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51.
This paper contains investigations of wear particles generated during the erosive wear of four different concrete, mixtures by high velocity water flow at velocities of about 700 m/s.i The wear particles were collected, dried and analyzed by sieve experiments. Based on the sieve analysis, specific surface and average grain diameter of the particle samples were estimated. 'Using simple, comminution relations, the specific crack length of every' sample is calculated. It is shown that all estimated parameters exhibit a strong relationship to characteristic material properties, such as compressive strength, Young's modulus, and absorbed fracture energy. It was found by regression analysis that the average debris wear size can be effectively characterized by the absorbed fracture energy of the concrete sample. It is concluded that these relations are the result of different paths of fracture propagation through the materials during the generation of a microcrack network. 相似文献
52.
对三种纱线在上浆前后的品质进行分析,这三种纱线均具有相同的支数和原料组分,但是分别由不同的厂家纺制,并且原棉的质量不一,对引起纱线断头,从而降低织机效率的纱线弱环的起因及其影响进行了研究,机器效率的降低与经纱中薄弱环节的增加有极大的相关性,研究表明大多数的断头都发生在低质量的纱中纱线的接头处,问题是在保证机器能在正常条件和现有原材料情况下完好运转时,阔幅,高密织机的效率受到多大程度的限制。 相似文献
53.
Gilbert Chahine Mari Koike Toru Okabe Pauline Smith Radovan Kovacevic 《JOM Journal of the Minerals, Metals and Materials Society》2008,60(11):50-55
This paper addresses the production of customized Ti-6Al-4V ELI dental implants via electron beam melting (EBM). The melting
of Ti-6Al-4V ELI powder produces implants with great biocompatibility, fi ne mechanical performance, and a high bone ingrowth
potential. The EBM technology is used to produce one-component dental implants that mimic the exact shape of the patient’s
tooth, replacing the traditional, three-component, “screw-like” standardized dental implants currently used. The new generation
of implants provides the possibility of simplifying pre-insertion procedures leading to faster healing time, and the potential
of better and stronger osseointegration, specifi cally through incorporating lattice structure design. 相似文献
54.
Electronic Commerce Research - Despite the existence of research in the field of electronic reverse auctions (eRAs), there is still a limited understanding of the determinants of auction savings... 相似文献
55.
Michal Drusan Erik Rakovský Jaromír Marek Radovan ebesta 《Advanced Synthesis \u0026amp; Catalysis》2015,357(7):1493-1498
Asymmetric catalytic multistep reactions enable the formation of structurally complex compounds from simple starting materials. Enantioselective Cu‐catalyzed 1,4‐additions of Grignard reagents to Michael acceptors form reactive chiral enolates. We show here that these chiral enolates react in a one‐pot fashion with naked carbenium ions, such as tropylium, 1,3‐benzodithiolium, and dianisylmethylium ions. The corresponding products were obtained in good yields, with enantioselectivities up to 96% ee and high diastereomeric purities.
56.
A thermokinetic model coupling finite-element heat transfer with transformation kinetics is developed to determine the effect
of deposition patterns on the phase-transformation kinetics of laser powder deposition (LPD) process of a hot-work tool steel.
The finite-element model is used to define the temperature history of the process used in an empirical-based kinetic model
to analyze the tempering effect of the heating and cooling cycles of the deposition process. An area is defined to be covered
by AISI H13 on a substrate of AISI 1018 with three different deposition patterns: one section, two section, and three section.
The two-section pattern divides the area of the one-section pattern into two sections, and the three-section pattern divides
that area into three sections. The results show that dividing the area under deposition into smaller areas can influence the
phase transformation kinetics of the process and, consequently, change the final hardness of the deposited material. The two-section
pattern shows a higher average hardness than the one-section pattern, and the three-section pattern shows a fully hardened
surface without significant tempered zones of low hardness. To verify the results, a microhardness test and scanning electron
microscope were used. 相似文献
57.
Marta Harničárová Jan Valíček Robert Čep Hakan Tozan Jana Müllerová Radovan Grznárik 《The International Journal of Advanced Manufacturing Technology》2013,69(1-4):81-91
The contribution deals with comparing non-traditional cutting technologies from the point of view of generated surface roughness. The comparison is carried out for technologies of abrasive waterjet cutting, oxygen cutting, laser and plasma cutting. As an experimental material, EN S355J0 structural steel and titanium CP-Ti Grade 2 was used. Surface topography measurement was done using a Mitutoyo Surftest SJ-401 instrument, and an optical profilometer MicroProf FRT was used for comparison and verification of acquired surface data. The aim of the contribution is to clarify, on the basis of experimental measurements, the behaviour of a topographic function after various ways of cutting; the knowledge of the function is necessary for solving both theoretical and practical technological tasks. The topographic function, which is a basis for the prediction of quality and control of the cutting processes, was derived in an original way. The use of individual technologies depends on technical and economical possibilities and on environmental influences. The results of measurement of cut surface roughness are in good accordance with the results of theoretical analysis. 相似文献
58.
Prabu Balu Syed Hamid Radovan Kovacevic 《The International Journal of Advanced Manufacturing Technology》2013,68(1-4):85-98
The localized high-energy input and high-cooling rate inherent in the laser-based powder deposition (LBPD) process yield deposits with superior mechanical and metallurgical properties. However, these characteristics induce thermal stresses within the deposited material that subsequently lead to cracks. This tendency is predominant in the LBPD of metal–ceramic composite materials such as nickel (Ni) and tungsten carbide (WC). In this study, the thermal behavior of single and multilayered compositionally graded Ni-WC composite material during LBPD is studied using an experimentally verified three-dimensional finite element model. The model incorporates both directional- and temperature-dependent material properties. The effect of the mass fraction of the reinforcement, laser power, scanning speed, powder flow rate, and preheating temperature on temperature, temperature gradient, cooling rate, and molten pool evolution are investigated. The distribution and dissolution of WC in Ni-WC deposits are analyzed in the light of the scanning electron microscope, energy-dispersive spectroscopy, and microhardness distribution. The dissolution of WC in the molten Ni varies based on the mass fractions of the Ni and WC and the prevailing thermal conditions such as molten pool temperature and cooling rate. Experimental and numerical results confirm that the desired composition gradient can be achieved in a multilayered Ni-WC composite material deposit by adjusting the laser power. The developed heat transfer analysis may be used to select the suitable process variables needed to achieve the desired properties in the LBPD of single and multilayered Ni-WC composite material. 相似文献
59.
60.
Milan Bižić Radovan Bulatović Dragan Petrović Milomir Gašić Mile Savković 《Engineering with Computers》2013,29(4):535-546
The paper presents a methodology for modeling profile of two circular-arc cams, which is based on the application of homogeneous coordinate transformation method. Analytical expressions that allow complete determining of all design parameters and coordinates of all the points of two circular-arc cams profile are defined. Also, analytical expressions for determining the kinematic performance such as displacement, velocity, acceleration and jerk are derived. The defined methodology is applied on concrete examples for which the analysis of the kinematic performance is also performed. Additionally, it is shown that a proper choice of the design parameters can significantly affect the improvement of the kinematic performance, especially the reduction of jerk as one of the most unfavorable occurrences in these mechanisms. The given methodology allows very efficient determination of all input data for parametric modeling and production of two circular-arc cams on numerical machines. This approach allows the fulfillment of one of the most important requirements of modern production–reduction of time necessary for design and manufacturing which causes reduction of costs. 相似文献