bluuebunny/crossref_metadata_2025_split huggingface dataset:
Finite Element Analysis to Investigate the Effect of Geometries of DWTT Specimens on the CTOA - An Interim Report
Authors: Xue J. , Williams B. , Xu S. , Tyson W. R. 
Published: October 2021

Abstract
This work forms part of the research effort to investigate the transferability of CTOA from standard DWTT specimens to other geometries, notably pipes. The focus of this work is on the effect of ligament size and thickness of DWTT specimens under bending load on CTOA. The damage mechanics models used in this work, namely the modified Xue-Wierzbicki (XW) model and the Modified Mohr-Coulomb (MMC) model, utilize fracture criteria that depend on stress state, i.e., stress triaxiality and Lode angle. Both the XW model and the MMC model predict similar trends regarding the effect of ligament size and thickness on CTOA. For both the standard and large DWTT models with various thicknesses investigated in this research, steady-state crack growth was achieved at a small crack extension of about one specimen thickness. The CTOA values measured on the surface are larger than those measured in the interior, which is consistent with experimental observation. Increase of thickness has negligible effect on interior CTOA, but leads to higher surface CTOA. Increase of width (ligament) decreases CTOA slightly. However, further work is needed on the models because not all features are correctly predicted. In particular, the fracture mode is predicted by the models to show increasing slant fracture with increasing thickness, contrary to expectation. Also, the effect of ligament size on CTOA in tension-loaded specimens should be investigated to assess transferability to pipe in which the loading is tensile.
A Method for Investigating Multi-Axial Fatigue in a PWR Environment
Authors: Gill Peter , Onwuarolu Paul , Smith Russell , Coult Ben , Kirkham Mark , Sutcliffe Matt , Cooper Karen , Schofield Tom , Madew Colin , McLennan Alec , Currie Chris 
Published: October 2021

Abstract
A significant amount of fatigue testing has taken place over the years to generate relationships between applied stress or strain range and cycles to failure. This has mainly been conducted on uniaxial test specimens in an air environment. More recently, fatigue testing has been conducted in a PWR environment as it is now well known that this has a deleterious impact on life. The test method presented in this paper considers bi-axial loading on a specimen that is compatible with PWR fatigue testing rigs. In order to achieve this, a specimen was designed to convert a uniaxial load into a biaxial load with no internal mechanism. Finite Element Analysis (FEA) was conducted to develop and refine the design, which accounted for frictional contact and bolt up stresses.
Initial testing was conducted on a 304L stainless steel specimen in a room temperature air environment. Digital Image Correlation (DIC) was used to validate the FEA and there was excellent agreement between predicted and observed strains. Once the strains were validated, a fatigue test was conducted to confirm that cracking was in the expected location, and that the number of cycles to failure was reasonable. Direct Current Potential Drop (DCPD) was used to indicate when a fatigue crack initiated, which was confirmed by visual inspection. The results showed that cracking occurred in the location of highest accumulated plastic strain and Von Mises Stress, and the number of cycles to failure was slightly lower than predicted but still within scatter.
Modeling of Plastic Zones and Fracture Paths in Representative Material Elements With Bulk Hydrides in Hydrided Irradiated Zr-2.5Nb Pressure Tube Materials Under Plane Strain Conditions
Authors: Wu Shengjia , Pan Jwo , Scarth Douglas A. 
Published: October 2021

