Abstract: Some of the activities of the Project Center for Nanotechnology and Advanced Engineering (PC-NAE), a joint initiative of the Greek National Center for Scientific Research Demokritos and the Russian Research Center Kurchatov Institute, in advanced manufacturing engineering are briefly outlined, focusing onto some recent trends and developments in manufacturing from macro-, micro-, to nanoscale of advanced materials in the important engineering topics nowadays from industrial, research and academic point of view: nanotechnology/ultraprecision engineering and advanced materials under shock loading, with industrial applications to net-shape manufacturing, bioengineering, energy and transport.
Abstract: Stresses are induced in a bulk high-Tc superconductor (HTS) by field-cooled magnetization. The stress distributions of a hollow cylindrical bulk HTS are numerically studied in the axisymmetric three-dimensional analysis. Shielding current distributions are obtained through a macroscopic numerical simulation with the Maxwell equations and the critical state model. Stress distributions are obtained by using the finite-difference method and iterative calculations. Maximum hoop stress during the field-cooled magnetization is discussed for open and fixed boundary conditions.
Abstract: The high pressure (50 MPa - 2 GPa) – high temperature synthesized MgB2 bulk materials are characterized by nearly theoretical density (1-2% porosity), 80-98% connectivity, extremely high critical current densities (e.g. at 20 K, in 0–1 T jc=1.3–1.0 MA·cm-2 (with 10% SiC) and jc= 0.92 – 0.73 MA·cm-2 (without doping)), large irreversibility fields (Birr(18.4 K) =15 T and Birr (0 K) = 32.5 T) and high upper critical fields (Bc2 (22 K) =15 T and Bc2(0 K) ~ 42.1 T). The transformation of grain boundary pinning to point pinning in MgB2-based materials with increasing manufacturing temperature (from 800 to 1050 oC) under pressures from 0.1 to 2 GPa correlates well with an increase in critical current density in low external magnetic fields caused by the redistribution of boron and the oxygen impurities in the material structure. As the manufacturing temperature increases, the discontinuous oxygen enriched layers transform into distinct Mg-B-O inclusions and the size and amount of inclusions of higher magnesium borides MgBX (X>4) are reduced. The effect of oxygen and boron redistribution can be enhanced by Ti or SiC additions.
Abstract: Behavior of both suspended micrometer-size magnetic particles and micrometer-size nonmagnetic abrasive particles in a micro-tube filled with a magnetic compound fluid is investigated by using discrete particles method based on the simplified Stokesian dynamics in order to reveal the polishing process of inner surface of the tube with an axial flow. Giving the axial flow of the appropriate velocity is effective on performing uniform polishing of the surface in the magnetic compound fluid polishing.
Abstract: We performed experiments regarding two-layer sloshing, using a magnetic fluid and silicone oil, and measured the dynamic pressure change using pressure transducers. We also investigated displacements of the free surface by comparing it with the dynamic pressure, clarifying the relation between them, both in the presence and absence of a magnetic field.
Abstract: A fast laser texturing technique has been utilized to produce micro/nanosurface textures in Silicon by means of UV femtosecond laser. We have prepared good absorber surface for photovoltaic cells. The textured Silicon surface absorbs the incident light greater than the non-textured surface. The results show a photovoltaic current increase about 21.3% for photovoltaic cell with two-dimensional pattern as compared to the same cell without texturing.
Abstract: Zinc Oxide (ZnO) /porous-silicon photovoltaic device was fabricated to detect fast ultraviolet (UV) radiation pulses. The photovoltaic UV detector, based on the deposition of the ZnO wide-band gap semiconductor material on nanospikes silicon layer to form a heterojunction, has fast response time to the UV pulses. The current voltage characteristic, the capacitance variation with the applied voltage and the ideality factor of the heterojunction were studied. The operation of the detector under the reverse bias of-2 volts has successfully detected an ultra-fast nitrogen laser pulses at 385 (nm).
Abstract: The previously proposed polarizable charge equilibrium (PQEq) force field model is parameterized for studying lead titanate (PT), lead zirconate (PZ), and their alloys: lead zirconate titanate (PZT). Several molecular dynamics (MD) simulations are performed to assess the degree of accuracy of the model. The phase transition temperatures, which are generally inaccurate in MD, are shown to be similar to experimental measurements. Also, the calculation of the ferroelectric hysteretic behavior, including the spontaneous polarization, saturated polarization and coercive fields, with extended MD is shown to give a qualitatively correct comparison between PT and PZT. The accuracy of the electronic properties in PQEq leads to direct application to a range of interesting problems such as enhanced properties of piezo- and ferro-electric nanostructures and the kinetics of domain walls in these materials.
Abstract: Thermomechanical properties of precipitated NiTi shape memory alloys are investigated using the finite element method. The precipitated material microstructure is explored using a representative volume element with embedded Ni4Ti3 precipitates. Features such as precipitate coherency and distribution of Ni within the matrix due to the precipitation process are individually explored and characterized. Changes in the material’s macroscopic thermomechanical response due to this precipitation are determined.