Atomistic simulation for configuration evolution and energetic calculation of crack in body-centered-cubic iron

2006 ◽  
Vol 21 (10) ◽  
pp. 2542-2549 ◽  
Author(s):  
Li-Xia Cao ◽  
Chong-Yu Wang
Keyword(s):  
Low Temperatures ◽  
Crack Tip ◽  
Dislocation Nucleation ◽  
Effect Of Temperature ◽  
Body Centered Cubic ◽  
Partial Dislocations ◽  
Higher Temperature ◽  
Crack Blunting ◽  
Increasing Temperature ◽  
Extended Dislocation

The molecular dynamics method has been used to simulate mode I cracking in body-centered-cubic iron. Close attention has been paid to the process of the atomic configuration evolution of the cracks. The simulation shows that at low temperatures, partial dislocations are emitted before the initiation of crack propagation, subsequently forming the stacking faults or multilayer twins on {112} planes, and then brittle cleavage and extended dislocation nucleation are observed at the crack tip accompanied by twin extension. These results are in agreement with the experimental observation that twinning and fracture processes cooperate at low temperatures. Furthermore, an energetics analysis has been made on the deformation behavior observed at the crack tip. The effect of temperature on the fracture process is discussed. At the higher temperature, plastic deformation becomes easier, and crack blunting occurs. With increasing temperature, the fracture resistance increases, and the effect of the lattice trapping can be weakened by thermal activation.

Atomistic simulation of fracture in Ni3Al

2008 ◽  
Vol 23 (6) ◽  
pp. 1597-1603 ◽  
Author(s):  
Hong-Xian Xie ◽  
Chong-Yu Wang ◽  
Tao Yu
Keyword(s):  
Atomistic Simulation ◽  
Crack Tip ◽  
Dislocation Core ◽  
Atomic Configuration ◽  
Close Attention ◽  
Shockley Partial ◽  
Simulation Process ◽  
Partial Dislocations ◽  
Higher Temperature ◽  
Dynamics Method

The molecular dynamics method has been used to simulate mode I cracking in Ni3Al. Close attention has been paid to the process of atomic configuration evolution of the cracks. The simulation results show that at low temperature, the Shockley partial dislocations are emitted before the initiation of the crack propagation, subsequently forming the pseudo-twins on (111) planes in crack-tip zone, and then the crack cleavage occurs. The emitting of the Shockley partial dislocations accompanies the crack cleavage during the simulation process. At the higher temperature, the blunting at the crack tip is caused by the [110] superdislocations emitted on (100) plane. The present work also shows that the dipole dislocations on (111) planes in the 1/2[110] dislocation core can be formed.

The Effect of Temperature on the Interaction of Phenanthroline-based Ligands with G-quadruplex: In Silico Viewpoint

2019 ◽  
Vol 22 (8) ◽  
pp. 546-554
Author(s):  
Mohadeseh Bazoobandi ◽  
Mohammad R. Bozorgmehr ◽  
Ali Mahmoudi ◽  
Ali Morsali
Keyword(s):  
Molecular Dynamics ◽  
Molecular Dynamics Simulation ◽  
Low Temperatures ◽  
Simulation Method ◽  
Dynamics Simulation ◽  
Effect Of Temperature ◽  
Quadruplex Structure ◽  
G Quadruplex ◽  
The Stability ◽  
Increasing Temperature

Aim and Objective: The stability of the G-quadruplex structure can increase its activity in telomerase inhibiting cancer cells. In this study, a molecular dynamics simulation method was used to study the effect of three phenanthroline-based ligands on the structure of G-quadruplex at the temperatures of 20, 40, 60 and 80°C. Materials and Methods: RMSD values and frequency of calculated RMSD in the presence and absence of ligands show that ligands cause the relative stability of the G-quadruplex, particularly at low temperatures. The calculation of hydrogen bonds in Guanine-tetrads in three different quadruplex sheets shows that the effect of ligands on the sheets is not the same so that the bottom sheet of G-quadruplex is most affected by the ligands at high temperatures, and the Guaninetetrads in this sheet are far away. Conformation factor was calculated as a measure of ligands binding affinity for each of the G-quadruplex residues. Results: The results show that the studied ligands interact more with the G-quadruplex than loop areas, although with increasing temperature, the binding area also includes the G-quadruplex sheets. The contribution of each of the residues involved in the G-quadruplex binding area with ligands was also calculated. Conclusion: The calculations performed are consistent with the previous experimental observations that can help to understand the molecular mechanism of the interaction of phenanthroline and its derivatives with quadruplex.

