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Search indexed NASA NTRS and DOE OSTI research on propulsion, heat transfer, battery materials and energy systems. Follow report and document links to the original sources.

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At least 415 records · Page 23
All sourcesNASA NTRSDOE OSTI
DOE OSTI2018

Comparative Study of the Standards and Guides of a Management System Applicable to Radioactive Waste - Paper 18292

A Management System may be defined as a set of standardized and interrelated practices that aim to improve effectiveness and produce better results. This system should be structured in such a way as to allow essential information to flow properly within the organization, including technical, administrative, production and human resources information, among others, within an adopted compliance model. There are, currently, several standards and guidelines for structuring a compliance model related to a management system. A system that covers various aspects of management in a single system is usually called integrated. Only the International Atomic Energy Agency - IAEA has a guide with this approach for radioactive waste: GS-G-3.3, 'The Management System for the Processing, Handling and Storage of Radioactive Waste' and GS-G-3.4, 'The Management System for the Disposal of Radioactive Waste'. The objective of this work is to present a comparison between existing standards, even if not specific for the management of radioactive waste, but which are widely used by companies. In due course, the result of this work will be object of proposal for specific standard to be presented to regulatory agency for this type of activity. This study should be useful for countries where there are no specific guidelines by the regulatory agency, adopting the best standard or guide as a conformity standards, creating and establishing a hybrid structure best suited to the safety and security aspects of the local culture. (authors)

12 MANAGEMENT OF RADIOACTIVE AND NON-RADIOACTIVE W↗
DOE OSTI2015

A comparative study of diffraction of shallow-water waves by high-level IGN and GN equations

This work is on the nonlinear diffraction analysis of shallow-water waves, impinging on submerged obstacles, by two related theories, namely the classical Green–Naghdi (GN) equations and the Irrotational Green–Naghdi (IGN) equations, both sets of equations being at high levels and derived for incompressible and inviscid flows. Recently, the high-level Green–Naghdi equations have been applied to some wave transformation problems. The high-level IGN equations have also been used in the last decade to study certain wave propagation problems. However, past works on these theories used different numerical methods to solve these nonlinear and unsteady sets of differential equations and at different levels. Moreover, different physical problems have been solved in the past. Therefore, it has not been possible to understand the differences produced by these two sets of theories and their range of applicability so far. We are thus motivated to make a direct comparison of the results produced by these theories by use of the same numerical method to solve physically the same wave diffraction problems. We focus on comparing these two theories by using similar codes; only the equations used are different but other parts of the codes, such as the wave-maker, damping zone, discretion method, matrix solver, etc., are exactly the same. This way, we eliminate many potential sources of differences that could be produced by the solution of different equations. The physical problems include the presence of various submerged obstacles that can be used for example as breakwaters or to represent the continental shelf. A numerical wave tank is created by placing a wavemaker on one end and a wave absorbing beach on the other. The nonlinear and unsteady sets of differential equations are solved by the finite-difference method. The results are compared with different equations as well as with the available experimental data.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
NASA NTRS1988

A comparative study of theoretical methods on Goertler instability

Goertler vortices arise in boundary layers along concave surfaces due to centrifugal effects and these vortices in combination with Tollmien-Schlichting (TS) waves and crossflow vortices may play an important role in triggering early transition. There have been two distinct theoretical approaches to solve the problem. In the classical, normal-mode approach (NMA) the linear development of Goertler vortices is reduced to an eigenvalue problem. In the other method, initiated by Hall, the governing partial differential equations for the perturbations which are parabolic in the streamwise direction, are solved as an initial value problem. This method predicts multiple neutral curves depending on how and where the mean flow is perturbed, unlike the NMA where a unique but different neutral curve is predicted by each investigator. The present paper attempts to compare the two techniques and shows that mutually compatible results can be obtained when physically consistent assumptions are made.

