bluuebunny/crossref_metadata_2025_split huggingface dataset:
How to Get Second-Order Accurate Solutions From the First-Order Accurate RELAP5 Code
Authors: Tiselj Iztok , Petelin Stojan 
Published: January 2022

Abstract
Equations of the typical ID two-fluid model of two-phase flow, which is used in today’s computer codes for the simulations in nuclear thermal-hydraulics (RELAP5, TRAC), can be written in vectorial form as:∂ψ∂t+C∂ψ∂x=P Numerical scheme in RELAP5 is based on direct discretization of the equations using first-order accurate temporal and spatial discretizations. Staggered grid is used and upwind scheme for the spatial discretization of the convection terms in the equations. Second-order accurate central differences are used only for the discretization of the pressure gradients in the momentum equations.
In this paper we have demonstrated the capability of the RELAP5/MOD3 code to trace the acoustic waves with second-order accuracy, if a very small time step is chosen for the simulations. This feature of the RELAP5 code is important especially for the simulations of the fast transients describing pressure waves, i.e. shocks, rarefaction waves, water hammer... Second-order accuracy cannot be achieved for the propagation of the temperature and void fraction waves.
Uncertainty Quantification of SB LOCA With CSAU Using Optimal Statistical Estimator
Authors: Prošek Andrej , Mavko Borut 
Published: January 2022

Abstract
When performing best estimate calculations uncertainty needs to be quantified. An optimal statistical estimator algorithm was adapted, extended and used for response surface generation. The objective of the study was to demonstrate optimal statistical estimator for uncertainty evaluation of single value or time dependent parameters when Code Scaling, Applicability and Uncertainty (CSAU) method is used for uncertainty quantification. The scenario selected was small-break loss-of-coolant accident with break in cold leg of a two-loop pressurized water reactor Westinghouse type. The uncertainty was quantified for RELAP5/MOD3.2 thermalhydraulic computer code.
The results showed that peak cladding temperature selected as one of primary safety criteria with added uncertainty does not exceed the safety limit. Uncertainty was additionally evaluated for nine time dependent parameters. This finding indicate that CSAU method can be applied to transients other than loss-of-coolant accident.
Boundary Layer Two-Phase Bubbly Flow Equation
Authors: Troshko Andrey A. , Hassan Yassin A. 
Published: January 2022

Abstract
Experimental data indicate that bubbly, turbulent, boundary layer has the same structure as its single-phase counterpart. The modified logarithmic law of the wall for the bubbly turbulent log layer is obtained. Eddy viscosity concept is used to obtain boundary layer equation. Total turbulent stress in the inner layer is assumed to be the sum of the local stress caused by bubbles in the log layer and the stress taking into account the inherent liquid turbulence and bubble-liquid interaction in the outer layer. The proposed two-phase law of the wall can be used as a boundary condition in multidimensional models of two-phase turbulent flows. It is applicable to the upward and downward flows with the value of void fractions in the log layer not more than 10%.
Simulation of a Subcooled Boiling Experiment Using RELAP5/MOD3.2 Computer Code
Authors: Hari Sridhar , Hassan Yassin A. , Tu Jiyuan Y. 
Published: January 2022

Abstract
The results of a low-pressure subcooled flow boiling experiment simulated with the RELAP5/MOD3.2 thermal-hydraulic computer program are presented. The objective of the present study is to assess the suitability of application of the RELAP5 computer program for the thermal hydraulic safety analysis of research reactors. These reactors as the High Flux Australian reactor HIFAR operate at near-atmospheric pressures with upward forced convective flow. Subcooled boiling phenomenon plays an important role in the heat transfer aspects of this reactor. It is found that the void fraction profile predicted by the code for the various experimental conditions differ considerably from the experimental results.
Analysis of VVER1000/320 Operational Transient With CATHARE Computer Program
Authors: Troshko Andrey A. , Hassan Yassin A. 
Published: January 2022

