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1.
A coupled simulation by the phase-field (PF) method and the finite element method based on the homogenization theory (FEH) is developed to predict the microstructure formations and mechanical properties of ferrite–pearlite steels. The formation of the phase during the isothermal transformation is simulated by the PF method. Furthermore, the FEH analysis is performed to clarify the effects of the predicted microstructure on the deformation behavior of the steels. In order to link to the FEH analysis, the microstructure in the steel is described by the representative volume element (RVE) based on the results of the PF simulation. The results reveal that although the macroscopic stress–strain relationship is mainly characterized by the volume fraction of the constituent phase, the localization of plastic strain is reduced due to the fine-grained phase. This numerical model provides a systematic way of predicting the mechanical properties of steel depending on the microstructure.  相似文献   

2.
The electronic structures and absorption spectra of perfect crystals and crystals containing lead vacancy for both sheelite(PbWO4) and sheelite-like(Pb7.5W8O32) structures have been calculated using density functional theory with the lattice structure optimized. The optical properties of lead tungstate exhibit anisotropy. Numerical calculation shows that the absorption spectra of the sheelite structure crystal containing exhibit additional absorption bands in the visible and near ultra-violet ranges. However, this is not the case for other structures of the PWO crystals such as the sheelite structure crystal without lead vacancy and the sheelite-like structure crystal with or without lead vacancy.  相似文献   

3.
A finite element simulation of a blister test of an elastic–plastic film, bonded to a substrate and subject to plane strain conditions, is performed. A traction-separation law models the fracture process ahead of the crack tip at the interface between the thin film and the substrate. Only two parameters are significant in describing the traction-separation law: adhesion energy, Γ0 and interface strength, . The dependences of the pressure, P, and the product of the pressure with the central deflection, PH, on the adhesion properties (Γ0 and ), the geometry and material properties of the film are studied. The latter quantity (PH) has the same unit as the adhesion energy, Γ0, and is “conceptually” appropriate for the analysis. We suggest a method to extract the adhesion energy, Γ0 and the interface strength, , independently from the total energy dissipated.  相似文献   

4.
Sensitivity to the locations of γ-ray interactions within a 32-fold segmented clover-type HPGe detector has been investigated through 90 Compton scattering of -rays from a collimated source. A mean position sensitivity of 0.44 mm at an energy of 373 keV is deduced by comparing the average pulse shapes for net charge collecting signals, as well as transient induced signals in neighbouring contacts, from 1007 pairs of three-dimensionally localized interaction points. The reconstruction of individual event locations based on a χ2 comparison with the measured set of basis waveforms is presented.  相似文献   

5.
While an antiferroelectric liquid crystal (AFLC) with dimeric molecules which take a bent molecular structure may show the phase transition from the isotropic liquid to the chiral smectic-C AFLC () phase via the nematic (N) phase, it has not been obvious yet why the and N phases may coexist in the phase sequence of the dimeric AFLC medium. In this study, the molecular alignment structures of the N and the SmCA phases of an achiral dimeric LC were researched in detail with a polarized Fourier transform infrared spectroscopy (FT-IR). The domain structure with two orientational directions is formed both in the SmCA and N phase, and the occupation ratio of two types of domain does not change in the phase transition. Since their alignment structures are basically same except for the existence of layer structure, their phases may coexist in the phase sequence of the dimeric AFLC.  相似文献   

6.
We have developed a high-efficiency pulsed slow positron beam for experiments with orthopositronium in vacuum. The new pulsing scheme is based on a double-gap coaxial buncher powered by an RF pulse of appropriate shape. The modulation of the positron velocity in the two gaps is used to adjust their time-of-flight to a target. This pulsing scheme allows to minimize non-linear aberrations in the bunching process and to efficiently compress positron pulses with an initial pulse duration ranging from 300 to 50 ns into bunches of 2.3 to 0.4 ns width, respectively, with a repetition period of . The compression ratio achieved is 100, which is a factor 5 better than has been previously obtained with slow positron beams based on a single buncher. Requirements on the degree, to which the moderated positrons should be mono-energetic and on the precision of the waveform generation are presented. Possible applications of the new pulsed positron beam for measurements of thin films are discussed.  相似文献   

7.
Fine-pitch gas electron multiplier (GEM) foils have been produced for cosmic X-ray polarimeters using a carbon dioxide laser etching technique. The finest hole pitch of the foil which can be produced repeatedly is and the smallest hole diameter is . The electron amplification factor was measured as a function of applied voltage. The behavior of the factor is almost the same as the -pitch standard foil fabricated by CERN. Our GEMs had no rate-dependent gain instability, which is expected of the GEMs having holes of good cylindrical geometry. The amplification factor of the foil in a mixture of 70% argon and 30% carbon dioxide reaches about 5000 without any micro-discharge at a voltage of 570 V between foil electrodes.  相似文献   

8.
The effect of precipitates on the mechanical properties of ZK60-Y alloy   总被引:7,自引:0,他引:7  
This paper investigated the influence of the microstructure on the mechanical properties of the forged ZK60-Y alloy under different heat treatments (T4, T5 and T6). The results show that the alloy at the direct artificial ageing treatment has superior strength and plasticity. X-ray analysis, SEM fracture observation and EDAX spectrum analysis reveal that bulk w-Mg3Y2Zn3 and coarsened rod-like MgZn′(β1) phases have great influence on the tensile properties of the alloy. Further investigations of the alloy aged at 180 °C, 200 °C and 225 °C for 0.5–100 h, respectively, suggest that the mechanical properties and the fracture characteristics are closely related with the variation of the rod-like β1 precipitation. The fracture observation of the samples aged at 200 °C indicates that with the increase of the density and the size of the rod-like β1 precipitation, more semi-cleavage planes will appear on the fracture surfaces.  相似文献   

9.
CaCu3 Ti4 O12x CaTiO3 ceramics (x=0,0.1,0.2,0.3,0.4 and 0.5) was studied by X-ray diffraction, scanning electron microscope and dielectric measurements. It was indicated that some CaTiO3 entered the boundaries of CaCu3 Ti4 O12 grains and/or subgrains. Dielectric measurement showed that the addition of CaTiO3 lowered the dielectric loss remarkably, especially at low frequencies, while the giant dielectric constant still remained. At room temperature, the dissipation factor of the x=0.5 sample was decreased to 0.02 over the frequency range from 50 to 2000 Hz, and the dielectric constant was kept to be 4000. We explain this phenomenon in terms of internal barrier layer capacitance model by using the impedance spectroscopy analysis.  相似文献   

10.
A Cockcroft–Walton high-voltage power supply with high stability and low-ripple voltage has been developed. This power supply has been operated in a ns pulse neutron generator. The maximum non-load voltage is 600 kV while the working voltage and load current are 550 kV and 15 mA, respectively. The tested results indicate that when the power supply is operated at 300 kV, 6.7 mA and the input voltage varies ±10%, the long-term stability of the output voltage is S=(0.300–1.006)×10-3. The ripple voltage is at 300 kV, 6.8–8.3 mA and the ratio of δUPP to the output voltage VH is δUP-P/VH=2.1×10-5.  相似文献   

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