Effect of Crack Blunting on the Ductile-Brittle Response of Crystalline Materials

1998 ◽  
Vol 539 ◽  
Author(s):  
D.M. Lipkin ◽  
G.E. Beltz ◽  
L.L. Fischer
Keyword(s):  
Crack Tip ◽  
Dislocation Nucleation ◽  
Crack Advance ◽  
Dislocation Emission ◽  
Crystalline Materials ◽  
Self Consistent ◽  
Crack Blunting ◽  
Cohesive Stresses ◽  
Crack Tip Geometry ◽  
Crack Tip Blunting

AbstractWe propose a self-consistent criterion for crack propagation versus dislocation emission, taking into account the effects of crack-tip blunting. Continuum concepts are used to evaluate the evolving competition between crack advance and dislocation nucleation as a function of crack- tip curvature. This framework is used to classify crystals as intrinsically ductile or brittle in terms of the unstable stacking energy, the surface energy, and the peak cohesive stresses achieved during opening and shear of the atomic planes. We find that ductile-brittle criteria based on the assumption that the crack is ideally sharp capture only two of the four possible fracture regimes. One implication of the present analysis is that a crack may initially emit dislocations, only to reinitiate cleavage upon reaching a sufficiently blunted crack-tip geometry.

Dislocation Nucleation Versus Cleavage in Ni3AI and Ni

1990 ◽  
Vol 213 ◽  
Author(s):  
Yuemin Sun ◽  
James R. Rice ◽  
Lev Truskinovsky
Keyword(s):  
Energy Release Rate ◽  
Energy Release ◽  
Release Rate ◽  
Crack Tip ◽  
Dislocation Core ◽  
Critical Energy ◽  
Dislocation Nucleation ◽  
Critical Energy Release Rate ◽  
Cutoff Radius ◽  
Extended Dislocation

ABSTRACTRecent advances in the modelling of dislocation nucleation from a crack tip are used here to compare the critical energy release rate associated with emission in Ni3Al and Ni. The method for analyzing nucleation makes use of a Peierls-type stress versus displacement relation ahead of the crack tip. It has been shown recently by Rice [1] that the energy release rate for emission scales with γus, the “unstable stacking” energy associated with the sliding of atomic planes past one another. The advantage of this approach is that it allows for an extended dislocation core during nucleation, thus eliminating the need for a core cutoff radius. Preliminary calculations which take into account only the shear stress on a slip plane show that it is more difficult to emit a dislocation in Ni3Al than in Ni. Working within the framework of the competition between atomic decohesion and blunting by dislocation emission, the implications for explaining the brittleness of Ni3Al are also discussed.

Glide of extended dislocation in III-V compounds

1987 ◽  
Vol 45 ◽  
pp. 308-311
Author(s):  
B.C. De Cooman ◽  
C.B. Carter
Keyword(s):  
High Temperatures ◽  
Low Temperatures ◽  
High Stress ◽  
Dislocation Dynamics ◽  
Dislocation Mobility ◽  
Weak Beam ◽  
Partial Dislocations ◽  
Doping Effects ◽  
Deformation Regime ◽  
Extended Dislocation

The study of dislocation dynamics has until recently been restricted to relatively high temperatures and low stresses due to the the brittle nature of most semiconductors. Although much is already known for this deformation regime, there is little information from controlled deformation at the low temperatures (i.e., T< 0.5Tm) and high stresses (τ≫ 10 MPa). Deformation of III-V compounds under such conditions has shown the following characteristics:a. High-stress deformation experiments give rise to well-defined dislocation configurations, which makes the study of doping effects on dislocation mobility directly visible. In addition, individual partial dislocations can be observed using weak-beam microscopy.