Abstract
A simulation of VVER1000/320 operational transient with CATHARE2 V1.3L was performed. This transient consisted of shutdown of primary side pump in one of the loops. Before the transient, reactor was at nominal operational condition with 72% power level.
The results of comparison between calculated and measured data indicated that the code was able to reasonably reproduce main phenomena taking place in both primary and secondary sides.
High Cycle Fatigue Behavior and Notch Size Effects in Ti-6Al-4V
Authors: Lanning David B. , Haritos George K. , Nicholas Theodore 
Published: January 2022

Abstract
The notch size effect of forged Ti-6Al-4V plate, loaded under high cycle fatigue (HCF) conditions, is investigated for both cylindrical and flat fatigue specimens. Cylindrical specimens were machined with three sizes of circumferential V-notches, with the smallest size dictated by the ability to machine within given tolerances. Flat dogbone specimens were machined with two sizes of opposite V-notches. All notches in both cylindrical and flat specimens have an elastic stress concentration factor of approximately Kt = 2.7. The state of stress at the notch root in the cylindrical specimens is biaxial. Thin flat specimens were chosen with the intent of minimizing the out-of-plane (through the thickness) stress component at the notch root. All specimens were cycled to obtain points on a Haigh diagram, also referred to as the modified Goodman diagram, for a constant life of 106 fatigue cycles. Specimens were cycled at stress ratios of R = 0.1, 0.5, and 0.8, at a frequency of 50 Hz. A step loading technique for generating a point on the Haigh diagram from a single test specimen was used, where the fatigue limit is found by fatiguing the specimen for 106 cycles at a stress level below which failure is expected. If failure does not occur, the stress level is raised and the specimen again fatigued for 106 cycles. This procedure is repeated until failure, after which the fatigue limit is calculated by interpolation. The validity of this technique for Ti-6Al-4V was demonstrated by generating constant amplitude stress-life data for comparison with the interpolated fatigue limits. The notch size effect is examined in light of the stress state at the notch root, and the appropriateness of the von Mises effective stress in characterizing the multiaxial state of stress in HCF is considered.
Effect of Step Testing and Notches on the Endurance Limit of Ti-6Al-4V
Authors: Bellows Richard S. , Bain Ken R. , Sheldon Jerry W. 
Published: January 2022

Abstract
The current Air Force High Cycle Fatigue (HCF) Materials Damage Tolerance Program investigating the fatigue behavior of Ti-6Al-4V requires the determination of initiation-based endurance limits both with and without associated damage modes. Step testing was evaluated as a means of generating endurance limits with a single specimen for the purpose of evaluating associated damage mode states. Notched specimens were evaluated in order to determine the effect of notches on the fatigue behavior so that geometrical effects associated with damage modes could be separated from non-geometrical (e.g., plasticity, residual stresses, cracking) effects. As part of this program, smooth bar S-N curves were generated at four stress ratios (−1, 0.1, 0.5, and 0.8) and compared to endurance limits determined by the step test method using a single specimen. Notch fatigue was conducted at two stress ratios and compared to smooth bar fatigue, and the effect of notch geometry and sampling volume under the notches was examined at a stress ratio of 0.1. The step test method agreed with the conventional S-N curve determined endurance limit in most cases. The different notch geometries and sampling volumes did not appear to effect notch fatigue behavior. This paper presents some of the preliminary results of this ongoing effort.
Mechanistically-Based Fracture Mechanics Models for the Prediction of Multiple Semi-Elliptical Crack Growth in Q1N (HY80) Pressure Vessel Steel Under Fatigue Loading
Authors: Soboyejo W. O. , Knott J. F. 
Published: January 2022

