bluuebunny/crossref_metadata_2025_split huggingface dataset:
Accurate Prediction of Large Ductile Tearing in Dissimilar Material Welds Using a Non-Local Gurson Model
Authors: Lacroix Rémi , Drouet Julie , Gallée Sébastien , Chapuliot Stéphane , Gilles Philippe 
Published: December 2016

The experimental assessment of ductile failure of Dissimilar Materials Welds (DMW) of NPP components can be challenging. For instance, the European project ADIMEW [1] has shown the technical complexity of the bending set-up on a DMW join at 300°C.
Such experiments are so scarce that their analysis is highly valuable to quantify the validity of alternative methods for assessing the ductile failure. This paper presents the application of the numerical simulation of ductile failure with a local approach in the case of the ADIMEW mock-up and discusses its validity.
Variations in Measured Fatigue Life in LWR Coolant Environments due to Different Small Specimen Geometries
Authors: Twite Marius , Platts Norman , McLennan Alec , Meldrum James , McMinn Andrew 
Published: December 2016

Small specimen fatigue testing is challenging in simulated LWR coolant environments at elevated temperatures and pressures. Two approaches to isothermal uniaxial testing in such environments have been developed: use of an autoclave to contain the environment around the specimen, which is conventionally of a solid design (e.g. circular cross-section, parallel sided gauge length); and use of a thin-walled hollow or tubular specimen, where the coolant environment passes through the bore of the specimen.
It is often assumed that fatigue lives measured using these two specimen designs are equivalent. However, recent isothermal strain-controlled fatigue endurance tests on a single heat of Type 304L stainless steel at Amec Foster Wheeler — on behalf of Rolls-Royce — have indicated a significant difference in life from testing of these different specimen designs in high temperature PWR coolant, with hollow specimens consistently giving shorter lives.
This paper presents those test results, and identifies a range of possible reasons for the differences in fatigue life through consideration of relevant literature and laboratory examination of failed specimens.
These new test results have potentially significant implications for test programmes in which solid specimen test results in air are compared to hollow specimen results in LWR environments, and for fatigue databases that include results from testing of both specimen types.
The use of a conversion factor, to be applied to fatigue lives from hollow specimens tests to allow comparison to solid specimen test results, is discussed. Further work to investigate the relevance of findings to further heats of material and to a wider range of loading conditions is identified.
The Application of Long and Short Cylindrical Shell Solutions for Stress and Flexibility Determination in a Single Mitred Bend
Authors: Orynyak Igor , Bogdan Andrii , Selivestrova Iryna 
Published: December 2016

The continuous pipe bend behavior is well elaborated in literature. It is characterized by local ovalization of each cross section during bending which results in enhanced flexibility of it as compared to straight pipe. When pipe bend approaches some other structural elements of a piping system the end effect take place which can be described by so called long shell solution. This long solution is, in fact, a semi-membrane Vlasov’s solution when the derivative of any geometrical or force function in axial direction is much smaller than in the circumferential one [1].
Mitred bend is formed by conjunction by welding of two oblique sections of initially straight pipes. Its behavior during loading by pressure or bending moment is not evident and poorly described in standards. The goal of this paper is to give a set of general functions within a thin cylindrical shell theory which will give the opportunity to consider the mitred bend as an element of a piping system. Here we additionally introduce the so called short solution when the derivative of any parameter in axial direction is much bigger than that in circumferential one. Its main goal is to give the local behavior of stress in the vicinity of the oblique weld. Each of these two solutions satisfy by differential equations of forth order.
The complete theoretical solution for a particular mitred bend is compared with
a) existing analytical solutions and formulas;
b) numerical results obtained by FEM with distinction of the zones of influence of a long as well as short shell solution;
c) experimental data on real mitred bends given in the literature.
Fatigue Crack Initiation and Propagation in Cr-Mo Steel Hydrogen Storage Vessels: Research on Design for Safe Life
Authors: Solin Jussi , Briottet Laurent , Acosta Beatriz , Bortot Paolo , Furtado Jader , Mecozzi Elisabetta , Dey Randy 
Published: December 2016