scholarly journals Temperature changes alter the acute toxicity responses of cypermethrin in Zebrafish

2018 ◽  
Vol 29 (1) ◽  
pp. 64-70 ◽  
Author(s):  
MH Uddin ◽  
MS Alim ◽  
SMM Islam ◽  
H Rashid ◽  
M Shahjahan
Keyword(s):  
Blood Glucose ◽  
Acute Toxicity ◽  
Probit Analysis ◽  
Effect Of Temperature ◽  
Temperature Changes ◽  
Temperature Regimes ◽  
Higher Temperature ◽  
T1 And T2 ◽  
Increasing Temperature ◽  
The Impact

The study was carried out to determine the effect of temperature changes on acute toxicity of pyrethroid pesticide cypermethrin in zebrafish. A two-day renewal bioassay system for 96h was conducted to find out LC50 value of cypermethrin at two temperature regimes i.e. 25°C and 30°C considering as T1 and T2, respectively. During the determination of LC50 in both temperatures, blood glucose (mg/dL) levels were measured at lower concentration (0.25 µg/L) of cypermethrin. The results of acute toxicity test at 96h LC50 values were calculated through probit analysis. It was found that 96h LC50 for T1 and T2 groups were about 2.1 and 1.4 µg/L, respectively. Significantly lower LC50 of cypermethrin at T2 compared to T1 showed that higher temperature increased the toxicity of cypermethrin. There was a significant increase (P<0.05) in blood glucose level (mg/dL) in 0.25 µg/L compared to 0 µg/L concentration of cypermethrin at both treatments. Dissolved oxygen decreased and free CO2 increased significantly (P<0.05) with increasing temperature, while the pH of the water was almost unchanged throughout the study period. The present study indicated the impact of increased temperature on pesticide toxicity in the aquatic ecosystem.Progressive Agriculture 29 (1): 64-70, 2018 

Phase transition and dislocation nucleation in Cu–Nb layered composites during physical vapor deposition

2008 ◽  
Vol 23 (4) ◽  
pp. 1009-1014 ◽  
Author(s):  
Jian Wang ◽  
Richard G. Hoagland ◽  
Amit Misra
Keyword(s):  
Phase Transition ◽  
Physical Vapor Deposition ◽  
Dislocation Nucleation ◽  
Face Centered Cubic ◽  
Body Centered Cubic ◽  
Layered Composites ◽  
Partial Dislocations ◽  
Deposition Parameters ◽  
Face Centered ◽  
Dynamics Simulations

Using classical molecular dynamics simulations, we have investigated the growth of {111} Cu on Nb {110} surface. Our results reveal that the deposited Cu layer initially grows as body-centered cubic (bcc) and Vernier misfits are observed in the interface of bcc Cu and bcc Nb. As it continues to grow, the bcc Cu {110} transforms into face-centered cubic (fcc) Cu {111}. The phase transition starts after the bcc Cu layer has accumulated about 3 monolayers and is finished depending on deposition parameters. Nuclei of fcc Cu {111} form in the top surface of Cu and grow in plane and toward the interface. Partial dislocations in the fcc Cu layer nucleate during the late stage of the transition, and the stacking faults grow as the Cu layer thickens.

EFFECT OF TEMPERATURE ON NET CARBON DIOXIDE EXCHANGE RATES OF TWELVE BARLEY VARIETIES

1968 ◽  
Vol 48 (4) ◽  
pp. 363-368 ◽  
Author(s):  
D. P. Ormrod ◽  
W. F. Hubbard ◽  
D. G. Faris
Keyword(s):  
Carbon Dioxide ◽  
Exchange Rates ◽  
Effect Of Temperature ◽  
Carbon Dioxide Exchange ◽  
Controlled Environment ◽  
Response Curves ◽  
Gradual Decline ◽  
Carbon Dioxide Uptake ◽  
Higher Temperature ◽  
Increasing Temperature

