bluuebunny/crossref_metadata_2025 huggingface dataset:
Overview of EAF Screening Results on the 900 MWe NPP French Fleet
Authors: Métais Thomas , Robert Nicolas , Genette Pierre , Etchegaray Nicolas
Published: December 2016

In the wake of numerous experimental tests carried out in air and also in a PWR environment, both abroad and in France, an update of the current thermal fatigue codification is underway in France. Proposals are currently being integrated in the RCC-M code [1].

In parallel, it is necessary to evaluate the impact of codification evolution on the RCS components. In the USA, such evaluations have already been implemented for license renewal to operate power plants beyond their initial 40 years of operation. In order to reduce the scope of the calculations to perform, a preliminary screening was carried out on the various areas of the primary system components: this screening is detailed in an EPRI report [2]. The output of this screening process is a list of locations that are most prone to EAF degradation process and it is on these zones only that detailed EAF calculations are carried out.

In France, a similar approach was defined in the perspective of the fourth ten-year visit of the 900 MWe plants (VD4 900 MWe) so as to map out all the locations that are most impacted by EAF and hence concentrate the calculation effort on these specific areas for the VD4 900 MWe.

In that respect, a specific methodology to evaluate the factor to account for environmental effects or Fen [3] based on correlations [4] for hot and cold shocks was established. These correlations use data that is readily accessible in transient description documents and stress reports such as temperature change, heat transfer coefficients, ramp duration and geometry. The need for these correlations is specific to the French context due to a need for a preliminary and yet precise idea of the overall impact of the modifications brought to the RCC-M code in fatigue before the VD4 900 MWe.

This paper presents the results of the screening method that was applied to the whole RCS of the 900 MWe NPP fleet.
Mechanistic Studies on Environmentally-Assisted Fatigue Crack Growth in Light Water Reactor Environments
Authors: Panteli Alexandra , Platts Norman , Tice David R.
Published: December 2016

Fatigue crack growth of austenitic stainless steels can be enhanced significantly in high temperature light water reactor coolant environments and an ASME Code Case, N-809, has recently been developed to provide fatigue crack growth rate curves for these alloys in pressurized water reactor environments. However, under some conditions, the enhanced rates can decrease to rates close to those in air at long rise times, a process referred to as retardation which is not taken account of in the Code Case. An improved understanding of the mechanisms of both enhancement and retardation would be beneficial to determining whether advantage could be taken of these retarded rates in plant assessment. A number of studies have been undertaken to evaluate fatigue crack growth behavior in both air and water environments in order to provide mechanistic insight. Progress on this work will be described. The data from air and inert environments support the proposed mechanism of environmentally enhanced fatigue by environmental enhancement of planar slip, although it is not yet possible to differentiate between the impact of oxidation and corrosion hydrogen on the level of enhancement in aqueous environments. Testing in high temperature water environments suggests that both corrosive blunting and/or oxide-induced closure mechanisms may contribute to crack growth rate retardation under specific circumstances.
Elastic Allowable Stress Basis for Elevated Temperature Design in the Creep Regime
Authors: Nadarajah Chithranjan , Hantz Benjamin F. , Krishnamurthy Sujay
Published: December 2016

ASME Section VIII, Division II, Boiler and Pressure Vessel Code does not have any design by analysis procedures for designing pressure vessel components in the creep regime. This publication presents a methodology for evaluating and categorizing elastic stresses calculated from finite element stress analysis when designing in the creep regime. The proposed methodology is compared with multi axial creep results for various pressure vessel components and found to be in reasonable agreement.
Effect of Loading Waveform and Spectrum Loading on the Fatigue Crack Growth Rate in Simulated Light Water Reactor Environments
Authors: Platts Norman , Rigby Keith , Tice David R. , Swan David I.
Published: December 2016

High temperature water environments, typical of light water reactor primary coolant, are known to lead to significant environmental enhancement of fatigue crack growth of austenitic stainless steels. For PWR environments. these effects have recently been codified in ASME Code Case N-809. However, just as for the detrimental effect of these environments on fatigue endurance, plant experience indicates that crack growth rates must be significantly lower than predictions based on laboratory data using simple sawtooth waveforms. In order to explain this discrepancy, a significant amount of research has been conducted to quantify factors leading to crack growth rate retardation with sulfur content having been identified as significant in promoting crack growth rate retardation. However, the inherent conservatisms in current analysis techniques may be just as significant in generating the perceived over-conservatism of environmental fatigue crack growth laws such as Code Case N-809.

