients approaches give identical results in a one-dimensional case, the acoustics method was employed in a three-dimensional problem, which consists of a flow spreader and a tapered channel configuration, and it was solved with the commercial FEM code Abaqus. The results show that there is a variation in the volume flow rate oscillation along the tapered channel width. The three-dimensional computational results can only be verified by measuring the velocity oscillation at the outlet of the tapered channel. The particle image velocimetry (PIV) measurements are in progress at the moment.
OOP Airbag Simulation Load Case via ALE Methodology
Authors: Khan M. Uzair , Moatamedi Moji , Souli M’hamed , Zeguer Tayeb
Published: July 2008

The deployment of an airbag is most fatal and dangerous to a passenger when they are in an out of position (OOP) situation, with the airbag making contact before it is fully inflated. This can lead to severe, if not life threatening, injuries to the passenger. This situation is more commonly associated with small females and children who are positioned near to the airbag module, i.e. in an OOP load cases. The aim of this research is to assess the response of a Hybrid III 5th Percentile female anthropomorphic dummy positioned in a FMVSS 208 low risk static airbag deployment OOP load cases using a transient dynamic finite element program called LS-DYNA. The simulation considers the standard procedures utilised in the LS-DYNA, where assumptions such as uniform airbag pressure and temperature are made, along with a more recently developed procedure that takes into account the fluid-structure interaction between the inflating gas source and the airbag fabric, referred to as Arbitrary Lagrangain Eulerian (ALE) theory. Both simulations were compared to test data received by Jaguar, indicating satisfactory results in terms of correlation, with the more recently developed procedure, ALE theory, showing the greatest accuracy, both in terms of graphical and schematic comparison, especially in the very early stages of the inflation process. As a result, the new simulation procedure model was utilised to research into the effects of changing the designs of the airbag module.
Developing a Physiologically Realistic Material Model of the Aorta for Use in Numerical Modelling
Authors: Pericevic Ian Owens , Moatamedi Moji , Zhao Aihong
Published: July 2008

In recent years there have been numerous attempts to accurately model phenomena that occur in the cardiovascular system of the human body. Problems of the cardiovascular system are commonly associated with low survival rates, thus attracting great interest. One specific area of concern are mechanisms by which the aorta suffers heavy damage during automotive impacts. A large number of fatalities could be prevented annually with the design of new safety systems arising from a proper understanding of these mechanisms. It is well known that such injuries are a result of complex interactions between the vessels, the blood they carry and other parts of the body. As such they can only be accurately modelled using advanced multi-physics software. This research examines a number of material models for use in aortic impact problems and aspires towards the development of a layered orthotropic blood vessel model.
Analysis of Multiple Co-Planar Surface Breaking Flaws Loaded in Tension Under Cleavage Failure Conditions
Authors: Sharples J. K. , Wilkes M. A. , Yellowlees S. F. , Beardsmore D. W. , Melvin G. T. , Hurlston R. , Watson C. T.
Published: July 2008

In procedures such as R6 and BS 7910 for assessing the structural integrity of structures, complex multiple flaws located in close proximity to each other are generally characterised as one, larger, single flaw. Recent studies have shown that the current characterisation rules may be non-conservative under some circumstances. Concurrent experimental and analytical programmes are being undertaken in order to further investigate this potential non-conservatism for situations where the possibility of cleavage failure has to be taken into account when assessing structures or components containing multiple flaws. The analytical work has involved inelastic finite element modelling in conjunction with numerical analysis based on the weakest link methodology for cleavage initiation to determine the probability of cleavage failure. This has allowed the probability of failure for the situation of multiple adjacent flaws to be compared with that for the single characterised flaw to determine whether the characterisation rules are conservative. Initial results from the cases studied so far indicate that: • For flaws that do not touch, the probability of cleavage failure for the single characterised flaw is higher than the original flaws, confirming that the characterisation process is conservative in this case (perhaps significantly so). • For low aspect ratio (depth/length ≪ 1.0) flaws in contact, the probability of cleavage failure for the single characterised is higher than the original flaws, confirming that the characterisation process is conservative in this case. • However, for high aspect ratio (depth/length ∼ 1.0) flaws in contact, the probability of cleavage failure for the single characterised flaw is lower than the original flaws, indicating that the characterisation process may be non-conservative in this case. This paper covers the initial stages of a much larger programme. The analyses presented in this paper are in the process of being extended to allow for crack-tip constraint effects. Early results from these further analyses indicate that the loss of constraint between interacting flaws may be a significant factor and could eliminate at least some of the perceived non-conservatism for the high aspect ratio flaw. Further work is also underway to examine the effect of any localised coalescence of defects (a re-entrant region); the current analyses consider defects that are only just in contact. Further papers are therefore expected.
An Inverse Method for Determining Thermal Load History Which Reduces Transient Thermal Stress
Authors: Ishizaka Takuya , Kubo Shiro , Ioka Seiji
Published: July 2008

