| |
Records |
Links |
|
Type |
Lee, W.-S.; Chen, T.-H. |
| |
Publication |
Mechanical and microstructural response of aluminum-scandium (Al-Sc) alloy as a function of strain rate and temperature |
Volume |
Journal Article |
Pages  |
2009 |
| |
Abstract |
Materials Chemistry and Physics |
|
| |
Corporate Author |
|
|
Publisher |
113 |
|
Editor |
2-3 |
| |
Summary Language |
734-745 |
Series Editor |
Al-Sc alloy; Strain rate sensitivity; Activation energy; Shearing; Dislocation; Precipitates |
|
Abbreviated Series Title |
This study applies a compressive split Hopkinson bar to investigate the mechanical response, microstructural evolution and fracture characteristics of aluminum-scandium (Al-Sc) alloy at temperatures ranging from -100 °C to 300 °C and strain rates of 1.2 × 103 s-1, 3.2 × 103 s-1 and 5.8 × 103 s-1. The relationship between the dynamic mechanical behaviour of the Al-Sc alloy and its microstructural characteristics is explored. The fracture features and microstructural evolution are observed using scanning and transmission electron microscopy techniques. The stress-strain relationships indicate that the flow stress, work hardening rate and strain rate sensitivity increase with strain rate, but decrease with increasing temperature. Conversely, the activation volume and activation energy increase as the temperature increases or the strain rate decreases. Additionally, the fracture strain reduces with increasing strain rate and decreasing temperature. However, at room temperature under a low strain rate of 1.2 × 103 s-1 and at a high experimental temperature of 300 °C under all three tested strain rates, the specimens do not fracture, even under large strain deformations. The Zerilli-Armstrong fcc constitutive model is used to describe the plastic deformation behaviour of the Al-Sc alloy. Comparing the predicted flow stress values with the experimental values over all the considered strain rate and temperature conditions, the maximum error between the two sets of results is found to be less than 4%. SEM observations show that the specimens fracture predominantly as a result of a shearing mechanism. Moreover, the surfaces of the fractured specimens are characterised by transgranular dimpled features, which are indicative of a ductile fracture mode. Fine Al3Sc precipitates are found to be distributed in the matrix and at the grain boundaries. Finally, the TEM analysis results reveal that the dislocation density increases, but the dislocation cell size decreases, with increasing strain rate. However, a higher temperature causes the dislocation density to decrease, thereby increasing the dislocation cell size. |
| |
Series Issue |
|
ISSN |
|
|
Medium |
|
| |
Expedition |
|
Notes |
|
|
Call Number |
|
|
Contribution Id |
|
|
Serial |
|
URL |
|
ISBN |
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
no |
|
NU @ karnesky @ |
|
10512 |
| Permanent link to this record |
| |
|
| |
|
Lee, Thomas C. M. |
|
ON ALGORITHMS FOR ORDINARY LEAST SQUARES REGRESSION SPLINE FITTING: A COMPARATIVE STUDY |
|
Journal Article |
|
2002 |
|
Journal of Statistical Computation and Simulation |
|
|
|
72 |
|
8 |
|
647-663 |
|
Bivariate smoothing; Generalized cross-validation; Genetic algorithms; Regression spline; Stepwise selection |
|
Regression spline smoothing is a popular approach for conducting nonparametric regression. An important issue
associated with it is the choice of a ‘‘theoretically best’’ set of knots. Different statistical model selection
methods, such as Akaike’s information criterion and generalized cross-validation, have been applied to derive
different ‘‘theoretically best’’ sets of knots. Typically these best knot sets are defined implicitly as the optimizers
of some objective functions. Hence another equally important issue concerning regression spline smoothing is
how to optimize such objective functions. In this article different numerical algorithms that are designed for