Abstract
Mechanistically-based fracture mechanics models are presented for the prediction of multiple semi-elliptical crack growth in Q1N (HY80) pressure vessel steel. Following a review of the mechanisms of multiple coplanar and non-coplanar semi-elliptical fatigue crack growth, mechanistically-based fracture mechanics models are presented for the prediction of fatigue crack growth. The models include simplified fracture mechanics idealizations of crack interaction and coalescence of coplanar and offset non-coplanar cracks. Predictions obtained from the models are shown to be in closer agreement with measured fatigue crack growth data than the predictions obtained from current ASME Section XI and BS PD 6493 codes. The implications of the models are discussed for the prediction of fatigue life of structures and components that contain multiple configurations of semi-elliptical fatigue cracks.
Structure and Behavior of Materials for Micromechanical Devices
Authors: Krulevitch Peter , Seward Kirk P. , Ackler Harold D. , Johnson George C. , Howe Roger T. 
Published: January 2022

Abstract
The mechanical behavior of thin film microfabricated devices depends in large part on the material microstructure, which in turn depends on the conditions under which the films are deposited. As a result of material sensitivities to various deposition parameters, new techniques have been developed for thorough characterization and monitoring of film properties such as modulus, residual stress, microactuator force generation, and fatigue. Residual stresses in films, which can lead to fracture, buckling, or curling of surface micromachined devices and can influence microactuator behavior, vary considerably with processing conditions. A study of as-deposited in situ phosphorus doped polycrystalline silicon shows a strong correlation between microstructure and residual stress. The gradient in residual stress through the film thickness was determined by measuring the substrate’s curvature, then etching away a thin layer of the film with a plasma etch, and repeating the process until the entire film was removed. These measurements were then compared with cross-sectional transmission electron micrographs of the films, an example of which is shown in Fig. 1. While the overall stress is compressive, crystallization occurring near the substrate results in a tensile stress component, inducing a stress gradient.
MEMS-Based Test Structures for IC Technology
Authors: Smee Stephen A. , Gaitan Michael , Joshi Yogendra 
Published: January 2022

Abstract
As Integrated Circuit (IC) device sizes shrink, intrinsic and thermo-mechanical stress in interconnects is an ever increasing reliability concern. Increasing device density leads to more interconnect layers and hence, greater probability of stress related failure through mechanisms such as electromigration, delamination and voids. Current state-of-the-art IC technology uses 5 interconnect layers. According to the 1997 SIA Roadmap, that number is expected to increase to 9 by the year 2012 [1]. As a result, methods to measure, model and reduce stresses in interconnects are needed to manufacture reliable, future generation IC’s.
Correlation of Fracture Initiation for Microscale Structures: Free-Standing Silicon and Silicon/Glass Interfaces
Authors: Dunn Martin L. , Suwito Wan , Labossiere Paul E. W. , Cunningham Shawn J. 
Published: January 2022

Abstract
We present recent results regarding correlation of fracture initiation for i) micromachined epitaxial silicon structures, and ii) silicon/glass anodic bonds used for encapulation of microelectromechanical systems. Regarding the epitaxial silicon structures, we have previously correlated fracture initiation from the sharp notches that arise during anisotropic etching in KOH using a critical value of the stress intensity that exists in the context of linear elasticity. This has successfully explained an interesting strength scaling with structural dimensions. In this talk, we present new results along these lines where we have considered additional structure geometries (double-edge-notched silicon specimens, roughly 600 μm long × 50 μm wide × 15 μm thick), loadings (in-plane flexure), and etching processes (deep reactive ion etching). Regarding fracture initiation of silicon/glass anodic bonds, we have fabricated a series of generic test structures by anodically bonding etched silicon wafers to glass wafers. We have carried out preliminary tests in tensile and flexural loading and interpreted these results in the framework of an analysis of the singular stress state at the resulting bimaterial notch. For both cases, we will discuss the suitability of using critical stress intensities to correlate fracture initiation under the condition of small-scale inelastic effects.
Load Transfer Characteristics in Metal/Matrix Composites due to a Fiber Breakage
Authors: Folias E. S. 
Published: January 2022