International standards and codes dedicated to design of pressure vessels are still unable to competitively ensure safe design and fitness for service of steel vessels for high pressure gaseous hydrogen. Emptying and shallow pressure cycles subject the material to hydrogen enhanced fatigue. A pre-normative project, MATHRYCE under the EU joint research program focused in this subject through material and component testing, analytical work, review of design methodologies and international collaboration.
An easy to implement, safe and economically competitive vessel design methodology is targeted. Steps towards this goal were taken by deepening our understanding on hydrogen enhanced fatigue in different kinds of laboratory specimens and real vessels designed for hydrogen service at maximum 45 MPa pressure. This included cyclic pressure testing of artificially notched vessels both in hydrogen and inert environment.
The effect of hydrogen pressure, frequency and mechanical loading parameters (ΔK, Sa) on fatigue crack initiation and propagation was analyzed. Attention was paid on the definition of “initiation” and influence of hydrogen on the relative parts of initiation and propagation on the fatigue life of a component. A good correlation between results with various test types was found. Particularly promising was the match between the measured — and estimated — crack growth rates in laboratory specimens and vessels. This supports our proposal for a safe design procedure based on crack growth and defect tolerant approach. Recommendations for implementation in a new international standard, on how to properly address hydrogen enhanced fatigue based on laboratory tests, were given and will be summarized in this presentation.
Our results indicate that crack initiation from inclusions or other small microstructural features is not necessarily affected by hydrogen to a similar extent as crack growth, but when initiated, the remaining life may be short due to fast growth. This is challenging for design and inspection rules to allow economically competitive construction of hydrogen equipment without compromising safety.
Computation of the Welding Process: The Engineering Practice Consolidated Thanks to R&D Tools
Authors: Rossillon Frédérique , Albrecht David 
Published: December 2016

The integrity of structures in nuclear power plants has to be assessed to meet given safety criteria. For a better understanding of the in-service loads in welded areas of PWRs components, the residual stresses resulting from the welding process have to be evaluated. For that purpose, numerical simulation of welding has proved efficient. However, in an industrial context, simple models have to be used to stay reliable, brief and easy to use.
Among all the steps required to run a suitable computation of the welding, this paper focuses on the calibration of the heat source. Two complementary approaches are applied to define an equivalent heat input, which coarsely include complex phenomena in the weld pool. The engineering practice is driven by a know-how: simplified method are used to get an efficient result in short modelling time. On the other hand, EDF R&D develops tools which quantify the difference between models and lead to an objective choice. The mix of both approaches enables to consolidate the engineering practice.
Effects of Multiple Parallel Flaws on Crack Opening Area
Authors: Walter Matthew , Sommerville Daniel 
Published: December 2016

Cracking in boiling water reactor (BWR) core shroud welds has been identified in operating nuclear plants worldwide. The Boiling Water Reactor Vessel and Internals Project (BWRVIP) has published several reports providing inspection and evaluation (I&E) guidance for intergranular stress corrosion cracking (IGSCC) in the core shroud of BWRs. This guidance is predominately focused on evaluating crack stability. Calculating through-wall leakage was not previously a focus of the existing BWRVIP I&E guidelines for the core shroud; however, there is some guidance in the current documentation. In recent years there has been some evidence of through-wall indications in the core shroud where the through-wall indications were aligned in an array of parallel, short, flaws.
BWRVIP-158-A contains rules for treating parallel flaws with respect to calculation of structural margin for both net section collapse (limit load) and brittle fracture (linear elastic fracture mechanics (LEFM)) failure modes. There is currently no BWRVIP document or other open literature, to the authors’ knowledge, that provides insight into whether the crack opening displacements (CODs) for an array of parallel through-wall cracks are larger than that calculated for a single through-wall crack. Developing an understanding of the effect of parallel cracks on the CODs and subsequent crack opening areas (COAs) of each crack is important in augmenting the existing guidance on how to appropriately disposition through-wall cracking in reactor internal components. Specifically, it is important to know if multiple parallel cracks can lead to individual COAs that are larger than for a single crack of the same length, in order to perform accurate leakage rate calculations.
This paper documents linear-elastic finite element analyses (FEA) performed to study the effect of a parallel crack configuration on the resulting COA for the set of cracks compared to the COA calculated if each crack was treated as an individual crack, without adjacent cracking present. Various separation distances, number of crack cases and crack lengths are considered. While the object of this work is to provide criteria for the evaluation of reactor internals, the results can be applied to evaluate COD and COA in any component for which the cracking configuration and inherent assumptions of LEFM are applicable.
FFS Assessment of Pressurized Equipment Utilizing a Thickness Mapping Tool
Authors: Hantz Benjamin , Akula Venkata M. K. , Leroux John 
Published: December 2016

For pressure vessels, loss of thickness detected during scheduled maintenance utilizing UT scans can be assessed based on Level 1 or 2 analyses as per API 579 guidelines. However, Level 1 and 2 analyses can point to excessively conservative assessments. Level – 3 assessments utilizing the finite element method can be performed for a more accurate estimate of the load carrying capacity of the corroded structure. However, for a high fidelity structural response prediction using the finite element method, the characteristics of the model must be accurately represented. Although the three nonlinearities, namely, the geometric, material, and contact nonlinearities can be adequately included in a finite element analysis, procedures to accurately include the thickness measurements are not readily available.
In this paper, a tool to map thicknesses obtained from UT scans onto a shell based finite element models, to perform Level – 3 analyses is discussed. The tool works in conjunction with Abaqus/CAE and is illustrated for two different structures following the elastic-plastic analysis procedure outlined in the API 579 document. The tool is intended only as a means to reduce the modeling time associated with mapping thicknesses. The results of the analyses and insights gained are presented.
Small Punch Testing on High Chromium Steels
Authors: Tonti Andrea , Holmström Stefan , Lega Daniela , Augugliaro Giuseppe , Delle Site Corrado , Antonini Alessandra , Alvino Antonello 
Published: December 2016

