bluuebunny/crossref_metadata_2025 huggingface dataset:
Analysis of the Rate of Adsorption of Moisture Onto Plutonium Oxide Powders
Authors: Laurinat James E. , Kesterson Matthew R. , Hensel Steve J.
Published: November 2014

Rates of adsorption of moisture onto plutonium oxide powders exposed to air are modeled. The moisture contents of these powders must be limited to minimize the radiolytic generation of flammable hydrogen gas when the plutonium oxide subsequently is stored in containment vessels. The pressure in the vessels is related to the amount of moisture adsorbed. Moisture adsorption rates are modeled for powders in two different containers used by the Savannah River Site (SRS) HB-Line facility, a B vial and a product can. The adsorption models examine the effects of the powder layer fill height, gas mixing conditions above the powder layer, and ambient relative humidity. Moisture distribution profiles are calculated to enable the evaluation of the effect of sampling location on the measured moisture content. The adsorption models are applied using the COMSOL Multiphysics® finite element code. The COMSOL® models couple moisture diffusion with thermal conduction and radiation. The models incorporate an equilibrium adsorption isotherm and a detailed model for combined radiation and conduction heat transfer in the powder, both developed at Los Alamos National Laboratory. The COMSOL® adsorption rate calculations are successfully benchmarked using an analytical, one-dimensional ash and pore diffusion model.
NESC VII Synthesis: A European Project for Application of WPS in RPV Assessment Including Biaxial Loading
Authors: Moinereau Dominique , Chapuliot Stéphane , Marie Stéphane , Jacquemoud Clémentine
Published: November 2014

The Reactor Pressure Vessel (RPV) is an essential component liable to limit the lifetime of PWR plants. The assessment of defects in RPV subjected to pressurized thermal shock (PTS) transients made at a European level does not necessarily take into account the effect of load history (warm pre-stress WPS) on the resistance of RPV material regarding to the risk of brittle failure. Numerous experimental, analytical and numerical results are available, which confirm the beneficial effect of warm pre-stress on RPV steels with an effective and significant increase of the material resistance regarding to the risk of brittle failure.

NESC VII, a new project dealing with WPS, launched in 2008 with the participation of numerous international organizations (involving R&D, Utilities and Manufacturers, Technical supports, Regulatory), is now finished. Based on experimental, analytical and numerical tasks, the project focused on topics generally not covered by past experience on WPS: biaxiality of loading on small and large-scale specimens, effect of irradiation, modeling (including analytical and numerical models) … Among these tasks, new original WPS experiments have been conducted on small and large scale specimens to study the influence of biaxial loading on WPS effect, using a fully representative RPV steel. All WPS experiments have been interpreted with a wide panel of methods, including analytical, engineering and numerical analyses. A description of NESC VII project is presented in this paper including a synthesis of the available experimental, analytical and numerical results.
Pilgrim Station Steam Separator Lifting Lug Material Evaluation and Analysis
Authors: Woods Katie E. , Frew Brian D. , Rui Yuting , Mehta Hardayal S. , Giannuzzi Anthony , Gustin Hal , Pace Raymond M.
Published: November 2014

During Refueling Outage 18 (RFO18, April 2011) Pilgrim Nuclear Power Station (PNPS) identified crack-like indications on the Steam Separator Lifting Lugs. A multi-disciplinary engineering effort was undertaken to determine the cause of the cracking and prepare the technical justification for long term operation of the lifting lugs. This approach focused on addressing the potential for future degradation due to the existing indications, and the resulting effects on the hardware and its function. A materials evaluation concluded that intergranular stress corrosion cracking (IGSCC), most likely associated with cold work present in the as-fabricated steam separator, was the cause of the indications found on the lifting lugs. To support long term operation of the lifting lugs at PNPS, a structural evaluation was completed using ANSI N14.6 and NUREG-0612 criteria with a conservative bounding configuration. Crack growth rates, based on BWRVIP-76 guidance of 5E-5 in/hr for length and 2.2E-5 in/hour for depth, were used in the analyses. The evaluation concluded that PNPS could continue with long term operation of the Steam Separator. Consistent with standard practice, a general heavy loads examination was performed in 2013 (RFO19), confirming no discernable changes. The general examination will be repeated in 2015 (RFO20), and an examination of the lifting lugs is planned for the 2017 Refueling Outage (RFO21) to confirm that the indication behavior is consistent with the evaluation results.
Low Cycle Fatigue: Probability and Statistical Modeling of Fatigue Life
Authors: Harlow D. Gary
Published: November 2014