The current work looks at the impact of waveform shape and spectrum loading on the level of environmental enhancement for a given stress intensity factor range and total rise time by considering simplified transients and loading spectra. The observations suggest that simplified definitions of total rise time used in fatigue assessments can lead to large over-estimation of actual fatigue damage. These data form the basis of an analytical methodology being developed by RollsRoyce (presented in a separate paper at this conference) aimed at partitioning damage across the loading cycle in order to remove over-conservatisms in current analytical methodologies.
Effect of Bend Angle on Gross Plastic Deformation of Pipe Bends for Out-of-Plane Bending: A Study Using Plastic Work Curvature Method
Authors: Bhattacharya Anindya , Bapat Sachin , Patel Hardik , Patel Shailan , Cross Michael P.
Published: December 2016

Bends are an integral part of a piping system. Because of the ability to ovalize and warp they offer more flexibility when compared to straight pipes. Piping Code ASME B31.3 [1] provides flexibility factors and stress intensification factors for pipe bends. Like any other piping component, one of the failure mechanisms of a pipe bend is gross plastic deformation. In this paper, plastic collapse load of pipe bends have been analyzed for various bend parameters (bend parameter = tRbrm2) under internal pressure and out-of-plane bending moment for various bend angles using both small and large deformation theories. FE code ABAQUS version 6.9EF-1 has been used for the analyses. The goal of the paper is to develop an expression for plastic collapse moment for a bend using plastic work curvature method when the bend is subjected to out-of-plane bending moment and internal pressure as a function of bend angle and bend parameter.
A Simple Approach for Including Weld Residual Stresses in the Calculation of Pipe Circumferential Through-Wall Crack Opening Displacements
Authors: Olson Richard
Published: December 2016

Current methodologies for predicting the crack opening displacement (COD) of circumferentially through-wall cracked pipe do not include the effect of weld residual stresses (WRS). Even the most advanced COD prediction methodology only includes the effect of applied axial force, bending moment, and crack face pressure. For some years, it has been known that weld residual stresses do alter the COD, but there has been no convenient way to include them in a COD prediction without doing case-specific finite element analyses.

This paper documents a generalized solution for including WRS effects on COD. The model uses a closed-form analytic solution to approximate the crack face rotations that the WRS would induce which, subsequently, can be added to the typical axial force-bending-crack face pressure COD solution. The methodology is described and the basic equations for the solution are presented. Following this, application to cases to evaluate the efficacy of the approach are presented which show a mixture of results ranging from amazingly good to “of questionable value” with respect to the FEA results.
Effect of Loading Modes on the Limit Behaviors for Pipe Bends Under Combined Loads
Authors: Li Jian , Zhou Changyu , He Xiaohua
Published: December 2016

Pipe bends are widely used in industrial piping and pipelines. Because of their flexibility properties, they can accommodate thermal expansions and absorb other externally induced loads. Under severe loading conditions, bends exhibit significant cross-section ovalization, associated with strains well beyond the elastic limit and fail because of excessive cross-section ovalization. The past references provide several studies on the ovalization induced loading capacity change. The main aim of the study is to establish the effects of load history on the calculated failure load, when a bend is subjected to a combination loading of in-plane bending, torsion and internal pressure. The results of the investigation show that geometric nonlinearity is a significant consideration when calculating plastic failure loads of pipe bends subject to combined loads. The limit load is path independent of the loading sequence in the cases of bending and torsion combinations. In the cases of pressure and moment combinations the proportional and pressure-moment load cases exhibit significant geometric strengthening, whereas the moment-pressure load case exhibits a little. The results according to the ASME Boiler and Pressure Vessel Code may show overall conservative in all loading conditions.
Investigation on Method of Elasto-Plastic Analysis for Piping System (Benchmark Analysis)
Authors: Arai Masashi , Kojima Nobuyuki , Kabaya Takuro , Hirouchi Satoru , Bando Masatsugu
Published: December 2016

This report proposes an elasto-plastic analysis method to be used for practical aseismic designing of nuclear piping systems. JSME (the Japan Society of Mechanical Engineers) initiated a task to establish an elasto-plastic analysis method for nuclear piping systems. During this task, benchmark analysis was conducted in order to examine the elastic-plasticity analytical method, in which our company decided to participate. Our policy for evaluation was that the material characteristics to be used in benchmark analysis were based on the standards for nuclear designs in Japan. As a consequence, we prepared a method to accurately simulate the vibration test on piping systems. The recommended elasto-plastic analysis method is thus specified as follows:

1) The elasto-plastic analysis method comprised of dynamic analysis on piping system modeled using beam elements and static analysis of the deforming elbow which was modeled using shell elements.

2) Bi-linear was applied as the elasto-plastic characteristics. The yield point was the standardized yield point times 1.2, and the second gradient was 1/100 the Young’s modulus. Kinematic hardening law was used as the hardening law.

3) Rain flow method and fatigue curve of an existing research were used to evaluate the fatigue life for the strain range obtained by elasto-plastic analysis.
Design of Cylindrical Steel Storage Tanks: A Linear Elastic Analysis Approach
Authors: Azzuni Eyas , Guzey Sukru
Published: December 2016

A cylindrical steel storage tank is a cylindrical shell subjected to internal hydrostatic pressure due to the stored liquid product. The hydrostatic pressure causes the shell to experience circumferential stress. This circumferential stress can lead to the yielding of the shell if its thickness is not designed properly. The design of step-walled steel storage tanks requires the calculation of the required thickness of each shell course.