Abstract
In this study, the load transfer characteristics of a broken fiber are investigated. The problem consists of a cylindrical fiber that is embedded into a matrix material. The fiber axis is assumed to coincide with the z-axis and a crack is assumed to be present on the plane z = 0 and for r &lt; a. Far away from the crack, the fiber is subjected to a uniform external load σo.
Moreover, adjacent to the crack and along the interface, the matrix and fiber surfaces are assumed to slide along the interface length −c &lt; z &lt; c, in the presence of a variable frictional force. On the other hand, perfect bonding is assumed to prevail all along the remaining interface, i.e., for |z| &gt; c.
For the solution of the problem, we utilize a Fourier Integral Transform whereby we reduce the problem to that of the solution of a singular integral equation along the interface path −c &lt; z &lt; c. The solution of the integral equation then allows the determination of the displacement and stress fields. Two areas of special interest immediately come to mind, (I) the neighborhood adjacent to the point |z| = c and r = a, and (ii) the neighborhood adjacent to the point z = 0 and r = a.
The analysis reveals that the usual stress singularity which is characteristic to problems of dissimilar materials with friction prevails and that the interface shear stress is non-uniform. Moreover, the ratio of fiber jump over fiber diameter is found to be related to the applied load as well as the material properties.
Prediction of Damage Evolution in Laminated Composites Subjected to Impact Loading
Authors: Allen D. H. , Searcy C. R. 
Published: January 2022

Abstract
Many structural components undergo significant structural damage when they are subjected to ballistic impact. Because this damage can lead to failure of monolithic components to perform their intended missions, composite structures have recently been developed to better withstand impact. The intent of these new types of composites is to provide tougher, yet lighter structures that will withstand significantly larger ballistic impact energies than do traditional monolithic structures. Although these new composite structures do indeed appear to provide increased toughness, they also undergo much more complicated damage mechanisms, so that it has become difficult to accurately predict the limits of usefulness of structures made with these materials.
It is evident that in order to develop design tools that can be used to assess the performance characteristics of these composite components, it is necessary to develop models that can accurately predict the evolution of damage of various types during actual impact events. This paper outlines a methodology based in continuum mechanics and utilizing advanced damage, fracture, and computational mechanics to obtain accurate predictions of damage evolution in laminated composite structures during ballistic impact. The evolution of damage is accounted for by the use of a cohesive zone model capable of predicting matrix, fiber, and interply cracking in ductile polymers. This model has been implemented to a global three dimensional finite element computer code for the purpose of predicting the evolution of damage during impact. The resulting algorithm is utilized herein to predict the types of damage events experimentally observed in laminated composite plates subjected to impact, and comparisons are made to two experimental results obtained by the author and coworkers.
Crack Propagating in a Bimaterial Functionally Graded Multilayered Composite Media
Authors: Muju Sandeep 
Published: January 2022

Abstract
The macroscopically anisotropic homogenization of a multilayered composite implicitly assumes that the spatial wavelength of material inhomogeneity is smaller than the macroscopic quantity of interest and hence, is a reasonable approximation of the bulk behavior [1]. However, close to the crack tip, gradients in field quantities are strongly influenced by the local heterogeneity, which the anisotropic homogenization fails to capture. Thus, given the insights from a homogenized continuum study, the next level of refinement is to study the effect of inhomogeneity on crack driving force.
Asymptotic studies of cracks perpendicular and parallel to a bimaterial interface and in a layer between two materials have been very widely researched over the past two decades. Recently the advent of the use of functionally gradient materials (FGM) in composites, nano-composites and other multi-material structural systems has spurred interest in the fracture mechanics of such inhomogeneous materials. The problems considered in the literature typically assume a functional form for the material property variation, usually in one direction only, and calculate the driving force at the crack tip for a crack at some orientation to the direction of variation. The interest in FGM’s is due to their superior performance as interfacial layers in general and in particular in high temperature applications. Discontinuities in material properties between joined material constituents act as stress concentrators, especially due to thermal expansion mismatches under thermal processing or service loads. The use of a FGM as an interfacial layer smooths the discontinuity and reduces the stress concentrations.
In this paper an analytic solution for the effect of periodic inhomogeneity on crack driving force is studied. Via Williams eigenfunction expansion approach it is seen that, for continuously differentiable moduli inhomogeneity the nature of the stress singularity at the crack tip is the same as in a homogeneous media, though the eigenvalue (Stress Intensity Factor) does depend on the inhomogeneity [1]. In order to study the effect of layered inhomogeneity on the Stress Intensity Factor(s), the Bueckner-Rice weight function approach for homogeneous media [2–3] is incorporated here to study the layered media problem. In this chapter the moduli perturbation approach, [4], is further extended to the case of multilayered media, especially in a functionally gradient material sense. It is shown that to the first order, the effect of moduli inhomogeneity, residual stresses and inelastic strains on crack tip stress intensity factor are superposable.
The results provide insight into the influence of residual stress and periodic moduli inhomogeneity on effective crack driving force for cracks propagating through multilayered bimaterial media. Further, this method in general allows one to study thermoelastic crack problems in complex heterogeneous media, alleviating difficulties associated with some of the traditional methods.
A Composite-Sheathed Compression Test for Characterizing Pressure-Hardening Materials
Authors: Chou Pei Chi , Flis William J. 
Published: January 2022

