bluuebunny/crossref_metadata_2025_split huggingface dataset:
DiffCode: A System for the Simulation of Diffusion Driven Phase Evolution in Solids
Authors: Sadasiva Subramanya , Subbarayan Ganesh 
Published: November 2015

Diffusion is an important mechanism for failure inducing phenomena in many applications. The common Pb-free solder alloys used in the current generation of electronics packages are complex multiphase multicomponent materials. As the scale of the solder joint decreases, it becomes increasingly important to account for the effect of surface phenomena such as grain boundary evolution, surface diffusion and interfacial reactions in the mechanics of the solder joints. The dynamics of these diffusion driven interfacial phenomena are affected by the state of stress and the electric current in the solid. The primary challenges to modeling the dynamics of evolution are the tracking of the interface while satisfying the boundary conditions for the bulk problem.
In previous work, the authors utilized the phase field method in conjunction with a commercial finite element code to study the effect of stress and electrical fields on the diffusion driven evolution of voids in solder interconnects. The utilization of commercial tools for the simulation of the stress, electrical and thermal fields allowed for the use of pre-existing meshes and allowed the study of electromigration failure in assemblies of solder joints. However, the use of commercial tools can be expensive and the options for parallel simulation are limited, restricting the size and complexity of the simulations.
In this work, the authors describe DiffCode, a parallel adaptive finite element code for three-Dimensional simulation of electromigration and stress migration driven failure due to void evolution and growth in solder as well as line interconnects using the phase field method. Several illustrative two-dimensional and three-dimensional electromigration driven void evolution simulations are demonstrated using the code.
Computational Modeling of Extreme Heat Flux Microcooler for GaN-Based HEMT
Authors: Lee Hyoungsoon , Won Yoonjin , Houshmand Farzad , Gorle Catherine , Asheghi Mehdi , Goodson Kenneth E. 
Published: November 2015

This study explores an extreme heat flux limit of microcooler for GaN-based HEMTs (high electron mobile transistors) which have local power densities exceeding 30 kW/cm2 using both solid conduction simulation and single-phase/two-phase conjugate simulations. Solid conduction simulation models are developed for full geometry of the microcooler to account for the overall thermal resistances from GaN HEMT to working fluid. This allows investigating the temperature distribution of the suggested microcooler. Parametric studies are also performed to investigate the impact of geometries and heat transfer coefficients on the junction temperature. The solid conduction simulation results using COMSOL Multiphysics agree well with single-cell ANSYS Fluent simulation results.
Separately, fluid-solid conjugate CFD (Computational Fluid Dynamics) simulation models provide the detailed flow information in the microchannel using a single-channel geometry with symmetry boundary conditions. Single-phase CFD simulations obtain the lower bound of total pressure drop and heat transfer coefficient at the microchannel walls for a mass velocity range of G = 6000–24000 kg/m2-s. The local temperatures and velocity distributions are reported that can help with identifying the locations of the maximum velocity and recirculation regions that are susceptible to dryouts. Two additional alternative tapered inlet designs are proposed to alleviate the significant pressure loss at the entrance of the SiC channel. The impact of the tapered inlet designs on pressure drops and heat transfer coefficients is also investigated.
Two-phase simulations in microchannel are conducted using Volume-of-Fluid (VOF) method embedded in ANSYS Fluent to investigate two-phase flow patterns, flow boiling, and temperature distributions within the GaN HEMT device and SiC etched mircochannels. A user-defined function (UDF) accounts for the phase change process due to boiling at the microchannel walls. The results show that the time relaxation factor, ri has a strongly influence on both numerical convergence and flow solutions.
Investigations on Crack-Like Leaks in Piping
Authors: Bläsius Christoph , Heckmann Klaus , Sievers Jürgen 
Published: November 2015

Methods to demonstrate break preclusion for pressure retaining components in nuclear power plants are summarized in the newly developed German safety standard KTA 3206, especially the requirements for the leak-before-break assessment of crack-like leaks. In this context numerical and simplified calculation methods for both the leak opening area and fluid flow rates of crack-like leaks were examined and validated on selected experiments.
Second topic of the paper is an accident analysis for a postulated leak in form of a through-wall crack in the pressurizer surge line (SL) of a German PWR Konvoi type. The initial size of the leak as well as the changing size depending on system pressure and temperature during the postulated leak accident was calculated with a FEM analysis model of a cooling loop. The reduction of the leak area amounts in the examined transient to ca. 25 % after 1 h and leads also to an approximately 23 % smaller leak rate. These results depend on the assumed position of the leak and on the initial leak size. Therefore, the results of accident analyses due to postulated leaks can be influenced by the change of the leak size during the course of the accident.
A Rational Methodology for Determination of Service Life for a Delayed Coker Drum
Authors: Aumuller John J. , Chen Jie , Carucci Vincent A. 
Published: November 2015

