318 research outputs found
Crystal plasticity model calibration for 316l stainless steel single crystals during deformation
Type 316L austenitic stainless steel is an important structural material used for the in-core components and pressure boundaries of light water reactors. In order to study degradation mechanisms in such a steel, like crack initiation and propagation, it is crucial to develop reliable crystal plasticity models at microscale that would account for anisotropic nature of the material and realistic modelling of grain topology. In this work we present a procedure for calibrating material properties of a slip-based crystal plasticity ïŹnite element model and investigate its suitability as a constitutive model for single-crystal tensile test simulations. The material properties include the anisotropic elastic and crystal plasticity material parameters that are calibrated against experimental tensile test curves for 316L stainless steel single crystals at selected crystallographic orientations. For the crystal plasticity material parameters a systematic sensitivity study using Bassani and Wu hardening law is performed
Phase behaviour of colloidal assemblies on 2D corrugated substrates
We investigate - with Monte Carlo computer simulations - the phase behaviour
of dimeric colloidal molecules on periodic substrates with square symmetry. The
molecules are formed in a two-dimensional suspension of like charged colloids
subject to periodic external confinement, which can be experimentally realized
by optical methods. We study the evolution of positional and orientational
order by varying the temperature across the melting transition. We propose and
evaluate appropriate order parameters as well as the specific heat capacity and
show that the decay of positional correlations belongs to a class of crossover
transitions while the orientational melting is a second-order phase transition.Comment: 13 pages, 9 figures, accepted in J. Phys.: Condens. Matte
Intergranular stress distributions in polycrystalline aggregates of irradiated stainless steel
In order to predict InterGranular Stress Corrosion Cracking (IGSCC) of
post-irradiated austenitic stainless steel in Light Water Reactor (LWR)
environment, reliable predictions of intergranular stresses are required.
Finite elements simulations have been performed on realistic polycrystalline
aggregate with a recently proposed physically-based crystal plasticity
constitutive equations validated for neutron-irradiated austenitic stainless
steel. Intergranular normal stress probability density functions are found with
respect to plastic strain and irradiation level, for uniaxial loading
conditions. In addition, plastic slip activity jumps at grain boundaries are
also presented. Intergranular normal stress distributions describe, from a
statistical point of view, the potential increase of intergranular stress with
respect to the macroscopic stress due to grain-grain interactions. The
distributions are shown to be well described by a master curve once rescaled by
the macroscopic stress, in the range of irradiation level and strain considered
in this study. The upper tail of this master curve is shown to be insensitive
to free surface effect, which is relevant for IGSC
Gated Communities and Neighborhood Livability in Doha
Gated communities are a widespread phenomenon now found in many regions around the world. A gated community is mainly characterized by a focus on physical security measures such as gates, walls, guards, and closed circuit surveillance cameras. For the past 50 years, there has been growing criticism about their negative impact on the livability of neighborhoods. Nevertheless, this phenomenon remains popular in the emerging cities of the Arabian Gulf region that are adopting this residential development strategy in their urban growth patterns. More than 454 residential gated communities were located in Doha, the capital of the state of Qatar, as per the 2014 census (Qatar map, 2014), and their numbers are growing.
Currently, there is a movement taking place in Qatar to restructure its urban planning principles in order to achieve a transformative move towards a more livable urban form. Therefore, the consistent emergence of such gated communities has become a stimulating piece of inquiry, as academics, engineers, and urban planners continue to question the suitability and potential impacts of gated communities as some of the most persistent and popular residential developments in Dohaâs neighborhoods.
This study investigates residential gated communities in Doha and their relation to a neighborhoodâs livability, focusing on the Al Waab neighborhood as a case study. Site analysis, observation, morphological analysis, focus group interviews, and a questionnaire survey were adopted as suitable methodological tools for the investigation of the study area. The analysis is grounded in a perspective that recognizes the phenomenon of gated communities, the notion of livability and its associated principles found in existing literature and contemporary urban planning movements. Additionally, the analysis looks to studies of best practice gated communitiesâ policies and planning responses from South Africa, Canada, and UK.
The results of the study illuminate a livability deficiency in the study area, finding that gated developments negatively impact density and diversity of land use, connectivity, and accessibility within the neighborhood, as well as discourage walkability adaptations, social interaction, and co-presence.