A conservative way of calculating each course’s thickness is using the one-foot method (1FM). This method calculates the required thickness to withstand the hydrostatic pressure one foot above the bottom edge of the shell course under consideration.

Another method, which is more refined than the 1FM, is the variable-design-point method (VDM), which finds the point in the course where the maximum circumferential stress is. VDM calculates the required shell thickness to withstand that maximum circumferential stress.

However, VDM does not capture the circumferential stress resulting from the bottom edge yielding moment accurately for some thank geometries.

A new linear analysis approach using thin-shell theory is presented in this paper. The approach captures the plastic yielding moment of the bottom edge accurately, and may produce more economical and safe designs than 1FM and VDM.
Numerical Analysis on Cavitation Erosion of a High Pressure Differential Control Valve
Authors: Zheng Zhijian , Ou Guofu , Ye Haojie , Jin Haozhe
Published: December 2016

The numerical simulation on the cavitation erosion of a high pressure differential control valve is conducted. The characteristic of cavitation flow is obtained by using full cavitation model and RNG k-ε turbulence model with actual operational conditions and fluid physical parameters. Results showed that: the flow velocity increases rapidly as the fluid passes through the gap between the valve spool and seat. Simultaneously the local static pressure decreases below the saturation pressure of the fluid, then the cavitation is formed. For the convergent - expansion structure, the flow separation occurs due to the pressure recovery, which leads to the formation of recirculation zone, where the cavitation cloud appears. The increases of fluid temperature and inlet pressure or the decreases of valve spool angle and valve opening result in the enlargement of cavitation area and enhancement of cavitation intensity. The numerical simulation results correlate well with actual failure morphologies, which proves that the method can be successfully applied in the cavitation prediction of a high pressure differential control valve.
Applicability of the Multilayer Kinematic Hardening Model to Predict Inelastic Behavior of Piping Systems Under Excessive Seismic Loading
Authors: Iwata Koji , Jin Chuanrong , Karakida Yasuhisa , Kasahara Naoto
Published: December 2016

For assessing possible failure of piping structures under excessive seismic loading, dynamic structural analysis methods employing advanced constitutive models need to be established. The multilayer kinematic hardening model for cyclic plasticity, which is applicable up to large strain, was proposed in the previous paper by the authors for carbon steel STS410 (JIS, Japanese Industrial Standard) to represent precisely nonlinear stress-strain relation as well as cyclic hardening, and was validated through its application to quasi-static cyclic bending tests of an elbow. In this paper, the applicability of the model to dynamic analysis of piping systems under earthquake loading is evaluated. An existing simulated earthquake excitation test of a piping system made of carbon steel STPT370 (JIS) is dealt with for validation of the finite element nonlinear dynamic analysis method using the presented model. To emphasize the advantage of this model, analyses using the conventional linear kinematic hardening model are also conducted. The results by the latter model are shown to be highly variable depending on the method of bilinear approximation of stress-strain curves. It is shown that the multilayer kinematic hardening model can predict well inelastic strains in piping systems under excessive earthquakes, which is important for the failure assessment.
Structural Integrity Assessment of RPV Under Severe Accident Conditions With Creep Constants Correlation
Authors: Kim Tae Hyun , Chang Yoon-Suk , Lee Bong-Sang
Published: December 2016

Creep behavior of nuclear materials is susceptible factor for structural integrity assessment. Particularly, RPV (Reactor Pressure Vessel) under severe accident with a core melting conditions may go through its wall penetration caused by direct contact with corium as well as additional unexpected failure by creep damage. Even though various experiments and analyses were conducted to resolve this special integrity issue, there are still many uncertainties which come from high temperature range, availabilities in only isothermal analysis and so on. In the present study, the state-of-the-art thermal, mechanical and creep properties of a representative RPV material, SA508 Gr. 3 C1. 1 were examined, with which correlation of creep in various loading conditions were determined. Subsequently, a user subroutine which defines the condition-dependent creep constitutive equation was developed and applied to RPV simulation, and relevant Larson-Miller Parameter was also newly fitted. Systematic numerical analyses were conducted by taking into account a typical accident scenario of external reactor vessel cooling. Finally, consequences of the creep effects such as the deformation shape, total strain and rupture time of vessel wall were compared with those of the existing study to enhance the accuracy of numerical analysis.
A Case Study Evaluating the Effects of High Cycle Thermal Loading Within a Pressurised Water Reactor Mixing Tee Using Conjugate CFD/FE Methods
Authors: Wilson James , Currie Chris , Jones Michael , Davenport Lewis
Published: December 2016

In nuclear plant piping systems thermal fatigue damage can arise at locations where there is turbulent mixing of different temperature flows. The severity of this phenomenon is difficult to assess via plant instrumentation due to the high frequencies involved. NESC report EUR 22763 EN, published in 2007, defines the “Level 1” screening criterion for the design of austenitic stainless steel mixing tees, based on recorded incidents of fatigue cracking in civil power plants. The experimental data indicates that damage due to High Cycle Thermal Loading (HCTL) is unlikely to occur if the temperature difference between the hot and cold inlet streams is less than 80°C.