Delayed unit coker drums operate in a severe service environment that precludes long term reliability due to excessive shell bulging and cracking of shell joint and shell to skirt welds. Thermal fatigue is recognized as the leading damage mechanism and past work has provided an idealized description of the thermo-mechanical mechanism via local hot and cold spot formation to quantify a lower bound life estimate for shell weld failure.
The present work extends this idealized thermo-mechanical damage model by evaluating actual field data to determine a potential upper bound life estimate. This assessment also provides insight into practical techniques for equipment operators to identify design and operational opportunities to extend the service life of coke drums for their specific service environments.
A modern trend of specifying higher chromium and molybdenum alloy content for drum shell material in order to improve low cycle fatigue strength is seen to be problematic; rather, the use of lower alloy materials that are generally described as fatigue tough materials are better suited for the high strain-low cycle fatigue service environment of coke drums. Materials such as SA 204 C (C – ½ Mo) and SA 302 B (C – Mn – ½ Mo) or SA 302 C (C – Mn – ½ Mo – ½ Ni) are shown to be better candidates for construction in lieu of low chromium alloy steel materials such as SA 387 grades P11 (1¼ Cr – ½ Mo), P12 (1 Cr – ½ Mo), P22 (2¼ Cr – 1 Mo) and P21 (3 Cr – 1 Mo).
Probabilistic Fracture Mechanics Evaluations That Consider Nozzles in the Extended Beltline Region of Reactor Pressure Vessels
Authors: Stevens Gary L. , Kirk Mark T. , Dickson Terry 
Published: November 2015

For many years, ASME Section XI committees have discussed the assessment of nozzle penetrations in various flaw evaluations for reactor pressure vessels (RPVs). As summarized in Reference [1], linear elastic fracture mechanics (LEFM) solutions for nozzle penetrations have been in use since the 1970s. In 2013, one of these solutions was adopted into ASME Code, Section XI, Nonmandatory Appendix G (ASME App. G) [2] for use in developing RPV pressure-temperature (P-T) operating limits. That change to ASME App. G was based on compilation of past work [3] and additional evaluations of fracture driving force [4][5].
To establish the P-T limits on RPV operation, consideration should be given to both the RPV shell material with the highest reference temperature as well as regions of the RPV (e.g., nozzles, flange) that contain structural discontinuities. In October 2014, the U.S. Nuclear Regulatory Commission (NRC) highlighted these requirements in Regulatory Issue Summary (RIS) 2014-11 [6].
Probabilistic fracture mechanics (PFM) analyses performed to support pressurized thermal shock (PTS) evaluations using the Fracture Analysis Vessels Oak Ridge (FAVOR) computer code [7] currently evaluate only the RPV beltline shell regions. These evaluations are based on the assumption that the PFM results are controlled by the higher embrittlement characteristic of the shell region rather than the stress concentration characteristic of the nozzle, which does not experience nearly the embrittlement of the shell due to its greater distance from the core. To evaluate this assumption, the NRC and the Oak Ridge National Laboratory (ORNL) performed PFM analyses to quantify the effect of these stress concentrations on the results of the RPV PFM analyses. This paper summarizes the methods and evaluates the results of these analyses.
Evaluation of Residual Stresses Induced by Repairs to Small Diameter Stainless Steel Pipe Welds
Authors: Hicks Trevor G. , Mabe William R. , Miller Jason R. , Mullen John V. 
Published: November 2015

Residual stresses within stainless steel pipe welds may cause or exacerbate in-service cracking. Significant investigative efforts have been devoted to the examination of piping residual stresses in large diameter piping using both finite element modeling and experimental techniques, but limited information is available for small diameter piping. Even less information is available for small diameter piping welds which have been repaired or re-worked during initial fabrication. This investigation used both experimental methods and analytical modeling to assess the impact of repair welding during initial fabrication on the residual stresses along the inner diameter (ID) of small diameter pipe specimens.
The investigation showed that tensile axial residual stresses were located in the heat affected zone (HAZ) along the ID of the pipe specimens adjacent to regions which were excavated and re-welded. Such repair welds were also shown to markedly increase the magnitude of the tensile axial residual stresses for weld configurations which otherwise had lower magnitude residual stresses.
Experimental and Numerical Study of Ductile Fracture Initiation in Aluminum 6061-T6
Authors: Rekik W. , Ancelet O. , Gardin C. 
Published: November 2015