Abstract
Plastic zones near bulk hydrides and fracture paths in representative volume elements (RVEs) with bulk hydrides in hydrided irradiated Zr-2.5Nb pressure tube materials are investigated by two-dimensional finite element analyses under plane strain conditions. Three RVEs with different distributions of bulk hydrides are selected from the micrographs of the radial-circumferential cross section of a hydrided irradiated Zr-2.5Nb pressure tube specimen. The bulk hydrides are assumed to be separated from the pressure tube material in the early stage of the loading and are assumed as cracks. The RVEs are subjected to high stress triaxiality loading conditions similar to those ahead of the front of an axial crack in a pressure tube specimen under internal pressure. The elastic-plastic stress-strain relation for the matrix materials in the RVEs follows that of a tensile test of a transverse tensile specimen cut from an irradiated Zr-2.5Nb pressure tube specimen. The computational results indicate that due to close proximity of bulk hydrides, narrow plastic zones emanating from the tips of bulk hydrides connect either to the tips of other neighboring bulk hydrides or to the neighboring fractured bulk hydride surfaces as the loading increases. Possible fracture paths are identified and presented by connecting the fractured bulk hydrides and the narrow plastic zones emanating from the tips of bulk hydrides. The features of the fracture surfaces of the RVEs based on these possible fracture paths are generally consistent with those ahead of the front of a crack in a curved compact tension specimen cut from a hydrided irradiated Zr-2.5Nb pressure tube specimen. The computational results also show that the macroscopic elastic modulus and maximum stress of the RVE increase as the net section percentage of the possible fracture path increases.
Self-Loosening Behavior of the Nut Due to Tension Change Considering the Inclination of Bearing Surface
Authors: Shoji Yasumasa 
Published: October 2021

Abstract
Self-loosening behavior is a topic which many researchers are tackling and the principle is coming clearer. Self-loosening occurs mainly when transverse load is applied to the bolt/nut system and the loosening also occurs when such other loads are applied as impact of the bolt (NAS3350 test type) or temperature difference between bolt and nut. The author reproduced the phenomena by using finite element analyses and found the self-loosening is caused by radial relative displacement between bolt and nut threads. On the other hand, some researchers say the self-loosening occur when the tension changes repeatedly while others say it doesn’t. This axial force phenomenon is not yet clear even in experiment. In this paper, the self-loosening phenomenon by the tension change is examined using Finite Element Analyses. The results show that the self-loosening depends on the inclination of the bearing surface. The loosening does not occur when the inclination of the bearing surface is small enough and it occurs when the inclination is large. As the inclination of the bolt head and nut is allowed within the engineering tolerance and flanges rotate when it fastened making the bolt head or nut bearing surface inclination, the self-loosening may happen for any bolts in nature if tension changes repeatedly.
Three-Dimensional Finite Element Analyses of Separation Work Rate For Crack Extension in a Thin Curved Compact Tension Specimen With Finite Step Nodal Release Method
Authors: Sung Shin-Jang , Wu Shengjia , Pan Jwo 
Published: October 2021

Abstract
Separation work rate as a function of the crack extension in a thin curved compact tension (CCT) specimen of Zr-2.5Nb pressure tube material is investigated by three-dimensional finite element analyses with the finite step nodal release method. The straight crack front for the crack extension is assumed. The crack extension is simulated by releasing the nodal points ahead of the initial straight fatigue crack front in the CCT specimen. The crack extension follows the available experimental crack extension-displacement data. The computational results show that the plastic zone size and shape change along the crack front as the crack extension increases. The computational results also show that the separation work rate is a function of the crack extension and is similar to the experimental J-R curve. The computational results suggest that in a two-dimensional finite element analysis of the crack extension in the thin CCT specimen with the cohesive energy approach, the cohesive energy can vary to account for the change of the constraint conditions along the crack front as the plastic zone size increases with the crack extension.
The Aeroacoustic Response of a Single Square Cylinder in Confined Cross Flow
Authors: Shaaban Mahmoud , Mohany Atef 
Published: October 2021

Abstract
Unstable flow patterns around arrangements of bluff bodies in different engineering applications can give rise to pressure oscillations, leading to excitation of strong acoustic resonance that can interrupt operation. In certain conditions, flow fluctuations arising from vortex shedding downstream of a circular cylinder are reported to excite severe acoustic resonance. On the other hand, cylinders of a square cross section are known to be particularly susceptible to mechanisms that involve coupling between the flow and a structural mode. It is not documented, however, if such coupling would occur between an acoustic mode and flow fluctuations downstream of a square cylinder. In this work, the possibility of excitation of acoustic resonance due to coupling between unsteady flow downstream of a single square cylinder with an acoustic cross mode of a rectangular duct is experimentally investigated. During the experiments, acoustic resonance was self-excited. Measurements of the acoustic pressure and the flow velocity are carried out for a single square cylinder of an edge length of 25.4 mm. Results show that aeroacoustic response characteristics for this configuration are not completely analogous to the case of a circular cylinder, with a number of features not reported before. A brief summary of the results is presented in this work.
Analysis of Test Method to Extract Material Properties From Candu Fuel Channel Spacers Made of Helical Springs
Authors: Metzger Donald , Gagnon Andre , Kashyap Tejasvi 
Published: October 2021