Kalburgi, Vijay↗
NASA NTRS2013

Comparative Study of Vibration Condition Indicators for Detecting Cracks in Spur Gears

This paper reports the results of an empirical study on the tooth breakage failure mode in spur gears. Of four dominant gear failure modes (breakage, wear, pitting, and scoring), tooth breakage is the most precipitous and often leads to catastrophic failures. The cracks were initiated using a fatigue tester and a custom-designed single-tooth bending fixture to simulate over-load conditions, instead of traditional notching using wire electrical discharge machining (EDM). The cracks were then propagated on a dynamometer. The ground truth of damage level during crack propagation was monitored with crack-propagation sensors. Ten crack propagations have been performed to compare the existing condition indicators (CIs) with respect to their: ability to detect a crack, ability to assess the damage, and sensitivity to sensor placement. Of more than thirty computed CIs, this paper compares five commonly used: raw RMS, FM0, NA4, raw kurtosis, and NP4. The performance of combined CIs was also investigated, using linear, logistic, and boosted regression trees based feature fusion.

Nanadic, Nenad↗
DOE OSTI2014

Structural, negative thermal expansion and photocatalytic properties of ZrV{sub 2}O{sub 7}: a comparative study between fibers and powders

Novel ZrV{sub 2}O{sub 7} microfibers with diameters about 1–3 μm were synthesized using a sol–gel technique. For comparison, ZrV{sub 2}O{sub 7} powders were prepared by the same method. The resultant structures were studied by X-ray diffraction, field-emission scanning electron microscopy and transmission electron microscopy. The results indicated that both the pure ZrV{sub 2}O{sub 7} microfibers and powders could be synthesized by the sol–gel technique. The thermal expansion property of the as-prepared ZrV{sub 2}O{sub 7} microfibers and powders was characterized by a thermal mechanical analyzer, both the fibers with cylindrical morphology and irregular powders with average size between 100 and 200 nm showed negative thermal expansion between 150 °C and 600 °C. The photocatalytic activity of the microfibers was compared to that of powders under UV radiations. The band gap of ZrV{sub 2}O{sub 7} microfibers decreased and its absorption edge exhibited red shift. The microfibers also had a higher surface area compared with the powders, resulting in considerably higher photocatalytic characteristics. The large surface area and the enhanced photocatalytic activity of the ZrV{sub 2}O{sub 7} microfibers also offer potential applications in sensors and inorganic ion exchangers. - Graphical abstract: (a and c) SEM photos of ZrV{sub 2}O{sub 7} powders and fibers. (b and d) TEM images of ZrV{sub 2}O{sub 7} powders and fibers. (e) Thermal expansion curves of ZrV{sub 2}O{sub 7} powders and fibers. (f) Degradation curves of ZrV{sub 2}O{sub 7} powders and ZrV{sub 2}O{sub 7} fibers. - Highlights: • Novel ZrV{sub 2}O{sub 7} fibers could be synthesized using sol–gel technique. • ZrV{sub 2}O{sub 7} powders with irregular shape are also prepared for comparison. • Both ZrV{sub 2}O{sub 7} microfibers and powders exhibit negative thermal expansion property. • ZrV{sub 2}O{sub 7} microfibers show outstanding photocatalytic activity under UV irradiation. • This synthesis technique can be easily extended to many other functional fibers.

36 MATERIALS SCIENCE↗
DOE OSTI2013

A dosimetric comparative study: Volumetric modulated arc therapy vs intensity-modulated radiation therapy in the treatment of nasal cavity carcinomas

