bluuebunny/crossref_metadata_2025_split huggingface dataset:
On the Design of Contact Member Surface Shape of Bolted Joints to Minimize Clamping Load Loss
Authors: Zhu Linbo , Hou Yifei , Bouzid Abdel-Hakim , Hong Jun 
Published: October 2018

Metal to metal contact between joint surfaces is widely used in bolted joints to obtain a rigid and a high performance connection. However, a significant amount of clamping load is lost when the joint is subjected to mechanical and thermal loading including creep and fatigue. In practice, to prevent bolt loosening, additional parts such as spring washers, double nut, spring lock washers, Nyloc nut and so on are used. Those methods are costly and influence the stability of the joint and affect its structural integrity.
It is well established that a small compression displacement in clamping parts leads to a big clamping load loss in stiff joints. This paper discusses the relationship between connection stiffness and clamping load and presents a method that improves clamping load retention during operation by a careful design of the member contact surface shape. A single bolted joint with two clamping parts is modeled using finite element method (FEM). A method is proposed to obtain a specific stiffness by an optimized geometrical shape of the joint contact surfaces. The result shows that the contact surface shape based on a gradually varying gap can improve the retention of the initial clamping load. Furthermore, a formula of the connection stiffness based on the curve fitting technique is proposed to predict residual clamping load under different external load and loosening.
Prediction of the Leakage Threshold for Hertzian Contact Seals: A Cellular Automata Model
Authors: Vande Voorde John , Van Wittenberghe Jeroen 
Published: October 2018

The prediction and evaluation of leakage and leak tightness is an important issue in a multitude of high-pressure applications, such as valves, flanges or threaded connections. Through the use of finite element techniques it is in general possible to determine the local contact conditions at the seal on a macroscopic level (to wit the extent of the contact area and the contact pressure in this area). However, the leak tightness of a contact area depends also on the surface topology, which is a microscopic characteristic. Therefore the assessment of leak tightness requires an evaluation criterion relating both scales. Over the years a lot of empirical evaluation criteria have been developed, each with their own application domain. However, in terms of modelling the leakage a big step forwards was made only in the last decades. The Persson method models the contact area microscopically using contact models developed in the field of tribology. This contact evaluation is then combined with results from percolation theory, which state that for a sufficiently large contact area and a uniform contact pressure leakage will occur beyond a well-specified threshold. This has yielded a potent way of evaluating leakage, but the application is limited by the requirement that the contact pressure be uniform. In many applications, such as valves or O-ring seals, the contact is Hertzian and the contact pressure distribution is not uniform but parabolic. This paper will report the first results of an effort to extent such models to Hertzian contact seals. A set of samples for leakage experiments was produced with varying surface topology. The surface of these samples is measured and the leakage behaviour under high pressure is evaluated. At the same time a cellular automata model was built and used to model percolation under non-uniform contact pressures in an effort to adapt the Persson model. Finally the experiments and the modelling results are brought together via a finite element model and compared to each other.
This paper will focus on the development of the cellular automata model and the obtained simulation results.
Application of the FAVOR-OCI Fracture Mechanics Computer Program to ASME Code Section XI, IWB-3610 Flaw Acceptance Criteria Evaluations
Authors: Dickson Terry L. , Williams Paul T. , Bass B. Richard , Klasky Hilda B. 
Published: October 2018

