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 finite 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 Doha’s neighborhoods. This study investigates residential gated communities in Doha and their relation to a neighborhood’s 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 communities’ 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