carrying out such optimization problems are compared by means of a simulation study. Both the univariate and
bivariate smoothing settings will be considered. Based on the simulation results, recommendations for choosing a
suitable optimization algorithm under various settings will be provided. |
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
no |
|
NU @ karnesky @ |
|
860 |
| Permanent link to this record |
| |
|
| |
|
Lee, B.; Elliott, T. S.; Mazumdar, T. K.; McIntyre, P. M.; Pang, Y.; Trost, H. - J. |
|
Knife-edge thin film field emission cathodes on (110) silicon wafers |
|
Journal Article |
|
1994 |
|
Journal of Vacuum Science & Technology A |
|
J. Vac. Sci. Technol. A |
|
B12 |
|
|
|
644-647 |
|
Field Emission |
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
no |
|
|
|
3238 |
| Permanent link to this record |
| |
|
| |
|
Lee, Woei-Shyan; Chen, Tao-Hsing; Lin, Chi-Feng; Chen, Ming-Shiang |
|
Impact deformation behaviour and dislocation substructure of Al-Sc alloy |
|
Journal Article |
|
2010 |
|
Journal of Alloys and Compounds |
|
|
|
493 |
|
1-2 |
|
580-589 |
|
Al-Sc alloy; Strain rate sensitivity; Activation volume; Adiabatic shear band; Dislocation; Precipitates |
|
This paper employs a compressive split-Hopkinson pressure bar to investigate the impact deformation behaviour of Al-Sc alloy under high strain rates of 1.2103s-1, 3.2103s-1 and 5.8103s-1, respectively, and temperatures of -100C, 25C and 300C. It is shown that for a constant temperature, the flow stress, work hardening rate and strain rate sensitivity increase with increasing strain rate, while the activation volume decreases. Conversely, for a constant strain rate, the flow stress, work hardening rate and strain rate sensitivity decrease with increasing temperature, while the activation volume increases. It is found that the impact deformation behaviour of Al-Sc alloy can be accurately described using the Zerilli-Armstrong constitutive equation. Optical microscopy (OM) observations reveal that the specimens fail principally as the result of an adiabatic shearing mechanism. Furthermore, scanning electron microscopy (SEM) observations show that the fracture surfaces are characterised by a dimple-like structure, which indicates a ductile failure mode. Transmission electron microscopy (TEM) observations indicate that the dislocation density and cell size are related to the strain rate, flow stress and temperature. Finally, the TEM observations suggest that the strengthening effect observed in the deformed Al-Sc alloy is the result of Al3Sc precipitates within the matrix and at the grain boundaries, which suppress dislocation motion and prompt an increase in the work hardening stress. |
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
0925-8388 |
|
|
|
|
|
|
|
|
|
|
|
|
|
no |
|
NU @ karnesky @ |
|
10784 |
| Permanent link to this record |
| |
|
| |
|
Rogozhkin, S.; Ageev, V.; Aleev, A.; Zaluzhnyi, A.; Leont’eva-Smirnova, M.; Nikitin, A. |
|
Tomographic atom-probe analysis of temperature-resistant 12%-chromium ferritic-martensitic steel EK-181 |
|
Journal Article |
|
2009 |
|
The Physics of Metals and Metallography |
|
|
|
108 |
|
6 |
|
579-585 |
|
|
|
Abstract At present, the temperature-resistant steels with a rapid reduction of induced radioactivity appear to be a perspective structural material for new-generation nuclear and thermonuclear reactors. Special attention is paid to the nanostructural state of the elaborated materials. In this work, for the first time, there have been carried out tomographic atom-probe studies of the chromium ferritic-martensitic steel EK-181 (RUSFER EK-181) with 12% Cr. Spatial distributions of chemical elements in the investigated volumes of the material with an atomic resolution have been obtained. The dimensions of the investigated portions of the material are on the order of 10 × 10 × 30 nm3. There have been observed nanosized preprecipitates (nanoclusters), i.e., regions enriched in V, Cr, and N atoms, with characteristic sizes of about 3 nm. |