The “Level 2” approach outlined by NESC provides a methodology for the calculation of a fatigue usage factor based on the assumption of a sinusoidal thermal loading at the most damaging frequency for a given ΔT. Advice is given on selection of heat transfer coefficient, fatigue curves, fatigue strength reduction factors and plasticity correction factors. Experience shows that these methods can be overly pessimistic when compared with plant operational experience.

This paper describes a case study using the more detailed NESC “Level 3” evaluation of HCTL at a Pressurised Water Reactor (PWR) mixing tee using a coupled Computational Fluid Dynamics and Finite Element Analysis (CFD/FE) analysis to evaluate the complete load spectra together with the ASME 2010 fatigue S-N curve. The CFD model used is “conjugate”, ie it calculates temperatures in both the fluid and the metal. Large Eddy Simulation (LES) was used to investigate HCTL effects using an appropriate mesh size to accurately predict the rapid fluctuations in metal temperature local to the surface. Metal temperature predictions using conjugate CFD analyses provided the input to finite element analysis, utilising rain-flow techniques, in order to derive fatigue usage factors in the areas of interest.

This study found that the severity of HCTL is influenced by various factors such as flow conditions, local geometry including bore match features, integral conical reducers that allow progressive change in pipe radius as well as branch pipe swirl penetration.
Primitive Model for the Random Excitation of a Tube Under Two-Phase Cross Flow
Authors: Borsoi Laurent , Piteau Philippe , Delaune Xavier , Antunes Jose
Published: December 2016

Flow-induced vibration of heat-exchangers tubes is particularly studied in the nuclear industry for safety and cost reasons. It implies to have, among others, relevant characterizations of the random buffeting forces the cross-flow applies to the tube bundle. Work is still needed in this domain, particularly for two-phase flow, to improve the available data as the ones for PWR steam generator, currently very envelope.

In parallel to get new experimental data, using “real” or substitutional mixtures (e.g. air-water instead of steam-water for PWR), it is essential to understand the basic excitation mechanisms which induce the vibrations under two-phase flow, as e.g. the influence of flow regimes. In this general framework, what can be learnt from deliberately simple models may be a contributive help.

As a first attempt on this issue, the paper deals with the elementary case of a single rigid tube under air-water cross flow. This case is part of experiments carried out at CEA-Saclay with bundles where both tube support reactions and flow characteristics are measured, with respectively piezo-electrical sensors and bi-optical probes (BOP). The information provided by the BOP (mean interface velocity, statistical distribution, etc.) feeds a primitive model of water “droplet” impulses on the tube, based on a lot of crude assumptions about impact velocity, momentum conservation, impulse shape, statistical independence, etc., and which uses analytical results of random processes constructed from the superposition of random pulses.

The “equivalent” excitation force, obtained in terms of dimensional PSD, is compared to the one measured in the drag and lift direction with an acceptable agreement, at least in order of magnitude.

Comments and lessons are drawn from this first attempt, and some paths are advanced to improve this kind of primitive models, especially for treating rigid square bundles under air-water cross flow.
The Digital Image Correlation Technique Applied to Single Specimen Testing Methodology
Authors: Le Delliou Patrick , Sonnefraud Christophe , Vincent Willy
Published: December 2016

The ASTM E 1820 standard provides procedures and guidelines for the determination of fracture toughness of metallic materials, characterized by the J-integral. The recommended specimens are single-edge bend, SEN(B), compact, C(T), or disk-shaped, DC(T). Two alternative procedures for measuring crack extension are provided in the standard, the basic procedure and the resistance curve procedure. The basic procedure involves physical marking of the crack advance and multiple specimens are used to develop an R-curve (or J-Δa curve). The resistance curve procedure is an elastic-compliance method where multiple points are determined from a single specimen. Other procedures for measuring crack extension are allowed, typically the electric potential drop method.

To use the elastic-compliance method, the displacement transducer (clip-gage) must have a very high resolution and stability, and a very low noise. For temperature ranging from −200°C to 100°C, a clip-gage with conventional strain gages (i.e. plastic resistance strain gages) gives generally good results. However, at higher temperatures, one must use either high temperature inductive or capacitive clip-gages, or conventional clip-gages placed outside of the oven and connected to the specimen by ceramic or quartz rods. In both cases, the results are not very satisfactory. So, for the measurement of the load-line displacement, a new method using the digital image correlation technique (DIC) was developed at EDF R&D. The CT specimens have integral-machined knife edges and a thermally resistant paint is sputtered on these edges, in order to have irregular patterns. During the test, a high resolution camera placed outside of the oven takes pictures of the knife edges at regular time intervals. These pictures are real time processed to calculate the relative displacements of the dots, and deduce the load-line displacement. The paper presents the technique and the results obtained on various materials.
Comparison of Stress Intensity Factors of Part Surface Flaws at Stress Concentration in Plate and Pipe Between FE Analysis and Weight Function Approach
Authors: Zhu Lei , Tao Joy (Xiaoya)
Published: December 2016