When high temperature fluid flows into a pipe, a temperature distribution in the pipe induces a thermal stress. It is important to reduce the thermal stress for managing and extending the lives of plants. In this problem heat conduction, elastic deformation, heat transfer, liquid flow should be considered, and therefore the problem is of multidisciplinary nature. In this paper an inverse method is proposed for determining the optimum thermal load history which reduces transient thermal stress considering the multidisciplinary physics. As a typical problem, transient thermal stress in a thin pipe during start-up was treated. It was assumed that the inner surface was heated by liquid flow and the outer surface was insulated for simplicity. The multidisciplinary complex problem was decomposed into a heat conduction problem with given internal wall temperature history, thermal stress problem with given temperature distribution, and heat transfer problem with given heat flux on an inner surface. An analytical solution of the temperature distribution of the radial thickness and the thermal hoop stress distribution was obtained. The maximum inner hoop tensile stress was minimized for the case where inner surface temperature Ts(t) was expressed in terms of the 3rd order polynomial function of time t. Finally, from the temperature distributions, the optimum fluid temperature history was obtained for reducing the transient thermal tensile stress.
Life Management of Main Steam and Hot Reheat Piping Systems: Part 2
Authors: Cohn Marvin J.
Published: July 2008

Since there have been several instances of weldment failures in main steam (MS) and hot reheat (HRH) piping systems, most utilities have developed programs to examine their most critical welds. Many utilities select their MS and HRH critical girth welds for examination by consideration of some combination of the ASME B31.1 Code [1] (Code) highest sustained stresses, highest thermal expansion stresses, terminal point locations, and fitting weldments. This paper suggests the use of an alternative life management methodology to prioritize material damage locations based on realistic stresses and applicable damage mechanisms. This methodology is customized to each piping system, considering applicable affects, such as operating history, measured weldment wall thicknesses, observed support anomalies, actual piping thermal displacements, and more realistic time-dependent multiaxial stresses. The high energy piping life consumption (HEPLC) methodology for MS and HRH critical girth welds may be considered as a rational approach to determine critical weldment locations for examinations and to determine appropriate reexamination intervals as a risk-based evaluation technique. The HEPLC methodology has been implemented over the past 15 years to provide more realistic estimates of actual displacements, stresses, and material damage based on the evaluation of field conditions. This HEPLC methodology can be described as having three basic phases: data collection, evaluation, and recommendations. The data collection phase includes obtaining design and post construction piping and supports information. The effects of current piping loads and anomalies are evaluated for potential creep/fatigue damage at the most critical weldments. The top ranked weldments of the HEPLC study are than selected as the highest priority examination locations. The author has completed many HEPLC studies of MS and HRH piping systems. The previous paper (Part 1) provided examples of data collection results and documentation of observed piping system anomalies. This paper will provide examples of evaluation results and recommendations, including a few case histories that have correctly ranked and predicted locations of significant creep/fatigue damage.
Use of Master Curve Technology for Assessing Shallow Flaws in a Reactor Pressure Vessel Material
Authors: Taylor N. , Minnebo P. , Bass R. B. , Siegele D. , Wallin K. , Kytka M. , Wintle J. , Wintle John
Published: July 2008

In the NESC-IV project an experimental/analytical program was performed to develop validated analysis methods for transferring fracture toughness data to shallow flaws in reactor pressure vessels subject to biaxial loading in the lower-transition temperature region. Within this scope an extensive range of fracture tests was performed on material removed from a production-quality reactor pressure vessel. The Master Curve analysis of this data is reported and its application to the assessment of the project feature tests on large beam test pieces.
Use of a Unified Model for the Fracture Toughness of Ferritic Steels in the Transition and on the Upper Shelf in Fitness-for-Service Assessment and in the Design of Fracture Toughness Experiments
Authors: EricksonKirk Mark T. , EricksonKirk MarjorieAnn
Published: July 2008