This work deals with the characterization of ductile damage in Aluminum 6061-T6 alloy.
In this paper we discuss the stress triaxiality effect on the initiation and the evolution of damage through a sequence of tensile tests conducted on round specimens with different rate of trixialities and tearing tests on precracked Compact Tension specimens. Scattering of ductility and toughness values was highlighted between the three characteristic directions studied in this topic.
Based on the experimental results, numerical simulation has been performed in order to analyze and predict ductile fracture initiation of this aluminum alloy by simulating void growth according to the Rice-Tracey micromechanical model.
The numerical simulation was conducted in two steps: first the critical void growth ratio (R / R0)c was evaluated for tensile cylindrical specimens with different degrees of triaxiality and then used to analyze crack growth initiation on Compact Tension specimen.
Due to the Al-6061-T6 highly sensitivity to triaxiality, a necessary adaptation of the Rice-Tracey model’s coefficient was made.
Upper Bound Estimates of the Contribution of an Unknown Residual Stress Field to Stress Intensity Factor
Authors: Coules Harry , Smith David 
Published: November 2015

When assessing the effect of residual stresses on the driving force for fracture of a structure containing a defect, it is necessary to determine the residual stress field either via measurement or process simulation (e.g. weld modelling). However, residual stresses can be difficult and time-consuming to measure and model, especially in welded components which are subject to complex patterns of deformation during manufacture in addition to material inhomogeneity. To avoid this, many assessment procedures provide compendia of conservative estimates of the residual stress distribution for a limited set of welded joints. Unfortunately the use of these conservative estimates can lead to unrealistic results.
In this article we propose alternative methods to account for the effect of residual stress on linear elastic defect assessments. We determine the maximum possible stress intensity factor that can be generated in a cracked component by any unknown self-equilibrating residual stress field. The limiting value of stress intensity factor can then be used to assess the acceptability of defects without the need for any residual stress data.
Stress Intensity Factor Handbook: Comparison of RSEM and ASME XI Codes
Authors: Faidy Claude 
Published: November 2015

For fracture mechanic applications at design level or during operation the basic parameter used is the elastic stress intensity factor K. This stress intensity factor can be evaluated through different methods: formulas, influence or weight functions or direct elastic finite element analysis of the cracked structure.
After a brief review of available methods to develop elastic analysis of the fracture mechanic parameter K (stress intensity factor), this paper will compare French RSE-M Appendix 5 handbook and corresponding ASME-XI draft Appendix A-3000 handbook under development for cylindrical cracked structures (pipes or vessels) in a first step. In a future step, other structures (elbows, thickness variation…) and other crack types or locations will be considered.
The cross reference validations and the technical white papers will be discussed in the paper.
A short overview of plasticity corrections proposed by these 2 different Codes will be presented, compared and discussed in accordance with the validation analysis available.
Finally, some differences between these 2 handbooks can have important safety consequences in their practical applications, some over-conservatism have to be better understand and will be discussed in term of consequences on different practical applications, like fatigue or corrosion crack growth, or critical crack size in brittle or ductile regime of nuclear components.
Automated Approach for Reciprocating Compressor Cylinders Design
Authors: Babbini Alberto , Orsi Gianni , Maleci Riccardo 
Published: November 2015

The design of a brand new reciprocating compressor cylinder is a difficult and time expensive task, involving CAD, FEA and CFD tools, which can take several months. Following standard approach, usually several trials are needed in order to achieve the most suitable solution. Every time it is necessary to change some design/model features, all the following operations have to be repeated: modifying the CAD model; meshing the model; calculating new loads and/or boundary conditions; configuring the results analyses; post process the results. Following standard methods each described operation has to be performed manually by a user.
This paper describes a method to achieve the automation of most of these manual operations, transferring the workload from human to hardware resources, with a consequent saving in time needed to achieve results and related quality.
Paper will describe the process (including details about FEA and CFD analyses) to design a cylinder with this method, compared with a traditional one. The comparison will show differences in delivery time, weight and total cost (engineering + production) between the cylinders.
Prediction of Fatigue Crack Initiation and Growth During Thermal Cycling
Authors: Wu Guiyi , Smith David , Tanner David 
Published: November 2015

