Ali Ramazani

Transformation-Induced, Geometrically Necessary, Dislocation-Based Flow Curve Modeling of Dual-Phase Steels: Effect of Grain Size

The flow behavior of dual-phase (DP) steels is modeled on the finite-element method (FEM) framework on the microscale, considering the effect of the microstructure through the representative volume element (RVE) approach. Two-dimensional RVEs were created from microstructures of experimentally obtained DP steels with various ferrite grain sizes. The flow behavior of single phases was modeled through the dislocation-based work-hardening approach. The volume change during austenite-to-martensite transformation was modeled, and the resultant prestrained areas in the ferrite were considered to be the storage place of transformation-induced, geometrically necessary dislocations (GNDs). The flow curves of DP steels with varying ferrite grain sizes, but constant martensite fractions, were obtained from the literature. The flow curves of simulations that take into account the GND are in better agreement with those of experimental flow curves compared with those of predictions without consideration of the GND. The experimental results obeyed the Hall-Petch relationship between yield stress and flow stress and the simulations predicted this as well.

Characterization of dual-phase steel microstructure by combined submicrometer EBSD and EPMA carbon measurements.

Electron backscatter diffraction (EBSD) and electron probe microanalysis (EPMA) measurements are combined to characterize an industrial produced dual-phase steel containing some bainite fraction. High-resolution carbon mappings acquired on a field emission electron microprobe are utilized to validate and improve the identification of the constituents (ferrite, martensite, and bainite) performed by EBSD using the image quality and kernel average misorientation. The combination eliminates the ambiguity between the identification of bainite and transformation-induced dislocation zones, encountered if only the kernel average misorientation is considered. The detection of carbon in high misorientation regions confirms the presence of bainite. These results are corroborated by secondary electron images after nital etching. Limitations of this combined method due to differences between the spatial resolution of EBSD and EPMA are assessed. Moreover, a quantification procedure adapted to carbon analysis is presented and used to measure the carbon concentration in martensite and bainite on a submicrometer scale. From measurements on reference materials, this method gives an accuracy of 0.02 wt% C and a precision better than 0.05 wt% C despite unavoidable effects of hydrocarbon contamination.

Different biokinetics of nanomedicines linking to their toxicity; an overview

In spite of the extreme rise to the knowledge of nanotechnology in pharmaceutical sciences, there are currently limited experimental works studying the interactions between nanoparticles (NPs) and the biological system. Adjustment of size and surface area plays the main role in the reaction between NPs and cells leading to their increased entrance into cells through skin, gastrointestinal and respiratory system. Moreover, change in physicochemical reactivity of NPs causes them to interact with circulatory and cellular proteins differentially leading to the altered parameters of their biokinetics, including adsorption, distribution, translocation, transformation, and elimination. A direct relationship between the surface area, reactive oxygen species generating capability, and proinflammatory effects of NPs have been found in respiratory tract toxicity. Additionally, complement-mediated hypersensitivity reactions to liposomes and other lipid-based nanodrugs have been well defined. Inhalation studies of some NPs have confirmed the translocation of inhaled materials to extra pulmonary organs such as central nervous system (CNS) via olfactory neurons and induction of inflammatory response. Injectable uncoated NPs have a tendency to remain on the injection site while the poly ethanol glycol (PEG)-coated NPs can be notably drained from the injection site to get as far as the lymph nodes where they accumulate. This confirms the existence of channels within the extracellular matrix for NPs to move along. Furthermore, induction of DNA strand breaks and formation of micronuclei have been recorded for exposure to some NPs such as single-walled carbon nanotubes.In the recent years, most of the studies have simply outlined better efficacy of nanodrugs, but few discussed their possible toxic reactions specially if used chronically. Therefore, we emphasize that this part of the nanoscience must not be undermined and toxicologists must be sensitive to set up suitable in vivo or in vitro toxicity models. A system for collecting data about the relationships between NPs’ structure-size-efficacy-toxicity (SSET) should be specified with special regard to portal of entry and target organ.

Template-Directed Directionally Solidified 3D Mesostructured AgCl–KCl Eutectic Photonic Crystals

3D mesostructured AgCl-KCl photonic crystals emerge from colloidal templating of eutectic solidification. Solvent removal of the KCl phase results in a mesostructured AgCl inverse opal. The 3D-template-induced confinement leads to the emergence of a complex microstructure. The 3D mesostructured eutectic photonic crystals have a large stop band ranging from the near-infrared to the visible tuned by the processing.