Models to predict the fracture and arrest behavior of ferritic steels have long been under development. The current, most widely accepted model of fracture toughness behavior is the ASTM E1921-02 “Master Curve” that is used to predict the variation of the median cleavage fracture toughness (KJc) with temperature in the transition temperature region, as well as predicting the scatter of data about the median at any given temperature. Recently, models describing the variation of crack arrest fracture toughness (KIa) and of ductile initiation fracture toughness (JIc) with temperature have also been proposed. Moreover, models are also available that relate these various temperature dependencies to each other, and relate them all a common parameter, the cleavage crack initiation fracture toughness index temperature To. Research work continues to better quantify these relationships and to more firmly understand their physical bases. Nevertheless, the ample empirical evidence on which the models are based and the existing physical understanding underlying the models suggests that they can be used as a tool in both fitness-for-service assessment and in the design of experiments conducted to investigate the fracture toughness of ferritic materials. While still being developed, these toughness-based models offer clear advantages relative to alternative (correlative) approaches in terms of reduced prediction uncertainty. In this paper we amalgamate the results of previous publications to provide an algebraic expression for the variation of KJc, KIa, and JIc with temperature that includes explicit quantification of the uncertainty in each variable. We also discuss the implications and potential applications of this combined model.
An Advanced Mixing Tee Mock-Up Called “The Skin of the Fluid” Designed to Qualify the Numerical LES Analyses Applied to the Thermal Evaluation
Authors: Braillard Olivier , Berder Olivier , Escourbiac Fre´de´ric , Constans Slim
Published: July 2008

Nowadays, the LES (Large Eddy Simulation) models have reached an advanced stage in the thermal hydraulic numerical analyses. Particularly, in the mixing tee geometry, the LES allows the thermal, temperature fluctuations cartography — both in amplitude and frequency — to be evaluated. However, for the purpose of mechanical studies a better determination of the fluctuation temperature which impacts the wall would be of significant interest, magnitude of the fluctuation being directly linked to the lifetime of the Tee. This demand steps of experimental qualifications based on cartographic comparisons between numerical and experimental results, not compatible with basic current experiments proposing only local measurements. A mixing tee mock-up (␀ 50 mm) called “the skin of the fluid” was designed to show the real time observation of the temperature fluctuations in the mixing area with a digital infrared device. With its low Biot number the mock-up is quasi permeable to the fluctuation and does not attenuate the temperature amplitude at high frequency, consequently, the infrared image represents the temperature fluctuations which impacts the wall. An existent LES numerical analysis performed with the TRIO U code (developed by the CEA) on the same geometry is shown for a first comparative approach.
Residual Stress Effects on Ductile Tearing
Authors: Sherry A. H. , Goldthorpe M. R. , Fonseca J. , Taylor K.
Published: July 2008

Residual stresses are internal stresses generated during the fabrication and/or operation of engineering structures. Such stresses can provide the major element of the driving force for crack initiation and growth. Structural integrity assessment procedures, provide guidance for the assessment of defects located within regions of high residual stress. However, such guidance may be conservative where the defect develops progressively during service. This paper describes recent experimental and numerical work aimed at quantifying such conservatisms and providing improved guidance for undertaking more realistic analyses. The results demonstrate that pre-loaded compact-tension specimens provide a useful means for studying the behaviour of cracks within residual stress fields. The magnitude of calculated crack driving forces due to residual stresses is influenced by the approach used to introduce cracks into the stress field, with progressive cracks providing lower levels of crack driving force than instantaneously introduced cracks. The J R-curve associated with cracks under primary or combined primary + secondary loading can apparently be rationalized when the total crack driving force is calculated using methods that take proper account of the influence of prior plasticity on the J-integral. However, it is noted that due to differences in the form of the crack-tip stress and strain fields for static and growing cracks, such values of J may be path dependent and influenced by the magnitude of the growth increment.
A New Plastic Correction β for Underclad Defect in a Vessel Submitted to a Pressurised Thermal Shock
Authors: Marie S. , Ne´de´lec M.
Published: July 2008