This paper presents an overview of added features in a new version of the FAVOR (Fracture Analysis of Vessels Oak Ridge) computer code called FAVOR-OCI. The original FAVOR code was developed at the US Department of Energy’s Oak Ridge National Laboratory (ORNL) under the sponsorship of the US Nuclear Regulatory Commission (NRC). FAVOR is applied by US and international nuclear power industries to perform deterministic and probabilistic fracture mechanics analyses of commercial nuclear reactor pressure vessels (RPVs). Applications of FAVOR are focused on insuring that the structural integrity of aging, and increasingly embrittled, RPVs is maintained throughout their licensed service life. Based on the final ORNL release of FAVOR, v16.1, FAVOR-OCI extends existing deterministic features of FAVOR while preserving all previously-existing probabilistic capabilities of FAVOR.
The objective of this paper is to describe new deterministic features in FAVOR-OCI that can be applied to analytical evaluations of planar flaws. These evaluations are consistent with the acceptance criteria of ASME Code, Section XI, Article IWB-3610, including Subarticles IWB-3611 (acceptance based on flaw size) and IWB-3612 (acceptance based on applied stress intensity factor). The linear elastic fracture mechanics (LEFM) capabilities of FAVOR-OCI also incorporate the analytical procedures presented in the Nonmandatory Appendix A, Analysis of Flaws, Article A-3000, Method of KI Determination, for both surface and subsurface (embedded) flaws.
The paper describes a computational methodology for determining critical values of fracture-related parameters that satisfy ASME Code Section XI acceptance criteria for flaws exposed to multiple thermal-hydraulic transients. These compute-intensive analyses can be carried out with a single execution of FAVOR-OCI. The new methodology determines critical values by solving for either the point of tangency or point of intersection between applied KI versus time histories and a user-selected cleavage initiation toughness material property (e.g., ASME KIc, FAVOR Weibull KIc, or Master Curve Weibull KJc) for surface or subsurface flaws. Situations where warm prestress conditions apply can also be addressed. The paper highlights a need for this new capability via applications to a recent independent review of safety cases for RPVs in two Belgian nuclear power plants (NPPs). That review required ASME Section XI assessments of several thousand embedded, quasi-laminar flaws in the wall of each RPV Analysis results provided by the new capability contributed to the technical bases compiled from several sources by the Belgian nuclear regulatory agency (FANC) and eventually used by FANC to justify the restart of these NPPs.
Numerical Study on Buckling Strength of Vertical Vessel Skirts With Access Opening
Authors: Takahashi Takuma , Miyashita Toshikazu , Kataoka Shunji , Uno Yoshiaki , Sato Takuya 
Published: October 2018

Vertical vessel skirts generally have access openings. The evaluation for buckling of vertical vessel skirts shall consider the effect of the opening. On the other hand, evaluation methods of buckling in present design codes are established based on the theory for a cylindrical shell without any opening. There is no method to assess effects of openings on buckling strength.
The purpose of this paper is to establish a new design method of vertical vessel skirts with access openings, by evaluating the effects of openings on buckling strength of cylindrical shells. The finite element analyses of buckling strength for cylindrical shells with and without openings were conducted by an eigenvalue analysis. A study was conducted on the effects of geometric parameters, such as skirt diameter, thickness, opening shape and application of reinforcements. The effects of openings on buckling strength were revealed by comparing the analysis results. Based on these results, the new design factor, Buckling Strength Reduction Factor (BSRF), was proposed for evaluating buckling strength. BSRF is the ratio of buckling strength of a cylindrical shell with an opening to that of a cylindrical shell without an opening. BSRF provides a practical simplified method to evaluate how an access opening affects skirt buckling strength.
Development of Structural Integrity Assessment Method for Flow-Induced Vibration of Reactor Internals in PWR
Authors: Sugiura Hirokazu , Watanabe Shigeyuki , Iwasaki Akihisa , Morita Hideyuki , Sakata Hideyuki , Nishikawa Yoshito 
Published: October 2018

For verifying the structural integrity of the reactor internals (RIs) in a pressurized water reactor (PWR) plant, it is important to estimate the vibration response of the core barrel (CB) due to flow turbulence. Instead of scale model test, the computational fluid dynamics (CFD) has been expected as a method to predict the turbulence forcing function for the response analysis of the CB. In this article, a hybrid approach combining empirical equations based on flow test and CFD analysis is proposed in order to predict the turbulence forcing function.
The scale model test of new RIs, which were developed by Mitsubishi Heavy Industries, Ltd., was conducted, and the pressure fluctuations for the turbulence forcing function and the vibration response of the CB were measured. The pressure fluctuations were calculated by CFD analysis, and the vibration analysis using the turbulence forcing function determined from the calculated pressure fluctuations was performed.
This article provides the scale model test data and the empirical equations of the turbulence forcing functions, and validation results of the proposed method to predict the turbulence forcing function using CFD.
Experimental Determination of the Static Equivalent Pressures of Detonative Explosions of Ethylene/O2/N2-Mixtures and Cyclohexane/O2/N2-Mixtures in Long and Short Pipes
Authors: Schildberg Hans-Peter 
Published: October 2018

