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Multiscale Defect Formation and Tran...

Seif, Dariush.

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Multiscale Defect Formation and Transport in Materials in Extreme Environments.

紀錄類型:	書目-電子資源 : Monograph/item
正題名/作者:	Multiscale Defect Formation and Transport in Materials in Extreme Environments./
作者:	Seif, Dariush.
面頁冊數:	146 p.
附註:	Source: Dissertation Abstracts International, Volume: 75-02(E), Section: B.
Contained By:	Dissertation Abstracts International75-02B(E).
標題:	Mechanical engineering. -
電子資源:	http://pqdd.sinica.edu.tw/twdaoapp/servlet/advanced?query=3599350
ISBN:	9781303485695

Multiscale Defect Formation and Transport in Materials in Extreme Environments.
Seif, Dariush.

Multiscale Defect Formation and Transport in Materials in Extreme Environments. - 146 p.

Source: Dissertation Abstracts International, Volume: 75-02(E), Section: B.

Thesis (Ph.D.)--University of California, Los Angeles, 2013.

In this dissertation, we develop computational models of point defect formation and transport in spatially heterogeneous stress and temperature fields. To accomplish this, first an atomistically-based description of point defects is developed using a combination of molecular statics calculations and continuum elasticity theory. This enables an accurate representation of point defect strain fields and their interaction energies in various strain fields. The continuum representation has been found to be accurate to within several percent of the atomistic calculations and was successfully tested against highly accurate first principles calculations in a published study.

ISBN: 9781303485695Subjects--Topical Terms:

649730
Mechanical engineering.

Multiscale Defect Formation and Transport in Materials in Extreme Environments.
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100 1 $a Seif, Dariush. $3 3194236
245 1 0 $a Multiscale Defect Formation and Transport in Materials in Extreme Environments.
300 $a 146 p.
500 $a Source: Dissertation Abstracts International, Volume: 75-02(E), Section: B.
500 $a Adviser: Nasr M. Ghoniem.
502 $a Thesis (Ph.D.)--University of California, Los Angeles, 2013.
520 $a In this dissertation, we develop computational models of point defect formation and transport in spatially heterogeneous stress and temperature fields. To accomplish this, first an atomistically-based description of point defects is developed using a combination of molecular statics calculations and continuum elasticity theory. This enables an accurate representation of point defect strain fields and their interaction energies in various strain fields. The continuum representation has been found to be accurate to within several percent of the atomistic calculations and was successfully tested against highly accurate first principles calculations in a published study.
520 $a Using the described point defect representation, we have performed calculations of the dislocation bias factor for irradiated metals, using a spatially-resolved rate theory solution we developed based on the finite element method. The flexibility of the model is fully exploited, leading to calculations with heightened resolution; accounting for the spatially-dependent, energetically favorable SIA orientations, one-dimensional diffusion mechanisms near the dislocation core, and full anisotropic elasticity. Our results for iron have shown that the effects of preferred SIA orientations should not be ignored near the dislocation core. Implementing minimum energy SIA configurations in iron decreases repulsive interactions and increases absorption, ultimately leading to much larger bias factors. On the other hand, we also find the use of anisotropic elasticity in the calculations to decrease bias factors by 45\% compared to those obtained using the isotropic formulation. An anisotropic implementation of the dislocation strain fields, however, gives larger interaction energy gradients, leading to increased drift diffusion and larger bias (12% and 6% increase in Fe and Cu, respectively).
520 $a Following the rapid transient stage of helium-vacancy cluster (bubble) nucleation under irradiation, the bubble growth phase proceeds over macroscopic timescales. Due to the complex nature of the problem, prediction of the time-dependent bubble size distribution in the helium-vacancy phase space has remained elusive. In this dissertation we approach the problem in two ways, both accounting for full material spatial resolution. In the first, we use a previously developed reduced set of rate equations to track the average bubble size through time, in a two-dimensional specimen under the typical stress and temperature gradients seen in plasma-facing components in fusion environments. With temperature gradients long known to have several orders of magnitude greater effect on bubble diffusion than associated stress gradients, our results conclusively revealed the important role of stress gradients on the near-surface average bubble size profile due to point defect diffusion processes.
520 $a Extending this spatially-dependent rate theory approach to capture the full bubble size distribution surface, we have developed a novel approach based on the theory of nonlinear stochastic differential equations. Here, we provide a framework to describe the full helium bubble size distribution as a function of time and space, in irradiated metals under stress and temperature gradients. Our findings show the important role of stochastic atomic fluctuations on the dispersion of the distribution around the mean. We find for smaller average bubbles sizes (early in the simulation), the spread of the distribution is large and stable. As bubbles begin to grow larger, the stochastic fluctuations have a reduced effect and the distribution begins to shrink, corresponding to a more uniformly sized bubble population.
520 $a To characterize the response of metals to shock loading, extensive molecular dynamics (MD) simulations have been performed. In light of recent experimental results obtained by laser-induced shock-loading on single-crystal nanopillars, MD simulations were performed on both nanofilm and nanopillar structures, the difference being the geometry and imposed boundary conditions in the directions transverse to the propagation direction of the shock wave. The dynamic response of the structures to shock loading was analyzed over a wide spectrum of impact stresses. State variables (stress, velocity, temperature, etc.) were computed as functions of time and position along the specimen. The results of this work have contributed to a greater understanding of the deformation mechanisms at work in metal nanostructures exposed to ultra-high strain rate loading conditions. (Abstract shortened by UMI.).
590 $a School code: 0031.
650 4 $a Mechanical engineering. $3 649730
650 4 $a Materials science. $3 543314
650 4 $a Nuclear engineering. $3 595435
690 $a 0548
690 $a 0794
690 $a 0552
710 2 $a University of California, Los Angeles. $b Mechanical Engineering. $3 2093961
773 0 $t Dissertation Abstracts International $g 75-02B(E).
790 $a 0031
791 $a Ph.D.
792 $a 2013
793 $a English
856 4 0 $u http://pqdd.sinica.edu.tw/twdaoapp/servlet/advanced?query=3599350