In the frame of the Reactor Pressured Vessel integrity demonstration, a defect assessment has to be performed considering a Pressurized Thermal Shock. Several approaches are proposed in different reference codes and standards. Usually, the analyses are based on analytical methods. An important effort has been made recently by CEA to improve these tools in the frame of R&D activities funded by IRSN. For the assessment of an underclad defect in a vessel submitted to a pressurized thermal shock, the plasticity induced by cladding yielding is considered through the amplification β of the elastic stress intensity factor KI in the ferritic part of the vessel. The current solution in the French RSE-M code has been developed from a fitting of F.E. calculation results. A more physical solution is proposed in this paper. It takes into account two phenomena: the amplification of the elastic KI due to the plasticity in the cladding and a plastic zone correction in the ferritic part. The first amplification is determined assuming that the plasticity in the cladding could be represented as an imposed opening displacement on the crack lips.
The Role of Turbulence Models for Predicting Thermal Stratification
Authors: Choi Seok-Ki , Kim Seong-O. , Choi Hoon-Ki
Published: July 2008

A numerical study of evaluation of turbulence models for predicting the thermal stratification phenomenon is presented. The tested models are the elliptic blending model (EBM), the two-layer model, the shear stress transport model (SST) and the elliptic relaxation model (V2-f). These four turbulence models are applied to the prediction of a thermal stratification in an upper plenum of a liquid metal reactor experimented at the Japan Nuclear Cooperation (JNC). The algebraic flux model is used for treating the turbulent heat fluxes for all the models. The EBM and V2-f models predict properly the steep gradient of the temperature at the interface of the cold and hot regions which is observed in the experimental data, and the EBM and V2-f models have the capability of predicting the temporal oscillation of the temperature. The two-layer and SST models predict the diffusive temperature gradient at the interface of a thermal stratification and fail to predict a temporal oscillation of the temperature. In general the EBM predicts best the thermal stratification phenomenon in the upper plenum of the liquid metal reactor.
Residual Stress Finite Element Analysis and Measurements of a Tube Penetration J-Groove Attachment Weld in a Hemispherical Head of a Large Ferritic Pressure Vessel: Part I — Centre Nozzle
Authors: Watson C. T. , Gregg A. , Dennis R. , Leggatt N. , Kingston E. , Smith D. J.
Published: July 2008

A programme of work was undertaken to gain an understanding of the residual stress levels in the tube penetration J-groove attachment welds in a hemispherical head of a large stainless steel clad ferritic pressure vessel. In this first part, of a two part paper, the finite element analyses that were carried out to model the centre nozzle penetration are described. Two axisymmetric residual stress finite element models were developed. One used an accurate representation of the weld bead deposition sequence and the other a bead lumping approach to model bead deposition. The results from the finite element analyses were compared with both surface and through thickness stress measurements. These measurements were taken on a mock-up weld that was representative of the actual component. The surface measurements were taken by using an incremental centre hole drilling technique (ICHD). The through thickness values were obtained from deep hole drilling (DHD) measurements. The DHD measurements were taken before and after the cladding of the mock-up. The analytical results from the two axisymmetric models showed the simpler blocked dump model approach to be reasonable in capturing the general level of stress. The finite element analysis results showed good agreement with the measurements in the radial direction, but predicted greater than the measured values in the hoop direction.
Residual Stress Finite Element Analysis and Measurements of a Tube Penetration J-Groove Attachment Weld in a Hemispherical Head of a Large Ferritic Pressure Vessel: Part II — Outer Nozzle
Authors: Dennis R. , Leggatt N. , Watson C. T. , Kingston E. , Smith D. J.
Published: July 2008

A programme of work was undertaken to gain an understanding of the residual stress levels in the tube penetration J-groove welds in a hemispherical head of a large stainless steel clad ferritic pressure vessel. This second part of a two-part paper describes the finite element analysis that was carried out to model an off-centre outer tube to vessel head weld. A 3D finite element residual stress model was developed. The complex bead deposition sequence of the actual weld was simulated by a bead lumping approach using 9 passes. The results from the finite element analyses were compared with both surface and through thickness stress measurements. These measurements were taken on a mock weld that was representative of the actual component. The surface measurements were taken by using an incremental centre hole drilling technique. The through thickness values were obtained from deep hole drilling measurements at three positions around the circumference of the weld. For this off-centre penetration the cladding process was not modelled nor was clad applied to the test mock-up. The finite element results and the measured values showed similar trends in the variation of stress around the circumference of the weld. A poor correlation between measurements and analytical results was obtained at the lower hillside position. A major reason for the discrepancy is believed to be that the bead lumping approach that was used in the finite element model was not a sufficiently refined representation of the actual weld bead deposition sequence. Note however that one of the aims of this finite element analysis was to quantify the variations between the centre tube presented in the first part of this paper and the off centre tube presented here. In this regard the finite element model and measurements compared well. The finite element model was also used to carry out two sensitivity studies that investigated the effects upon residual stress of tube geometry and material properties. For the case where a nozzle tube was extended significantly below the vessel head inner surface the results showed the stresses to be significantly higher than the baseline case.
Scaling Laws for Model Test Based BWR Steam Dryer Fluctuating Load Definitions
Authors: Sommerville Daniel V.
Published: July 2008

