bluuebunny/crossref_metadata_2025_split huggingface dataset:
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.
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.
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.
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.
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.
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.
Comparison of Fracture Toughness Properties of Advanced Ferritic ODS-Alloys Based on 0.2T C(T) Specimen Tests
Authors: Eiselt Charles C. , Hoelzer David T. , de Carlan Yann , Hein Hieronymus , Serrano Marta , Diano Pascal , Schendzielorz Herbert , Seubert Andreas 
Published: December 2016

Based on the good experiences gained by using small specimens made of ferritic RPV materials, the Master Curve fracture toughness approach was applied to determine the fracture mechanical properties of oxide dispersion strengthened (ODS-) materials. A ferritic ODS-alloy (Fe-14Cr-1W-Ti-Y2O3) has been produced through the powder metallurgical production path via hot extrusion and hot isostatic pressing (HIP). Optimized oxide dispersion strengthened (ODS)-alloys have a promising potential to meet the foreseen requirements of components in future Gen IV power plants due to their high creep strength and swelling resistance under irradiation at elevated operational temperatures. The fracture toughness was characterized with mini 0.2T C(T) specimens in different material orientations (R-L / L-R) in the ductile-brittle and upper shelf region in the un-irradiated state, accounting especially for the ODS-material’s anisotropy as one key effect of manufacturing. Despite all tests were performed in orientation required by ASTM standards E 1921 and E 1820 not all validity criteria (e.g. height of yield strength, evenness of the crack, admissible K during testing or admissible stable crack growth) were met by the ODS-material: consequently, a valid T0 value and a standard-compliant Master Curve could not be determined for the ODS-material in the transition region especially in the respective R-L orientation, also due to a comparably low fracture toughness over the whole evaluated temperature range. Promising fracture toughness properties were obtained in the crack growth direction perpendicular to the prior main deformation (extrusion) direction, where a KJQ value of 196 MPa√m at T = 22°C was measured. Within the ductile regime, only a JQ = J0.2BL technical initiation toughness value could be calculated and at T = 22°C, a comparably large JQ of 137kJ/m2 is obtained for specimens with crack growth direction perpendicular to the extrusion direction, while in extrusion direction the toughness is again low.
In addition two further ODS-materials (14YWT and PM2000) were tested and compared to the alloys above. Non-conformances of ODS relating to the material requirements in ASTM standards E1921 and E1820 were finally detected and explained.