The purpose of this study was to evaluate the differences between volumetric modulated arc therapy (VMAT) and intensity-modulated radiation therapy (IMRT) in the treatment of nasal cavity carcinomas. The treatment of 10 patients, who had completed IMRT treatment for resected tumors of the nasal cavity, was replanned with the Philips Pinnacle{sup 3} Version 9 treatment-planning system. The IMRT plans used a 9-beam technique whereas the VMAT (known as SmartArc) plans used a 3-arc technique. Both types of plans were optimized using Philips Pinnacle{sup 3} Direct Machine Parameter Optimization algorithm. IMRT and VMAT plans' quality was compared by evaluating the maximum, minimum, and mean doses to the target volumes and organs at risk, monitor units (MUs), and the treatment delivery time. Our results indicate that VMAT is capable of greatly reducing treatment delivery time and MUs compared with IMRT. The reduction of treatment delivery time and MUs can decrease the effects of intrafractional uncertainties that can occur because of patient movement during treatment delivery. VMAT's plans further reduce doses to critical structures that are in close proximity to the target volume.

61 RADIATION PROTECTION AND DOSIMETRY↗
DOE OSTI2015

A Randomized Phase 2 Study Comparing 2 Stereotactic Body Radiation Therapy Schedules for Medically Inoperable Patients With Stage I Peripheral Non-Small Cell Lung Cancer: NRG Oncology RTOG 0915 (NCCTG N0927)

Purpose: To compare 2 stereotactic body radiation therapy (SBRT) schedules for medically inoperable early-stage lung cancer to determine which produces the lowest rate of grade ≥3 protocol-specified adverse events (psAEs) at 1 year. Methods and Materials: Patients with biopsy-proven peripheral (≥2 cm from the central bronchial tree) T1 or T2, N0 (clinically node negative by positron emission tomography), M0 tumors were eligible. Patients were randomized to receive either 34 Gy in 1 fraction (arm 1) or 48 Gy in 4 consecutive daily fractions (arm 2). Rigorous central accreditation and quality assurance confirmed treatment per protocol guidelines. This study was designed to detect a psAEs rate >17% at a 10% significance level (1-sided) and 90% power. Secondary endpoints included rates of primary tumor control (PC), overall survival (OS), and disease-free survival (DFS) at 1 year. Designating the better of the 2 regimens was based on prespecified rules of psAEs and PC for each arm. Results: Ninety-four patients were accrued between September 2009 and March 2011. The median follow-up time was 30.2 months. Of 84 analyzable patients, 39 were in arm 1 and 45 in arm 2. Patient and tumor characteristics were balanced between arms. Four (10.3%) patients on arm 1 (95% confidence interval [CI] 2.9%-24.2%) and 6 (13.3%) patients on arm 2 (95% CI 5.1%-26.8%) experienced psAEs. The 2-year OS rate was 61.3% (95% CI 44.2%-74.6%) for arm 1 patients and 77.7% (95% CI 62.5%-87.3%) for arm 2. The 2-year DFS was 56.4% (95% CI 39.6%-70.2%) for arm 1 and 71.1% (95% CI 55.5%-82.1%) for arm 2. The 1-year PC rate was 97.0% (95% CI 84.2%-99.9%) for arm 1 and 92.7% (95% CI 80.1%-98.5%) for arm 2. Conclusions: 34 Gy in 1 fraction met the prespecified criteria and, of the 2 schedules, warrants further clinical research.

62 RADIOLOGY AND NUCLEAR MEDICINE↗
DOE OSTI2021

A Comparative Study of Layer Heating and Continuous Heating Methods on Prediction Accuracy of Residual Stresses in Selective Laser Melted Tube Samples

Thermal distortion and residual stresses are two important factors that affect the quality and reliability of steel parts manufactured by laser powder bed fusion (LPBF) processes. A cost-effective model for evaluation of those heat effects is needed to refine the manufacturing process and provides insights into the product design and heat treatment. In this study, the layer heating method and sophisticated track-layer scanning method were applied to simulate the thermo-mechanical response of IN625 tube parts built by LPBF. Based on the similarity of temperature field in each layer deposit, a swept mesh was constructed to perform the thermal analysis for top layer, with the rest of layers referring to the temperature by node number offsetting. A novel explicit finite element analysis code accelerated by graphics processing unit was used for the massive-element numerical analysis. The computational accuracy and efficiency of the layer heating and track-layer scanning methods were compared in detail. It is shown that layer heating method can efficiently capture the pattern of stress distribution with reasonable accuracy in stress magnitude. The grouped track-layer scanning method can predict the residual stress and strain more accurately at a higher cost (5 ~ 10×). The elastic strain distribution was compared with the measurement by X-ray diffraction, confirming the accuracy of residual stress prediction.