Abstract
In a particular nuclear application, separation between two concentric tubes is supported by helical springs installed in the annular space. Evaluation of material degradation due to the unique operating environment requires testing of ex-service spring material. Testing is done by compressing short segments of the spring material between two surfaces as per the loading mode in operation. Nominally, the specimen behaves like multiple rings loaded uniformly in parallel, but analysis of test results based on this approximation neglects significant end effects.
A detailed analysis addresses the transition from the free end boundary condition through to where the coils become confined by friction to behave like rings. The thin ring solution is compared with finite element results as well as test results. Trends from the detailed thin ring solution correspond closely to the finite element and test results. A more precise relationship between the total applied load and the maximum stress in the material is determined.
Comparison of Ni-Steel Dissimilar Joints for Coke Drum External Weld Repairs Based on Isothermal Low-Cycle Fatigue Tests
Authors: Zhang Shutong , Romo Sebastian , Giorjao Rafael Arthur , Penso Jorge , Guo Haixia , Yuen Simon , Ely Lisa , Ramirez Antonio J. 
Published: October 2021

Abstract
Low-cycle fatigue failure has been widely accepted as the key mechanism causing damages of coke drums during cyclic thermal-mechanical loadings. Common damages of coke drums known as bulging and cracking are associated with accumulative plasticity caused by thermal and mechanical strains. External repairs using temper-bead welding techniques are implemented to repair welds in the damaged areas of coke drums, which provide structural support to the vessels. Compared with matching filler metals, Ni-base fillers including alloy 625 and alloy 182 are compatible with both low-alloy steel base metal and internal clads in terms of weldability and thermal expansion. However, the differences of yield strengths and cyclic hardening behaviors of nickel-base alloys from base metals compromise the fatigue resistances of weld joints. In this study, alloy 182 and alloy 625 repair coupons were evaluated and compared based on isothermal low-cycle fatigue tests. Low-cycle fatigue behaviors of both weld metals and 1.25Cr-0.5Mo base metal were measured at 1.0%, 1.5% and 2.0% strain amplitudes. Test results indicate both nickel-base filler metals exhibit overmatching strength over the base metal due to cyclic hardening. Low-cycle fatigue tests of Heat Affected zone (HAZ) samples show the failures of alloy 625 weld joints occur in the base metal, while the failures of alloy 182 weld joints occur along the fusion boundary. The observations show strength mismatch and fatigue resistance are the key factors to determine failure locations of the joints. In addition, cyclic hardening coefficients based on kinematic hardening model were extracted from experimental data to simulate the cyclic behaviors of the weld joints. Finite element simulation results were shown to be consistent with experimental data at stabilized cycles. Cyclic behaviors of weld metal and base metal within a weld transition sample were calculated based on the numerical model.
Evaluation of Cracks Embedded in Zones With Large Scale Plasticity in Subsea HPHT Equipment – Comparing FAD and Driving Force Approaches
Authors: Kulkarni Mandar , Lopez Carlos , Kluk Daniel , Chappell John 
Published: October 2021

