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1.
The effect of hard anodic oxide and plasma electrolytic oxide coatings on the fatigue strength of 7475-T6 aluminium alloy has been investigated. The coated aluminium alloy was tested using constant load uniaxial tensile fatigue machine. Hard anodising led to an appreciable reduction in the fatigue strength of 7475-T6 alloy of about 75% for a 60 μm thick coating. Further, plasma electrolytic oxidation resulted in reduction of the fatigue strength of about 58% for a 65 μm thick oxide coating. The decrease in fatigue strength of the hard anodic oxide coatings was associated with the stress concentration at the microcracks in the coating. The better fatigue performance of the PEO coatings was attributed to the development of the compressive residual internal stress within the coatings. The reduction in the fatigue strength of the PEO coatings as compared to the uncoated material was associated with the development of the tensile residual internal stress within the substrate. This may cause an early crack initiation in the substrate adjacent to the coating. 相似文献
2.
Mostafa I. Yacoub Dan S. Necsulescu Jurek Z. Sasiadek 《Journal of Intelligent and Robotic Systems》2016,83(3-4):585-602
Operation of mobile robots in off-road environment requires the attention to the torque saturation problem that occurs in the wheels DC motors while climbing hills. In the present work, off-road conditions are utilized to benefit while avoiding torque saturation. Energy optimization algorithm using predictive control is implemented on a two-DC motor-driven wheels mobile robot while crossing a ditch. The predictive control algorithm is simulated and compared with the PID control and the open-loop control. Predictive control showed more capability to avoid torque saturation and noticeable reduction in the energy consumption. Furthermore, using the wheels motors armature current instead of the supply voltage as control variable in the predictive control showed more efficient speed control. Simulation results showed that in case of known ditch dimensions ahead of time, the developed algorithm is feasible. Experimental examination of the developed energy optimization algorithm is presented. The experimental results showed a good agreement with the simulation results. The effects of the road slope and the prediction horizon length on the consumed energy are evaluated. The analytical study showed that the energy consumption is reduced by increasing the prediction horizon until it reaches a limit at which no more energy reduction is obtained. This limit is proportional to the width of the ditch in front of the mobile robot. Curve fitting is applied to the obtained results to address further the effect of the parameters on the energy consumption. 相似文献
3.
The difficulties encountered in fabricating Ni3Al-based intermetallic alloys into final structural components, due to their limited workability as a result of their inherent high yield strength and low ductility at elevated temperatures, are an important issue that have restricted the commercial applications of these materials. The Osprey spray deposition process is capable of delivering near-net-shape preforms, thereby avoiding the technical problems related to the hot working of these materials, e.g. hot rolling of slabs. The present work concerns an investigation of the cold rollability of a chromium-containing Ni3Al intermetallic alloy produced with the Osprey process. The sliced preform with a thickness of 7 mm was successfully cold rolled through multipasses into sheets with a thickness of 0.7 mm and a good surface finish. The material has been found to have a high working hardening rate at room temperature. The maximum total reduction permissible without resulting in rolling defects is 30%. Thus, for larger reductions, intermediate annealing between rolling passes is necessary and it has been optimized to be at 1100°C for one hour. The repeated cold rolling and the recrystallization occurring during intermediate annealing change the initial microstructural features and grain size of the Osprey-spray-deposited material. The cold-worked and annealed intermetallic sheets with a thickness of 0.7 mm have a yield strength of 570 and 730 MPa and a elongation value of 33 and 7%, at room temperature and at 700°C, respectively. Fractography shows a transition from the transgranular fracture mode at low temperatures to the intergranular fracture mode at temperatures above 650°C. 相似文献
4.
