bluuebunny/crossref_metadata_2025_split huggingface dataset:
Direct Observation of Elastic and Plastic Strain Fields During Ductile Tearing of a Ferritic Steel
Authors: Coules Harry E. , Horne Graeme C. M. , Peel Matthew J. , Oliver Sam J. , Van Gelderen Derreck G. A. , Connolley Thomas 
Published: December 2016

Residual and thermal stresses have a considerable effect on the process of brittle fracture. In addition to this, the effect of these stresses on elastic-plastic fracture is known to be significant. This is accounted for in structural integrity assessment methodologies such as R6 Rev 4 and BS 7910:2013 by introducing factors representing the interaction between primary and secondary stresses (those that do and do not contribute towards plastic collapse, respectively).
The initiation of ductile tearing in a ferritic pressure vessel steel was studied experimentally. Energy-dispersive X-ray diffraction was used to determine lattice strains in the vicinity of a crack tip in modified compact tension specimens at incremental loading steps until the initiation of ductile tearing. The X-ray diffraction measurements allowed the stress field to be evaluated with a high spatial resolution. At the same time, the pattern of total strain at the surface of the specimen was observed using digital image correlation. Prior to the experiment, two samples were subjected to localised out-of-plane compression ahead of the crack tip to introduce a residual stress field and hence significant crack loading in the absence of external load. Stress and strain field data for cracked specimens, with and without a pre-existing residual stress field, indicated significant differences in the development of plastic strain up to the point of tearing initiation. It is shown that this can only be explained when both residual stress and prior material hardening are taken into account.
Study on Dynamic Response by Alternating and Static Load
Authors: Otani Akihito , Kai Satoru 
Published: December 2016

An inertia force in a seismic response of structure excited by an earthquake generates the seismic force acting on the structure. The handling of seismic forces has been being discussed in terms of how the seismic force on a piping controls the deformation of the piping, load-controlled or displacement-controlled. A seismic design code for nuclear facilities applied in Japan qualifies this kind of seismic forces as primary stress components which shall be limited to prevent any plastic collapse, on the assumption that the seismic force mainly consists of load-controlled loads and the deformation due to earthquakes is caused by the loads. The authors studied about a condition of plastic collapse occurrence by the relationship between response acceleration and displacement of SDOF system. And it was represented in a previous paper that plastic collapse hardly occurred to soft structure due to an inertia force generated from response acceleration tended to oppose a response displacement.
Several elastic plastic response analyses of elastic-perfectly-plastic SDOF model are performed with applying dynamic load and both of dynamic load and static load. By the results of the analyses, three forces, which are inertia force, element force and external force, are investigated the relations against the deformation.
Structural Analysis Approach for Risk Assessment Under BDBE
Authors: Kasahara Naoto , Nakamura Izumi , Machida Hideo , Okamoto Koji , Sato Takuya 
Published: December 2016

Based on the lessons learned from the Fukushima nuclear power plant accident, it is recognized the importance of the risk assessment and mitigation for failure consequences to avoid catastrophic failure of pressure equipment during severe accidents (SA) and excessive earthquake.
The objectives of structural design (from the first layer to the third layer of the defense-in-depth) is strength confirmation under assumed loading conditions. On the other hand, ones of risk assessment and mitigation (the forth layer of the defense-in-depth) is prediction of realistic failure scenarios.
Through investigation of failure locations and modes of main components under both severe accident and excessive earthquake, different failure modes from DBE(Design Basis Events) were identified for BDBE(Beyond Design Basis Events). To clarify these modes, the failure mechanisms were studied with some strength experiments.
For most of failure modes, their dominant parameters are inelastic strain rather than stress. So that large scale inelastic analysis methods were studied and extended to very high temperature and large strain.
By using above results, this paper has proposed the new structural analysis approach for risk assessment under BDBE. This is the extension of “design by analysis” concept. However it is clearly different from design approach from next viewpoints.
(1) Additional failure modes to design condition
Such additional failure modes induced by excessive loadings are considered for as local failure, creep rupture, creep buckling, ratcheting collapse and so on.
(2) Identification of dominant failure modes
Design codes require conservative evaluation against all of assumed failure modes. On the other hand, risk assessment needs adequate failure scenarios, where failure locations, modes and their order are important. For that reason, dominant failure modes have to be identified. To identify dominant modes, failure mode map concept was proposed.
(3) Best estimation
To estimate realistic accident phenomena, the best estimation is required. Therefore, dominant strength parameters and criteria without safety margins should be adopted. Through strength mechanism investigations, plastic and creep strain are recognized as more dominant parameters than stress for many failure modes. So that realistic inelastic analyses are recommended for BDBE.
Development of Seismic Isolation Systems for Sodium-Cooled Fast Reactors in Japan
Authors: Kawasaki Nobuchika , Watakabe Tomoyoshi , Wakai Takashi , Yamamoto Tomohiko , Fukasawa Tsuyoshi , Okamura Shigeki 
Published: December 2016