Low cycle fatigue (LCF) induces damage accumulation in structural components used in various applications. LCF typically describes conditions for which plastic strains are larger than elastic strains. In order to certify and qualify a structural component, manufactured from a given material, that requires high reliability for operation and safety, fundamental material properties should be experimentally investigated and validated. The traditional strain–life approach serves as the underlying experimental method for most LCF investigations. Building upon that background, the purpose of this paper is to investigate the statistical variability and appropriately model that variability for life in LCF. Specifically, the variability associated with the median behavior in a strain–life graph for data is examined. The ensuing analyses are based on data for a cold-rolled, low carbon, extra deep drawing steel; ASTM A969 which is appropriate for applications where extremely severe drawing or forming is envisioned. It is frequently used in the automotive industry for components such as inner door components and side body components. For substantiation of the proposed modeling techniques, data for 9Cr-1Mo steel is also investigated. Such steel is frequently used in the construction of power plants and other structures that experience operating temperatures in excess of 500°C. The commonly used universal slopes approach for fatigue life modeling for which the strain–life computation employs the standard Coffin–Manson relationship is compared to a statistical methodology using a distribution function frequently used in structural reliability. The proposed distribution function for characterizing the fatigue life is a generalized Weibull distribution function that empirically incorporates load history and damage accumulation.
Study on the Seismic Response of Cable Tray Considering Sliding Motion of Cable
Authors: Ito Tomohiro , Azuma Yasuhiko , Shintani Atsuhiko , Nakagawa Chihiro
Published: November 2014

In various industrial plants such as thermal power plants, nuclear power plants, and chemical plants, many cable trays are generally used to support cables for control signals. Cable trays are very long, and thus are supported from ceilings or walls by many supporting structures. When the cable trays are subjected to strong seismic excitations, the trays or the supporting structures vibrate with large amplitudes. In the worst cases, they can collapse, and plants can lose control of systems, which can lead to severe accidents. Therefore, it is very important to maintain the structural integrity of cable trays during seismic events including recent severe earthquakes such as the East Japan Earthquake in 2011.

Cable trays are generally made of thin steel plates with sides folded in the vertical direction, and with cables simply placed on the tray. Thus, cables can slide when the inertia force on the cables exceeds the friction force between the tray and cables. The mass of the cables is relatively large compared to that of a tray, thus the natural frequency of the tray will change significantly due to the cable sliding motion. Consequently, seismic responses of cable tray will also depend on the sliding motion of cables. Therefore, cable trays are seen as highly nonlinear structural systems.

In this study, seismic responses of cable trays are investigated analytically considering cable sliding motions. A cable tray is modeled by a two-degree-of-freedom system. Response acceleration, and the displacements of the tray and the cable are evaluated for both sinusoidal and seismic inputs by varying the cable mass or friction coefficient between the tray and cables. It is confirmed that the sliding motion of the cable has a very large influences on the seismic responses of the cable-tray system.
Recent Amendments of EN13445-3, Clause 18 and Related Annexes: Detailed Assessment of Fatigue Life
Authors: Rudolph Jürgen , Baylac Guy , Wilhelm Paul , Wintle John , Buennagel Emilie
Published: November 2014

The European Pressure Vessel Standard EN 13445 provides in its part 3 (Design) a simplified method for fatigue assessment (Clause 17) and a detailed method of fatigue assessment (Clause 18). Clause 18 “Detailed Assessment of Fatigue Life” is under revision within the framework of the European working group CEN/TC 54/WG 53 - Design methods. The latest amendments of Clause 18 are to be presented. All these amendments aim at a significant increase in user friendliness and clear guidelines for application. The following items are to be mentioned in particular in that context:

• Fatigue assessment of welded components based on structural stress and structural hot-spot stress approaches

• Detailed guidelines for determining relevant stresses and stress ranges

• Cycle counting proposals.

The fatigue assessment of welded components is part of paragraphs 18.6 “Stresses for fatigue assessment of welded components and regions” (determination of relevant stress ranges) and 18.10 “Fatigue strength of welded components” (relevant weld details and revised fatigue curves). The basic rules for unwelded components essentially remain unchanged. Stress analyses for clause 18 are usually based on detailed finite element analyses (FEA). As an essential amendment for the practical user the determination of structural stress ranges for the fatigue assessment of welds is further detailed in the new informative annex NA “Instructions for structural stress oriented finite elements analyses using brick and shell elements”. Here, different applicable methods for the determination of structural stresses are explained in connection with the requirements of the finite element models and analyses.

The cycle counting issue is comprehensively treated in the new informative annexes NB “Cycle Counting for a given Load History” and NC “Cycle Counting for Design Data Evaluation” including detailed proposals for implementation in an algorithmic programming framework.
Experimental Study on Composite Containment Vessels
Authors: Dong Qi , Gu Yan
Published: November 2014

In this paper, we present experimental results of tests performed on composite containment vessels. The experimental observations of dynamic response of glass fiber composite vessels and carbon fiber composite vessels are compared, in which the carbon fiber composite vessels demonstrate better performance than that of glass fiber composite vessels. The study on the failure of composite vessels is also presented, in which it is found that failure modes of glass fiber composite vessels and carbon fiber composite vessels are different. The current study may contribute to the further understanding on the design and application of composite containment vessels.
Comparison of Stress and Strain Analysis Techniques for Assessment of Bulges in Coke Drums
Authors: Samman Mahmod , Tinoco Ediberto B. , Marangone Fábio C.
Published: November 2014