36 MATERIALS SCIENCE↗
NASA NTRS1994

Installed F/A-18 inlet flow calculations at 30 degrees angle-of-attack: A comparative study

NASA Lewis is currently engaged in a research effort as a team member of the High Alpha Technology Program (HATP) within NASA. This program utilizes a specially equipped F/A-18, the High Alpha Research Vehicle (HARV), in an ambitious effort to improve the maneuverability of high-performance military aircraft at low subsonic speed, high angle of attack conditions. The overall objective of the Lewis effort is to develop inlet technology that will ensure efficient airflow delivery to the engine during these maneuvers. One part of the Lewis approach utilizes computational fluid dynamics codes to predict the installed performance of inlets for these highly maneuverable aircraft. Full Navier-Stokes (FNS) calculations on the installed F/A-18 inlet at 30 degrees angle of attack, 0 degrees yaw, and a freestream Mach number of 0.2 have been obtained in this study using an algebraic turbulence model with two grids (original and revised). Results obtained with the original grid were used to determine where further grid refinements and additional geometry were needed. In order to account properly for the external effects, the forebody, leading edge extension (LEX), ramp, and wing were included with inlet geometry. In the original grid, the diverter, LEX slot, and leading edge flap were not included due to insufficient geometry definition, but were included in a revised grid. In addition, a thin-layer Navier-Stokes (TLNS) code is used with the revised grid and the numerical results are compared to those obtained with the FNS code. The TLNS code was used to evaluate the effects on the solution using a code with more recent CFD developments such as upwinding with TVD schemes versus central differencing with artificial dissipation. The calculations are compared to a limited amount of available experimental data. The predicted forebody/fuselage surface static pressures compared well with data of all solutions. The predicted trajectory of the vortex generated under the LEX was different for each solution. These discrepancies are attributed to differences in the grid resolution and turbulence modeling. All solutions predict that this vortex is ingested by the inlet. The predicted inlet total pressure recoveries are lower than data and the distortions are higher than data. The results obtained with the revised grid were significantly improved from the original grid results. The original grid results indicated the ingested vortex migrated to the engine face and caused additional distortions to those already present due to secondary flow development. The revised grid results indicate that the ingested vortex is dissipated along the inlet duct inboard wall. The TLNS results indicate the flow at the engine face was much more distorted than the FNS results and is attributed to the pole boundary condition introducing numerical distortions into the flow field.

Smith, C. Frederic↗
DOE OSTI2014

Induced lattice strain in epitaxial Fe-based superconducting films on CaF{sub 2} substrates: A comparative study of the microstructures of SmFeAs(O,F), Ba(Fe,Co){sub 2}As{sub 2}, and FeTe{sub 0.5}Se{sub 0.5}

The microstructures of SmFeAs(O,F), Ba(Fe,Co){sub 2}As{sub 2}, and FeTe{sub 0.5}Se{sub 0.5} prepared on CaF{sub 2} substrates were investigated using transmission electron microscopy. The SmFeAs(O,F)/CaF{sub 2} interface is steep, without a disordered layer. By contrast, a chemical reaction occurs at the interface in the cases of Ba(Fe,Co){sub 2}As{sub 2} and FeTe{sub 0.5}Se{sub 0.5}. The reaction layers are located on opposite sides of the interface for Ba(Fe,Co){sub 2}As{sub 2} and FeTe{sub 0.5}Se{sub 0.5}. We found that the lattice distortion of the three superconducting films on the CaF{sub 2} substrates enhances the T{sub C} values compared with films prepared on oxide substrates. The origin of this lattice deformation varies depending on the superconducting material.