Sodium-cooled Fast Reactors (SFRs) have components with thinner walls as compared with light water reactors, although Japan is an earthquake-prone country. Thus, seismic isolation systems have been conventionally employed in SFR system design to reduce seismic forces on the systems in Japan.
Implementation of seismic design in the reactor core and buckling design in the reactor vessel requires 8 Hz (or less) vertical frequency’s isolation system being applied. This paper introduces three isolation concepts to achieve the frequency.
The isolation systems, which enable vertical 8 Hz natural frequency, comprise thicker laminated rubber bearings (TRBs). By combining coned disk springs with TRBs, vertical natural frequency is in a range from roughly 3 Hz to 5 Hz. Combining pneumatic springs to RBs and adding the rocking suppression system, vertical natural frequency becomes under 1 Hz. All isolation systems need horizontal damping like oil dampers.
A vertical 8 Hz isolation system with TRBs and oil dampers is under development in Japan as a principal isolation concept. This system was selected because of its simple configuration and fewer issues to be resolved in the development. Since TRBs and oil dampers are basic isolation elements, they can be applied to other isolation systems.
The response acceleration of 5 Hz vertical isolation is 50% of that of 8 Hz based on the analytical survey. A series of static tests of coned disk springs was carried out to confirm design equations. Based on these knowledge, 5 Hz vertical isolation system with TRBs and the coned disk springs can be designed.
The response acceleration of 1 Hz vertical isolation is 10% of that of 8 Hz. A rocking suppression system was studied in the past, and the further simplification of this system is the largest challenge for this concept.
These three isolation concepts are isolation candidates for SFRs in Japan. To obtain enough seismic margins for each plant site, these isolation systems need to be developed.
Measurement of Flow-Induced Forces: Multiple Flexible Tubes in a Triangular-Pitch Bundle Subjected to Two-Phase Cross-Flow
Authors: Deri Enrico , Ries Olivier , Adobes André 
Published: December 2016

Flow-induced vibrations of Steam Generator 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 progressively updated in order to cover most of existing tube bundle configurations.
Within this framework, a new test rig was presented in a previous conference with the aim of assessing parallel triangular tube arrangement submitted to a two-phase cross-flow. This paper presents the fluid-induced forces measured on a set of flexible tubes placed in a triangular pitch bundle both in the lift and drag directions. Two-phase flow excitation spectra are presented as well.
Identification of the Gradient of Mechanical Properties in Electron Beam Welded Joints of Thick Al6061-T6 Plate
Authors: Rekik W. , Ancelet O. , Gardin C. 
Published: December 2016

In this paper, the mechanical behavior of the different metallurgical zones of the Electron Beam welded joint of thick Aluminum alloy 6061-T6 plates was identified by means of a single tensile test on round specimen oriented transversely to the fusion line.
Commonly, the analysis of tensile tests allows a global characterization of the weld joint behavior. However, in this work, specific post processing of results was developed in order to determine in addition to standard findings, the local behavior on each position of the weld joint. The identified behavior laws are then simplified using the Hollomon analytical model. Hence, an evolution of the Hollomon parameters (n, K) along the weld joint is proposed.
To validate the experimental methodology and the analytical approach, the experimental tensile test on crossed tensile specimen was numerically modeled. Experimental results and numerical simulations were in a good agreement which denotes of the reliability of the identified gradient model.
In a second step, for more accurate characterization of the electron beam welded joint, an optimized geometry of tensile specimen was numerically dimensioned and tested.
From these analyses, a relatively large heat affected zone with significant gradients of mechanical properties was highlighted. The fusion zone was qualified as the softest metallurgical zone but with a high strain hardening effect in contrary with the heat affected zone where the fracture occurs.
Numerical Welding Simulation of a Vessel Head Adapter: Influence of Modelling Assumptions
Authors: Gallee Sébastien , Robin Vincent , Gommez Florence , Courtin Stéphan , Brosse Alexandre , Lacroix Rémi , Leconte François 
Published: December 2016