A set of four operating coke drums experienced variable degrees of bulging and bulging-induced cracks. Internal laser scans were obtained for these drums to accurately define their geometry. Then, the severity of bulging was analyzed using stress and strain analysis techniques. In this paper, results of the two methods are presented and compared to failure history.
3D Simulation of a Peripheral Adapter J-Groove Attachment Weld in a Vessel Head
Authors: Mourgue Philippe , Robin Vincent , Gilles Philippe , Gommez Florence , Brosse Alexandre , Gallee Sebastien
Published: November 2014

In Pressurized Water Reactors, most of heavy components and pipes have a large thickness and their manufacturing processes often require multi-pass welding. Despite the stiffness of these components, the distortion issue may be important for operational requirements (e.g. misalignment) or controllability reasons (Non Destructive Examinations have to be achievable, therefore ovalization should be limited). These requirements may be difficult to achieve by simply adjusting welding processes. Indeed because of the complexity of mechanisms involved during a welding operation and the high number of influencing parameters, this process is still essentially based on the experience of the welder. Furthermore the experimental estimation of the stress and distortion level in the component remains a difficult task that is subject to errors even if techniques are currently improved to become more accurate. These are the reasons why AREVA has put a large effort to improve welding numerical simulations, in order to have a better understanding of the involved physical phenomena and also to predict the residual state through the structure. Computational welding mechanics is used to qualify the manufacturing processes in the very early phase of the welded component design. Within the framework of a R&D program whose main objective was to improve tools for the numerical simulation of welding regarding industrial needs, AREVA has decided to validate new methodologies based on 3D computation by comparison with measurements. For this validation task the chosen industrial demonstrator was a Control Rod Drive Mechanism (CRDM) Nozzle with a J-groove attachment weld to the vessel head. For such an application, operations of post-joining straightening have to be limited, if not prohibited, because of their cost or the impossibility to use them in front of a steel giant. The control of distortion during welding operations is a key issue for which simulation can be of great help. Regarding distortion issues, both accurate metal deposit sequence modeling and respect of the real welding parameters are mandatory, especially for multi-pass operation on such a complex geometry.

The aim of this paper is to present the simulation of the distortion of a peripheral adapter J-groove attachment weld mock-up. This new full 3D simulation improves the result of the previous one based on lumped pass deposits. It is the result of a fruitful collaboration between AREVA and ESI-Group.
Effects of Mechanical Loading on Residual Stress and Fracture: Part I — Background to the BS 7910:2013 Rules
Authors: Hadley Isabel , Smith Simon
Published: November 2014

Failure of welded structures due to the presence of flaws is typically driven by a mixture of applied and residual stresses, yet in most cases only the former are known accurately. In as-welded structures, a typical assumption is that the magnitude of welding residual stress is bounded by the room temperature yield strength of the parent material. The UK flaw assessment procedure BS 7910:2013 also assumes that mechanical loading (either as a result of proof testing or during the initial loading of an as-welded structure) will bring about a relaxation in residual stress. Conversely, the UK structural assessment code for nuclear structures, R6, contains a warning on the ‘limited validation’ of the BS 7910 approaches for stress relaxation and suggests that they should be used ‘with caution’. The aim of this study was therefore to review the basis of the BS 7910 clauses on stress relaxation with a view to harmonising the BS 7910 and R6 rules for cases in which the original welding residual stress distribution is not known.

The residual stress relaxation clauses of BS 7910:2013 date back to the 1991 edition of PD 6493 and have not changed substantially since then. A considerable programme of work was carried out by TWI at the time to justify and validate the clause, but the full underlying details of the work have not hitherto been available in the public domain, and are described in a separate companion paper. The approach proposed in BS 7910 combines ‘global’ relaxation of residual stress (Qm) under high mechanical load with ‘local’ enhancement of crack tip driving force through the adoption of a simplified primary/secondary stress interaction factor, ρ.
Sizing and Design of Compressors for Large Scale LDPE Plants
Authors: Bächli Hubert , Allenspach Andreas
Published: November 2014

For the production of low density polyethylene, ethylene has to be compressed up to 3,500 bar. To manage these pressures appropriate compressor designs are selected. In recent years, the size of these plants has increased up to 400 kt/a. The increased mass flow results in increased dimensions required for all compressor parts. This paper discusses the challenges of the sizing and design of the compressors for such large-scale plants.
Micromechanisms of Hydrogen-Assisted Cracking in Super Duplex Stainless Steel Investigated by Scanning Probe Microscopy
Authors: An Bai , Iijima Takashi , San Marchi Chris , Somerday Brian
Published: November 2014