Stress intensity factor (SIF) is one of the key parameters in structural integrity assessment. Weight function method has been used in flaw acceptance assessment codes and standards, such as R6 and BS7910, to calculate SIF of a semi-elliptical (part) surface flaw. In this method, stress distribution across the section thickness is described by a polynomial equation, and SIF is estimated using geometry functions fi and stress components σi. The SIF solutions are available for both the deepest and the surface points of part surface flaw in R6 and BS7910. However, a case study from this work shows that the SIF estimation using the current methods are not always conservative when a flaw is at stress concentration, such as weld toe. This results in an optimistic limiting defect sizes and jeopardizes the safety. To account for the effect of stress concentration on SIF, one solution is to use SIF magnification factor and stress concentration factor, but this approach could be overly conservative. Although the original research used power law stress distribution in calculation of SIF, it is not clear whether the developed geometry function factors are suitable for a flaw at steep gradient stress concentration zone. The same question is for the similar SIF solutions of French RCC-MR code, as the model used to derive the SIF does not include stress concentration.

This paper briefly reviews the weight function SIF solutions and compares them with the 3D FEA results of surface flaws in plate and pipe with various dimensions and flaw sizes. The guidance is provided on how to use weight function SIF solutions for surface flaws at stress concentration region for structural integrity analysis.
Toward an Improved Understanding of Effect of Linear Heat Input on Heat-Affected Zone Tempering in Temper Bead Welding
Authors: Zhang Kaiwen , Enneking Jeffrey A. , Grimmett Bennett B. , Zhang Wei
Published: December 2016

In temper bead welding, the heat input from welding is purposefully utilized to temper the hard microstructure for improving toughness. An optimal temper bead welding requires careful control of heat input and bead placement. In this study, the effect of linear heat input on heat-affected zone (HAZ) tempering was studied by a combination of experimental testing and numerical modeling. Temper bead welding experiments were performed on SA-533 steel using three different heat inputs while keeping the power ratio constant. The extent of tempering in the HAZ was quantified using micro-hardness mapping. A 2-D weld heat transfer model, using the double-ellipsoidal heat flux equation, was developed to calculate the temperature evolution. The peak temperatures experienced in the substrate’s HAZ was correlated to the hardness distribution. The results indicate that the linear heat input can have a significant influence on the extent of tempering in temper bead welding.
Modelling of a Stud Arc Welding Joint for Temperature Field, Microstructure Evolution and Residual Stress
Authors: Soltanzadeh Hadi , Hildebrand Jörg , Kraus Matthias , Asadi Mahyar
Published: December 2016

This paper presents a modelling study and analysis performed on a stud welding including thermal, microstructure and stress calculation. The main concern of this work is toward controlling undesirable residual stresses and the evolution of material properties, as well as the chance of estimating cracks especially with regard to future services of structures. Historically, prediction of welding features is being pursued by welding engineers to enable them for optimal design and mitigation of adverse effects. Stud welding is among the welding processes that are not often addressed by means of modelling and associated activities to develop a comprehensive valid prediction. The aim of this research is to present a modelling practice for a stud weld joint to capture the transient thermal profile, consequent evolution of microstructural phase fractions, and stress calculation using a thermomechanical model based on FE methods (SYSWELD package). The material properties are fed into the model as temperature dependent. The microstructure model is based on t8/5 cooling trajectory on CCT diagram that captures transformation from Austenite phase, and the residual stress calculation is compared to experimental measurement for the sake of validation.
Probabilistic Seismic Response of Coupled Tank-Piping Systems
Authors: Abbiati Giuseppe , Bursi Oreste S. , Caracoglia Luca , Di Filippo Rocco , La Salandra Vincenzo
Published: December 2016

Dynamic analysis is an integral part of seismic risk assessment of industrial plants. Such analysis often neglects proper coupling between structures of coupled systems, which introduces uncertainty into the system and may lead to erroneous results, e.g., incorrect fragility curves, in comparison with the actual behavior of the analyzed structure. Hence, it is important to study the effect of uncertainties on the dynamic characteristics of a system, when coupling effects are both neglected and included.