In nuclear industry, most of heavy components and reactor coolant lines have a large thickness and their manufacturing processes require multi-pass welding. When low-alloy steel components are concerned, the assembly process is often performed in several stages, such as a cladding, a buttering and a Post Weld Heat Treatment (PWHT) before joining two materials without phase transformations. The distortions induced by the welding operation might be an issue and residual stresses could be significant and play a role on the weldability. For these reasons, AREVA has placed a lot of effort to improve the reliability of numerical simulation of its welding processes, in order to have a better understanding of the involved phenomena and also to predict the residual stress state through the structure [1], [2] and [3] because this numerical simulation can be used to select the manufacturing process in the early phase of welded component design.
The aim of the simulations presented in this paper is the investigation of the final residual state of a nozzle placed at the central position of the vessel head. The computations are performed according a robust methodology packaged in AREVA OSS tool [4] which is based on SYSWELD™ Finite Element solver [5]. Two welding configurations are investigated. The first one is a mock-up with an “open” narrow gap, the groove filling being performed by a manual welding process using electrode coatings. The second one is a mock-up with a “closed” narrow gap, the groove filling being performed by an automatic TIG process. After the comparison of these two configurations, a special investigation is performed on the “open” narrow gap mock-up. The influence of the vessel head buttering before the groove filling is investigated, as well as the efficiency of the PWHT performed after the buttering operation.
On the Use of Miniaturized CT Specimens for Fracture Toughness Characterization of RPV Materials
Authors: Chaouadi Rachid , van Walle Eric , Scibetta Marc , Gérard Robert 
Published: December 2016

The tendency to reduce specimen size for fracture toughness characterization of structural materials is gaining a spectacular interest in particular for irradiated materials. Indeed, the miniaturized compact tension (mini-CT) with a size of 10×10×4.2 mm is becoming very popular. With such a small volume, a large number of mini-CT specimens can be extracted from broken Charpy impact specimens and therefore makes this geometry very attractive and consequently several round robin exercises are organized to qualify this geometry. SCK•CEN has gained a lot of experience since the first usage of this geometry more than a decade ago. This geometry was qualified and tested in both unirradiated as well as irradiated condition.
This paper overviews the SCK•CEN experience using the mini-CT geometry for fracture toughness characterization. In particular, it discusses the reliability of this geometry in comparison to large specimens such as the precracked Charpy and compares the advantages and limitations of such a geometry to derive some recommendations.
Vessel Design for Unintended Detonation: A Comparison of Alternative Code Rules
Authors: Gross David J. , Ligon Thomas C. , Minichiello John C. 
Published: December 2016

The Hanford Tank Waste Treatment and Immobilization Plant (WTP) will process waste slurries that have the potential to generate flammable gases and will utilize a number of atmospheric vessels to store these slurries at various stages of the waste treatment process. Throughout the design process, provisions have been made to ensure that these flammable gasses are vented from these vessels and to eliminate potential sources of ignition. However, Bechtel National, Inc. (BNI) would like to be able to demonstrate that these vessels are capable of withstanding a limited number of unintended detonations.
It is well known that pressure vessels may be designed for internal detonations. However, these loadings tend to cause very brief transients of high stress that can make traditional stress-based design rules to be difficult to meet. In the past decade, a number of strain-based design methodologies have become available, including ASME Boiler and Pressure Vessel Code (BPVC), Section VIII, Division 2, Part 5; ASME Section VIII, Division 3; ASME Section VIII, Division 3 Code Case 2564; and API 579-1 / ASME FFS-1. Each of these sets of rules permits some degree of plasticity in vessel design, but there are key differences in the specific provisions.
In this paper, the use of these different sets of Code rules will be demonstrated in the context of the design of a WTP vessel for a single unintended detonation, and the advantages and disadvantages of these alternative design approaches will be discussed.
Effect of Piping Loads on Vessel Support and Foundation Design
Authors: Stefanovic Radoslav , Doctor Christopher , Miller George , Diaz-Barrie May , Sharif Alexander , Ranieri Peter , Pynten Kirsten 
Published: December 2016