Understanding the micromechanisms of hydrogen-assisted fracture in multiphase metals is of great scientific and engineering importance. By using a combination of scanning electron microscopy (SEM), scanning tunneling microscopy (STM), atomic force microscopy (AFM) and magnetic force microscopy (MFM), the micromorphology of fracture surface and microcrack formation in hydrogen-precharged super duplex stainless steel 2507 are characterized from microscale to nanoscale. The results reveal that the fracture surfaces consist of quasi-brittle facets with riverlike patterns at the microscale, which exhibit rough irregular patterns or remarkable quasi-periodic corrugation patterns at the nanoscale that can be correlated with highly localized plastic deformation. The microcracks preferentially initiate and propagate in ferrite phase and are stopped or deflected by the boundaries of the austenite phase. The hydrogen-assisted cracking mechanisms in super duplex stainless steel are discussed according to the experimental results and hydrogen-enhanced localized plasticity theory.
Determination of Norton Creep Law From Small Punch Test
Authors: Feng Xiangsai , Qin Yanfeng , Ma Kai , Guan Kaishu
Published: November 2014

The present work focused on a miniature test named small punch creep test which have been employed to electric power, petro-chemical, nuclear power and other fields widely in the last three decades.

Under normal circumstances, engineering application pay more closer attention to the Norton creep law. To determine the Norton creep law, at least three creep curves were needed by traditional method, it’s time consuming and uneconomic. In present paper, the small punch creep tests were carried out following the CEN code of practice. Based on Chakrabarty’s membrane stretch model and Norton power law, the results of small punch creep tests and finite element method have been compared and discussed. A completely novel and economical approach was proposed to determine the parameters of Norton creep law more accurately and conveniently. The results show that, if scopes of parameters known, the Norton creep law could be determined accurately even from one creep curve only.
Numerical Approach for the Consideration of Hold Time Effects
Authors: Reese Sven H. , Seichter Johannes , Klucke Dietmar , Karabaki H. Ertugrul , Mayinger Wolfgang
Published: November 2014

In recent years the Environmentally Assisted Fatigue (EAF) became an item, which has to be considered additionally in terms of ensuring a conservative determination of the actual component’s health status resp. the CUF. For practical application, the consideration of the so called Fen-factor leads to the reduction of the admissible cycles in fatigue calculations. Beyond that the influence of elevated temperatures has been identified as one parameter having a negative influence on the admissible cycles as well. For example the German KTA 3201.2 defines for austenitic steels separate fatigue curves for temperatures above 80°C and for temperatures below 80°C. In summary on the one hand parameters influencing component’s lifetime negatively have to be considered in terms of conservative calculations. On the other hand, there are other parameters which influence the component’s fatigue lifetime in a positive manner. As such positive effects are neglected so far, CUF allowing for EAF tend to become over conservative leading to oversized components. Therefore, positive effects should be considered as well in the framework of a comprehensive and detailed analysis making sure not to overdesign components.

When taking a closer look on the operational behavior of primary circuit components, fatigue loading is mainly defined by long steady-state periods with no significant changes in the loadings and by normally short outage periods with no thermal loading. For example fatigue of a PWR surge-line is mostly caused by short in-surge and out-surge events during start-up or shut-down of the plant. Normal operation transients mostly not cause fatigue relevant events in the surge-line. Fatigue of PWR spray-lines is primarily generated by very few spray-events during a one-year period of operation. Spray events are mainly caused by significant load ramps. Subsequently the fatigue status of primary circuit components is controlled by long periods with no fatigue relevant loading at operating temperature and few additional loading patterns in between. Experimental investigations have shown that hold time effects have a positive influence on fatigue lifetime of austenitic stainless steel materials.

Anyhow, no quantification of these effects has been published in recent years. Within this publication an engineering based approach will be developed to quantify the hold time effect based on literature and published data. On the basis of a practical example the influence of hold time effects will be quantified and a direct comparison to lifetime reducing effect of EAF and temperature will be drawn.
Repairing Corrosion Damage the Smart Way: A Story of Vessel Redemption
Authors: Turnquist Michael , Brown Gregory
Published: November 2014

The application of emerging fitness-for-service standards in conjunction with advanced modeling and ultrasonic thickness (UT) inspection is demonstrated with the recent assessment and repair of a CO2 absorber vessel. UT inspection discovered four regions of localized metal loss on the internal surface of a CO2 absorber vessel shell. Of the four regions, two were directly adjacent to major structural discontinuities, including two nozzles, one of which contained a reinforcing plate or repad.

In order to define the critical locations of metal loss and estimate a corrosion rate, thickness data for the regions of metal loss was provided in the form of 1 inch by 1 inch equally-spaced, rectangular thickness grid from two separate inspection dates. Based on the estimated corrosion rate, and the specified operation interval, the rate of metal loss was determined to be significant enough to require repair. This conclusion was based on the fact that in certain locations, the metal loss was estimated to grow through-wall before the end of the specified operation interval.