Abstract
Knowledge of the constitutive behavior of explosives is necessary for the development of exploding devices that are safe to handle and transport and that are effective in use. The plastic deformation of most explosives is strongly affected by pressure and by strain rate. Pressure-hardening effects may be determined directly by a uniaxial-compression test performed in a special hydraulic apparatus that applies a lateral pressure to the specimen. However, the apparatus is expensive and testing explosives presents some risk to it.
Previously, to investigate both pressure- and rate-hardening effects, we developed a modified Taylor cylinder-impact test in which the explosive specimen is encased in a confining sheath (or sleeve) of a well-characterized material, typically a ductile metal such as copper. The sheath, which is stiffer than the explosive, serves to confine the specimen to provide increased pressure and also maintains its integrity. Computations using a large-deformation dynamic plasticity code (hydrocode) are then fitted to the test results (the shape of the deformed specimen) to provide an estimate of the constitutive parameters.
To refine our results, we are currently developing a similar quasi-static compression test that uses a confining sheath to develop the pressure in the specimen. In our cylinder-impact tests, the copper sheath was able to generate pressures up to about 0.5 GPa. In quasi-static compression tests, however, a copper sheath fails at much lower pressures. To provide the higher pressures required, we are using instead a sheath of graphite- or glass-fiber composite material. The fibers are aligned in the circumferential direction to provide a very large hoop strength, with little axial stiffness. The axial load is thus carried mainly by the explosive specimen.
To design the sleeve and for post-test fitting of results, we have modified a finite-element hydrocode to include an anisotropic (orthotropic) elastic-plastic constitutive formulation to model the composite. Compressibility behavior is modeled using an established fit to Murnaghan_s pressure-volume relation. To describe the yield surface, both the simple Drucker-Prager criterion and a non-linear relation will be tried.
This test will be used to characterize first mock explosives, then, once validated, actual explosives. Advantages of the new test include economy and low risk of damage to test equipment.
An Overview of Shear Deformation Theories and Their Relationships to the Classical Theory
Authors: Reddy J. N. 
Published: January 2022

Abstract
The paper presents a review of various shear deformation theories of beams and plates and a critical evaluation of the theories from analysis points of view. In particular post-computation of stresses in composites is revisited and alternative approaches are discussed in light of Pagano’s works on the subject. In addition, relationships for bending, vibration, and buckling solutions of shear deformation theories in terms of the corresponding solutions of the classical theory are discussed. These relationships may be used to determine the solutions of shear deformation theories by knowing the corresponding solutions of the classical theory. These relationships are also used to develop finite element models of the shear deformation theories of beams and plates. These finite element models, unlike the conventional finite element models, are free of so-called shear locking.
Dedication: This work is dedicated to Nicholas J. Pagano, a friend and colleague, on his sixty fifth birthday.