36 MATERIALS SCIENCE↗
NASA NTRS2004

What Multilevel Parallel Programs do when you are not Watching: A Performance Analysis Case Study Comparing MPI/OpenMP, MLP, and Nested OpenMP

With the current trend in parallel computer architectures towards clusters of shared memory symmetric multi-processors, parallel programming techniques have evolved that support parallelism beyond a single level. When comparing the performance of applications based on different programming paradigms, it is important to differentiate between the influence of the programming model itself and other factors, such as implementation specific behavior of the operating system (OS) or architectural issues. Rewriting-a large scientific application in order to employ a new programming paradigms is usually a time consuming and error prone task. Before embarking on such an endeavor it is important to determine that there is really a gain that would not be possible with the current implementation. A detailed performance analysis is crucial to clarify these issues. The multilevel programming paradigms considered in this study are hybrid MPI/OpenMP, MLP, and nested OpenMP. The hybrid MPI/OpenMP approach is based on using MPI [7] for the coarse grained parallelization and OpenMP [9] for fine grained loop level parallelism. The MPI programming paradigm assumes a private address space for each process. Data is transferred by explicitly exchanging messages via calls to the MPI library. This model was originally designed for distributed memory architectures but is also suitable for shared memory systems. The second paradigm under consideration is MLP which was developed by Taft. The approach is similar to MPi/OpenMP, using a mix of coarse grain process level parallelization and loop level OpenMP parallelization. As it is the case with MPI, a private address space is assumed for each process. The MLP approach was developed for ccNUMA architectures and explicitly takes advantage of the availability of shared memory. A shared memory arena which is accessible by all processes is required. Communication is done by reading from and writing to the shared memory.

Jost, Gabriele↗
DOE OSTI2022

A Comparative Study of Compressive Effects on the Morphology and Performance of Carbon Paper and Cloth Electrodes in Redox Flow Batteries

Compressing porous carbon electrodes is a common approach to improve flow battery performance, but the resulting impact on electrode structure, fluid dynamics, and cell performance is not well understood. Herein, microtomographic imaging, load cell testing, and flow cell diagnostics are employed to characterize how compression‐induced changes impact pressure drop, polarization, and mass‐transfer scaling. Five different compressions are tested, spanning ranges typically used in literature, for AvCarb 1071 cloth (0%, 9%, 20%, 25%, 32%) and Freudenberg H23 paper (0%, 8%, 12%, 17%, 22%). It is found that the two electrode structures have distinct responses to compression, resulting in differing optimal conditions identified for each material; specifically, the Freudenberg H23 exhibits lower combined ohmic, charge‐transfer, and mass‐transport values at 8% compression, resulting in improved electrochemical performance across all compressive values, as compared to the optimal AvCarb 1071 compression (20%). Overall, Freudenberg H23 exhibits a greater sensitivity to compression with peak electrochemical activity correlating with increased permeability, whereas AvCarb 1071 is insensitive to compressive loads but produces lower electrochemical performance. Herein, the trade‐offs of mechanical robustness on fluid‐dynamic and electrochemical performance between the two electrodes are demonstrated by the aforementioned findings, suggesting each could be used for specific operating environments.

25 ENERGY STORAGE↗
NASA NTRS1992

A comparative study of two codes with an improved two-equation turbulence model for predicting jet plumes

Compressible jet plumes were studied using a two-equation turbulence model. A space marching procedure based on an upwind numerical scheme was used to solve the governing equations and turbulence transport equations. The computed results indicate that extending the space marching procedure for solving supersonic/subsonic mixing problems can be stable, efficient and accurate. Moreover, a newly developed correction for compressible dissipation has been verified in fully expanded and underexpanded jet plumes. For a sonic jet plume, no improvement in results over the standard two-equation model was seen. However for a supersonic jet plume, the correction due to compressible dissipation successfully predicted the reduced spreading rate of the jet compared to the sonic case. The computed results were generally in good agreement with the experimental data.