Computational analysis using guidelines per API 579-1/ASME FFS-1 [1] was used to evaluate an appropriate repair procedure. This included evaluation of repair plate placement and sizing using advanced modeling techniques including elastic-plastic material behavior and contact interaction. The effect of future metal loss was included based the estimated corrosion rate. The result of this assessment was a repair design that provided sufficient protection against excessive plastic deformation and allowed for continued operation through the specified operating interval. Thus, repairing the vessel based on fitness-for-service (FFS) criteria allowed for continued use of the vessel and avoided costly replacement. The lessons learned provide insight into the improved design of vessel repairs.
Experimental Study of a Flexible Oscillating-Foil Propulsion System With Variable Stiffness and Inertia
Authors: Richards Andrew J. , Oshkai Peter
Published: November 2014

Considerable effort has been devoted to the development of flexible flapping fins and wings as propulsion mechanisms for robotics applications. The present work contributes to this research field by considering the effects of inertia, stiffness, resonant frequency and oscillation kinematics on the thrust generation and efficiency of flexible oscillating foils. The findings are derived from experimental measurements of the forces applied to foil models, which were undergoing an oscillating motion in water. In addition, a semi-empirical model of the foil structure was developed to characterize the fluid-structure interaction phenomena. The ratio of the oscillation frequency to structural resonant frequency was found to be one of the principal parameters, which determined the propulsive efficiency. However, when comparing the performance of foils with equivalent resonant frequencies but different levels of stiffness and inertia, stiffer and heavier foils were found to achieve greater thrust production. The improved performance of the heavier foils compared to lighter ones is attributed to a decrease in the damping ratio. The lower damping ratio allowed for a greater amplitude of the motion of the deforming part of the foil which resulted in increased thrust.
Shakedown Boundary of a 90–Degree Back–to–Back Pipe Bend Subjected to Steady Internal Pressures and Cyclic Out–of–Plane Bending Moments
Authors: Abdalla Hany F.
Published: November 2014

Ninety degree back–to–back pipe bends are extensively utilized within piping networks of modern nuclear submarines and modern turbofan aero–engines where space limitation is considered a supreme concern. According the author’s knowledge, no shakedown analysis exists for such structure based on experimental data. In the current research, the pipe bend setup analyzed is subjected to a spectrum of steady internal pressures and cyclic out–of–plane bending moments. A previously developed direct non–cyclic simplified technique, for determining elastic shakedown limit loads, is utilized to generate the elastic shakedown boundary of the analyzed structure. Comparison with the elastic shakedown boundary of the same structure, but subjected to cyclic in–plane bending moments revealed a higher shakedown boundary for the out–of–plane bending loading configuration with a maximum bending moment ratio of 1.4 within the low steady internal pressure spectrum. The ratio decreases towards the medium to high internal pressure spectrum. The simplified technique outcomes showed excellent correlation with the results of full elastic–plastic cyclic loading finite element simulations.
Closed-Form Relations for Stress Intensity Factor Influence Coefficients for Axial ID Surface Flaws in Cylinders for Appendix A of ASME Section XI
Authors: Xu Steven X. , Lee Darrell R. , Scarth Douglas A. , Cipolla Russell C.
Published: November 2014

Analytical evaluation procedures for determining the acceptability of flaws detected during in-service inspection of nuclear power plant components are provided in Section XI of the ASME Boiler and Pressure Vessel Code. Linear elastic fracture mechanics based evaluation procedures in ASME Section XI require calculation of the stress intensity factor. In Article A-3000 of Appendix A of the 2013 Edition of ASME Section XI, the calculation of stress intensity factor for a surface crack is based on characterization of stress field with a cubic equation and use of stress intensity factor influence coefficients. The influence coefficients are only provided for a flat plate geometry.

The ASME Section XI Working Group on Flaw Evaluation is in the process of rewriting Article A-3000 of Appendix A. Major updates include the implementation of an alternate method for calculation of the stress intensity factor for a surface flaw that makes explicit use of the Universal Weight Function Method and does not require a polynomial fit to the actual stress distribution, and the inclusion of stress intensity factor influence coefficients for the cylinder geometry. Tabular data of influence coefficients for the cylinder geometry are available in API 579-1/ASME FFS-1 2007. Effort has been made to develop closed-form relations for the stress intensity factor influence coefficients for the cylinder geometry based on API data. With the inclusion of the explicit weight function approach and the closed-form relations for influence coefficients, the procedures of Appendix A for the calculation of stress intensity factors can be used more efficiently. The development of closed-form relations for stress intensity factor influence coefficients for axial ID surface flaws in cylinders is described in this paper.
A New Test-Bench for Studying Vibrations of Tubes in Parallel Triangular Bundles Under Two-Phase Cross-Flow
Authors: Deri Enrico , Nibas Joël , Adobes André
Published: November 2014

Flow-induced vibrations of Steam Generator (SG) tube bundles are a major concern for the operators of nuclear power plants. In order to predict damages due to such vibrations, EDF has developed the numerical tool GeViBus, which allows one to evaluate safety margins and thereafter to optimize the SG maintenance policy.

The software is based on a semi analytical model of fluid-dynamic forces and dimensionless fluid force coefficients which need to be assessed by experiment. The database of dimensionless coefficients is steadily updated in order to cover all tube bundle configurations found in EDF power plants.

