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排序方式: 共有311条查询结果,搜索用时 31 毫秒
251.
252.
Guercio Giuseppe Del Manuela Galati Abdollah Saboori Paolo Fino Luca Iuliano 《金属学报(英文版)》2020,33(2):183-203
Electron beam melting(EBM) process is an additive manufacturing process largely used to produce complex metallic components made of high-performance materials for aerospace and medical applications.Especially,lattice structures made by Ti-6A1-4V have represented a hot topic for the industrial sectors because of having a great potential to combine lower weights and higher performances that can also be tailored by subsequent heat treatments.However,the little knowledge about the mechanical behaviour of the lattice structures is limiting their applications.The present work aims to provide a comprehensive review of the studies on the mechanical behaviour of the lattice structures made of Ti-6A1-4V.The main steps to produce an EBM part were considered as guidelines to review the literature on the lattice performance:(1) design,(2) process and(3) post-heat treatment.Thereafter,the correlation between the geometrical features of the lattice structure and their mechanical behaviour is discussed.In addition,the correlation among the mechanical performance of the lattice structures and the process precision,surface roughness and working temperature are also reviewed.An investigation on the studies about the properties of heat-treated lattice structure is also conducted. 相似文献
253.
Ahmad Shaabani Azadeh Tavousi Tabatabaei Fatemeh Hajishaabanha Shabnam Shaabani Mozhdeh Seyyedhamzeh Mina Keramati nejad 《Journal of Sulfur Chemistry》2018,39(4):367-379
KMnO4/guanidinium-based sulfonic acid as a green organocatalytic oxidative system can be used effectively for the selective oxidation of organic compounds in n-hexane as a nonpolar and inert solvent at room temperature in good yields. The use of this approach is described for the oxidation of alkyl arenes, alcohols, and sulfides. 相似文献
254.
Abdollah Khosravanian Mostafa Dehghani Mahdieh Pazirofteh Morteza Asghari Amir H. Mohammadi Davood Shahsavari 《International Journal of Hydrogen Energy》2018,43(5):2803-2816
Comprehensive structural/molecular simulations have been undertaken to study the poly(benzimidazoles) (PBI) membrane combined with four different nano-oxide materials (ZnO, Al2O3, SiO2 and TiO2) for purification and production of hydrogen from natural gases. Composite membranes were built with different amounts of nano-oxide materials to investigate the influence of nano-oxide content on the PBI membrane performance. Several structural characterizations such as FFV, WAXD and also a thermal one (glass transition temperature) were done to study the structural properties of all simulated membrane cells. Moreover, MSD and adsorption isotherms tasks were used to estimate the diffusivity and solubility of hydrogen molecules through the latter mixed matrix membranes (MMMs), respectively. Permeability and permselectivity of H2 penetrate molecules were also carefully calculated using the aforementioned penetrating factors (diffusivity and solubility). Results show a significant improvement in structural and transport properties by increasing the nanomaterials content, which could be due to the growth of penetration pathways through the membranes. Furthermore, membranes with SiO2 yield the best results compared to other three nano-oxide fillers. H2 gas yields the best results that help the storage and separation of this precious gas from other gas molecules, which present in natural gases. Compared to the previous studies and literature results, the current results are accurate and reliable to describe the structural and transport properties of PBI/nano-oxides composites. 相似文献
255.
Ali Naderi Abdollah Khoei Khayrollah Hadidi 《Analog Integrated Circuits and Signal Processing》2010,65(2):217-223
This paper proposes the method to implement a general form of membership functions for fuzzy systems in CMOS technology. These
membership functions are a general form of triangular types and those functions which are used in linguistic hedge fuzzy logic,
hence can offer better performance in almost all applications. The comparison between the proposed method and previously reported
works shows better performance in all parameters. Designed circuits to implement these types of membership functions are simulated
using HSPICE by level 49 parameters (BSIM3v3) in 0.35 μm standard CMOS technology. Current mode realization of the circuits
leads to simple and intuitive configurations. The Rational Power Generator Module (RPGM) generates powers with the resolution
of 0.03125 and using seven programming bits. The simulation results of RPGM demonstrate a RMS error of 1.42% and a maximum
power consumption of 1.05 mW. 相似文献
256.
Ali Karambakhsh Abdollah Afshar Pejman Malekinejad 《Journal of Materials Engineering and Performance》2012,21(1):121-127
In this research, color anodizing of Ti-6Al-4V alloy was performed in phosphoric acid solution of 0.4 M concentration and
within 30 s in different voltages (10-120 V) of a DC power supply. The effect of anodizing voltages on the color and thickness
of anodized layers on Ti-6Al-4V alloy surface was surveyed. Thickness and refractive index of layers were measured by spectrophotometery
and reflectance curves. According to the results, thickness of layers increased with increasing anodizing voltage and was
in the range of 38-167 nm. Also the refractive index of anodic film was approximately constant at about 2 and increased inconsiderably
with increasing anodizing voltage. Corrosion resistance of the anodized samples in 20 and 50 V was surveyed in physiological
solutions of Ringer’s solution, Artificial Saliva solution, and Ringer’s + 150 mM H2O2 solution at the temperature of 37 °C by potentiodynamic polarization method. The anodized sample in 50 V indicated lower
corrosion rate than the non-anodized sample as well as the sample which was anodized in 20 V in all solutions. The non-anodized
sample indicated the highest corrosion rate of about 0.25 μA cm−2. 相似文献
257.