The Small Punch test is a miniaturized non-intrusive methodology that allows performing creep tests using very small specimens. It can be used for the residual lifetime assessment of in service components.
In the last years, numerous applications of Small Punch Testing as well as related pre-normative work and Round Robin exercises have led to new insights which motivate a revision of the current Code of Practice for Small Punch Testing (CWA 15627, Dec. 2007) and/or its transfer in an EN norm.
In this paper we present the state-of-art of the small punch technique: its performances, usefulness and critical aspects have been discussed and some examples have been reported. Some measurements carried out during the round-robin exercises have been reported: several testing laboratories are cooperating in a round-robin on a virgin P92 material. The tests are still in progress, so only preliminary data will be shown in this paper.
A series of measurements performed during the pre-normative time will also be shown: a serviced (116,000 hours) ASME A213 T91 tube, installed in a petrochemical plant has been investigated. Small punch tests were performed and the residual life was then estimated by Omega Method. A microstructure characterization has been also reported.
The results obtained encourage new efforts for material testing by SPT; sampling, however, was found as a critical step if the analyzed material may suffer from localized damage.
Experimental and Numerical Analysis of Structures With Bolted Joints Subjected to Low Impact Load: Part 1
Authors: Karpanan Kumarswamy , O’Toole Brendan 
Published: December 2016

Bolted joints are the most common type of fastener in army vehicles and play a very important role in maintaining the structural integrity of combat vehicles. In combat, these vehicles may be subjected to various kinds of shock loading, such as initiated by a mine blast, projectile impact, or frontal crash.
This study analyzes the transient behavior of structures with bolted joints subjected to impact or shock loads using experimental methods and Finite Element Analysis (FEA). Factors such as damping that affect the bolted joint structures for shock loading are studied. Only a limited amount of published literature describes the proper method for analyzing transient shock propagation across bolted connections for high-impact loading. The initial case study focused on a simple cantilever beam with a bolted lap joint subjected to relatively low levels of impact force. The second case study used a flat plate bolted to a hat-section. These simple configurations are representative of structures found in many military ground vehicles that can be subjected to transient impact and blast loads. These structures were subjected to low-impact loading (non-destructive) using impact hammers and high-impact loading (destructive) using an air gun. The responses were measured using accelerometers. LS-DYNA FE solver was used to simulate the shock propagation in the bolted structures.
For all the bolted structures, the modal analysis was performed both experimentally and numerically. The results are in excellent agreement for the lower modes and exhibit a small deviation in the higher modes. Secondly, the time history responses of experimental and FE analysis are compared. This is a two-part paper. In this first paper, a simplified bolted connection (bolted cantilever beam) is used for studying the low-impact shock propagation.
A High-Accuracy Approach to Finite Element Analysis Using the Hexa 27-Node Element
Authors: Marcal Pedro V. , Fong Jeffrey T. , Rainsberger Robert , Ma Li 
Published: December 2016

In most finite-element-analysis codes, accuracy is achieved through the use of the hexahedron hexa-20 elements (a node at each of the 8 corners and 12 edges of a brick element). Unfortunately, without an additional node in the center of each of the element’s 6 faces, nor in the center of the hexa, the hexa-20 elements are not fully quadratic such that its truncation error remains at h2(0), the same as the error of a hexa-8 element formulation.
To achieve an accuracy with a truncation error of h3(0), we need the fully-quadratic hexa-27 formulation. A competitor of the hexa-27 element in the early days was the so-called serendipity cubic hexa-32 solid elements (see Ahmad, Irons, and Zienkiewicz, Int. J. Numer. Methods in Eng., 2:419–451 (1970) [1]). The hexa-32 elements, unfortunately, also suffer from the same lack of accuracy syndrome as the hexa20’s.
In this paper, we investigate the accuracy of various elements described in the literature including the fully quadratic hexa-27 elements to a shell problem of interest to the pressure vessels and piping community, viz. the shell-element-based analysis of a barrel vault. Significance of the highly accurate hexa-27 formulation and a comparison of its results with similar solutions using ABAQUS hexa-8, and hexa-20 elements, are presented and discussed. Guidelines are proposed for selection of better elements.
Introduction of Warm Pre-Stress Concept in French RPV Structural Integrity Assessment: Part II — RSE-M Appendix
Authors: Marie Stéphane , Chapuliot Stéphane , Moinereau Dominique , Ait-Bachir Malik , Jacquemoud Clémentine , Tanguy Benoit 
Published: December 2016