Along this line, this paper intends to define and compare the fragility curves of both an isolated (decoupled) and a coupled tank-piping system subjected to seismic loading. In particular, for the decoupled case, we estimated the probability of exceedance of main engineering demand parameters within the Performance-Based Earthquake Engineering (PBEE) framework. Moreover, for the coupled case, to take into account the presence of the tank as boundary condition for the piping system, two sources of uncertainty were considered: i) the tank aspect ratio; ii) the piping-to-tank attachment height ratio. In addition, to model the tank slippage, both a Filtered White Noise (FWN) characterized by a Kanai-Tajimi spectrum and the non-stationarity of the seismic input were taken into account by means of the stochastic linearization. All these elements allow for the estimation of fragility curves for different limit states in the coupled case.
Application of Numerical Modeling for Predicting the Fatigue Crack Growth of an Elliptical Crack in Kelly Valves
Authors: Ahmadimoghaddamseighalani Hamidreza , Mertiny Pierre
Published: December 2016

Kelly valves, also known as full opening safety valves, are widely used in the oil and gas industry for the purpose of blowout prevention. Crack propagation in the stem hole feature of Kelly valves is of concern during service in drilling operations as fatigue may lead to catastrophic failure. A computational tool to predict the fatigue life of these valves when a crack is present was therefore created. The present paper describes the numerical modeling approach in which an elliptical crack in the stem hole feature was introduced. To predict the fatigue life of the valve based on the J-integral method, ANSYS Workbench was used for a FEA analysis in conjunction with Microsoft EXCEL and Iron Python programming.
Bifurcation Analysis and the Role of Normal Form Symmetries on the Harmonic Forced Inline Oscillation of the Cylinder Wake
Authors: Nabatian N. , Mureithi N. W.
Published: December 2016

Vortex shedding over a cylinder is strongly affected by the cylinder oscillation. The dynamics of the cylinder wake subjected to harmonic forced excitation in the inline direction at Re = 200 is investigated in this work. Two dominant modes of the transverse velocity field are considered to model and predict the nonlinear interaction of 2D vortex shedding. The normal form symmetries have the main role in the pattern formation. The interaction of two steady modes in the presence of O(2) × S1 symmetry is described by equivariant theory. Considering the symmetries, the amplitude equations are developed with the frequency saturation information included by the addition of complex coefficients. The reduced model is expanded up to 7th order, in order to include the spatio-temporal effects. The coefficients of the model are obtained from 2D simulations of the cylinder wake flow.

The physical significance of the inline amplitude oscillation on the wake dynamics is captured by the variation of the two linear coefficients of the low order model. Similarly to the numerical results, as the amplitude of oscillation increases, two limit cycles undergo the symmetry-breaking bifurcation leading to a quasi-periodic state. The existence of the second frequency in addition to the natural shedding frequency is manifested as the small amplitude oscillation in the quasi-periodic state. For a forcing amplitude A/D = 0.5, the quasi-periodic state undergoes a torus doubling bifurcation. The dominant frequency of the bifurcated S mode matches the lift coefficient shedding frequency at A/D = 0.5 obtained from the numerical computation. The lift coefficient signal is not absolutely periodic due to the presence of the other peaks in addition to the dominant one at St = 0.1 representing the quasi-periodic flow pattern. The modulated travelling waves bifurcated from the low order model have mode S as the basic v-velocity mode which verifies the symmetric torus-doubled transverse velocity pattern observed in CFD simulation. Thus the proposed low order model can predict, with reasonable accuracy, the bifurcation sequence of the forced cylinder wake dynamic transitions observed in the numerical computation results.
Hydrogen Induced Intergranular Failure in Armco Iron Under Fatigue Crack Propagation
Authors: Bilotta Giovambattista , Arzaghi Mandana , Hénaff Gilbert , Benoit Guillaume , Halm Damien
Published: December 2016

Hydrogen generally results in a degradation of fatigue crack growth resistance in metals depending on the nature of the hydrogen interaction with crystalline defects developed during a cyclic loading. In this paper we present the first results regarding the characterization of the microstructure and the mechanical properties of Armco Iron with a ferritic microstructure, and the investigation of embrittlement under gaseous hydrogen environment. For this purpose, fatigue crack propagation tests were performed on CT40 specimens under high pressure gaseous hydrogen using Hycomat test bench, at the Pprime Institute in Poitiers.

The fatigue crack growth rate data obtained so far at the 35 MPa of hydrogen pressure and at loading frequency of 20 Hz indicate a sharp increase in crack growth rates in a narrow range of stress intensity factor amplitudes. Also, it was observed that by decreasing the loading frequency to 2 or 0.2 Hz at the above mentioned hydrogen pressure no significant change in this transition regime happens. Scanning electron microscope observations of the fracture surfaces are used to support the explanations proposed for the hydrogen inducted intergranular failure in this material.
Surrogate Model Development and Validation for Reliability Analysis of Reactor Pressure Vessels
Authors: Hoffman William M. , Riley Matthew E. , Spencer Benjamin W.
Published: December 2016

In nuclear light water reactors, the reactor core is contained within a thick walled steel reactor pressure vessel (RPV). Over time, material embrittlement caused by exposure to neutron flux makes the RPV increasingly susceptible to fracture under transient conditions. Because of parameter uncertainties, probabilistic methods are widely used in assessing RPV integrity.

For efficient probabilistic analysis, techniques to rapidly evaluate the stress intensity factor for given flaw geometry and stress conditions are essential. The stress intensity factor influence coefficient (SIFIC) technique is widely used for this purpose, but is limited to axis-aligned flaw geometries. To consider a wider range of flaw geometries, surrogate models to compute stress intensity factors are explored.

