Procedia Materials Science最新文献

The assessment of the structural integrity of Steam Generator Tubes (SGTs) in nuclear power plants has been receiving increasing attention in the literature in the last years due to the negative impact related to their failures. Diverse failure prediction methodologies were proposed in the past to ensure tube integrity by fulfilling regulatory authorities’ requirements. They have lead however to overly conservative plugging or repairing criteria like the so-called “40% criterion”. In the present work, in line with modern approaches, an alternative more realistic methodology based on the Failure Assessment Diagram (FAD) is proposed. With that purpose, different studies available in the literature dealing with the experimental determination of fracture toughness of SGT materials were firstly reviewed. Using the results reported in these researches, the FAD was used for predicting the failure modes (i.e., ductile fracture or plastic collapse) of defective SGTs for varied crack geometries and loading conditions. The present analysis indicates the potentiality of the FAD as a comprehensive methodology for predicting the failure loads and failure modes of flawed SGTs.

Polycrystalline Sr_1-2xNa_xSm_xBi₄Ti₄O₁₅ (SNSBT) belongs to bismuth layer structured ferroelectric (BLSF) materials with x=0.1 have been prepared by sol gel method. XRD analysis confirms single phase formation with orthorhombic structure. Scanning electron micro graph of the material shows plate like grains with random orientation. Dielectric and impedance measurements carried out from room temperature to 600^oC at different frequencies. Piezoelectric and electromechanical coupling coefficients are calculated from resonance and anti-resonance frequencies. Cole-Cole plots showed non-Debye behaviour.

This paper demonstrates techniques for modelling fluid-structure interactions using COMSOL Multiphysics v 4.2a, which illustrates how to solve for the flow in a continuously deforming geometry using the Arbitrary Lagrangian-Eulerian (ALE) technique and corresponding deformation, displacement analysis. The present work reports the computation of the deformation and displacement in structure along with the fluid flow in a continuously deforming geometry, for different types of structures like circular, rectangular, ellipse, which are placed inside of the flow channel as an obstacle. Fluid structure interaction between wind and sails, modelling of parachutes, fluid structure thermal calculation, stability and response of aircraft wings, the flow of blood through arteries, response of bridges and tall buildings to winds, prediction of aero elastic parameters in military aircrafts, vibration of turbine and compressor blades and the oscillation of heat exchangers can also be analysed using this method

Recently application of nano/bio materials for enhanced oil recovery (EOR) has been examined by few researchers, but there exists ambiguous concepts about simultaneous injection of nanoparticles/biomaterials. Therefore, in this study the heavy oil displacement mechanisms using simultaneous injection of nanosilica/biosurfactant have been investigated in a glass micromodel. In order to better illustrate the influence of nano/bio material different flooding scenarios containing distilled water, nanosilica/distilled water, biosurfactant/distilled water and nanosilica/biosurfactant/distilled water have been conducted. Experimental results indicate that simultaneous presence of nanoparticles and bioproducts have synergy on each other and because of IFT reduction, improving the mobility ratio and increasing the injected fluid viscosity; the oil recovery can be achieved about 58%. Furthermore, nanoparticles can play as an inhibitor to avoid asphaltene precipitation.

Composite films of TPS with talc nanoparticles were obtained by thermo-compression in order to study the effect of this filler on structure, optical, and thermal properties. TPS-talc films showed good appearance and homogeneous thickness. Talc addition increased the amount of rigid phase in nanocomposite films, thus their cross-sections resulted more irregular than those of TPS ones. Talc preferential orientation within matrix and good compatibility between particles and TPS were evidenced. TEM observation showed scattered randomly dispersed individual talc platelets. Matrix crystallinity degree was not significantly affected by particles presence. Nanocomposite films were optically transparent due to the laminar morphology and nanosized particles. Materials microstructure presented glycerol- and starch-rich domains. Talc incorporation higher than 3% w/w increased softening resistance of nanocomposites as stated by DMA assays. TPS relaxation temperature of glycerol-rich phase was shifted to higher values since talc nanoparticles reduce starch chains mobility.

Space radiation environment is composed by a variety of particles with energies ranging from keV to some GeV. These particles are either trapped into the magnetic field of the Earth or are passing through the Solar System. Some of the satellite electronics is based on silicon devices which suffer degradation due to environmental radiation. To study heavy ion and other particles effects we designed and fabricated MOS (metal oxide semiconductor) ad hoc capacitors. Radiation damage test were made using the Van de Graaf (TANDAR) heavy ion accelerator. In situ characterization was performed by means of C-V (capacitance-voltage) measurements during irradiation experiments and from the curves obtained the characteristic parameters were estimated.

Titanium alloys are characterized by great versatility arising from the ability to obtain a wide spectrum of properties by controlling the alloying elements and thermo-mechanical treatments that determine the microstructure. The determining factors for the workability of titanium alloys are related to the structure of the alpha phase (HCP) and the strong dependence of the alpha and beta phases on processing variables such as temperature, strain and strain rate. Therefore, proper selection and control of these parameters in each deformation step is critical to obtain an optimum combination of mechanical properties and microstructure of the final product.

The tested material is titanium commercially pure (Ti CP (Ti Gr4)), which despite being an alpha alloy, it is seen that small amounts of iron can change the microstructural evolution of the alloy.

The current study was undertaken to study the effect of different amounts of Al-5Ti-1B master alloy (0.01, 0.03, 0.05, 0.1, 0.3, 0.5, 1% weight percent) and T6 heat treatment on the microstructural evolution and mechanical properties of Al-8%Mg alloy. Microstructural assessment was carried out by optical microscopy (OM) and scanning electron microscopy (SEM) equipped with energy dispersive spectrometer (EDS) analysis. Obtained results showed that the addition of Al-5Ti-1B master alloy obviously improved the morphology of Al (α) and it was found that refined specimens have finer grains (< 250 μm) in comparison with un-refined specimen. After grain refining, the morphology of columnar alpha dendrites turn into rosette like and semi globular. The increase of Al-5Ti-1B content up to 0.1 wt. %, resulted in improvement of ultimate tensile strength (UTS) from 245 MPa to 359 MPa which shows 31% enhancement. Result of T6 heat treatment revealed a significantly enhancement on both ultimate tensile strength (UTS) and elongation values. Fractography examinations of the alloy showed an inter-dendritic fracture surface of Al-8%Mg alloy, changes to more homogenous dimples after grain refining process.

To analyze the behavior of molybdenum powders during hot isostatic pressing (HIP) at sintering temperatures, microscopic modeling of plastic densification mechanisms, power-law creep and diffusion based on equations found byArzt et al. [Metallurgical Transactions (1983) 14A] was performed. The results show that at high temperatures (T> 0.5T_m, where T_m is the meltingtemperature) and pressures higher than 15 MPa, high relative densities (D> 0.95) can be obtained by power-law creep and diffusion mechanisms, the former being more prevalent. HIP diagrams against temperature, pressure and time were plotted to describe densification mechanisms and were compared with literature values.