Search

The Charpy impact test is an experimental method for determining a material's dynamic properties at different temperatures to investigate tested materials' ductile to brittle transition behavior. The percentages of ductile and brittle fractures can be evaluated based on the fracture area of Charpy specimen (according to API E23 standard) by visual techniques, which do not provide exact percentages of these fractures. In this study, a method is proposed to calculate the exact percentage of ductile fractures using image processing, which makes it possible to quantitatively examine different parts of the fracture surface with high accuracy. All steps of image processing are described for eleven Charpy standard specimens of API X70 steel, tested at temperatures between +20 to -80 °C with a temperature increment of 10 °C. In this research, converting a qualitative image of a fracture surface to a quantitative matrix is described for the first time. Prediction of the shape of ductile and brittle parts of the fracture surface at temperatures between +20 and - 80 °C is one of the results of this study. The percentages of ductile fractures using image processing for temperatures of +20, 0, -20, -40, -40, -60 and -80 °C were obtained as 100, 100, 86, 53, 36 and 0, respectively. The transition temperature was -45 °C for this steel, corresponding to 50% ductile fracture. [ABSTRACT FROM AUTHOR]

In this paper, BSCCO bismuth-based superconductor material is prepared by the electrodeposition method. The electrolyte compositions are based on bismuth nitrate [Bi(NO3)3] copper nitrate [Cu (NO3)2], calcium nitrate [Ca(NO3)2], strontium nitrate [Sr(NO3)2] and DMSO [(CH3)2SO] as the solvents. The properties of BSCCO are studied by X-ray diffraction (XRD) and scanning electron microscope (SEM). In the electrodeposition method, copper (Cu) and silver (Ag) are used as the anode and cathode, respectively. The optimal efficiency for electrodeposition of a superconductor material is observed at voltage: 5V and temperature: 55˚C. BSCCO-2212 phase in the electrodeposited sample is confirmed by XRD. The sample shows nano-leaf morphology, with a transition temperature (Tc) is 85 K.

In this paper, Bi-Sr-Ca-Cu-O (BCSCCO) system superconductor is made by the solid state reaction method. The effect of doping Pb, Cd, Sb, Cu and annealing time on the critical temperature and critical current density have been investigated. The microstructure and morphology of the samples have been studied by X-ray diffraction, scanning electron microscope and energy dispersive X-ray. The results show that the fraction of Bi-2223 phase in the Bi- based superconductor, critical temperature and critical current density depend on the annealing temperature, annealing time and the kind and amount of doping .

We fabricated YBa2Cu3-xMxO7- d (M=Ni, Fe) bulk samples, with stochiometric amount 0≤x≤0.045 by sol-gel method. The phase analysis and microstructure of specimens were examined by XRD and SEM. The electrical resistivity was measured using standard four probe technique for 77-300K. Investigation of XRD spectrum by MAUD shows Ni and Fe ions substitute in Cu(2) and Cu(1) site, respectively. Transition temperature decreases in 93-87K for Ni-doped samples and 93-92K for Fe-doped series. It seems that the suppression of superconductivity has no direct correlation with the magnetism of ions itself .

Bi-based and Ag-doped superconductors were irradiated by neutrons. Experimental result showed that XRD patern-intensity of irradiated Bi-based sample was decreased and The Tc of these samples were decreased by 7-10 K. The neutron irradiated sample was also found to decrease by 50% the normal state resistivity of samples. Therefore, neutron irradiation is a useful method to improve the superconductivity behavior of Bi-based materials.

In this work Bi1.6Pb0.4Sr1.9Ca2.1Cu3O10-y superconducting system (Bi2223) has been prepared by solid state reaction and the effect of nanoalumina additive on the phase formation and supercoducting properties have been investigated. XRD investigations show that addition of 0.2 wt% of nanoalumina on the superconducting system improved Bi-2223 phase formation . The results show that Jc increases from 36 A/cm2 for the nanoalumina free sample to 107 A/cm2 for the sample with 0.5 wt% nanoalumina.On the other hand results show that the transition temperature (Tc) of all samples is around 108 K and addition of nanoalumina has not affected Tc significantly .

Polymer-graphite powder composite behaves as a low-conductive material which can be used as an automatic fuse for adhesive connector in electrical circuits. The conductivity of this composite, below its transition temperature, Tt, depends on concentration of carbon powder, slowly decreases as the temperature increases. Meanwhile, the electrical resistivity of this material in transition temperature region severely increases. The amount of Tt was found to be ~148oC for polyethylene-carbon independent of its concentration. In this work, the rate of change in electrical resistance of thiscomposite in terms of temperature, carbon concentration and γ-ray irradiation dose has been investigated. Also, the values of Tt and the peak resistance temperature, Tp of samples in each case were determined. The results show that both values of Tt and Tp decrease with increasing of irradiation dose. It has been found that the concentration of carbon powder has no significant effect on the transition temperatures of samples.

Oscillatory behavior of transition temperature in supper lattice, Ni/Au/Ni, has been observed as a function of spacer layer, Au. The observed oscillation period is almost the half period of interlayer exchange coupling. The high temperature susceptibility of a two - dimensional lattice is evaluated within the Bethe-Peierls-Wiess approximation in the presence of a random field with square distribution. This susceptibility is used to evaluate the transition temperature of coupled planes as a function of spacer thickness. The calculated transition temperature of coupled planes oscillates as half period of interlayer exchange coupling and falls below the results of the uncoupled films at some values of the average spacer thickness that were experimentally observed. Additionally, the transition temperature depends on the distribution function of random field at the small thickness of spacer.