In the recent past (PVP2013-97677, PVP2014-28197, PVP2015-45286, PVP2016-63223) we had started to determine the static equivalent pressures (pstat) of the eight detonative pressure scenarios in long and short pipes for different detonable gas mixtures. The pstat-values are of vital importance for process design: by assigning static equivalent pressures to the highly dynamic detonative pressure peaks it is possible to apply the established pressure vessel guidelines, which can only cope with static loads, in the design of detonation pressure resistant pipes. In the previous publications the parameter R was defined as the ratio between pstat at the location where transition from deflagration to detonation occurs and pstat in the region of the stable detonation. One important finding was that R depends on the reactivity of the gas mixture. So far, R cannot be predicted from first principles or from combustion parameters, but can only be determined experimentally. The ratio R has a special significance, because it not only determines pstat for the Deflagration to Detonation Transition (DDT) in long pipes (first detonative pressure scenario), but also gives a good estimate for two of the three scenarios relevant in the design of short pipes: DDT and the coalescence of DDT and reflection.
The present paper concludes the test series conducted at BASF during the last 4 years. It presents additional experimental data showing the variation of R over the entire detonative range of Ethylene/O2/N2 mixtures and along the stoichiometric line of Cyclohexane/O2/N2 mixtures. Based on the variation of R for these ternary mixtures and for the mixtures presented in the preceding publications, a typical variation of R for a general combustible/O2/N2-mixture is estimated over the entire explosive range. By means of this estimation the static equivalent pressures of the six design-relevant detonative pressure scenarios of any combustible/O2/N2-mixture can now be derived combining the parameter R with the Chapman-Jouguet pressure ratio, which can be calculated in a straightforward manner from thermodynamic properties.
Simulation of Acoustic-Structure Interaction by Using Finite Element Analysis in Reactor Pressure Vessel of PWR
Authors: Maeta Koji , Matsuyama Keisuke , Sugiura Hirokazu , Watanabe Shigeyuki , Morita Hideyuki , Iwasaki Akihisa , Nishikawa Yoshito 
Published: October 2018

The reactor coolant pump (RCP) in a pressurized water reactor (PWR) plant generates pressure pulsations at multiple frequencies. These pressure pulsations excite the acoustic modes inside the reactor vessel (RV), and cause significant acoustic loads on the reactor internals (RIs). For verifying the structural integrity of the RIs, it is important to predict the acoustic loads, which is used for vibration analysis of the RIs. Traditionally, an analytical method, assuming that structures are rigid, has been used in order to predict the acoustic pressure distributions inside the RV [1]. However, water in actual PWR plant is heavy enough to influence structural response, so that it is required to use methods for a coupled structural acoustic system.
In this article, the coupled structural-acoustic analysis using the commercial software ANSYS is proposed in order to predict the acoustic loads, and the applicability of this method is discussed. The structural-acoustic interactions inside the RV are investigated by element tests and the scale model test. The acoustic pressures measured by these tests are compared with the calculated results.
Thermo-Mechanical Justification of the FA3 RPV Cover and Bottom Domes Under Normal and Upset, Emergency and Faulted Loading Situations
Authors: Chapuliot S. , Sportisse M. , Hardouin J. , Vidard S. 
Published: October 2018

This paper describes in a synthetic manner the work performed for the thermo-mechanical justification of the FA3 cover and bottom domes. Details on the postulated defects definition, thermo-hydraulics loading determination, thermo-mechanical model definition and margin evaluation are provided.
As a conclusion it is shown that despite the presence of the Carbon macro-segregation, the mechanical justification of both domes could be achieved with significant margins.
Towards a Process for the Assessment of Mixed Mode I+II Fracture Toughness
Authors: Bouydo Afaf , Lacroix Valéry , Chaouadi Rachid , Mares Vratislav 
Published: October 2018