Within this framework, we present a new test rig dedicated to the parallel triangular tube arrangement submitted to a two-phase cross-flow. A new test loop is constructed as well, allowing fluid-elastic instability to be induced on the test rig for various qualities. The details of the experimental arrangement are presented together with the preliminary validation tests.
Simulation of the Creep and Fatigue Damages in High-CR Steel Components Based on a Modified Becker-Hackenberg Model
Authors: Wang Jiong , Steinmann Paul , Rudolph Jürgen , Willuweit Adrian
Published: November 2014

Components of conventional power plants are subject to three potential damage mechanisms and their combination (accumulation) with impact on lifetime considerations: creep, fatigue and ratcheting. Currently, there is a growing need for advanced material models which are able to simulate these damage phenomena and can be implemented effectively within finite-element (FE) codes. This constitutes the basis of an advanced component design. In this work, a constitutive material model, named as the modified Becker-Hackenberg model, is proposed to simulate the thermo-mechanical behavior of high-Cr steel components subject to complex loading conditions. Both creep and viscoplasticity are taken into account in the model, which are viewed as two different kinds of inelastic mechanisms. The key features of the creep strain, i.e., the minimum creep rate and the average creep rupture time, are evaluated by using two Larson-Miller parameters. The cyclic viscoplastic strain is predicted through the conventional Chaboche-type modeling approach, where suitable constitutive evolution equations are adopted to capture the cyclic softening effect, ratcheting effect, time recovery effect and temperature rate effect. All the material parameters involved in this model are identified by using a strategy of stress-range separation. This constitutive model is further implemented in a commercial FE software to simulate the thermo-mechanical behaviors of high-Cr steel components with technologically relevant dimensions. The strain and stress evolution data obtained from the model can be further used for the fatigue damage assessment of high-Cr steel components subject to creep-fatigue interactions. Within an ongoing work, a multiaxial fatigue analyzer is developed to predict the fatigue lifetime of high-Cr steels subject to cyclic loading conditions respectively — in a further step — creep-fatigue interaction.
Spinning Behaviour of Diametral Acoustic Modes in Deep Axisymmetric Cavities With Chamfered Edges
Authors: Barannyk Oleksandr , Oshkai Peter
Published: November 2014

Spinning behaviour of diametral acoustic modes associated with self-sustained flow oscillations in a deep, axisymmetric cavity located in a long pipeline was investigated experimentally. High-amplitude pressure fluctuations resulted from the excitation of the diametral acoustic modes by the fully-turbulent flow in the pipeline. The unsteady pressure was measured at three equally spaced azimuthal locations at the bottom of the cavity. This arrangement allowed calculation of the azimuthal orientation of the acoustic modes, which were classified as stationary, partially spinning or spinning. Introduction of shallow chamfers to the upstream and the downstream edges of the cavity resulted in changes of azimuthal orientation and spinning behaviour of the acoustic modes. In addition, introduction of splitter plates in the cavity led to pronounced change in the spatial orientation and the spinning behaviour of the acoustic modes. The short splitter plates changed the behaviour of the dominant acoustic modes from partially spinning to stationary, while the long splitter plates enforced the stationary behaviour across all resonant acoustic modes.
Fluid Mode Excitation in Launch Vehicle Feed Lines Induced by Pogo Accumulator Venting
Authors: Dotson Kirk W. , Sako Brian H. , Nguyen Trinh T.
Published: November 2014

Launch vehicles with liquid rocket engines have feed lines through which propellants flow to the engine. To prevent feedback between structural responses and propellant pressure and flow oscillations, a compliant device called a pogo accumulator is typically installed in the propellant feed line. Even if a catastrophic interaction is thus averted, the fluid-induced structural responses may exceed those for important flight events such as liftoff and atmospheric buffeting. In that case, the fluid-induced excitation must be predicted in order to ensure adequate structural margins for the launch vehicle and space vehicle hardware. Venting of compliant gas in the pogo accumulator prior to engine shutdown is known to exacerbate the fluid-induced excitation. In particular, for the Atlas V launch vehicle, a 5–7 Hz fluid mode with large pressure gains at the aft end of the liquid oxygen feed line often excites structural modes just prior to engine cutoff. A methodology for the prediction of these structural responses is presented.
Methodological Aspects for Numerical Analysis of Lid Systems for SNF and HLW Transport Packages
Authors: Linnemann Konrad , Ballheimer Viktor , Sterthaus Jens , Wille Frank
Published: November 2014

The regulatory compliance of the containment system is of essential importance for the design assessment of transport packages for radioactive materials. The requirements of the IAEA transport regulations SSR-6 for accident conditions implies high load on the containment system of Type B(U) packages. The integrity of the containment system has to be ensured under the mechanical and thermal tests.