Conventional approaches to assess fatigue under combined thermal and mechanical loading often utilize a fatigue design curve. In this paper models based on the physics and mechanics for the initiation and growth of fatigue cracks in stainless steel are first explained. The models are based on experimental evidence gathered for the initiation and growth of small cracks created during strain controlled laboratory tests. This evidence is then linked with data for the growth of large fatigue cracks in stainless steel. In the paper these models are coupled with finite element analyses to explore the fatigue initiation and growth of cracks in stainless steel pipes subjected to thermal cycling. It is assumed that the material behaviour is elastic-perfectly plastic, rate independent and fatigue occurs in air.
The stress and strain fields for pipes subjected to a range of thermal loading conditions are explored. The fields are shown to be sensitive to parameters such as the Biot and Fourier numbers that include pipe dimensions, physical properties, dwell time and thermal conditions. Of particular interest is the temperature range and dwell time during thermal loading. Finite element analyses are then used to determine the stress and strain ranges created by thermal loading and these ranges are used in the crack initiation and growth models to estimate fatigue life.
Material Test and Analysis for Pressure Vessel Rupture Study Under Fire in Plant
Authors: Itoh Yoshiyasu , Waki Yoshiyuki , Kasuya Kazuyuki 
Published: November 2015

In case fire incident occurs in Oil and Gas plant, pressure vessels will be exposed to fire. Though entire system will be depressurized when the fire is detected, internal pressure may still remain in the pressure vessels. Therefore, pressure vessels, if leakage of its internal fluids will escalate the incident, shall be confirmed that they will withstand internal pressure without rupture at least until internal pressure is decreased down to safe level. For design for such critical pressure vessel, a pressure vessel rupture study is conducted in addition to design code calculations. As safer plant design is requested in recent projects, demands for the pressure vessel rupture study are also growing.
In this research, material data at high temperature range, that are necessary to obtain reliable results by the pressure vessel rupture study, were measured for carbon steel and stainless steel type304 and type304L. In addition, pressure vessel rupture studies were performed for two sample pressure vessels by means of FEM analyses and calculation methods in published design guidelines.
Hydrogen-Enhanced Fatigue of a Cr-Mo Steel Pressure Vessel
Authors: Briottet L. , Moro I. , Furtado J. , Solin J. , Bortot P. , Tamponi G. M. , Dey R. , Acosta-Iborra B. 
Published: November 2015

The current international standards and codes dedicated to the design of pressure vessels do not properly ensure fitness for service of vessels used for gaseous hydrogen storage and subjected to hydrogen enhanced fatigue. In this context, the European project MATHRYCE intends to propose an easy to implement vessel design methodology based on lab-scale tests and taking into account hydrogen enhanced fatigue.
In the present document the lab-scale experimental developments and results are presented. The material considered was a commercially available Q&T low alloy Cr-Mo steel from a seamless pressure vessel. Due to the high hydrogen diffusion at room temperature in such steel, all the tests were performed under hydrogen pressure to avoid outgassing. Different types of lab-scale tests were developed and used in order to identify the most promising one for a design code. The effect of mechanical parameters, such as H2 pressure, frequency and ΔK, on fatigue crack initiation and propagation was analyzed. In particular, special attention was paid on the influence of H2 on the relative parts of initiation and propagation in the fatigue life of a component.
The second part of the work was dedicated to cyclic hydraulic and hydrogen pressure tests on full scale vessels. Three artificial defects with different geometries per cylinder were machined in the inner wall of each tested cylinder. They were specifically designed in order to detect fatigue crack initiation and fatigue crack propagation with a single test.
The final goal of this work is to propose a methodology to derive a “hydrogen safety factor” from lab-scale tests. The proposed method is compared to the full-scale results obtained, leading to recommendations on the design of pressure components operating under cyclic hydrogen pressure.
Study of the Hydrogen Embrittlement Sensitivity of an X4CrNiMo 16.5.1 Stainless Steel and the Associated Electron Beam Weld
Authors: Cusenza Florent , Ringeval Sylvain , Thiébaut Stéphanie , Buy François , Paris Thomas , Moro Isabelle , Briottet Laurent , Vignal Vincent 
Published: November 2015

X4CrNiMo 16.5.1 steel (commercial name APX4) is a low carbon martensitic stainless steel known for its remarkable mechanical characteristics and its good resistance to corrosion. The use of APX4 in the manufacture of high pressure gas vessels requires a thorough understanding of its resistance to Hydrogen Embrittlement (HE) as the gas can contain traces of hydrogen, and martensitic steels, and their welds, are generally very sensitive to HE.
This paper deals with the first part of this study, involving the characterization of the microstructure and the mechanical properties of each zone of the electron beam weld (melted zone and four different heat affected zones), and the investigation of their embrittlement in a hydrogen environment. For this purpose, tensile tests were performed in hydrogen gas at various pressures on both the base metal and the welded samples.
In situ tensile tests with picture correlation analysis have been planned for the subsequent part of our study. These experiments will enable us to track the strain in the different zones and examine the effect of hydrogen on their mechanical behavior.
These results, combined with permeation tests, should lead to a complete model for predicting hydrogen location inside the vessel as a function of time and local properties, as well as the associated embrittlement.