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
no |
|
NU @ karnesky @ |
|
10767 |
| Permanent link to this record |
| |
|
| |
|
Sinnott, Susan; Mao, Zugang; Lee, Kiho |
|
Computational Studies of Molecular Diffusions through Carbon Nanotubes Based membrances (Invited) |
|
Journal Article |
|
2002 |
|
Computer Modeling in Engineering and Science |
|
|
|
3 |
|
5 |
|
575-587 |
|
|
|
Nanofluidics is an area that has been under study for some time in zeolites and idea nanoporous systems. Computational studies of the behavior of molecules in nanoporous structures have played an important role in understanding this phenomenon as experimental studies of molecular behavior in nanometer-scale pores are difficult to perform. in this paper computational work to study molecular motion and the separation of molecular mixtures in carbon nanotube systems is reported. The systems examined include organic molecules, such as CH4, C2H6, n-C4H10, and i-c4H10, and inorganic molecules, such as CO2. The interatomic forces in the molecular dynamics simulations are calculated using a classical reactive empirical bond order hydrocarbon potetial coupled to lernard-Jones and coulombic potentials. Molecules moving at thermal velocities corresponding to 300K are predicted to diffuse from areas of high density to areas of low density through the nanotubes. The simulations indicate how the structure and size of molecules and the nanotubes influence molecular diffusion through the nanotubes and the separation of the molecular mixtures. |
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
no |
|
NU @ z-mao2 @ |
|
198 |
| Permanent link to this record |
| |
|
| |
|
Lee, J. S.; Liu, K. S.; Lin, I. N. |
|
Electron field emission characteristics of planar diamond film array synthesized by chemical vapor deposition process |
|
Journal Article |
|
1997 |
|
Applied Physics Letters |
|
Appl. Phys. Lett. |
|
71 |
|
|
|
554-556 |
|
Field Emission |
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
no |
|
|
|
2549 |
| Permanent link to this record |
| |
|
| |
|
Rogozkin, S.; Chernobaeva, A.; Aleev, A.; Nikitin, A.; Zaluzhnyi, A.; Erak, D.; Shtrombakh, Ya.; Zabusov, O.; Debarberis, L.; Zeman, A. |
|
The Effect of Post-Irradiation Annealing on VVER-440 RPV Materials Mechanolocal Properties and Nano-Structure Under Re-Irradiation |
|
Journal Article |
|
2009 |
|
ASME Conference Proceedings |
|
ASME Conf. Proc. |
|
2009 |
|
43703 |
|
553-562 |
|
|
|
The present work provides the analyses of embrittlement behavior and atom probe tomography study of nano-structure evolution of VVER-440 RPV materials under irradiation and re-irradiation. Specimens from VVER-440 weld with high level of cupper (0.16 wt.%) and phosphorus (0.027–0.038 wt.%) were irradiated in surveillance channels of Rovno Nuclear Power plant unit 1 (Ro-1). The embrittlement behavior has been assessed by transition temperature shift. |
|
|
|
|
|
|
|
Asme |
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
no |
|
NU @ karnesky @ |
|
10983 |
| Permanent link to this record |
| |
|
| |
|
Kim, D.; Kwon, S. J.; Lee, J. D. |
|
New cathode structures of Si-based field emitter arrays |
|
Journal Article |
|
1996 |
|
Int. Vac. Microelectron. Conf., 9th (1996), 534-537 Publisher: Nevskii Kur'er, St. Petersburg, Russia. |
|
|
|
|
|
|
|
534-537 |
|
Field Emission |
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
no |
|
|
|
2007 |
| Permanent link to this record |
| |
|
| |
|
Ju, B. K.; Kim, S. - J.; Lee, Y. H.; Park, B. S.; Baik, Y. - J.; Lim, S.; Oh, M. H. |
|
Characterization of CVD diamond film and diamond-tip field emitter array for FED applications |
|
Journal Article |
|
1996 |
|
Int. Vac. Microelectron. Conf., 9th (1996), 530-533 Publisher: Nevskii Kur'er, St. Petersburg, Russia. |
|
|
|
|
|
|
|
530-533 |
|
Field Emission |
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
no |
|
|
|
2002 |
| Permanent link to this record |