The containment system of German transport packages for spent nuclear fuel (SNF) and high level waste (HLW) usually includes bolted lids with metal gaskets. BAM Federal Institute for Materials Research and Testing as the German competent authority for the mechanical and thermal design assessment of approved transport packages has developed the guideline BAM-GGR 012 for the analysis of bolted lid and trunnion systems. According to this guideline the finite element (FE) method is recommended for the calculations. FE analyses provide more accurate and detailed information about loading and deformation of such kind of structures. The results allow the strength assessment of the lid and bolts as well as the evaluation of relative displacements between the lid and the cask body in the area of the gasket groove.

This paper discusses aspects concerning FE simulation of lid systems for SNF and HLW transport packages. The work is based on the experiences of BAM within safety assessment procedures. The issues considered are the assessment methods used in the BAM-GGR 012 for bolted lid systems along with the nominal stress concept which is applied for bolts according to that guideline. Additionally, modeling strategies, analysis techniques and the interpretation of the results are illustrated by the example of a generalized bolted lid systems under selected accident conditions of transport.
Flow Around a Leading-Edge Slat: Part I — Turbulent Flow Statistics
Authors: Richard Patrick R. , Wilkins Stephen J. , Hall Joseph W.
Published: November 2014

As aircraft engine noise continues to decrease with advancing research, the focus has been partially shifted to airframe noise. One of the main sources of airframe noise are high lift devices, which includes the leading-edge slat on wings. The leading-edge slat works along with the tail flap to provide increased lift to the aircraft during takeoff and landing. This paper will present the findings of an experimental investigation aimed at identifying the sources of noise produced by the leading-edge slat geometry. The main focus of the experiments was the slat cove. Small scale wind tunnel experiments were undertaken at the University of New Brunswick using Particle Image Velocimetry (PIV) to obtain time-averaged Turbulent Kinetic Energy (TKE), Reynolds stresses and vorticity. The experiments were performed at Reynolds numbers of 156,000 and 312,000 for an angle of attack of 20 degrees. The results indicate the presence of a strong shear-layer formed at the slat cusp which is likely to be an significant source of aeroacoustic noise.
Ductile Fracture Assessment of Plates Under Biaxial Loading
Authors: Meek Caroline , Ainsworth Robert
Published: November 2014

There is currently little detailed advice on biaxial and triaxial effects on fracture in fitness-for-service codes and engineering assessment procedures. There has been historical and recent research into such effects using numerical, finite element and experimental investigations into biaxial effects on fracture toughness and J-integral estimation.

However, these studies cover only limited ranges of loadings with, for example, few investigations into loading regimes where the biaxial ratio exceeds unity, i.e. where the loading in the direction of a crack exceeds the crack opening force. This paper first briefly summarises a literature review focussing on the experimental information available on the effects of biaxial loading on ductile fracture. It transpires that although there have been a number of numerical and experimental investigations of biaxial fracture a systematic examination of the effects of biaxial loading is missing in terms of the effect on the crack driving force. Therefore, the paper develops advice for assessment of simple plate geometries under a wide range of biaxial loading conditions to provide advice and recommendations for future inclusion in fitness-for-service codes.
Low Cycle Fatigue Behavior in Air and in PWR Water of a Type 304L Austenitic Stainless Steel Manufactured by Hot Isostatic Pressing Process
Authors: De Baglion Laurent , Cedat Denis , Ould Pascal , Chitty Walter-John
Published: November 2014

In most industries and more particularly in the Nuclear one, the use of new materials or new manufacturing methods is really challenging because “safety” is still the key point. Among many characterizations required for a new steel grade or a new manufacturing process to be accepted and then introduced in a Nuclear design code, the fatigue properties must be determined with great care.

Nowadays, the consideration of the Pressurized Water Reactor (PWR) primary water environment effect on the Low Cycle Fatigue (LCF) behavior of Austenitic Stainless Steels is an important issue for both Nuclear Power Plants (NPP) lifetime extensions and new builds as described in NUREG/CR-6909 [1].

This study aims to present the LCF behavior in Air and in PWR water at 300°C of a type 304L steel manufactured by Powder Metallurgy coupled with Hot Isostatic Pressing process (PM/HIP) and to compare them with those observed on 304L nuclear grade products such as rolled plate or forged branch [2–5]. It appears that the LCF behavior in Air and in PWR water of this 304L HIP material is better or at least similar to the one observed on classical 304L steels.
An Experimental Study of Dynamics of Towed Flexible Cylinders
Authors: Kheiri Mojtaba , Païdoussis Michael P. , Amabili Marco
Published: November 2014

In this paper, some experiments are described which were designed to illustrate the dynamical behaviour of towed flexible cylinders and to test the theory. A silicone rubber cylinder was manufactured such that it was almost neutrally buoyant when immersed in water. The cylinder was terminated by plexiglas end-pieces and was held in horizontal water flow by a length of nylon thread (towrope). Video capturing along with image processing techniques were used to measure the transverse displacement of the cylinder in the horizontal plane. For the cylinder with relatively streamlined nose and tail end-pieces, non-flexural (rigid-body), as well as flexural instabilities developed as the flow velocity was increased; using a sufficiently blunt tail end-piece significantly stabilized the system, while shortening the towrope was not very effective for stabilizing the system. The experimental observations are generally in qualitative agreement with the nonlinear theory. Quantitative comparison of various quantities, e.g. the instability thresholds, between experiment and theory, based on the estimated values of some of the theoretical nondimensional parameters, is also fairly good.
Verification of Elastic-Perfectly Plastic Methods for Evaluation of Strain Limits: Analytical Comparisons
Authors: Carter Peter , Jetter R. I. , Sham T.-L. (Sam)
Published: November 2014

