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排序方式: 共有142条查询结果,搜索用时 15 毫秒
1.
Mohammad Mahdi Attar Farzan Barati Mahdi Ahmadpour Ehsan Rezapour 《Journal of Mechanical Science and Technology》2016,30(6):2583-2591
The objective of this study is to investigate the effects of geometrical and physical parameters on failure modes and failure loads in unidirectional polymeric matrix composites with two serial pin loaded holes, analytically and experimentally. It is assumed that all of unidirectional fibers in the laminate lie in one direction while loaded by a load p 0 at infinity, parallel to the direction of the fibers. To derive equilibrium equations based on a Shear-Lag theory, a rectangular arrangement of fibers is considered and with the proper use of boundary and boundness conditions, stress and displacement fields are computed within the laminate, along with the surrounding pinholes. Finally by using the Hashin criterion failure modes and failure loads are estimated. To validate analytical results based on shear-lag theory, an experimental program is carried out. A very good agreement is observed between two procedures. Based on results, in small sizes of two pins, the dominant failure mode is bearing and with the increasing of hole sizes, failure modes are changed to tension and shear modes. 相似文献
2.
Zoya Sadighi Abolghasem Ataie Mohammad Reza Barati 《Metals and Materials International》2014,20(1):77-81
In this study, barium-doped lanthanum manganite, La0.8Ba0.2MnO3, was synthesized via a mechano-thermal route employing high energy ball milling and subsequent heat treatment. The structural evolution, morphology and thermal behaviour of the powders were evaluated using XRD, FESEM, and DTA/TGA, respectively. DTA/TGA results showed that the calcination temperature of the carbonates significantly decreased by increasing the milling time. The results revealed that single phase perovskite was formed at 900 °C in a milled sample for 2 h and this temperature decreased to 600 °C by increasing the milling time to 30 h. The mean crystallite size also decreased from 32 to 20 nm by increasing the milling time from 2 to 30 h. The reaction sequence of La0.8Ba0.2MnO3 formation via the mechano-thermal route is proposed using XRD and DTA/TGA results. FESEM micrographs showed that the mean particle size of the perovskite phase is increased slightly from 30 to 40 nm by increasing the heat treatment temperature from 600 to 900 °C. 相似文献
3.
I. Rahmani B. Barati V. Majazi Dalfard L. Hatami-Shirkouhi 《Neural computing & applications》2014,24(5):1153-1161
Performance evaluation and efficiency analysis is considered to be one of the critical responsibilities of the management department. This paper investigates and assesses the efficiency and performance of Iranian insurance companies through nonparametric frontier analysis (FA) models. The two well-known nonparametric FA models, data envelopment analysis (DEA) and free disposal hull, are utilized to separate the efficient companies from the inefficient companies, and two well-known super-efficiency analysis models are utilized to rank the efficient units. For the further analysis, critical inputs are also identified for inefficient companies using DEA sensitivity analysis which is a powerful tool for planning performance improvement project, and the reference sets are also identified as the benchmark pattern for each inefficient unit. Managerial insights and implications of the study are discussed finally. 相似文献
4.
5.
Hydraulic fracturing has been used by the oil and gas industry as a way to boost hydrocarbon production since 1947. Recent advances in fracturing technologies, such as multistage fracturing in horizontal wells, are responsible for the latest hydrocarbon production boom in the US. Linear or crosslinked guars are the most commonly used fluids in traditional fracturing operations. The main functions of these fluids are to open/propagate the fractures and transport proppants into the fractures. Proppants are usually applied to form a thin layer between fracture faces to prop the fractures open at the end of the fracturing process. Chemical breakers are used to break the polymers at the end of the fracturing process so as to provide highly conductive fractures. Concerns over fracture conductivity damage by viscous fluids in ultra‐tight formations found in unconventional reservoirs prompted the industry to develop an alternative fracturing fluid called “slickwater”. It consists mainly of water with a very low concentration of linear polymer. The low concentration polymer serves primarily to reduce the friction loss along the flow lines. Proppant‐carrying capability of this type of fluids is still a subject of debate among industry experts. Constraints on local water availability and the potential for damage to formations have led the industry to develop other types of fracturing fluids such as viscoelastic surfactants and energized fluids. This article reviews both the traditional viscous fluids used in conventional hydraulic fracturing operations as well as the new family of fluids being developed for both traditional and unconventional reservoirs. © 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014 , 131, 40735. 相似文献
6.
