涂层硬质合金刀片切削性能的试验研究

对涂层硬质合金刀片与未涂层硬质合金刀片进行了切削力、刀具磨损及刀具耐用度的对比试验，并做了摩擦系数的计算，论述了涂层硬质合金刀具的优越性能、实际使用价值及推广意义。     

Depletion of Antioxidants from a HDPE Geomembrane in a Composite Liner

The results of two series of accelerated aging tests are reported. Both series of tests were conducted at temperatures of 85, 70, 55, and 26°C over a period of about 3?years. In the simulated liner series, the top of the geomembrane was covered with a geotextile (protection) layer that was exposed to simulated municipal solid waste (MSW) landfill leachate while the bottom of the geomembrane was in contact with a hydrated geosynthetic clay liner. In the immersion series, the geomembrane was immersed in the simulated MSW leachate, and hence, both sides were exposed to leachate. The results from oxidative induction time tests indicate that the antioxidant depletion is about 2.2–4.8 times faster for the leachate immersed geomembrane than for geomembrane in a composite liner. The higher rates are attributed to the higher extraction of antioxidants from two sides of the geomembrane immersed in leachate. The measured antioxidant depletion rates are extrapolated to a range of temperatures (0–60°C) using Arrhenius modeling. At a liner temperature of 35°C, the calculated time for the depletion of antioxidants is about 40?years for a geomembrane in a composite liner compared to 10?years if it is simply immersed in leachate. These tests suggest that to obtain realistic estimates of geomembrane service life one needs data from tests that simulate the expected field conditions and that prediction based on immersion tests may underestimate the service life.     

Effects of MEA fabrication method on durability of polymer electrolyte membrane fuel cells

To study the effects of fabrication methods on the durability of polymer electrolyte membrane fuel cells (PEMFCs), membrane-electrode assemblies (MEAs) were fabricated using a conventional method, a catalyst-coated membrane (CCM) method, and a CCM-hot pressed method. Single cells assembled with the prepared MEAs were operated galvanostatically at 600 mA cm⁻² for 1000 h for the conventional MEA and the CCM MEA and for 500 h for the CCM-hot pressed MEA. During operation, i-V curves, impedance spectra, and cyclic voltammograms were measured roughly every 100 h. Before and after long-term operation, the physical and chemical characteristics of the MEAs were analyzed using mercury porosimetry, X-ray diffraction (XRD), scanning electron microscopy (SEM), electron probe microanalysis (EPMA), and Fourier transformation infrared spectroscopy (FTIR). Under the operating conditions, the CCM MEA exhibited the lowest degradation rate as well as the highest initial performance.     

The influence of reusing ‘Formtex’ controlled permeability formwork on strength and durability of concrete

The effects of the reuse of ‘Formtex’ Controlled Permeability Formwork (CPF) liner on strength and durability properties of concrete were investigated at two different water-cement ratios and the results are reported in this paper. Test blocks were cast using the CPF on one side and impermeable formwork (IF) on the opposite side of the mould so that direct comparisons could be made between the two. The strength was assessed using the Limpet pull-off tester and both the air permeability and the water absorption (sorptivity) were measured using the Autoclam Permeability System. Both these instruments measured the ‘covercrete’ properties. In addition, cores cut from the test specimens were subjected to an accelerated carbonation test and a chloride exposure test. The results showed that the ‘Formtex’ CPF increases the surface strength and the durability of concrete compared to the IF. There was an almost complete elimination of blowholes. The permeability of concrete decreased and its resistance to the ingress of both carbon dioxide and chlorides increased when CPF was used. The beneficial effects of the Formtex CPF were most evident in concrete of higher water-cement ratio. With the reuse of the Formtex liner twice, that is a total of three uses, the performance of the CPF to improve the properties of concrete remained almost the same. In this research the CPF liner was cleaned thoroughly between each use, which must be adhered to for site applications for reproducing the beneficial effects observed in the laboratory.     

Fundamental mechanisms limiting solid oxide fuel cell durability

The fundamental issues associated with solid oxide fuel cell (SOFC) durability have been reviewed with an emphasis on general features in SOFCs and respective anode and cathode related phenomena. As general features, physicochemical properties and cell performance degradation/failure are correlated and bridged by the electrode reaction mechanisms. Particular emphasis is placed on the elemental behaviour of gaseous impurities and the possible role of liquids formed from gaseous substances. The lifetime of a state-of-the-art Ni cermet anodes is limited by a variety of microstructural changes, which mainly result from material transport-, deactivation- and thermomechanical mechanisms. Anode degradation can mainly be influenced by processing, conceptual and operating parameters. Designing a redox stable anode is currently one of the biggest challenges for small scale SOFC systems. Degradation mechanisms of different cathode materials are reviewed with a focus on the intrinsic degradation of doped lanthanum manganites (e.g. LSM) and doped lanthanum ferro-cobaltites (LSCF). Manganese-based perovskites can be regarded to be sufficiently stable, while for the better performing LSCF cathodes some intrinsic degradation was detected. New materials that are supposed to combine a better stability and high performance are also shortly mentioned.     

Aging of HDPE Geomembrane in Three Composite Landfill Liner Configurations

Laboratory-accelerated aging experiments conducted to examine the depletion of antioxidant from a geomembrane (GM) underlain by a geosynthetic clay liner (GCL) are described. Three different “protection” layers between the GM and overlying gravel and leachate are examined: (1) A traditional nonwoven geotextile (GT); (2) a GT-GCL; and (3) a GT-sand-GT layer. The GT-GCL protection layer gives an antioxidant depletion rate 0.59 to 0.66 times slower than the GT layer alone. The GT-sand-GT layer gives depletion rates 0.72–0.75 times that of the conventional GT alone. Based on Arrhenius modeling, the time required for depletion of antioxidants at 35°C is estimated to be 65 years for a GM with a GT-GCL protection layer, 50 years for a GT-sand-GT layer, and 40 years for a conventional GT protection layer. These times are all significantly greater than the depletion time for GM immersed in leachate (10 years) for the geomembrane tested.     

Effects of Duct Types and Emulsifiable Oils on Bond and Friction Losses in Posttensioned Concrete

Emulsifiable oils are often used in posttensioned construction to reduce friction losses and provide temporary corrosion protection for tendons prior to grouting. This paper addresses the effects of two emulsifiable oils and three duct types on bond and friction losses. Bond test results indicate that corrugated galvanized steel ducts provide better anchorage than corrugated HDPE ducts. Rigid steel pipes performed poorly because of failure at the duct-concrete or grout-duct interface. Bond test results also indicate that the ultimate strength of posttensioned specimens with oiled tendons is similar to or better than the ultimate strength of specimens with unoiled tendons. However, specimens with oiled tendons experienced greater slip at a given load than specimens with unoiled tendons. Friction test results indicate that current recommended design values for the coefficient of friction for steel pipes and galvanized ducts are accurate. However, the measured coefficient for HDPE ducts is significantly less than the AASHTO-recommended value. Friction tests also indicate that lubrication of the tendon reduces the friction coefficient by 15% in rigid steel pipes and HDPE ducts if stressing occurs while the oil is fresh.     

预应力混凝土结构耐久性研究现状

本文对国内外预应力混凝土结构耐久性研究现状进行了分析和总结,认为有必要进行大量工作来研究预应力混凝土结构的耐久性,并建议短期借鉴混凝土结构的耐久性研究成果。