Abstract
Fracture mechanics assessments for pressure vessels are performed to determine critical flaw sizes and/or estimate the fatigue life of a growing crack as a means of establishing inspection intervals for the equipment. In most cases the evaluation is performed based on methods described in API 579-1/ASME FFS-1 and BS7910. The approaches described in these standards are mostly based on a linear elastic fracture mechanics approach. Even though plasticity can be accounted for by using a failure assessment diagram (FAD); however, even with this approach the effect of plastic strain around the crack is not explicitly considered.
This paper presents an approach as per API 579, Annex 9G.5 which recommends utilizing a driving force method whereby the J-integral is directly evaluated from an elastic-plastic finite element model. The main goal is to study differences between the FAD approach against the elastic-plastic J-integral approach wherein the crack is modeled explicitly. Simplified representative geometries are considered for this study. Two scenarios for the plastic zone are considered a) crack present during initial loading with no residual plastic strain and b) crack in a residual stress zone. Different crack sizes are considered for this comparison study ranging from small cracks completely embedded within the plastic region and larger cracks with partial embedment.
The paper presents comparison studies which highlight the key differences between different analysis approaches with the aim of identifying the most conservative assessment method for different crack geometries.
Numerical Prediction of the Phase Difference in Tube Bundles Experiencing Streamwise Fluidelastic Instability
Authors: Rehman Sameer A. , Hassan Marwan , El Bouzidi Salim , Weaver David , Elbanhawy Osama 
Published: October 2021

Abstract
Recent experimental investigations have shown that tube arrays can become unstable in the streamwise direction. This is contrary to the long-held notion that fluidelastic instability is only a concern in the direction transverse to the flow. The possibility of streamwise fluidelastic instability (FEI) as a potential threat to the integrity of tube bundles was confirmed by the recent failures of newly installed replacement steam generators. A number of investigations were conducted to uncover the nature of this mechanism. A theoretical framework was developed by Hassan and Weaver [1] to model streamwise fluidelastic instability in a bundle of flexible tubes. The model utilized a simple time lag expression for the flow channel area perturbation. The current work aims at developing a numerical model to precisely predict the flow perturbation characteristics in a tube bundle due to streamwise tube motion. Flow simulations were carried out for single phase fluid flow in a parallel triangle tube bundle array with 1.2, 1.5 and 1.7 pitch to diameter ratios. The numerical model was benchmarked against numerical and experimental results available in the FEI literature. Simulations were carried out for a range of reduced flow velocities. The model results showed that the upstream flow perturbation magnitude and phase are different from those obtained in the downstream of the moving tube. The obtained flow perturbation characteristics were implemented in the Hassan and Weaver [1] model and the streamwise FEI threshold was predicted.
Comparison of Candidate Steady Loading Elevated Temperature Design-by-Analysis Methods
Authors: Dewees David , Mann J. Adin , Nadarajah Chithranjan , Messner Mark , Hantz Ben , Andersen David 
Published: October 2021

Abstract
Design-by-Analysis is distinguished from Design-by-Formula or Design-by-Rule in that specific failure modes are identified, and detailed analysis of each failure mode is compared to criteria specific to each failure mode. Several ASME Boiler and Pressure Vessel code committees continue to work on design-by-analysis methods in the elevated temperature range, where creep rupture is a failure mode with steady loading. The Subgroup on Elevated Temperature Design, which reports to Section I and Section VIII and collaborates with Section III, has been evaluating eight different analysis methods for six example problems. The two Design-by-Formula methods are from Section I and Section VIII Division 1 and the Design-by-Analysis methods are (1) Linear Elastic Analysis with revised stress limits, (2) Isochronous Curve Limit Load, (3) STP-PT-070 Limit Load Analysis, (4) Detailed Inelastic Methods using the MPC Omega creep models, (5) ASME CC2843 (simplified NH method),and (6) Section III Division 5 Draft Code Case for Limit Load Analysis. The test cases include (1) Grade 11 Steam Outlet Header, (2) Grade 91 Header Endplate, (3) Grade 91 Steam Outlet Header, (4) Grade 91 Steam outlet Header 2, (5) Grade 91 Steam Piping Lateral and (6) Type 304 Stainless Spherical Vessel/Nozzle. To ensure a common comparison, a common material definition was used based on the ASME FFS-1/API579 material models. Each of the analysis methods and examples will be described along with a comparison of the maximum pressure predicted by each method for each problem.
A Comparative Study of Radial Nozzle Criteria; Section VIII, Division 2, Part 4.5.5 to Part 5.2.2
Authors: Boyak Craig 
Published: October 2021