In fracture mechanics, a flaw behavior in pressure vessels is assessed with respect to the material fracture toughness.
Fracture toughness which most Fitness-for-Service (FFS) codes relies on, only considers mode-I crack opening. However, in presence of tilted flaws, like quasi-laminar hydrogen flakes, this mode-I toughness may be too severe, and a mixed mode I+II fracture toughness seems to be more appropriate.
In order to address the assessment of the fracture toughness curve, mixed mode I+II tests were performed by the authors on ferritic steel samples by adjusting the standard mode I CT specimen geometry to a geometry subjected to mixed mode I+II. Then, XFEM simulations of the mixed mode tests were performed in order to calculate the J-integral along the crack front.
Based on tests and calculations results, the paper explains how the authors work towards proposing a method to measure the material fracture toughness in case of flaws subjected to mixed mode (I+II) loading.
A Comparative Study of Pressure Area Method of Nozzle Compensation in ASME Section VIII Division 2 and PD 5500 for Restrictions in Nozzle Dimensions
Authors: Gopalakrishnan Shyam , Mathkar Ameya 
Published: October 2018

Clause 4.5 of ASME Section VIII Division 2[1] provides rules for compensation of openings in cylindrical shells having fitted nozzles.
The rules provided in Clause 4.5.5 of ASME Section VIII Division 2[1] are based on pressure-area method which is based on ensuring that the reactive force provided by the vessel material is greater than or equal to the load from the pressure.
Clause 3.5.4 of PD 5500[5] provides rules for compensation of opening and nozzle connections.
Clause 3.5.4.3 provides requirements for the design of isolated openings and nozzle connections in the form of design procedure. Clause 3.5.4.4 provides requirements for groups of openings and the procedure allows the checking of chosen geometry.
Clause 3.5.4.9 of PD 5500[5] provides rules for compensation of openings by pressure-area method to those geometries which confirms to the geometric limitations specified therein. This method has extensive satisfactory use in European Code of practice and has been adopted in BS EN 13445-3 also.
The key element in applying the pressure area method is to determine the dimensions of the reinforcing zone, i.e., the length of the shell, height of the nozzle and reinforcing pad dimensions (if reinforcing pad is provided), that resist the applied pressure.
In comparison to certain restrictions in PD 5500[5] there appears to be no restriction on the physical dimensions of the nozzle or shell in ASME Section VIII Division 2[1], as long as the required area AT is obtained and the stresses are within allowable limits.
It is therefore possible that all of the required area AT is obtained either from the nozzle or from the shell. While both these alternatives would be acceptable in ASME Section VIII Division 2[1] design, the actual stresses at the shell/nozzle junction may vary considerably.
The work reported in this paper — a comparative study of pressure area method of nozzle compensation in ASME Section VIII Division 2[1] and PD 5500[5] for restrictions in nozzle dimensions was undertaken to compare the results obtained from both the Codes and is an extension of work carried out and published as PVP2015-45564.
Using Virtual Testing to Study the Influence of Constraint on Fracture Properties
Authors: Seal Christopher , Ainsworth Robert 
Published: October 2018

This paper presents a study in which the influence of constraint is investigated using a ductile damage model based on a stress modified failure strain. This model, proposed by Oh et al, has been used to successfully predict the J-R curve of standard compact tension (CT) test pieces for a range of different materials. Further work has shown how the model can also predict the fracture behaviour of non-standard CT test specimens, in which a blunt notch is used in place of a sharp crack.
Continuing on from this work, the paper predicts the J-R curves of single edge notch tension (SET) test pieces with both a sharp crack and blunt notches.
ATLAS PLUS: Design of Large Scale Fracture Mechanics Tests on a Ferritic Pipe
Authors: Nicak Tomas , Bolinder Tobias , Keim Elisabeth , Eriksson Alexander , Le Delliou Patrick , Dahl Anna , Wallin Kim 
Published: October 2018