Four surrogate modeling techniques are applied here to compute SIFICs from a set of training data, including two different response surface polynomials, a model utilizing ordinary kriging and another using interpolation. Errors in the SIFICs are assessed for all of these techniques. These techniques are benchmarked against a benchmark solution by computing the time history of the stress intensity factor for an axis-aligned, semi-elliptical surface breaking flaw in an RPV subjected to a transient loading history. All of these techniques compare well with the benchmark solution.
Time to Initiation of Tertiary Creep Property of Grade 91 Steels
Authors: Kimura Kazuhiro , Sawada Kota
Published: December 2016

Creep deformation property of Grade 91 steels was analyzed on more than 370 creep curves over a wide range of time to rupture from about 10 hours to beyond 100,000 hours, in order to evaluate time to 1% total strain, time to minimum creep rate and time to initiation of tertiary creep. Time to initiation of tertiary creep was assessed as a 0.2% offset with a slope of minimum creep rate. It is difficult to determine time to minimum creep rate precisely, which is a basis of 0.2% offset, however, it has been confirmed that time to initiation of tertiary creep is not sensitive to the time when the creep rate indicates minimum value. Life ratio of 1% total strain time against creep rupture time increases up to about 60% with increase of temperature and decrease of stress. Life ratio of time to initiation of tertiary creep also tends to increase with decrease in stress. However, change of it is in a range of 50 to 60% of creep rupture life over a wide range of creep rupture life from 10 hours to 100,000 hours, and it is not sensitive to creep test temperature. Over a range of temperatures from 500 to 600°C and up to about 200,000 hours, a temperature and time-dependent stress intensity limit, St is controlled by 67% of minimum stress to rupture. However, a difference between 67% of minimum stress to rupture and 80% of minimum stress to initiation of tertiary creep decreases with increases in temperature and time, and both values approach each other in the long-term beyond about 100,000 hours at 600°C. In the long-term beyond about 10,000 hours at 650°C, St is controlled by 80% of minimum stress to initiation of tertiary. The stable life fraction of time to initiation of tertiary creep establish a reliability of a temperature and time-dependent stress intensity limit value.
Moly Disulfide in Bolting Applications
Authors: Oldiges Donald , Hamilton Scott
Published: December 2016

Molybdenum disulfide (MoS2) is a popular lubricant, however a study completed in the early 1990’s stated that this type of lubricant can lead to stress corrosion cracking (SSCC) of the bolting materials. However, over the past 20 years, many bolting applications using molybdenum disulfide based compounds have been found to provide better galling resistance to the bolt assembly than many other components. It has also been shown to have a few other less desirable traits such as potential for corrosion in specific environments. Therefore, for successful bolting applications one must consider all the pros and cons of the anti-seize compound they select. One of the negative properties of molybdenum compounds is their link to SSCC on some alloys in specific environmental conditions. This paper focuses on corrosion potential.
Evaluation of Stress in Vibrating Cylindrical Shells due to Acoustic Loading Based on Theory of Shells
Authors: Kataoka Shunji , Hida Takahiro
Published: December 2016

Acoustically induced vibration (AIV) is recognized as a vibration of piping systems caused by the acoustic loading at the downstream of the pressure reducing devices. For decades several industrial practices which are derived from past experiences, have been applied for the design of piping system, however it is known that the practices includes uneven design margins. Due to the increase of the large capacity reducing devices, the demands of the development of reasonable screening and design method for AIV are increasing. A detailed assessment of fatigue life using finite element analysis has become popular and clarified the effect of acoustic load on several specific components; however, there are no clear way to explain the susceptibility against AIV depending on its diameter and thickness. Therefore the discussions based on engineering principles are required. In this paper, the vibration of cylindrical shells due to acoustic loading was discussed based on the theory of cylindrical shells. Results of several numerical studies based on the theoretical formulas were presented on the natural frequency and modal stress of vibrating shells on various geometries. Thus, the key factors to affect the vibrating shell stresses were clarified and some simplified formula to evaluate the vibrating shell stress was proposed.
Development on Rubber Bearings for Sodium-Cooled Fast Reactor: Part 3 — Ultimate Properties of a Half Scale Thick Rubber Bearings Based on Breaking Test
Authors: Fukasawa Tsuyoshi , Okamura Shigeki , Yamamoto Tomohiko , Kawasaki Nobuchika , Hirotani Tsutomu , Moriizumi Eriko , Sakurai Yu , Masaki Nobuo
Published: December 2016