Izabela Wysocka Agata Markowska‐Szczupak Piotr Szweda Jacek Ryl Maya Endo‐Kimura Ewa Kowalska Grzegorz Nowaczyk Anna Zieliska‐Jurek 《Indoor air》2019,29(6):979-992
The photocatalytic deactivation of volatile organic compounds and mold fungi using TiO2 modified with mono‐ and bimetallic (Pt, Cu, Ag) particles is reported in this study. The mono‐ and bimetal‐modified (Pt, Cu, Ag) titanium(IV) oxide photocatalysts were prepared by chemical reduction method and characterized using XRD, XPS, DR/UV‐Vis, BET, and TEM analysis. The effect of incident light, type and content of mono‐ and bimetallic nanoparticles deposited on titanium(IV) oxide was studied. Photocatalytic activity of as‐prepared nanocomposites was examined in the gas phase using LEDs array. High photocatalytic activity of Ag/Pt‐TiO2 and Cu/Pt‐TiO2 in the reaction of toluene degradation resulted from improved efficiency of interfacial charge transfer process, which was consistent with the fluorescence quenching effect revealed by photoluminescence (PL) emission spectra. The photocatalytic deactivation of Penicillium chrysogenum, a pathogenic fungi present in the indoor environment, especially in a damp or water‐damaged building using mono‐ and bimetal‐modified (Pt, Cu, Ag) titanium(IV) oxide was evaluated for the first time. TiO2 modified with mono‐ and bimetallic NPs of Ag/Pt, Cu, and Ag deposited on TiO2 exhibited improved fungicidal activity under LEDs illumination than pure TiO2. 相似文献
5.
G. J. S. Dawes L. E. Fratila-Apachitei B. S. Necula I. Apachitei G. J. Witkamp J. Duszczyk 《Journal of materials science. Materials in medicine》2010,21(1):215-221
The aim of the present study was to investigate the morphology and function of a drug eluting metallic porous surface produced
by the immobilization of poly lactide-co-glycolide microspheres bearing dexamethasone onto plasma electrolytically oxidized
Ti–6Al–7Nb medical alloy. Spheres of 20 μm diameter were produced by an oil-in-water emulsion/solvent evaporation method and
thermally immobilized onto titanium discs. The scanning electron microscopy investigations revealed that the size distribution
and morphology of the attached spheres had not changed significantly. The drug release profiles following degradation in phosphate
buffered saline for 1000 h showed that, upon immobilisation, the spheres maintained a sustained release, with a triphasic
profile similar to the non-attached system. The only significant change was an increased release rate during the first 100 h.
This difference was attributed to the effect of thermal attachment of the spheres to the surface. 相似文献
6.
Derk J. Swider Luuk Beurskens Sarah Davidson John Twidell Jurek Pyrko Wolfgang Prüggler Hans Auer Katarina Vertin Romualdas Skema 《Renewable Energy》2008,33(8):1832-1842
This paper compares conditions and costs for RES-E grid connection in selected European countries. These are Germany, the Netherlands, the United Kingdom, Sweden, Austria, Lithuania and Slovenia. Country specific case studies are presented for wind onshore and offshore, biomass and photovoltaic power systems, as based on literature reviews and stakeholder interviews. It is shown that, especially for wind offshore, the allocation of grid connection costs can form a significant barrier for the installation of new RES-E generation if the developer has to bear all such costs. If energy policy makers want to reduce the barriers for new large-scale RES-E deployment, then it is concluded that the grid connection costs should be covered by the respective grid operator. These costs may then be recouped by increasing consumer tariffs for the use of the grid. 相似文献
7.
Results are reported which show the effect of different degassing modes on the properties of the Al-20Si-3Cu-1 Mg powder.
The paper complements previous papers [1–3] concerning the conventional and modified degassing of the same powder. This research
was mainly directed to study the influence of temperature on the tensile properties, ultimate tensile strength, σUTS, and elongation, ɛ, of extrudates obtained of Al-20Si-3Cu-1Mg compacts non-degassed, conventionally degassed, and treated
by a modified process, namely degassing assisted by flushing with a depurative gas such as argon or nitrogen. The processing
of the Al-20Si-3Cu-1Mg P/M powder must include a degassing step which significantly improves the tensile properties, at room
and elevated temperatures, of the products of compacted powder with respect to those of the products whose compacts were non-degassed.
It is apparent that degassing assisted by flushing with argon or nitrogen gives products with higher tensile properties than
those of the products conventionally degassed under optimal conditions of temperature and time and much higher than those
of the non-degassed products. The tensile results are in agreement with the theoretical approach to the gas entrapment and
evolution of the aluminium powders presented in previous papers. 相似文献
8.