Abstract
A study is presented which compares nozzle thickness requirements based ASME Section VIII, Division 2, Parts 4 and 5[1]. Specifically, the simplified geometry of a set-in, radial nozzle without inward projection or repad is considered. The comparative technique considers a design pressure at the capacity of the shell and identifies the minimum nozzle thickness that satisfies applicable stress limits. For Part 4, the methodology of 4.5.5 is used. For Part 5, the elastic method in 5.2.2 is used. The study employs these techniques for R/t geometries of 20 to 180 and d/D ratios of 0.01 to 0.3. The comparison indicates elastic analysis Part 5 methods can improve the design from that of Part 4 over some, but not all, configurations within the study’s scope. The bounds of where the elastic analysis Part 5 methods benefit are identified. In the process of the study’s effort, numerous responses are identified and compared between design methodologies. The comparison is one of needed nozzle thickness for similar geometries. Behavior responses are shown from the range of configurations in the large simulation set created by the Part 5 method. For the Part 4 response, charts are shown that identify the required nozzle thickness based on the varying reinforcing limit logic employed in that method.
Comparison of Valve Failure Rates Estimated From Field Failure Data to Those Predicted by Calibrated FMEDA
Authors: Bukowski Julia V. , Goble William M. , Harris Stephen P. 
Published: October 2021

Abstract
This paper presents the results of three comparative studies. In each study the failure rate of one specific valve at one specific facility is estimated from field failure data (FFD). Each estimate is compared to the failure rate predicted for that valve by the Calibrated FMEDA™ technique. The predicted failure rates consider the failure rate variations due to valve application, to fluid service, and to each specific facility’s Site Safety Index (SSI) which accounts for various aspects of safety culture. The results show that the predictions are quite good, i.e., all predictions lie within a 70% confidence interval constructed from each valve’s FFD and near the estimated mean failure rate for each valve.
Development and Characterization of Shape Memory Polymers for Non-Invasive Biomedical Applications
Authors: Jeewantha Janitha , Emmanuel Chris , Herath Madhubhashitha , Islam Mainul , Epaarachchi Jayantha 
Published: October 2021

Abstract
This paper details a shape memory polymer (SMP) synthesis and characterization process has been undertaken to develop a bio-medical material for fabricating non-invasive custom prosthetic components and orthosis devices. The glass transition temperature of a one-way SMP epoxy is tailored for external biomedical applications since human skin is sensitive to high temperature (&gt; 45°C). The key shape memory properties of shape fixity ratio, shape recovery ratio and shape retention properties were comprehensively analyzed, and thermomechanical properties were verified. SMPs can be customized for the purpose; thus, SMP prosthetic and orthosis devices will be ideal for first aid and emergency treatments until proper medical attention is received. Finally, brief details of an SMP bone immobilization casting method are provided to explain the application further.
Voltage-Dependent Medium-Term Synaptic Plasticity in Biomolecular Synapses
Authors: Maraj Joshua J. , Ringley Jessie D. , Sarles Stephen A. 
Published: October 2021

Abstract
Biomolecular assemblies of phospholipids and the pore forming species monazomycin were constructed using the droplet interface bilayer technique to mimic synaptic properties. Electrical characterization of the interface confirms the existence of multiple forms of short-term synaptic plasticity in response to constant stimuli. Memory of prior stimulation can last up to 20 minutes suggesting an unaccounted mechanism of longer term memory retention, termed “medium-term synaptic plasticity.” Monazomycin doped biomembranes were stimulated by a series of step voltage inputs with varying off-times ranging from one to twenty minutes. Percentage of peak current obtained inactivation percentage, and change in inactivation percentage were compared. Peak current is reduced in subsequent stimulations and gradually restores back to 100% after 20 minutes. Inactivation percentage is also reduced but recovers at 20 minutes. Initial current right after application increases and remains elevated up to 20 minutes. Multiple sinusoidal voltage inputs were performed with −80 mV step inputs in between. I-V hysteresis for these inputs were compared. The peak negative current of the hysteresis decreased while the positive peak increased after each cycle. Medium term synaptic plasticity is believed to be the result of lingering concentration differences at the interfaces and lingering presence of nonconducting monazomycin in the bilayer.