Balakrishnan, L.↗
DOE OSTI2015

A comparative study of transport properties of monolayer graphene and AlGaN-GaN heterostructure

The electronic transport properties of monolayer graphene are presented with an Ensemble Monte Carlo method where a rejection technique is used to account for the occupancy of the final states after scattering. Acoustic and optic phonon scatterings are considered for intrinsic graphene and in addition, ionized impurity and surface roughness scatterings are considered for the case of dirty graphene. The effect of screening is considered in the ionized impurity scattering of electrons. The time dependence of drift velocity of carriers is obtained where overshoot and undershoot effects are observed for certain values of applied field and material parameters for intrinsic graphene. The field dependence of drift velocity of carriers showed negative differential resistance and disappeared as acoustic scattering becomes dominant for intrinsic graphene. The variation of electron mobility with temperature is calculated for intrinsic (suspended) and dirty monolayer graphene sheets separately and they are compared. These are also compared with the mobility of two dimensional electrons at an AlGaN/GaN heterostructure. It is observed that interface roughness may become very effective in limiting the mobility of electrons in graphene.

36 MATERIALS SCIENCE↗
DOE OSTI2016

SU-F-T-315: Comparative Studies of Planar Dose with Different Spatial Resolution for Head and Neck IMRT QA

Purpose: To quantitatively investigate the planar dose difference and the γ value between the reference fluence map with the 1 mm detector-to-detector distance and the other fluence maps with less spatial resolution for head and neck intensity modulated radiation (IMRT) therapy. Methods: For ten head and neck cancer patients, the IMRT quality assurance (QA) beams were generated using by the commercial radiation treatment planning system, Pinnacle3 (ver. 8.0.d Philips Medical System, Madison, WI). For each beam, ten fluence maps (detector-to-detector distance: 1 mm to 10 mm by 1 mm) were generated. The fluence maps with larger than 1 mm detector-todetector distance were interpolated using MATLAB (R2014a, the Math Works,Natick, MA) by four different interpolation Methods: for the bilinear, the cubic spline, the bicubic, and the nearest neighbor interpolation, respectively. These interpolated fluence maps were compared with the reference one using the γ value (criteria: 3%, 3 mm) and the relative dose difference. Results: As the detector-to-detector distance increases, the dose difference between the two maps increases. For the fluence map with the same resolution, the cubic spline interpolation and the bicubic interpolation are almost equally best interpolation methods while the nearest neighbor interpolation is the worst.For example, for 5 mm distance fluence maps, γ≤1 are 98.12±2.28%, 99.48±0.66%, 99.45±0.65% and 82.23±0.48% for the bilinear, the cubic spline, the bicubic, and the nearest neighbor interpolation, respectively. For 7 mm distance fluence maps, γ≤1 are 90.87±5.91%, 90.22±6.95%, 91.79±5.97% and 71.93±4.92 for the bilinear, the cubic spline, the bicubic, and the nearest neighbor interpolation, respectively. Conclusion: We recommend that the 2-dimensional detector array with high spatial resolution should be used as an IMRT QA tool and that the measured fluence maps should be interpolated using by the cubic spline interpolation or the bicubic interpolation for head and neck IMRT delivery. This work was supported by Radiation Technology R&D program through the National Research Foundation of Korea funded by the Ministry of Science, ICT & Future Planning (No. 2013M2A2A7038291)

60 APPLIED LIFE SCIENCES↗
DOE OSTI2020

A comparative study of silver- and palladium-exchanged zeolites in propylene and nitrogen oxide adsorption and desorption for cold-start applications