In recent years some Boiling Water Reactors have experienced significant steam dryer cracking. In some cases this cracking has necessitated unplanned outages to implement steam dryer repairs and has also resulted in de-rated operation of the affected units. In response to these recent steam dryer failures, GE has initiated a research program focused on identifying the nature of the fluctuating loads experienced by the steam dryer and developing predictive methods that can be used to develop load definitions for steam dryers. The physical mechanisms responsible for excitation of aero-acoustic resonances are not easily modeled using purely analytic methods; therefore, GE has decided to perform model tests to investigate the nature of the expected steam dryer loading. The objectives of the study documented in this paper are to: 1) Provide guidance regarding how to preserve, in the model, the significant fluid phenomena occurring in the plant, and 2) Derive scaling laws to convert model data to plant load predictions.
The Influence of Armor Material Parameters on the Penetration by Long-Rod Projectiles
Authors: Walters William P. , Williams Cyril L.
Published: July 2008

The Alekseevski-Tate equations have long been used to predict the penetration, penetration velocity, rod velocity, and rod erosion of long-rod projectiles or kinetic-energy penetrators [1]. These nonlinear equations were originally solved numerically, then by the exact analytical solution of Walters and Segletes [2, 3]. However, due to the nonlinear nature of the equations, the penetration was obtained implicitly as a function of time, so that an explicit functional dependence of the penetration on material properties was not obtained. Walters and Williams [4, 5, 6] obtained the velocities, length, and penetration as an explicit function of time by employing a perturbation solution of the non-dimensional Alekseevski-Tate equations. Algebraic equations were obtained for a third-order perturbation solution which showed excellent agreement with the exact solution of the Tate equations for tungsten heavy alloy rods penetrating a semi-infinite armor plate. The current paper employs this model to rapidly assess the effect of increasing the impact velocity of the penetrator and increasing the armor material properties (density and target resistance) on penetration. This study is applicable to the design of hardened targets.
Horizontal Ground Random Excitation of Structures Carrying a Rigid Container Partially Filled With Liquid
Authors: Ikeda Takashi , Ibrahim Raouf A.
Published: July 2008

Nonlinear random interaction of an elastic structure carrying a container, partially filled with liquid, under horizontal narrowband random excitation is investigated. The modal equations of motion are derived by using Galerkin’s method, taking into account the nonlinearity of the hydrodynamic force when the natural frequency of the structure is close to the natural frequency of liquid sloshing. The system response statistics are numerically estimated using Monte Carlo simulation. The influences of the excitation center frequency, its bandwidth and liquid level on the system response are studied. As a result, it is found that the mean square response of the structure decreases as the center frequency approaches to the natural frequency of the structure, and that the sloshing in the container has an effect on the vibration suppression of the structure response.
On Comparison of Various Formulations for Evaluation of Dynamic SIFs in FGMs
Authors: Meenakshi T. , Rao B. N.
Published: July 2008

This paper presents three interaction integrals for calculating dynamic stress-intensity factors (SIFs) for a crack in two-dimensional functionally graded materials of arbitrary geometry. The method involves the finite element discretization, where the material properties are smooth functions of spatial co-ordinates and three interaction integrals for mixed-mode dynamic fracture analysis. These integrals can also be implemented in conjunction with other numerical methods, such as meshless method, boundary element method, and others. Numerical examples involving mixed-mode problems are presented to evaluate the accuracy of dynamics SIFs calculated by the proposed interaction integrals. Comparisons have been made between the dynamic SIFs predicted by the proposed three interaction integrals and available reference solutions in the literature, generated either analytically or by finite element method using various other fracture integrals or analyses. An excellent agreement is obtained between the results of the proposed interaction integrals and the reference solutions.
An Improved Method for Recovering Residual Stress From Strain Measurements in Cylinders and Rings
Authors: Parker Anthony P.
Published: July 2008