The results also show that people are motivated to move into gated communities for security reasons mainly related to reduced traffic and a safer environment for their children. The conclusions on the livability disparity of the study area and gated communities are used to propose recommendations to better adapt the gated communities into the urban fabric and make sure that they are more livable and better integrated into the existing city.
Certainly, this case study can be applied to similar gated community situations that share the same characteristics of gated enclaves, ultimately contributing to further discussion on the overall livability of gated communities in general and specific cases such as Doha
The Influence of Information Technology on Performance of Accountants in Tripoli, Libya
This study is part of a larger study to explore and community, Factors that affect the organizational culture and adoption of information systems for the oil in Libya and
banking sectors, And the results showed that there is a direct relationship between the positive and dimensions of societal culture, And the results showed that there were no
differences in the community, Dimensions of culture between the two sectors covered in this study. This means that is affected by the adoption of the culture and community, Other factors that deserve investigation and future implication
Anomalous scaling of conductivity in integrable fermion systems
We analyze the high-temperature conductivity in one-dimensional integrable
models of interacting fermions: the t-V model (anisotropic Heisenberg spin
chain) and the Hubbard model, at half-filling in the regime corresponding to
insulating ground state. A microcanonical Lanczos method study for finite size
systems reveals anomalously large finite-size effects at low frequencies while
a frequency-moment analysis indicates a finite d.c. conductivity. This
phenomenon also appears in a prototype integrable quantum system of
impenetrable particles, representing a strong-coupling limit of both models. In
the thermodynamic limit, the two results could converge to a finite d.c.
conductivity rather than an ideal conductor or insulator scenario.Comment: 6 pages, 3 figures. Submitted to PR
Grain boundary stresses in elastic materials
A simple analytical model of intergranular normal stresses is proposed for a
general elastic polycrystalline material with arbitrary shaped and randomly
oriented grains under uniform loading. The model provides algebraic expressions
for the local grain-boundary-normal stress and the corresponding uncertainties,
as a function of the grain-boundary type, its inclination with respect to the
direction of external loading and material-elasticity parameters. The knowledge
of intergranular normal stresses is a necessary prerequisite in any local
damage modeling approach, e.g., to predict the intergranular stress-corrosion
cracking, grain-boundary sliding or fatigue-crack-initiation sites in
structural materials.
The model is derived in a perturbative manner, starting with the exact
solution of a simple setup and later successively refining it to account for
higher order complexities of realistic polycrystalline materials. In the
simplest scenario, a bicrystal model is embedded in an isotropic elastic medium
and solved for uniaxial loading conditions, assuming 1D Reuss and Voigt
approximations on different length scales. In the final iteration, the grain
boundary becomes a part of a 3D structure consisting of five 1D chains with
arbitrary number of grains and surrounded by an anisotropic elastic medium.
Constitutive equations can be solved for arbitrary uniform loading, for any
grain-boundary type and choice of elastic polycrystalline material. At each
iteration, the algebraic expressions for the local grain-boundary-normal
stress, along with the corresponding statistical distributions, are derived and
their accuracy systematically verified and validated against the finite element
simulation results of different Voronoi microstructures.Comment: 28 pages, 20 figure
Phosphonic acid derivatives used in self assembled layers against metal corrosion
The preparation of self assembled molecular(SAM) layers needs molecules with a small hydrophilic and a big hydrophobic molecular parts. Special molecules were chosen where the head group was in all cases phosphonic group,
but there were significant differences in the other molecular part. In one case a medium sized carbon chain with a single double bound, in the second case a long alkyl chain with fluoro atoms, and in the third case a polymer molecular part represented the hydrophobic molecular section. Our work was focused on the preparation and characterization of their SAM layers they formed on solid
surfaces under the different conditions. The molecular films were deposited from organic solvents on different metal surfaces covered by oxide layer. In the case of the layer with double bounds, polymerization of the molecules
on the surface with UV light was applied. The modified surfaces were characterized by the wettability and
their anti-corrosion activity was determined in linear polarization experiments. According to the numerical results the wettability of the surfaces differed
significantly, i.e., we successfully modify the solid surface with the coatings. The anti-corrosion activity of the coated surfaces depends on the molecules used for layer
deposition. The samples with fluoro-alkyl chains gave the
best results, not only their contact angles were very high but their anti-corrosion effectiveness was the best
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