Control System for Free-Floating Space Manipulator Based on Nonlinear Model Predictive Control (NMPC) 总被引:1,自引:0,他引:1
Tomasz Rybus Karol Seweryn Jurek Z. Sasiadek 《Journal of Intelligent and Robotic Systems》2017,85(3-4):491-509
Manipulator mounted on an unmanned satellite could be used for performing orbital capture maneuver in order to repair satellites or remove space debris from orbit. Use of manipulators for such purposes presents unique challenges, as high level of autonomy is required and the motion of the manipulator influences the position and orientation of the manipulator-equipped satellite. This paper presents a new control system that consists of two modules: trajectory planning module (based on trajectory optimization algorithm) and Model Predictive Controller. Both modules take into account the free-floating nature of the satellite-manipulator system. Proposed control system was tested in numerical simulations performed for a simplified planar case. In the first set of simulations Nonlinear Model Predictive Control (NMPC) was used to ensure realization of a square reference end-effector trajectory, while in the second set control system was used for optimizing and then ensuring realization of the trajectory that leads to grasping of the rotating target satellite. Simulations were performed with disturbances and with the assumed non-perfect knowledge of parameters of the satellite-manipulator system. Results obtained with NMPC are better than results obtained with the controller based on the Dynamic Jacobian inverse and with the Modified Simple Adaptive Control (MSAC). 相似文献
9.
A. R. Eivani S. Valipour H. Ahmed J. Zhou J. Duszczyk 《Metallurgical and Materials Transactions A》2011,42(4):1109-1116
In this article, a new relationship for the calculation of the Zener drag pressure is described in which the effect of the
size distribution of nanoscale dispersed particles is taken into account, in addition to particle radius and volume fraction,
which have been incorporated in the existing relationships. Microstructural observations indicated a clear correlation between
the size distribution of dispersed particles and recrystallized grain sizes in the AA7020 aluminum alloy. However, the existing
relationship to calculate the Zener drag pressure yielded a negligible difference of 0.016 pct between the two structures
homogenized at different conditions resulting in totally different size distributions of nanoscale dispersed particles and,
consequently, recrystallized grain sizes. The difference in the Zener drag pressure calculated by the application of the new
relationship was 5.1 pct, being in line with the experimental observations of the recrystallized grain sizes. Mathematical
investigations showed that the ratio of the Zener drag pressure from the new equation to that from the existing equation is
maximized when the number densities of all the particles with different sizes are equal. This finding indicates that in the
two structures with identical parameters except the size distribution of nanoscale dispersed particles, the one that possesses
a broader size distribution of particles, i.e., the number densities of particles with different sizes being equal, gives rise to a larger Zener drag pressure than that
having a narrow size distribution of nanoscale dispersed particles, i.e., most of the particles being in the same size range. 相似文献
10.
HA Lehr AS Weyrich RK Saetzler A Jurek KE Arfors GA Zimmerman SM Prescott TM McIntyre 《Canadian Metallurgical Quarterly》1997,99(10):2358-2364
Cigarette smoking within minutes induces leukocyte adhesion to the vascular wall and formation of intravascular leukocyte-platelet aggregates. We find this is inhibited by platelet-activating factor (PAF) receptor antagonists, and correlates with the accumulation of PAF-like mediators in the blood of cigarette smoke-exposed hamsters. These mediators were PAF-like lipids, formed by nonenzymatic oxidative modification of existing phospholipids, that were distinct from biosynthetic PAF. These PAF-like lipids induced isolated human monocytes and platelets to aggregate, which greatly increased their secretion of IL-8 and macrophage inflammatory protein-1alpha. Both events were blocked by a PAF receptor antagonist. Similarly, blocking the PAF receptor in vivo blocked smoke-induced leukocyte aggregation and pavementing along the vascular wall. Dietary supplementation with the antioxidant vitamin C prevented the accumulation of PAF-like lipids, and it prevented cigarette smoke-induced leukocyte adhesion to the vascular wall and formation of leukocyte-platelet aggregates. This is the first in vivo demonstration of inflammatory phospholipid oxidation products and it suggests a molecular mechanism coupling cigarette smoke with rapid inflammatory changes. Inhibition of PAF-like lipid formation and their intravascular sequela by vitamin C suggests a simple dietary means to reduce smoking-related cardiovascular disease. 相似文献