The traditional method for determining the residual stress from experimental strain readings in axisymmetric configurations can produce large discrepancies in stress predictions, particularly radial stress. By numerical calculation of autofrettage residual stress in a long thick cylinder and subsequent numerical modeling of release of axial stress during the cutting of a short ring sample, a potential preexisting radial and hoop residual stress field is calculated. These stress values are converted to radial and hoop strains at a number of discrete radial locations. Numerical strain values are then randomized to enforce a standard deviation some 25% higher than that for a typical experimental procedure. Pairs of randomized, discrete strain values are used to predict associated residual stresses using the traditional method. This produces wide scattering of predicted stress values, particularly radial stress, and showed high sensitivity to assumed Poisson’s ratio. A simple, alternative strain-stress analysis procedure (ASSAP) is proposed. ASSAP enforces equilibrium requirements and essential stress free boundary conditions at the bore. ASSAP is shown to improve prediction of radial residual stress by around an order of magnitude in the near-bore region, and to effectively eliminate the sensitivity to Poisson’s ratio. The predicted radial stress profile is of sufficient quality to define the associated hoop stress profile. The predicted radial and hoop stress profiles are in close agreement with the original numerical solutions for the ring. Numerical and ‘recovered’ bore hoop stresses are within 1.4%. This work also demonstrates a significant limitation of methods that involve the cutting of axially short ring samples from a long, autofrettaged cylinder. Release of axial stress during cutting creates a reduction in compressive bore hoop stress. Such a discrepancy would be very significant if ring, rather than long-cylinder, values were used in fatigue lifetime calculations.
Development of a Residual Stress Simulation Benchmark for a Single Bead-on-Plate Weldment
Authors: Bouchard Peter J. , Edwards Lyndon , Youtsos Anastasius G. , Dennis Roger
Published: July 2008

Finite element weld residual stress modelling procedures involve complex non-linear analyses where many assumptions and approximations have to be made by the analyst. Weld modelling guidelines for inclusion in the R6 defect assessment procedure are in preparation and will be accompanied by a series of validation benchmarks that can be used to evaluate the accuracy of weld modelling procedures and assess their suitability for use in fracture assessments. It is intended to base one of the benchmarks on a stainless steel bead-on-plate weldment that has been extensively studied by members of Task Group 1 of the NeT European Network project. This paper uses round robin residual stress measurements from the NeT project to derive a statistically based ‘best estimate’ distribution of transverse stress passing through the wall-section at mid-length of the bead-on-plate weldment. The accuracy of a state-of-the-art residual stress prediction is benchmarked against the best estimate measurements using a root mean square error analysis and comparisons of decomposed components of stress. The appropriateness of using the predicted residual stresses in fracture assessments is assessed by comparing stress intensity factors based on the measured and predicted distributions of stress. The results from these studies will be used to help establish accuracy targets and acceptance criteria for the welding benchmark.
Comparison of Leak Rates From Alloy 82/182 Butt Weld Cracks for Leak-Before-Break Applications
Authors: Nana A. D. , Yoon K. K.
Published: July 2008

The discovery of leaking cracks in Alloy 82/182 bimetal welds at the V.C. Summer Nuclear Station has lead the industry to reassess the Leak-Before-Break (LBB) analysis of the reactor coolant system pressure boundary piping components involving Alloy 600 base metals and Alloy 82/182 welds. The leaking cracks were attributed to primary-water-stress-corrosion-cracking (PWSCC). To-date, LBB analysis submittals to the NRC have not considered PWSCC cracks in bimetal welds or Alloy 600 base metals and the leak rate calculations have only considered the conventional fatigue crack morphology. There are limited observed in-service leakage cracks of Alloy 82/182 pipe butt welds with plant measured leak rate data. Effects of PWSCC induced crack morphology involving these welds is investigated through various modeling techniques. The differences in leakage prediction when evaluating as a fatigue crack versus assessing as a PWSCC crack is addressed for various PWR LBB piping systems. The impact of this finding to the overall LBB assessment is discussed. Additionally, the LBB results are compared against the results from another paper.