Here, silver and palladium ion-exchanged BEA zeolites (Si/Al = 12.5) and silver ion-exchanged ZSM-5 zeolites (Si/Al = 15) were studied for their ability to adsorb and desorb propylene and NO under simulated diesel exhaust conditions. The adsorption experiment results demonstrated the excellent ability of bare BEA zeolites to adsorb propylene, but only a small amount of NO. The presence of H 2 O inhibited the adsorption of both C 3 H 6 and NO. Ion-exchanging BEA zeolites with Ag (1.2 and 5.1 wt.% Ag/BEA) attenuated the inhibiting effect of H 2 O on C 3 H 6 adsorption, while NO storage remained inhibited. Adsorption experiments indicated that C 3 H 6 and NO competed with each other for Pd sites with C 3 H 6 showing stronger adsorption compared to NO, whereas Ag sites preferentially adsorbed C 3 H 6 . DRIFTS data indicated the formation of nitrate, formate and acetate species on Ag and Pd, while C 3 H 6 and NO adsorption was also observed on the zeolite hydroxyl groups in the absence of H 2 O. However, the C 3 H 6 and NO adsorption on the zeolite hydroxyl groups was significantly inhibited in the presence of H 2 O. Additionally, nitrosyl, acrolein and carbonate species were formed over 1.0 wt.% Pd/BEA. The effluent analysis during the temperature-programmed desorption in the DRIFTS reactor revealed that adsorbed C 3 H 6 and NO reacted during the release to form oxidation reaction byproducts. The 1.0 wt.% Pd/BEA zeolite showed the greatest oxidation ability during desorption with the majority of stored C 3 H 6 converted to CO 2 .

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2019

A Comparative Study on Artificial Neural Network, Phenomenological-Based Constitutive and Modified Fields–Backofen Models to Predict Flow Stress in Ti-4Al-3V-2Mo-2Fe Alloy

The flow curve was obtained from the superplastic tensile tests in the temperature range of 1033-1153 K and strain rate range of 0.001-0.1 s{sup −1}. Results showed that strain hardening (SH) was insensitive to deformation parameter variation but with the nature of material, while stable state (SS) and dynamic softening (DS) were significantly associated with a thermal activated process. The occurrence of secondary hardening and softening was attributed to discontinuous dynamic recrystallization. And the generation of necklace microstructure at grain boundaries was caused by bulging. Based on the experimental data, the artificial neural network (ANN), phenomenological-based constitutive (PBC) and modified Fields–Backofen (MFB) models were developed, and their predictability and adaptability for the description of the flow behavior during hot processing were evaluated by analyzing the employed standard statistical parameters. Comparatively, ANN model is capable of tracing the complex flow behavior including SH, SS and DS substages. Concerning PBC model, it can not only predict flow stress with satisfactory accuracy, but also represent the flow trend with the larger strain. MFB model adapts well to the flow curve with a broad SH region without DS effect.

36 MATERIALS SCIENCE↗
DOE OSTI2019

Comparative Study of the Geometric Effects on Fracture Behaviors of Side-Grooved and Plain-Sided Compact Tension Specimens

This paper investigates the fracture response and crack-tip constraint of two typical compact tension specimens. They are pre-cracked plain-sided and side-grooved specimens. In order to clarify the significant effects of geometric parameters on the crack-tip stress fields, an extensive series of detailed 3D elastic–plastic finite element analyses have been carried out. Taking the standard ratio of geometric parameters as a basis, several non-standard geometric parameters are adopted in the calculation for comparison, including specimen thickness, width, crack length. Accordingly, the variation of local J-integral and crack-tip opening displacement have been vigorously investigated over the crack front. Most importantly, the crack-tip stress fields are analyzed in detail with the emphasis on the stress triaxiality and opening mode stress. Furthermore, the crack-tip plastic strain and deformation are compared under small-scale yielding and large-scale yielding between plain-sided and side-grooved specimens, and the constraint parameter Q is employed to explain the distribution of the near-tip plastic strain. Through the vigorous research work, the variation of fracture behavior caused by geometric parameters is reasonably explained and understood.

36 MATERIALS SCIENCE↗