A new appendix is introduced in the RSE-M code, devoted to in-service operation on PWRs, dealing with the assessment of a defect in the Reactor Pressure Vessel. This new appendix reflects the current French practice and introduces a second criterion to consider the Warm Pre-Stress (WPS) effect.
This appendix is applicable to under clad defects and defects partially in the cladding, and covers nominal, incidental and accidental conditions. The main criterion is the classical comparison between the stress intensity factor (amplified to account for the plasticity of the cladding) and the material toughness (taking into account the irradiation induced ageing). For incidental and accidental situations, if the conventional criterion is not verified, an alternative criterion is proposed to take into account the WPS effect. The criterion corresponds to the ACE criterion developed by AREVA, CEA and EDF taking into account the effective material toughness depending on the loading history.
The present paper presents this new RSE-M appendix and provides some basic elements of justification and validation on the ACE criterion.
Seismic Performance of Piping Anchored to Concrete in Case of Nonlinear Load-Bearing Behavior of Post-Installed Anchors
Authors: Dwenger Fabian , Kerkhof Klaus 
Published: December 2016

In nuclear power plants, post-installed anchors are used for connections between concrete structure and non-structural components such as piping systems. Piping is usually connected to concrete fastenings by pipe hangers. Dynamic loading during an earthquake leads to dynamic interactions between concrete structure and non-structural component. These dynamic interactions result in dynamic loads which have to be transferred by fastenings such as anchor plates with post-installed anchors. Besides the vibrational behavior of the subsystems, the dynamic behavior of the coupled system concrete-fastening-piping is also influenced by the load-bearing behavior of the anchors. At anchor loads close to ultimate load, the load-bearing behavior of anchors is highly nonlinear due to plastic deformation of the anchor bolt and cracking of the concrete. Additionally, permanent displacement of anchors which already occurs at smaller loads can lead to change of pipe hanger stiffness characteristics and nonlinear vibrations of the component.
For an ongoing research project, various numerical design calculations are carried out for a test set-up. The test set-up is designed to study the dynamic interactions and effects mentioned above.
In order to investigate the necessity for a coupled analysis of the structural and non-structural part of the test set-up, one study in this paper deals with the effect of coupling/decoupling on calculated natural frequencies and pipe hanger loads.
For simulating the nonlinear behavior of the fastening during seismic loading, anchor models with different levels of complexity were developed which were then implemented in a large-scale finite element model of the test set-up. Comparative seismic analyses in the time domain with different anchor models are presented which are carried out as preliminary simulations for the design of the test set-up.
Simplified Computation of Creep Damage Propagation
Authors: Marriott Douglas L. , Stumph Herbert E. , Sreeranganathan Arun , Matice Christopher J. 
Published: December 2016

The commonly accepted approach to dealing with material damage as the cause of structural failure is to treat the most highly distressed location in the structure as an equivalent simple test and to define failure of the structure as a whole as being failure at that point location.
The exception to this rule is plastic deformation. Yielding at a point was recognized several decades ago as being an excessively conservative definition of component failure and it is now standard design practice to accept failure as being the limit load, which is only reached, sometimes after extensive propagation of a plastic zone.
Other material failure mechanisms also occur after a finite period of damage propagation, but this additional strength, or life, is not usually taken into account, partly because the damage mechanisms themselves are not always well defined, and partly because of the computational difficulty involved in assessing the propagation of damage.
Creep rupture falls into the category of a mechanism which can enjoy an extensive period of damage propagation before structural failure occurs, but the difficulty of evaluating it quantitatively has meant that it continues to be dealt with as essentially a point failure phenomenon.
Relatively recently, many of the problems associated with assessing creep damage have been resolved, on the material side by increased use of so-called “continuum damage mechanics” based models such as Kachanov and Omega and, on the computational side, by the exponential growth in the capabilities of advanced Finite Element Analysis. It is now possible in principle to trace the entire life of a complex component, down to final disintegration. However, this capability still comes at a significant cost, and there is still room for simplification in order to bring this capability to a wider range of potential users.
This paper describes a process for evaluating the propagation of creep damage, down to the point of total disintegration, using approximations which exist within the standard capabilities of a typical FE design package. This innovation does not do anything that cannot be done today using the full repertoire of computational tools that exist, notably user subroutines, but provides a simpler platform which can be used to push damage evaluation further into the activities of day-to-day design with a significant reduction in the resource allocation currently required to do the job.
Results are compared with creep experiments on notched bars.