The current rules in Subsection NH for the evaluation of strain limits and creep-fatigue damage using simplified methods based on elastic analysis have been deemed inappropriate for Alloy 617 at temperatures above 1200°F (650°C) because, at higher temperatures, it is not feasible to decouple plasticity and creep; which is the basis for the current simplified rules. To address this issue, proposed code rules have been developed which are based on the use of elastic-perfectly plastic analysis methods and which are expected to be applicable to very high temperatures. The proposed rules are based on the use of an elastic-perfectly plastic material model with a pseudo yield strength selected to ensure that the accumulated strain and creep-fatigue damage with meeting the currently specified limits in Subsection NH. For this phase of the verification process, the proposed rules have been compared using simplified example problems to the results obtained from application of the current Subjection NH rules for both simplified methods and full inelastic analysis. The Subsection NH 316 stainless steel properties data are used for these comparisons. Results of calculations for a testing program underway on Alloy 617 at 950C are given.
Impact of Deformation Stiffness Beyond Yield Point of Pipe Support Structures on Nonlinear Seismic Response Analysis
Authors: Takahashi Tsuneo , Maekawa Akira
Published: November 2014

The importance of safety evaluation for beyond design conditions has come to be required since the accident at the Fukushima Daiichi Nuclear Power Plant as a consequence of the Great East Japan Earthquake. Real simulations of seismic response for the plant structures and components enhance establishment of reasonable design margins and safety evaluation criteria in a situation beyond design-basis accidents. For piping systems, nonlinear seismic response analysis considering plastic deformation of pipe support structures can lead to a safety evaluation based on more rational input values.

This study discussed seismic response of a piping system and its appropriate analysis method when a plastically deformable pipe support structure was subjected to a much larger seismic load than the designed one. Seismic response analyses of the piping system including a plastically deformable pipe support structure were conducted for various input acceleration levels. The vibration characteristics, response acceleration, and moment of piping were compared in relation to the amount of plastic deformation of the pipe support structure. As a result of the comparisons, a support model with the elastic fully plastic property was proposed as a simple and proper method to calculate the seismic response of the piping system considering the plastic deformation of the pipe support structure.
Study on Equivalent Stress to Control Average Inelastic Behavior of Perforated Plates
Authors: Kultayev Yeldos , Kasahara Naoto
Published: November 2014

Next generation reactors which are subjected to elevated temperatures must be designed to account for inelastic deformation along with elastic one. In order to simplify design analysis of perforated portions, conventionally axisymmetric models with equivalent elastic materials are employed. To extend to inelastic analysis, a method of Effective Stress Ratio (ESR) has been studied in recent years. Previous studies have shown that perforated plates have their own ESR and it is a function of geometry and is independent from their materials.

In this study the only geometry dependence and physical meaning of ESR were clarified. ESR results were compared with Reference Stress Method (RSM) results for unit-ligaments with various ligament efficiencies. It was revealed that RSM results coincide with ESR. First meaning of ESR is stress ratio between solid plate and perforated plate at the same reference stresses. Second meaning of this ratio is how plasticity properties of equivalent solid plate have to be changed to give the same steady state deformation rate at the same mean boundary stress. Moreover, to clarify stress redistribution control mechanism at different ligament efficiencies, simple models were developed and an estimation method based on simple models was proposed for engineering use.
Finite Element Simulation of a Gust Response of an Ultralight 2-DOF Airfoil
Authors: Horáček Jaromír , Sváček Petr
Published: November 2014

Flexibly supported two-degrees of freedom (2-DOF) airfoil in two-dimensional (2D) incompressible viscous turbulent flow subjected to a gust (sudden change of flow conditions) is considered. The structure vibration is described by two nonlinear ordinary differential equations of motion for large vibration amplitudes. The flow is modeled by Reynolds averaged Navier-Stokes equations (RANS) and by k–ω turbulence model. The numerical simulation consists of the finite element (FE) solution of the RANS equations and the equations for the turbulent viscosity. This is coupled with the equations of motion for the airfoil by a strong coupling procedure. The time dependent computational domain and a moving grid are taken into account with the aid of the arbitrary Lagrangian-Eulerian formulation. In order to avoid spurious numerical oscillations, the SUPG and div-div stabilizations are applied. The solution of the ordinary differential equations is carried out by the Runge-Kutta method. The resulting nonlinear discrete algebraic systems are solved by the Oseen iterative process. The aeroelastic response to a sudden gust is numerically analyzed with the aid of the developed FE code. The gust responses exhibit similar oscillations as those found in literature.