Failure Initiation in Dual-Phase Steel

This research work aims to model the failure initiation in dual-phase (DP) steel. A microstructure based approach by means of representative volume elements (RVE) is employed to evaluate the microstructure deformation and the failure initiation on the mesoscale. In order to determine cohesive parameters for martensite cracking, a two level approach has been performed experimentally. First, in-situ bending test in SEM with EBSD measurements before and after the test showed that the crack initiation occurs in martensite islands. Then, mini tensile tests with DIC technique were carried out to identify macroscopic failure initiation strain values. RVE modeling combined with extended finite element method (XFEM) was utilized to model martensite cracking on mesoscale. The identified parameters were validated by comparing the predictions with the experimental results.

Development and Characterization of Thermosensitive Polymer- CoatedIron Oxide Nanoparticles as a Novel Ferrofluid

In this work, we aim to study the development and characterization of thermosensitive polymer-coated iron oxide nanoparticles as a novel ferroFluid (fF) with thermosensitive properties. For this purpose, polymerization was conducted in the presence of various ratios of N-isopropylacrylamide (NIPAAm), acrylamide (AAm) and N-vinylpyrrolidone (NVP) as monomers, and N,N´-azobisisobutyronitrile (AIBN) as an initiator. Particles having average sizes of 8 nm and 8–10 nm were respectively observed for Fe3O4/fF and Fe3O4/polymers. As visualized by transmission electron microscopy (TEM) images, both the coated and uncoated iron oxide nanoparticles were uniform in shape and seem to have been monodispersed. Vibrating sample magnetometry (VSM) measurements of Fe3O4/VTES-fF and Fe3O4/Poly (NIPAAm- AAm NVP) at room temperature showed that they had a superparamagnetic nature with saturation magnetization values of 23.14 emu/g and 4.33 emu/g, respectively. In the thermosensitivity analysis, the lower critical solution temperature (LCST) was around 36-40°C, as determined by UV-Vis absorption spectroscopy. Furthermore, the polymerization of (NIPAAm-AAm-NVP) with the surface modified magnetic ferroFluid was confirmed by Fourier transform infrared (FTIR) spectroscopy and thermogravimetric analysis (TGA). These aqueous, stable, magnetic nanoparticles coated with temperature-sensitive polymers have attracted great attention because of their various applications in the fields of biotechnology and medicine.

Template-Directed Directionally Solidified Three-Dimensionally Mesostructured AgCl-KCl Eutectic Photonic Crystals.

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Thermal conductivity of pillared graphene-epoxy nanocomposites using molecular dynamics

Thermal conductivity in a pillared graphene-epoxy nanocomposite (PGEN) is studied using equilibrium molecular dynamics simulations. PGEN is a proposed material for advanced thermal management applications because it combines high in-plane conductivity of graphene with high axial conductivity of a nanotube to significantly enhance the overall conductivity of the epoxy matrix material. Anisotropic conductivity of PGEN has been compared with that of pristine and functionalized carbon nanotube-epoxy nanocomposites, showcasing the advantages of the unique hierarchical structure of PGEN. Compared to pure carbon allotropes, embedding the epoxy matrix also promotes a weaker dependence of conductivity on thermal variations. These features make this an attractive material for thermal management applications.Thermal conductivity in a pillared graphene-epoxy nanocomposite (PGEN) is studied using equilibrium molecular dynamics simulations. PGEN is a proposed material for advanced thermal management applications because it combines high in-plane conductivity of graphene with high axial conductivity of a nanotube to significantly enhance the overall conductivity of the epoxy matrix material. Anisotropic conductivity of PGEN has been compared with that of pristine and functionalized carbon nanotube-epoxy nanocomposites, showcasing the advantages of the unique hierarchical structure of PGEN. Compared to pure carbon allotropes, embedding the epoxy matrix also promotes a weaker dependence of conductivity on thermal variations. These features make this an attractive material for thermal management applications.

Modelling the Process Chain of Cold Rolled Dual Phase Steel for Automotive Application

This project aims to develop a virtual process chain for the production of components out of cold-rolled dual-phase (DP) steel. The simulation chain starts with cold-rolled strip. During intercritical annealing process all relevant steps like recrystallization, austenite formation and grain growth, ferrite and martensite transformation including bainite fractions and quasi-tempering during hot dip coating and coiling are taken into account. Concerning the final mechanical properties transformation induced micro eigenstresses are described as well as strain partitioning on microscale during cold forming. This multi-scale and process-spanning approach enables the local properties in the part for varying composition and processing conditions. Thus, it can be used for the knowledge driven design and optimization of tailored material and process. To describe all the steps along the process chain, various simulation programs have been linked. By comparison of simulation and experimental results the predictability of this approach can be shown an in a later stage the integrative simulation approach will be further developed towards application for material and process design.