In the present investigation, novel poly(vinyl alcohol)/organoclay/silver (PVA/OMMT/Ag) tricomponent nanocomposite (NC) films with different compositions were prepared by solution intercalation method under ultrasonic irradiation process. The NC films were obtained by mixing a colloidal solution consisting of Ag nanoparticles (NPs) (3, 5, 7 and 9 wt%) with a water solution of PVA and OMMT (10 wt%) via solution casting method. The scanning electron microscopy (SEM), transmission electron microscopy (TEM), X-ray diffraction, Fourier transform infrared spectroscopy, and thermogravimetric analysis (TGA) were utilized to characterize the morphology and properties of the PVA/OMMT/Ag NC films. TGA confirmed that the heat stability of the nanocomposite was improved. The enhancement in the thermal properties of the hybrid materials was due to strong hydrogen bonding between OH groups of PVA, free acid functionalized groups of OMMT, and the Ag NPs. SEM and TEM results also showed that the OMMT and Ag NPs were dispersed homogeneously in the PVA matrix on nanoscale. 相似文献
7.
Yu Dawei Liu Feng Zhang Jiajing Barati Mansoor 《Metallurgical and Materials Transactions B》2019,50(5):2186-2196
Metallurgical and Materials Transactions B - Production of ferronickel alloy by thermal treatment of nickeliferous pyrrhotite (Pyrr) tailings was studied by both thermodynamic assessment and... 相似文献
8.
In the present investigation, at first, the surface of titanium dioxide (TiO2) nanoparticles was modified with γ-aminopropyltriethoxy silane as a coupling agent. Then a new kind of poly(vinyl alcohol)/titanium dioxide (PVA/TiO2) nanocomposites coating with different modified TiO2 loading were prepared under ultrasonic irradiation process. Finally, these nanocomposites coating were used for fabrication of PVA/TiO2 films via solution casting method. The resulting nanocomposites were fully characterized by Fourier transform infrared spectroscopy (FT-IR), powder X-ray diffraction (XRD), thermogravimetric analysis/derivative thermal gravimetric (TGA/DTG), transmission electron microscopy (TEM), scanning electron microscopy (SEM) and atomic force microscopy (AFM). The TEM and SEM results indicated that the surface modified nanoparticles were dispersed homogeneously in PVA matrix on nanoscale and based on obtained results a possible mechanism was proposed for ultrasonic induced nanocomposite fabrication. TGA confirmed that the heat stability of the nanocomposite was improved. UV–vis spectroscopy was employed to evaluate the absorbance and transmittance behavior of the PVA/TiO2 nanocomposite films in the wavelength range of 200–800 nm. The results showed that this type of films could be used as a coating to shield against UV light. 相似文献
9.
The paper deals with calculations of the J-integral for a plate weakened by U-notches under Mode I bending loading in the case of a material obeying a linear elastic law. The main aim of the study is to suggest some new equations suitable for calculations of the J-integral under bending loading. Although some closed-form solutions exist in the literature based on elliptic integrals, some expressions, simple to be implemented, are useful as a rapid engineering tool. 相似文献
10.
The purification of metallurgical grade silicon (MG-Si) using a combination of solvent refining and physical separation is
studied. MG-Si was alloyed with iron and solidified under different cooling rates in order to grow pure Si dendrites from
the alloy. The Si dendrites were then separated using a gravity-based method. The separation method relies on the significantly
different densities of Si and FeSi2, and it uses a heavy liquid with specific gravity between the two phases to float the light Si particles to the surface of
the liquid, while the heavy iron silicide sinks. The effects of the particle size and cooling rate on the yield and separation
efficiency of the Si phase were investigated by quantifying the fraction of Si in the sinks and floats. The results demonstrate
that the crushing size of the particles prior to separation should be approximately the same as the width of the dendrites
in order to maximize the separation efficiency while simultaneously lowering the grinding cost. 相似文献