Cast films of a high molecular weight linear polypropylene (L-PP) were prepared by extrusion followed by stretching using a chill roll. An air knife was employed to supply air to the film surface right at the exit of the die. The effects of air cooling conditions, chill roll temperature, and draw ratio on the crystalline orientation, morphology, mechanical and tear properties of the PP cast films were investigated. The crystallinity and crystal size distribution of the films were studied using differential scanning calorimetry (DSC). It was found that air blowing on the films contributed significantly to the uniformity of the lamellar structure. The orientation of crystalline and amorphous phases was measured using wide angle X-ray diffraction (WAXD) and Fourier transform infrared (FTIR). The amount of lamellae formation and long period spacing were obtained via small angle X-ray scattering (SAXS). The results showed that air cooling and the cast roll temperature have a crucial role on the orientation and amount of lamellae formation of the cast films, which was also confirmed from scanning electron microscopy (SEM) images of the films. Tensile properties and tear resistance of the cast films in machine and transverse directions (MD and TD, respectively) were evaluated. Significant increases of the Young modulus, yield stress, tensile strength, and tensile toughness along MD and drastic decreases of elongation at break along TD were observed for films subjected to air blowing. Morphological pictograms are proposed to represent the molecular structure of the films obtained without and upon applying air cooling for different chill roll temperatures. Finally, microporous membranes were prepared from annealed and stretched films to illustrate the effect of the PP cast film microstructure on the morphology and permeability of membranes. The observations of SEM surface images and water vapor transmission rate of the membranes showed higher pore density, uniform pore size, and superior permeability for the ones obtained from the precursor films prepared under controlled air cooling. 相似文献
258.
Hadi Mokhtari Abdollah Aghaie Javad Rahimi Ashkan Mozdgir 《The International Journal of Advanced Manufacturing Technology》2010,50(5-8):811-822
This paper develops a hybrid approach for stochastic time–cost trade-off problem (STCTP) in PERT networks of project management, where activities are subjected to linear cost functions. The main objective of proposed approach is to improve the project completion probability in a prespecified deadline from a risky value to a confident predefined probability. To this end, we construct a nonlinear mathematical program with decision variables of activity mean durations, in which the objective function is concerned with minimization of project crashing direct cost. In order to solve the constructed model, we present a hybrid approach based on cutting plane method and Monte Carlo (MC) simulation. To illustrate the process of proposed approach, the approach was coded using MATLAB 7.6.0 and two illustrative examples are discussed. The results obtained from the computational study show that the proposed algorithm is an effective approach for the STCTP. 相似文献
259.
In this paper, a load increment method for Modal Adaptive Pushover Analysis (MAPA) for plane frame buildings is presented. In this method, the Newton-Raphson iterative algorithm is used along the flow path normal to the Davidenko curves with modified convergence rate. Contrary to the previous arc-length methods, this algorithm, which uses the Homotopy approach, is based upon the new mathematical concepts. In order to evaluate the proposed method, two steel frames are analyzed using the algorithm presented and the results are compared with Non-linear Dynamic Analysis (NDA), FEMA-273 Nonlinear Static Analysis (NSA) and the Modal Pushover Analysis (MPA) procedures. When the NDA results are taken as reference, it is seen that the proposed method is capable of estimating efficiently the seismic response of frame buildings with moderately good accuracy. 相似文献
260.
Abdollah Hajalilou ;Mansor Hashim ;Halimah Mohamed kamari ;Kazem Javadi ;Samikannu Kanagesan ;Mohammad Parastegari 《金属学报(英文版)》2014,(6):1144-1151
ZrC nanoparticles in the matrix of Fe were produced by the mechanically activated self-propagating hightemperature method using ZrO2/C/Mg/Fe powder mixtures. The effects of milling time, Fe content, and combustion temperature as well as the formation route for synthesizing ZrC powder particles were studied. The samples were characterized by XRD, SEM, TEM, and DTA. The XRD results revealed that, after 18 h of mechanical activation, ZrO2/ZC/Mg/Fe reacted with the self-propagating combustion(SHS) mode at 870 °C producing the ZrC–Fe nanocomposite. It was also found that both mechanical activation and Fe content played key roles in the ZrC synthesis temperature. With a Fe content of(5–40) wt%, the SHS reaction proceeded favorably and both the ZrC formation temperature and the adiabatic temperature(Tad) decreased. The Mg O content was removed from the final products using a leaching test process by dissolving in hydrochloric and acetic acids. 相似文献