This paper describes the results of static loading tests using a half-scale thick rubber bearing to investigate ultimate properties application for a Sodium-cooled-Fast-Reactor (SFR). The thick rubber bearing, which has a rubber layer roughly three times thicker in comparison with conventional rubber bearings, has been developed by the authors to ensure seismic safety margins for components installed in the reactor building, and to reduce seismic response in the vertical direction as well as horizontal direction. The thick rubber bearings, 1600 mm in diameter at full scale, have been designed to provide a rated load of about 10000 kN with a horizontal natural period of 3.4 s and a vertical natural period of about 0.133 s. The fundamental restoring-force characteristics of the thick rubber bearings has been already cleared through the static loading tests using a half-scale thick rubber bearing, 800 mm in diameter. However, variations of the restoring force characteristics and ultimate properties have not been obtained yet. These validations are essential from the point of view of Probabilistic Risk Assessment (PRA) for a base isolated nuclear plant as well as to verify the structural integrity of the thick rubber bearing. The purpose of this paper is to indicate the variation of the stiffness and damping ratio concerning restoring force characteristics and the breaking strain or stress as ultimate properties through static loading tests using the half-scale thick rubber bearings.
Findings From the Benchmark Analyses on an Elbow In-Plane Bending Test and a Piping System Test
Authors: Nakamura Izumi , Otani Akihito , Shibutani Tadahiro , Morishita Masaki , Shiratori Masaki
Published: December 2016

For introducing the elastic-plastic behavior effect in the seismic safety estimation of nuclear piping systems, benchmark analyses on a static in-plane bending test on an elbow (the pipe element test) and a piping system test under one-directional excitation (the piping system test) were conducted. As for the benchmark analyses on the pipe element test, 14 groups participated in the benchmark analysis. The variation of the elastic-plastic analyses and the factors which affect the analytical results are examined by comparing the analytical results with the experimental results. From the examination of analytical results, it is shown that the decision of the yield stress for the analysis rather than the secondary gradient affects a lot on the load deflection curve or the strain behavior, when the stress-strain relationship is simulated by bi-linear approximation. The strain ranges are well simulated by the analyses, though the residual strains scatter a lot. The failure mode in the experiment was the fatigue failure at the flank of the elbow, and it was well predicted by the participants’ analyses. As for the benchmark analyses on the piping system test, ten groups participated in the benchmark analysis. The eigenvalue analyses are well estimated by the all participants, but the dynamic response and strain behavior of pipes under random input waves vary widely. The findings from the benchmark analyses would be reflected to the inelastic analysis guideline for the seismic safety estimation of nuclear piping systems under beyond design seismic input.
Fatigue Limit Improvement by Needle-Peening for Stainless Steel Welded Joint Containing a Crack-Like Defect
Authors: Fueki Ryutaro , Takahashi Koji
Published: December 2016

The effects of needle-peening on the bending fatigue limit of an austenitic stainless steel JIS-SUS316 welded joint containing an artificial semi-circular slit on the weld toe were investigated. Peening was applied to specimens with a semi-circular slit at depths of a = 1.0 mm and 1.5 mm. Then, plane bending fatigue tests were carried out at a stress ratio of R = 0. The fatigue limits of welded specimens containing a semi-circular slit were increased for the peened specimens. Peened specimens with slit sizes of a = 1.0 mm had high fatigue limits that were nearly equal to those of non-slit, peened specimens. We observed that a semicircular slit with a depth of less than a = 1.0 mm could be rendered harmless by peening. Additionally, the values of fatigue limit and the maximum depth of a semi-circular slit that can be rendered harmless by peening were predicted based on fracture mechanics, where we assume that a semi-circular slit is equivalent to a semi-circular crack. The prediction results were consistent with experimental results.
Development and Standardization of Small Punch Testing Techniques in China
Authors: Guan Kaishu , Xu Limeng , Wen Cheng , Zhong Jiru
Published: December 2016

In the recent years, small punch testing (SPT) techniques has made great progress in China. The SPT was studied to estimate the tensile properties, the fracture toughness and ductile-to brittle transition temperature, and the creep behavior. In 2012, a standard of small punch testing was issued in China and the application of SPT in power generation and petrochemical industry has become a prime candidate. The present paper concentrates on progress of technique and standardization and industrial acceptance in assessing the structure integrity in China. China has carried out close cooperation with Material & Metallurgical research Ltd in Czech to compare Standards between China and EU code. The size of specimen and jig was researched and compared each other. The influence of jig and test machine was researched and improved the specific requirement of jig and test machine. The evolution of stress state of deformation process of specimen in SPT was clarified. The results showed that at initial stage the elastic bending stress is predominant and then the stress state dominated by membrane stress with the decreasing of elastic bending stress and the increasing of punch displacement. The reason for introducing the specimen thickness h2 to the equation for correlating yield load of SPT with yield strength, and the reason for introducing specimen thickness h to equation for correlating the maximum load of SPT with tensile strength were provided respectively. The correlation equation of ductile to brittle transition temperature and SPT energy transition temperature TSP was established and it was successfully used to evaluate embrittlement of hydrogenation reactor. Small punch creep testing by reverse finite element simulation was carried out and used to evaluate the creep life in power generation industry. Fracture toughness and Master curve using SPT by reverse finite element simulation combined with local approach was studied.