It is a common challenge for pressure vessel and foundation engineers to determine the effects of piping loads on the foundation and vessel support design and to find out the appropriate design method to be used. Pressure Vessel Codes specify loadings to be considered in the vessel design but limited guidance is provided on the application of piping loads when designing vessel supports. Consideration of piping loads in the design of vessel supports and foundation is left to the engineer’s judgment.
Vessel supports are typically designed to withstand the operating weight of the vessel, seismic and wind loading. Pressure vessel literatures provide well-established methodologies in considering these loads in the design of vessel supports. Civil engineering literature, such as the American Society of Civil Engineers (ASCE) Wind Loads for Petrochemical and Other Industrial Facilities [11] or the ASCE Guidelines for Seismic Evaluation and Design of Petrochemical Facilities [17], provide well documented procedures and guidelines for evaluating wind and seismic loads. However, there is limited literature on how to account for external loads from attached piping.
Typical major project schedules have vessels and their supports/foundations designed well before the development of the piping design that provides calculated actual nozzle and piping loads on the vessel. This paper reviews the type of piping loads, how the piping loads are translated to the vessel support/foundation and provides a proposal for simplified approach analysis on how to apply these piping loads in the design of the vessel support/foundation. There might be cases where the piping loads will cancel out, but that may not always be the case. Ignoring and not considering nozzle loads in the support design/foundation may not be appropriate for all vessels.
The intent of this paper is to also make the Vessel Engineer aware of ways to reduce these loads and to encourage communication with Stress Engineers in regards to flexibilities and other factors used to calculate nozzle/piping loads. In most cases, the vessel shell and nozzles are considered as rigid anchors in the piping stress analysis. By using the proper flexibility at nozzle junctions and the global vessel flexibility, the effect of piping loads in the design of the vessel support can be reduced. There is little or no industry guideline on how to include loads due to the thermal expansion or contraction of piping. Since the thermal loads and calculation of flexibility are the least understood part of the analysis, this paper provides background including examples of how these loads and flexibilities can be calculated.
In short, the intent of the paper is to provide a better understanding of how piping loads are translated to the vessel support and to provide some design guidelines that are not readily available in current literature and are not clearly specified in the industry codes or standards.
The Conservatism of Leak Before Break Analysis in Terms of the Applied Moment at Cracked Section
Authors: Kim Yeji , Oh Young-Jin , Park Heung-Bae 
Published: December 2016

In leak before break (LBB) analysis, applied moment at the position of a postulated crack is a key parameter. The current procedures of LBB analysis use the value of design basis loads that are calculated with the assumption that the pipe does not contain a crack and follows the linear elastic behavior. Therefore, this can lead to conservative results of LBB evaluation compared with the case that considers the effect of plastic behavior of cracked pipe on the calculation of the applied moment at the cracked section [2].
This paper aims to quantitatively investigate the conservatism of the existing LBB analysis in terms of the applied moment at the cracked section. The calculation results using the current procedures with linear elastic pipe model without a crack were compared with the results from the cracked pipe analysis. To consider nonlinearity of crack behavior and pipe material, the time history analysis methods that were verified using the simulated seismic pipe system experiment in the IPIRG-2 program were employed.
The comparison results indicated that the applied moment at the cracked section decreases when the effect of crack and nonlinear behavior are considered in the analysis. Therefore, the current procedures of LBB analysis are significantly conservative compared with the elastic-plastic time history analysis. Base on this detailed analysis, the additional safety margin can be secured in the LBB analysis.
Three-Dimensional Analysis of Corrosion Surface on Outer Surface of Piping by Use of Fractal Concept
Authors: Yamagiwa Kenta 
Published: December 2016

In this study, the three-dimensional geometry of simulated corrosion surface was compared with that of actual corrosion surface by use of fractal concept that was useful to understand the feature of self-similar pattern. To discuss the difference, fractal dimension (Fd) and fractal boundary (λb) are used. The method to make the simulated surface was that the nitric acid was dropped on steel (JIS SB410) plate to make a dimple on it by corrosion. The actual corrosion surface was provided from the piping which used in the actual chemical plant. To calculate Fd and λb of these corrosion surfaces, three-dimensional geometry was measured by the 3D-geometry measurement system (Keyence VR-3000). The measured size was respectively about 90×60mm (4000×3000 pixels). Next, wavelet transform was applied to the three-dimensional geometry. Fd and λb were calculated from the wavelet coefficient instead of the power spectrum. The mother wavelet was the Gabor function that is the combination of sinusoidal wave and Gaussian function.
In the result, the difference of Fd between the simulated surface and the actual surface was obtained. The average Fd of the simulated surface was about 2.2. On the other hand, the average Fd of the actual surface was more than 2.6. It means the actual surface is more complex than the simulated surface. The λb of the actual surfaces was not obtained, because the linier relationship was satisfied in every frequency. However, the λb of the simulated surface was about 1cm. It was similar to the dimple’s diameter. Therefore, there is a difference between the simulated surface and the actual surface by applying the concept of fractal though they look similar by the human observation. The relationship between the burst pressure, Fd and λb will be discussed.