Seedlings of 12 barley varieties were grown in a controlled environment to 21 days of age and then transferred to an apparatus for measuring net carbon dioxide exchange rates. Rates were measured at temperatures ranging from 4 to 34 °C and the results were plotted to provide a response curve for each variety. The response curves were not clearly different between varieties, but some trends were evident. The varieties Husky, Parkland and Vantmore had response curves of similar shape with marked increases with increasing temperature to 14 to 18 °C. Asa, Olli and Pirkka showed a more gradual rise to about 20 °C. Varieties O.A.C. 21, Vantage and Wolfe showed a very rapid increase in carbon dioxide uptake to about 6 °C followed by very little change to 20 °C, leading into a gradual decline. Stavropol, Trebi and White Gatami had maximum rates at a higher temperature. The patterns presented by the varieties may be related to different areas of origin and production. Varieties were markedly different at low temperatures but differed little in response to temperatures near 34 °C. Absolute rates of net carbon dioxide exchange differed markedly among varieties.

Nucleation of Disorder in Fe3Al Alloys

1967 ◽  
Vol 25 ◽  
pp. 312-313
Author(s):  
P. R. Swann ◽  
W. R. Duff ◽  
R. M. Fisher
Keyword(s):  
Electron Microscopy ◽  
Transmission Electron Microscopy ◽  
Annealing Temperature ◽  
Antiphase Domain ◽  
Effect Of Temperature ◽  
Domain Structures ◽  
Transmission Electron ◽  
Domain Boundaries ◽  
Higher Temperature ◽  
The One

Recently we have investigated the phase equilibria and antiphase domain structures of Fe-Al alloys containing from 18 to 50 at.% Al by transmission electron microscopy and Mössbauer techniques. This study has revealed that none of the published phase diagrams are correct, although the one proposed by Rimlinger agrees most closely with our results to be published separately. In this paper observations by transmission electron microscopy relating to the nucleation of disorder in Fe-24% Al will be described. Figure 1 shows the structure after heating this alloy to 776.6°C and quenching. The white areas are B2 micro-domains corresponding to regions of disorder which form at the annealing temperature and re-order during the quench. By examining specimens heated in a temperature gradient of 2°C/cm it is possible to determine the effect of temperature on the disordering reaction very precisely. It was found that disorder begins at existing antiphase domain boundaries but that at a slightly higher temperature (1°C) it also occurs by homogeneous nucleation within the domains. A small (∼ .01°C) further increase in temperature caused these micro-domains to completely fill the specimen.

scholarly journals Evaluation of the Possibility of Using 1.4462 and 1.4501 Steel as a Construction Material for Apparatus Operating at an Increased Temperature and with Corrosive Factors

Materials ◽  
2021 ◽  
Vol 14 (14) ◽  
pp. 4014
Author(s):  
Karol Prałat ◽  
Andżelika Krupińska ◽  
Marek Ochowiak ◽  
Sylwia Włodarczak ◽  
Magdalena Matuszak ◽  
...  
Keyword(s):  
Construction Material ◽  
Construction Materials ◽  
Optical Microscope ◽  
Passive Layer ◽  
Initial State ◽  
Time Intervals ◽  
Significant Deterioration ◽  
Higher Temperature ◽  
Increasing Temperature ◽  
Steel Heat

The objective of this study was to determine the requirements for steels used as construction materials for chemical apparatus operating at an elevated temperature and to correlate them with the properties of the tested steels. The experimental part examined the influence of the annealing process on the structure and properties of X2CrNiMoN22-5-3 (1.4462) and X2CrNiMoCuWN25-7-4 (1.4501) steel. Heat treatment was carried out on the tested samples at a temperature of 600 °C and 800 °C. Changes were observed after the indicated time intervals of 250 and 500 h. In order to determine the differences between the initial state and after individual annealing stages, metallographic specimens were performed, the structure was analyzed using an optical microscope and the micro-hardness was measured using the Vickers method. Potentiostatic tests of the samples were carried out to assess the influence of thermal process parameters on the electrochemical properties of the passive layer. An increase in the hardness of the samples was observed with increasing temperature and annealing time, the disappearance of magnetic properties for both samples after annealing at the temperature of 800 °C, as well as a significant deterioration in corrosion resistance in the case of treatment at a higher temperature.

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