This paper summarizes the design calculations performed by Framatome, EDF, KIWA INSPECTA and VTT for three large scale tests on ferritic pipes made of material WB 36 (15 NiCuMoNb 5).
The large scale tests will be performed on a 4-point bending test facility provided by EDF under displacement control at room temperature.
The overall goal of the planned large scale tests is to demonstrate the effect of the crack tip constraint on the fracture toughness at the component level. Results of those tests will be utilized to develop and validate advanced tools for structural integrity assessment within WP 3 particularly with respect to the transferability of material properties from small scale specimens to large scale components as well as for the development and validation of a procedure for the determination of component fracture resistance curves.
Three configurations of the initial defect with different constraint conditions (one through-wall and two surface cracks) are considered.
The design calculations are divided into two parts. In the first part an optimization of three different crack shapes is performed on basis of the standard fracture mechanics approach (based on J-Integral) without consideration of the constraint effect.
In the second part a quantification of the crack tip constraint for the selected crack configurations from part I is performed. The effect of the constraint on the crack initiation and propagation for the selected crack configurations shall be assessed and compared between each other.
Based on these calculations the final flaw configuration for each large scale experiment is selected.
Performance of Depressurization Devices to Dynamic Loads Generated by Arcing in Liquid Filled Transformers
Authors: Iyer Ashwin Padmanaban , Goj Anne , Ahmed Omar K. 
Published: October 2018

This study provides a methodology that can be used to evaluate the dynamic performance of fast depressurization devices used in liquid-filled oil transformers. Liquid-filled transformers are susceptible to explosions due to internal arcing if the dielectric insulation fails. The internal arc vaporizes a portion of the liquid and generates a sudden pressure wave. The first peak of the pressure wave has been measured to be as high as 13 bars, with time durations on the order of milliseconds [1]. Transformer tanks have a typical static withstand limit of approximately 1 bar gauge [2]. It is thus imperative that the tank be depressurized before the static pressure reaches such a threshold. One industry-accepted Fast Depressurization System [3] used to depressurize transformers after an internal arc is based on a patented rupture disk design [4]. This study compares the dynamic performance of this disk to results from a successful test campaign using a rupture disk as the depressurization device. Limiting loading rate values from the test campaign are then used to comment on the effectiveness of the design.
The evaluation methodology is based on Pressure-Impulse (P-I) curves. The P-I curve was generated by running a series of Implicit Dynamic analysis using Code_Aster [5]. This iterative process first required establishing a failure mode that is consistent with actual observed failure in the field and observable in the Finite Element Analysis (FEA) model. The criteria were then used in interpreting the response of the Rupture Disk to a series of different half-sine wave pulse loading of varying amplitudes and time-periods.
The generated P-I curve was then compared to loading rates observed in the test campaign [1] as well as three other higher loading rates (1.28 times, 2 times, 3.8 times, and 10.25 times the reported experimental rate) to qualitatively assess the effectiveness of the design. Results indicated that disk functions extremely effectively as a Fast Depressurization System as also corroborated by the test campaign.
Although this methodology is used for the rupture disk, it is expected that this methodology can be extended to compare the dynamic performance of other depressurization devices.
The Experimental Work in Support to ATLAS+ Project
Authors: Moinereau Dominique , Le Delliou Patrick , Dahl Anna , Kayser Yann , Szavai Szabolcs , Tatar Levente , Bolinder Tobias , Serrano Marta , Besson Jacques , Nicak Tomas , Wallin Kim , Marie Stéphane 
Published: October 2018

The 4-years European project ATLAS+ project was launched in June 2017. Its main objective is to develop advanced structural assessment tools to address the remaining technology gaps for the safe and long term operation of nuclear reactor pressure coolant boundary systems.
The transferability of ductile material properties from small scale fracture mechanics specimens to large scale components is one of the topics of the project. A large programme of experimental work is to be conducted in support of the development and validation of advanced tools for structural integrity assessment within the framework of the work-package 1 (WP 1): Design and execution of simulation oriented experiments to validate models at different scales.
The experimental work is based on a full set of fracture mechanics experiments conducted on standard specimens and large scale components (several pipes and one mock-up), including a full materials characterization. Three materials are considered:
• a ferritic steel 15NiCuMoNb5 (WB 36)
• an aged austenitic stainless steel weld
• a VVER (eastern PWR) dissimilar metal weld (DMW)
The paper presents the WP 1, the experimental programme and summarizes the first results.